22: Arrhythmias: Diagnosis and Management


CHAPTER 22
Arrhythmias: Diagnosis and Management


Santiago O. Valdes1, Jeffrey J. Kim1, and Wanda C. Miller‐Hance2,3


1 Department of Pediatrics, Section of Cardiology, Electrophysiology and Pacing, Texas Children’s Hospital, Houston, TX, USA


2 Department of Anesthesiology, Perioperative and Pain Medicine, Arthur S. Keats Division of Pediatric Cardiovascular Anesthesiology, Baylor College of Medicine and Texas Children’s Hospital, Houston, TX, USA


3 Department of Pediatrics, Section of Cardiology, Baylor College of Medicine and Texas Children’s Hospital, Houston, TX, USA


Introduction


The practice of pediatric cardiovascular anesthesiology has evolved significantly over the years, expanding beyond the operative setting to many non‐surgical environments. Anesthetic care for infants, children, and adolescents who have or are at risk for, cardiac rhythm disturbances is now provided at various locations, including operating rooms, critical care units, emergency facilities, treatment rooms, and cardiac catheterization/electrophysiology laboratories. The same is true for other patients with congenital heart disease (CHD) beyond childhood. General knowledge of arrhythmia diagnosis and management is essential for anesthetic care in any of these settings, although in some cases, consultation with a specialist is required. This chapter provides a practical approach to pediatric cardiac arrhythmias and rhythm disturbances most commonly affecting patients with CHD, focusing on the diagnosis, mechanisms, and acute management strategies. A brief review of anti‐arrhythmic drug (AAD) therapies and the basic principles of cardiac pacing in children, as applicable to the practice of anesthesia, is also presented.


Cardiac rhythm disturbances


Sinus bradycardia


Sinus bradycardia is characterized by a heart rate below the norm for the patient’s age and by a normal, sinus P wave. Slow heart rates can be observed during sleep or may be secondary to a high vagal tone. During significant sinus bradycardia, an escape rhythm may arise from the atrium, junction, or ventricle. In otherwise healthy children, this is usually a benign rhythm with no hemodynamic consequences. Patients with certain forms of CHD, however, are more prone to slow heart rhythms that may indeed be clinically significant. Those with heterotaxy syndromes are included in this category because of the absence, displacement, or hypoplasia of the true sinus node in these patients [1].


Intraoperatively, sinus bradycardia can result from vagal stimulation during induction of anesthesia, laryngoscopy, endotracheal intubation, or tracheal suctioning. Sinus bradycardia may also be related to drug administration (e.g., opioids) or other mechanisms of increased parasympathetic activity. This type of sinus bradycardia rarely results in significant hemodynamic compromise and can usually be treated by removing the stimulus or by administering a chronotropic agent such as atropine or epinephrine (See Box 22.1). Slow sinus rates can be seen during cardiac surgical manipulations around the sinus node or after interventions such as the closure of atrial septal defects (ASDs) and cardiac transplantation.


Sinus bradycardia can also be due to hypoxemia, hypothermia, hypotension, drugs, acidosis, electrolyte abnormalities, or increased intracranial pressure. Hypoxemia‐related bradycardia should be treated promptly with oxygenation and ventilation as appropriate. The approach to other forms of secondary sinus bradycardia should focus on addressing the underlying cause. For worrisome low heart rates, particularly in small infants, drugs such as atropine or glycopyrrolate, should be considered. Ongoing bradycardia with clinical evidence of compromised cardiac output requires immediate escalation of therapy that, in most cases, includes epinephrine administration, cardiopulmonary resuscitation, and consideration of temporary pacing.


Low atrial rhythm


A low atrial rhythm is characterized by atrial activation that spreads upward from a focus on the low atrium. The electrocardiogram (ECG) shows inverted P waves in the inferior leads (II, III, and aVF). A slow atrial rhythm implies that another region of the heart has assumed the pacemaker activity of the sinus node. Although this rhythm may be associated with conditions that affect sinus node function intraoperatively, it is most commonly the result of surgical manipulation (Figure 22.1). In most individuals, this is a normal variant and rarely has a hemodynamic consequence.


Sinus node dysfunction


Sinus node dysfunction often termed sick sinus syndrome, encompasses a spectrum of disorders characterized by slow or irregular heart rates that have a variety of escape rhythms and that frequently alternate with the periods of tachycardia. The respondent’s tachycardia may be atrial tachycardia, atrial flutter, or atrial fibrillation. The term tachycardia‐bradycardia syndrome is frequently used to characterize this association. The surgical interventions most likely to be associated with sinus node dysfunction include extensive atrial baffling procedures, such as Mustard and Senning operations, and the Fontan procedure. The management of symptomatic patients may include pacemaker implantation, pharmacological therapy for tachyarrhythmias, atrial anti‐tachycardia pacing (ATP), and, in some cases, transcatheter or surgical ablation.


Sinus tachycardia


Sinus tachycardia is more commonly seen in the perioperative period than sinus bradycardia. It is often the result of painful stimuli or stress, hypovolemia, anemia, medications (e.g., inotropic agents), a high catecholamine state, surgical manipulation, or fever. Sinus tachycardia can often be differentiated from pathologic supraventricular arrhythmias by its variability in rate and its normal P‐wave axis. Treatment is directed at the underlying cause. Prolonged periods of sinus tachycardia may impair diastolic filling time, limit ventricular preload, and compromise systemic cardiac output. Patients at higher risk of hemodynamic compromise have substantial ventricular hypertrophy or non‐compliant (“stiff”) ventricles with associated diastolic dysfunction, such as in certain types of cardiomyopathies or obstructive outflow lesions (e.g., tetralogy of Fallot).

Schematic illustration of low atrial rhythm.

Figure 22.1 Low atrial rhythm. Intraoperative tracing depicting a single electrocardiographic lead (lead II), arterial blood pressure tracing (ART), and central venous pressure (CVP) waveform. Note the negative P‐wave morphology in the first portion of lead II, consistent with atrial activation arising from the low atrium. The second half of the recording shows a change in the P‐wave morphology (positive) and a slightly faster heart rate as the atrial impulse later originates from the high atrium (likely the sinus node).


Junctional rhythm


Junctional rhythm is characterized by QRS complexes with a morphology identical to that of sinus rhythm without preceding P waves. This arrhythmia is thought to originate in the bundle of His. It often occurs in patients with sinus bradycardia or with sinus node dysfunction. In this rhythm, there is normal atrioventricular (AV) nodal conduction, but it is sometimes difficult to determine if the junctional beats are slightly faster than the atrial beats or there is 1 : 1 ventriculoatrial (V:A) conduction retrograde through the AV node. During surgery, this may occur as a result of cardiac manipulation and dissection around the right atrium. In addition to the ECG features described above, the arterial and venous pressure waveforms can change during junctional rhythm (Figure 22.2). The central venous pressure tracing may show a tall a wave, termed as cannon a wave, which is due to late atrial contraction against a closed tricuspid valve. An associated decrease in stroke volume and cardiac output, resulting from the absence of the normal atrial systolic contribution to ventricular filling, may manifest as a reduction in systemic arterial blood pressure. Temporary atrial pacing at 10–20 beats/min (bpm) above the junctional rate can be used to document normal AV nodal conduction, and it frequently restores AV synchrony.

Schematic illustration of junctional rhythm.

Figure 22.2 Junctional rhythm. Intraoperative recording showing the features of a junctional rhythm. Note the retrograde (negative) P wave after each QRS complex. The central venous pressure tracing shows prominent cannon a waves corresponding to right atrial contraction against increased resistance from a closed tricuspid valve. This may result in decreased ventricular filling and reduced cardiac output. ART1, systemic arterial blood pressure (scale 0–100 mmHg); CVP, central venous pressure (scale 0–60 mmHg); SpO2, arterial oxygen saturation by pulse oximetry.


Conduction disorders


Bundle branch block


In an unoperated patient, bundle branch block is an uncommon ECG finding. An incomplete right bundle branch block (RBBB) pattern or intraventricular conduction delay can be seen in patients with right ventricular volume overload (e.g., ASDs, anomalous pulmonary venous drainage). In rare cases, an RBBB can be congenital and idiopathic. An RBBB pattern is frequently seen in postoperative patients after interventions for lesions such as tetralogy of Fallot, right ventricular outflow tract pathology, and AV septal defect (AVSD; also referred to as AV canal or endocardial cushion defect). This conduction abnormality may be related to a ventriculotomy incision, resection of infundibular muscle, damage to the moderator band, or, in some cases, closure of a ventricular septal defect (VSD). A left bundle branch block (LBBB) pattern is uncommon but may be found after surgical procedures involving the left ventricular outflow tract.


Atrioventricular block


First‐degree AV block

First‐degree AV block is characterized by a prolonged PR interval beyond what is considered normal for age. Each P wave is followed by a conducted QRS complex. This type of rhythm disturbance can be a normal variant in healthy individuals but can also be seen in a variety of disease states (e.g., structural heart defects associated with stretching of the atria, rheumatic fever). In general, a prolonged PR interval in an otherwise healthy child is a benign condition and requires no treatment.


Second‐degree AV block

There are four types of second‐degree AV block. The two predominant types, Mobitz type I (Wenckebach) and Mobitz type II, involve a periodic failure to conduct atrial impulses to the ventricle. In type I second‐degree AV block, the PR interval lengthens progressively until the next atrial impulse cannot be conducted to the ventricle. These failures of conduction manifest on the surface ECG as P waves without associated QRS complexes and concomitant shortening of the RR intervals (Figure 22.3). This rhythm disturbance can occur during periods of high vagal tone and is generally considered a benign phenomenon that requires no therapy.

Schematic illustration of mobitz type I second-degree atrioventricular block (Wenckebach).

Figure 22.3 Mobitz type I second‐degree atrioventricular block (Wenckebach). The tracing shows progressive lengthening of the PR interval and eventual failure of an atrial impulse to conduct.


In the less frequent type II second‐degree AV block, there is a constant PR interval before an atrial impulse that suddenly fails to conduct. This conduction abnormality is more concerning because of its potential for progression. It can be seen in patients after surgery for CHD and is thought to be due to damage to the His bundle or distal conduction system.


The third type of second‐degree AV block is two to one AV block (2:1). In 2:1, every second P wave is blocked. In most cases, this is a type of Mobitz type I or Wenckebach block and is secondary to high vagal tone. It is rare for 2:1 to progress to a higher degree of AV block or to require treatment.


The fourth type of second‐degree AV block is a high‐grade AV block, which is evidenced by two or more non‐conducted P waves in succession that would normally be expected to conduct. Temporary pacing and close patient observation may be warranted because hemodynamically significant bradycardia or continued progression of the conduction deficit may ensue.


Third‐degree (complete) AV block

Third‐degree AV block is characterized by the total failure of atrial impulses to be conducted to the ventricles. There is complete dissociation of the electrical activity between the atria and ventricles, and the ventricular rate is usually slow and regular. In third‐degree AV block, the ventricular escape rate may be narrow (if originating from the perinodal region) or wide (if originating from within the ventricle). The diagnostic feature on the ECG is that all atrial impulses that should be conducted to the ventricle fail to do so (Figure 22.4).


Complete AV block may be either congenital or acquired. Congenital complete AV block in infants with otherwise structurally normal hearts may be due to intrauterine exposure to maternal antibodies associated with collagen vascular diseases (e.g., lupus). Patients at high risk of complete AV block include those with congenitally corrected transposition (L‐transposition of the great arteries with ventricular inversion) and those with polysplenia (left atrial isomerism) [1]. Acquired postoperative AV block is thought to result from damage to the compact AV node or bundle of His and may be transient or permanent. The surgical procedures most commonly associated with the onset of complete AV block include repair of AVSD, closure of VSD, resection of obstructive subaortic tissue, and interventions in patients with congenitally corrected transposition [2]. In children, reported incidences of surgical AV block are as high as 2–4%. Normal conduction eventually recovers in more than 60% of patients, usually within the first 10 postoperative days [3, 4]. Acute treatment includes temporary pacing (either AV sequential pacing or ventricular pacing only). If the rate of the junctional escape rhythm is high enough to support stable hemodynamics, temporary pacing can be set as a backup with close monitoring of the underlying cardiac rhythm. Important considerations in patients with surgical AV block include careful surveillance for the return of AV conduction and frequent evaluation of temporary pacing wire thresholds. The ventricular output of the temporary pacemaker should be set well above the capture threshold to increase the margin of safety (please refer to the section on temporary pacing). Permanent cardiac pacing is generally indicated in patients who do not recover from complete AV block within 10–14 days after surgical intervention. A small minority of patients have late recovery of their native AV nodal conduction after surgically acquired complete AV block [3, 4].

Schematic illustration of complete atrioventricular block.

Figure 22.4 Complete atrioventricular block. Surface electrocardiogram showing complete dissociation between the atria and ventricles, related to inability of the atrial impulses to be propagated to the ventricular myocardium. Note that the ventricular rate is regular.


When providing anesthetic care to a patient with complete AV block but no implanted pacemaker, the following should be considered:



  • Drugs and resuscitation equipment. Immediate availability of emergency agents such as isoproterenol and epinephrine, in addition to resuscitation equipment, is essential.
  • Transcutaneous cardiac pacing. Equipment (pacing pads and unit) should be available in case extracardiac pacing becomes necessary. Placing the pacing pads before anesthetic induction may be prudent.
  • Access to temporary transvenous pacing. Although insertion of a temporary pacing catheter before anesthetic care has been suggested in children with complete AV block, a retrospective study of this approach showed that using this catheter routinely had no benefit [5].

Supraventricular arrhythmias


Premature atrial contractions


Isolated premature atrial contractions (PACs) are relatively common in infants and small children. The early P waves frequently have an abnormal axis and morphology and are typically followed by a normal QRS complex. Atrial bigeminy is characterized by a PAC that follows every sinus beat (Figure 22.5). On occasion, the PACs block at the AV node or conduct aberrantly, displaying an abnormally wide QRS. Blocked PACs can mimic bradycardia, and aberrantly conducted PACs can resemble ventricular ectopy. Most PACs are benign, requiring no therapy. An investigation may be warranted in cases of symptomatic, frequent, or complex (multifocal) PACs. This type of rhythm can be the result of irritation from a central venous catheter or other type of intracardiac line. Radiographic or echocardiographic assessment of catheter/wire tip position should be considered because appropriate adjustments can eliminate the atrial ectopy.


Supraventricular tachycardia


Supraventricular tachycardia (SVT) is the most common clinically significant arrhythmia in infants and children. This rhythm disturbance is characterized by a narrow or “usual” complex QRS morphology and can occur in structurally normal hearts, as well as in various forms of CHD. “Usual” complex describes a QRS morphology in tachycardia similar to that seen during normal sinus rhythm. This is important because patients with CHD often have abnormalities on their baseline ECG, including a bundle branch block pattern. On occasion, widening of the QRS duration in SVT can be due to aberrancy in the right or left bundle branches or to the tachycardia mechanism itself (i.e., antidromic SVT; refer to the discussion later in this chapter). When the QRS complex is wide, distinguishing between supraventricular and ventricular tachycardia can be challenging.

Schematic illustration of atrial bigeminy.

Figure 22.5 Atrial bigeminy. Intraoperative recording obtained from a child after creation of a Glenn anastomosis, showing a premature atrial contraction after each sinus beat during atrial bigeminy. Note that the premature atrial complexes have a different P‐wave morphology from that of the sinus beats, because the premature complexes originate from a region of the atrium other than the sinus node. The variability in the arterial blood pressure shown in the tracing is due to the shortened diastolic filling time during the premature beats. ART1, systemic arterial blood pressure (scale 0–100 mmHg); LA3, left atrial pressure (scale 0–100 mmHg); PA2, pulmonary artery pressure (scale 0–100 mmHg); SpO2, arterial oxygen saturation by pulse oximetry.


Two general categories of SVT are recognized: automatic and reentrant. These can be differentiated by evaluating characteristics of the tachycardia (Table 22.1). The most common mechanisms of SVT and their ECG features are noted in Table 22.2. Evaluation of a tachyarrhythmia usually includes a surface 15‐lead ECG and a continuous rhythm strip to document onset, termination, and response to medications (e.g., adenosine) or pacing maneuvers. Strips obtained from the bedside or transport monitors are helpful for determining tachycardia rate, but they are usually not sufficient for definitive diagnosis or to distinguish among tachycardia mechanisms.


Atrial electrogram

In the postoperative patient, an atrial electrogram (AEG) can be useful in both diagnosis and management of rhythm problems. This type of ECG recording is obtained from the temporary atrial wires placed toward the end of surgery (Figure 22.6). Typically, atrial wires emerge on the right side of the chest wall and ventricular wires on the left side, although this configuration may vary. Although both a standard 15‐lead ECG and an AEG record the same electrical cardiac activity, these electrical sequences display distinctly different configurations in different leads. On an AEG, the P waves are larger in amplitude, making them easily recognizable because the recording is obtained from wires attached directly to the atrial myocardium. Therefore, in situations in which P waves are not clearly identified on a surface ECG, an AEG may assist in defining atrial activity and the relationship between atrial and ventricular depolarization (Figure 22.7). Such recordings can help clinicians to differentiate between atrial and junctional arrhythmias [6]. For example, during junctional tachycardia, the AEG displays P waves that are either superimposed on the R waves or dissociated from them. In most reentrant SVTs, the PR interval is longer than the RP interval, whereas in sinus rhythm, the PR interval is shorter than the RP interval. An AEG is also helpful in defining the type of an AV block if present and can facilitate the differential diagnosis of sinus node dysfunction vs. various degrees of AV block.


AEGs can be obtained from bedside monitors (Figure 22.6) or standard 15‐lead ECG machines [7]. With a bedside or operating room monitor, it is best to use a rhythm strip with two or more channels so that AEG and ECG recordings can be viewed simultaneously. There are various ways to obtain an AEG along with a standard tracing, depending on various equipment‐related factors (e.g., the recorder, epicardial wires, lead configuration).


The following methods of obtaining an AEG require the use of a standard 15‐lead ECG machine:



  • If two atrial wires are present, each lead is attached to the connectors that usually correspond to the right and left arm leads (an alligator clip can be used, if necessary). This allows for a bipolar AEG (large deflection of atrial depolarization with trivial or no signal representative of ventricular activity) to be recorded in lead I. The chest (precordial) leads provide ECG standard tracings. By evaluating the atrial activity as displayed by the AEG (lead I) and the ventricular impulses represented by the QRS complexes on the chest leads (V1–V6), the electrical sequence of cardiac events can be assessed.

    Table 22.1 Characteristics of supraventricular tachycardia mechanisms












































    Features of the tachycardia Automatic Reentrant
    Onset and termination “Warm‐up” at initiation, “cool‐down” at termination Abrupt
    Mode of initiation Spontaneous Premature beats
    Ability to initiate/terminate with timed premature beats No Yes
    Variation in tachycardia rate Wide Narrow
    Response to catecholamines Increased rate None or slight rate increase
    Response to adenosine None Termination
    Response to drugs that increase refractoriness Variable Slowing or termination
    Response to overdrive pacing Transient suppression, quick resumption Termination
    Response to cardioversion None Termination

    Table 22.2 Mechanisms and electrocardiographic features of supraventricular tachycardia




























    Diagnosis Electrocardiographic features
    Automatic tachycardias
    Ectopic atrial tachycardia or atrial ectopic tachycardia Atrial rates of 90–330 bpm
    Incessant rhythm
    From atrial focus distinct from the sinus node
    Abnormal P‐wave morphology and/or axis
    Distinct P waves preceding QRS complexes
    No influence of AV block on tachycardia
    Junctional ectopic tachycardia Narrow QRS tachycardia
    Incessant rhythm
    AV dissociation (often)
    Atrial rate slower than the ventricular rate
    Capture beats frequently seen (QRS complexes slightly earlier than expected from antegrade conduction of normal sinus impulses)
    Reentrant tachycardias
    Atrial flutter Sawtooth pattern or more discrete undulating P waves (leads II, II, aVF)
    Variable rates of AV conduction seen (1:1, 2:1, 3:1, or 4:1)
    Atrioventricular reentrant tachycardia (accessory pathway‐mediated from concealed bypass tract or Wolff‐Parkinson‐White syndrome) P waves immediately following the QRS complex, on ST segment or T wave
    AV block results in termination of tachycardia
    Atrioventricular nodal reentry tachycardia P waves buried within QRS and not discernible
    AV block results in termination of tachycardia

    AV, atrioventricular


  • If only a single atrial lead is available, this can be attached to one of the chest leads to obtain a corresponding AEG. In this case, the limb leads can be used to provide a reference for ventricular activity (Figures 22.6 and 22.7).
  • An alternate lead configuration may utilize a single atrial lead and a skin lead as a substitute for the arm leads to obtain an atrial tracing in lead I, and other leads serve as a reference. A rhythm strip should be printed out so that the recordings can be examined.

In addition to assisting in arrhythmia diagnosis and the selection of appropriate treatment, temporary atrial wires can be used for rapid atrial pacing in attempts to terminate SVT due to reentrant mechanisms or to overdrive suppress an automatic focus.


General management principles for SVT

Management of SVT depends on the clinical status of the patient, the type of tachycardia, and the precise electrophysiologic mechanism that is causing SVT (Table 22.3). If the tachyarrhythmia is associated with significant hemodynamic compromise, emergent therapy is indicated. Synchronized direct‐current cardioversion (0.5–1.0 J/kg) should be considered for a patient with any acute tachyarrhythmia associated with low cardiac output, recognizing that this approach does not always restore normal sinus rhythm.

Schematic illustration of procedure to obtain an atrial electrogram.

Figure 22.6 Procedure to obtain an atrial electrogram. Setup for recording an atrial electrogram by using a bedside (or operating room) monitor and a double alligator clamp to connect the atrial temporary pacing wire to the chest (C) or V lead (brown‐colored). Alternate lead configurations may be used as described in the text to obtain equivalent tracings.

Schematic illustration of atrial electrogram.

Figure 22.7 Atrial electrogram. Full electrocardiographic tracing with an atrial electrogram in lead V1. Note the easily discernible P waves in the atrial electrogram, which confirm that the rhythm is that of atrial flutter with 2:1 conduction.


Table 22.3 Acute therapy of perioperative arrhythmias without evidence of hemodynamic compromise














































Rhythm disturbance Treatment considerations
Sinus bradycardia See Box 22.1
Sinus tachycardia Correct underlying cause
Premature atrial contractions Evaluate the position of a central venous line or intracardiac catheter Assess/correct electrolyte disturbances (e.g., hypokalemia)
Focal (ectopic) atrial tachycardia or atrial ectopic tachycardia Correct fever, electrolyte abnormalities
Adequate sedation
Consider the potential detrimental role of inotropes/vagolytics
ß‐blockers – use with caution if depressed cardiac function
Digoxin
Procainamide
Amiodarone
Sotalol
Flecainide
Propafenone
Ivabradine
Multifocal (chaotic) atrial tachycardia As in ectopic atrial tachycardia
Goals are rate control and decreased automaticity
Accelerated junctional rhythm Correct fever
Consider the potential detrimental role of inotropes/vagolytics
Temporary atrial pacing
Junctional ectopic tachycardia Correct fever and electrolyte abnormalities
Consider the potential detrimental role of drugs (e.g., inotropes)
Adequate sedation (dexmedetomidine)
Surface cooling to 34–35 °C
Temporary atrial pacing (for JET rates <180 bpm)
Amiodarone
Hypothermia plus procainamide
Sotalol
Ivabradine
Atrial flutter Adenosine to confirm the diagnosis
Atrial overdrive pacing
Digoxin
Procainamide
Amiodarone
Sotalol
Propafenone
Atrial fibrillation Digoxin (except in Wolff–Parkinson–White syndrome)
ß‐blockers
Procainamide
Quinidine
Amiodarone
Sotalol
Atrioventricular reentrant tachycardia or atrioventricular nodal reentrant tachycardia Consider vagal maneuvers
Adenosine
Atrial overdrive pacing
Procainamide
Amiodarone
Sotalol
Premature ventricular contractions Identify and treat underlying cause
Lidocaine
Ventricular tachycardia Lidocaine
Amiodarone
Procainamide
Sotalol
Magnesium (for torsades de pointes)
ß‐blockers
Phenytoin (for digitalis toxicity)
Ventricular fibrillation Lidocaine (adjunct to defibrillation/prevent recurrence)
Amiodarone (adjunct to defibrillation/prevent recurrence)

Atrial tachycardias

The automaticity of atrial tissue accounts for the majority of supraventricular arrhythmias in this group [8]. In general, these rhythm disorders are more recalcitrant and difficult to treat than reentrant ones.


Focal atrial tachycardia

Focal atrial tachycardia (AT) originates from a single focus in the atrium outside of the sinus node. In the past, this rhythm disturbance was thought to be due solely to enhanced automaticity. Thus, it was often referred to as an automatic or ectopic AT (EAT; also known as atrial ectopic tachycardia, or AET). In rare cases, however, focal AT is triggered or microreentrant in origin and is not due to a true ectopic focus. These forms of AT cannot be easily differentiated on the basis of the surface ECG alone. The clinical characteristics of EAT follow those outlined in Table 22.1 for automatic tachycardias. EAT may be incessant or episodic. The diagnosis is made by identifying abnormal P‐wave morphology, axis, or both on a surface ECG or rhythm strip (Figure 22.8). Also, the PR interval may differ from that in sinus rhythm. Atrial rates in EAT are faster than usual sinus rates for the age and physiologic state of the patient. If the atrial rates are very rapid, some of the atrial impulses may not be conducted to the ventricles because of AV node refractoriness.


Ectopic AT is relatively rare and is generally found in two different clinical scenarios [9, 10]. A child with a structurally normal heart can develop EAT as a primary phenomenon. In older children, EAT can be incessant and, on rare occasions, lead to the development of ventricular systolic impairment or result in dilated cardiomyopathy due to the chronicity of the tachycardia. In neonates and infants, EAT often follows a more benign course and frequently resolves spontaneously early in life. A patient with CHD can also develop EAT in the postoperative period after cardiac surgery. In such cases, EAT tends to be episodic and transient, usually resolving within days. It has been reported that postoperative patients who developed EAT tended to have a lower preoperative oxyhemoglobin saturation, increased inotropic support both pre‐ and postoperatively, and a previous atrial septostomy [11]. No specific cardiac repair has been associated with the development of EAT.


Management principles for postoperative EAT


  • General considerations. The management of postoperative EAT includes the treatment of fever if present, adequate sedation, correction of electrolyte abnormalities, and the withdrawal of medications that cause sympathetic stimulation (e.g., inotropic agents) or have vagolytic properties.
  • Anti‐arrhythmic therapy. The institution of pharmacologic treatment is based on overall heart rate, the duration of the tachycardia, and the hemodynamic status of the patient. Treatment relies on clinical judgment and is influenced by ventricular function. There are no large studies on anti‐arrhythmic drug efficacy in postoperative EAT. Medications such as esmolol, procainamide, and amiodarone can be effective in slowing the tachycardia rate [12]. Oral agents (class I, II, and III drugs) can also be of benefit. Digoxin has a minimal effect on the atrial focus but can decrease the ventricular response by slowing AV conduction [13].
    Schematic illustration of ectopic atrial tachycardia.

    Figure 22.8 Ectopic atrial tachycardia. Fifteen‐lead electrocardiogram in a 6‐year‐old child with ectopic atrial tachycardia. The characteristic features of the tachycardia are shown, including a faster‐than‐expected heart rate for age and an abnormal P‐wave axis (left atrial focus).


  • Ablation therapy. In very few postoperative patients, EAT can be incessant and life‐threatening, and consideration should be given to transcatheter ablation of the atrial focus [14]. It has been reported that propofol anesthesia may not be appropriate for children undergoing catheter ablation of EAT, because administering this drug may terminate the tachycardia and prevent it from being induced by isoproterenol infusion (See Chapter 34) [15].
  • Other modalities. Atrial pacing and cardioversion are unlikely to resolve EAT.

Multifocal atrial tachycardia

Multifocal atrial tachycardia (MAT), also known as chaotic atrial rhythm, is an uncommon atrial arrhythmia characterized by multiple (at least three) P‐wave morphologies [16]. These different morphologies correspond to multiple foci of automatic atrial activity. Characteristic ECG features include variable PP, RR, and PR intervals and typical atrial rates that exceed 100 bpm. MAT can be seen in young infants without structural heart disease, in postoperative CHD patients, and in children with non‐cardiac medical conditions [17, 18]. Treatment focuses on ventricular rate control or decreasing automaticity, or both. Drugs such as digoxin, procainamide, flecainide, amiodarone, and propafenone have been found to be successful in converting MAT to sinus rhythm in children [19]. Adenosine, pacing, and direct‐current cardioversion are usually ineffective.


Junctional tachycardias

The automaticity of junctional tissue accounts for the majority of supraventricular arrhythmias in this group [8]. These rhythm disorders tend to be somewhat resistant to standard pharmacological therapy.


Accelerated junctional rhythm

Accelerated junctional rhythm is an arrhythmia that arises from the AV junction. Characteristics of this automatic rhythm include a narrow or “usual” QRS pattern with no preceding P wave. There is either VA dissociation, with ventricular rates faster than atrial rates, or the presence of 1 : 1 VA conduction retrograde via the AV node. Temporary atrial pacing at a rate of 10–20 bpm faster than the junctional rate often re‐establishes AV synchrony and effectively suppresses the automatic junctional rhythm. Changes in the patient’s physiologic state (including fever), chronotropic agents, and endogenous catecholamines can stimulate the automatic junctional focus, increasing junctional rates. This rhythm is usually well‐tolerated and is easily managed with temporary pacing and control of the patient’s underlying physiologic state.


Junctional ectopic tachycardia

Junctional ectopic tachycardia (JET) is another automatic rhythm that arises from the AV junction. It is a narrow or “usual” complex tachycardia without preceding P waves. It is distinguishable from accelerated junctional rhythm on the basis of the patient’s heart rate and hemodynamic status. This tachyarrhythmia has been classically defined by heart rates above 160 or 170 bpm with resultant hemodynamic compromise [20]. The diagnosis of JET has also been considered if the junctional rate exceeds the 95th percentile of heart rate for age [21]. There is either VA dissociation with ventricular rates faster than atrial rates or the presence of 1:1 VA conduction (Figure 22.9). If 1:1 VA conduction is identified, a trial of adenosine or rapid atrial pacing may be beneficial to differentiate JET from other reentrant forms of SVT on an AEG.


This type of tachycardia typically occurs in the immediate postoperative period and usually results in hemodynamic instability and significant morbidity and may contribute to mortality [22–24]. It occurs most commonly after surgical intervention for tetralogy of Fallot, VSD, AVSD, transposition of the great arteries, and total anomalous pulmonary venous return [25]. Other risk factors for the development of JET are long ischemic cross‐clamp and cardiopulmonary bypass times, young age, and the need for inotropic support [26, 27]. Excessive retraction of tissues to allow for intracardiac surgical exposure anecdotally has also been linked to JET. Several strategies have been used to decrease the incidence of postoperative JET. The administration of magnesium during cardiopulmonary bypass decreases the incidence of postoperative JET, its use appears to be more effective in higher complexity surgeries [28, 29]. Another strategy that has shown promise in the reduction of postoperative JET is the use of dexmedetomidine in the perioperative period [30, 31].


Management principles for postoperative JET

Numerous therapies have been advocated for JET [23, 24, 26, 32]. Strategies for acute care include the following:



  • General considerations. Core temperature cooling (to 33–35 °C) in the younger patient by the use of cooling blankets, fans, or cold compresses has been shown to be of benefit in reducing the tachycardia rate [33–35]. Shivering, if significant, should be minimized to prevent potentially detrimental increases in oxygen consumption. Additional suggested approaches include withdrawing or decreasing vagolytic agents and any medications associated with catecholamine stimulation and correcting abnormal levels of electrolytes, especially magnesium, potassium, and calcium.
  • Atrial pacing. Temporary atrial pacing at heart rates 10–20 bpm above the JET rate establishes AV synchrony and often improves hemodynamics. However, if the JET rate is faster than 180 or 190 bpm, overdrive atrial pacing often confers a little benefit.
  • Anti‐arrhythmic medications. The two most widely used drugs for JET are amiodarone and procainamide [26, 32, 36–38]. Amiodarone has a longer onset of action and a longer half‐life than procainamide. The drug has been shown to reduce the heart rate in JET patients during the initial bolus infusion [36, 37]. Core cooling is often continued but is not generally needed for efficacy. Administering amiodarone may be a way to avoid having to evaluate clinical signs reflecting the adequacy of cardiac output (distal peripheral perfusion, skin temperature) in a patient with hypothermia and tachycardia. Amiodarone does not directly influence ventricular function and is generally thought to cause less likelihood of hypotension during the initial bolus infusion than procainamide does. However, the drug should be administered with caution, given its potential adverse events (hypotension, bradycardia, AV block). The benefits of procainamide are that it has a faster onset of action and a shorter half‐life than amiodarone. However, procainamide appears to be effective mainly when used with core cooling. It may also cause a decrease in systemic vascular resistance, with resultant hypotension, particularly during bolus infusions. Procainamide can also have negative inotropic properties. Usually, a fluid bolus or other volume expander should be given before or during procainamide therapy to maintain adequate hemodynamics. Both amiodarone and procainamide have been shown to be effective in the treatment of JET in published retrospective studies; however, the main determinant of drug selection in clinical practice is influenced by physician/institutional preference. Because amiodarone and procainamide can each cause QT prolongation and proarrhythmic side effects, these two drugs should not be administered concomitantly. Intravenous sotalol has been shown in case reports to be of use in the management of post‐operative JET. Further studies are needed to determine the safety and efficacy of sotalol in the management of postoperative JET [39]. Another novel anti‐arrhythmic agent that has shown promise in the management of JET is ivabradine (alone and in combination with amiodarone) [40–43]. Ivabradine is available only for oral administration, so its use is limited to patients that can tolerate oral medications. Anecdotal evidence suggests that digoxin loading can slow the JET rate, but this has not been well documented in the literature. ß‐blockers and calcium‐channel blockers can depress myocardial contractility, a feature that may limit their use in the immediate postoperative period. In this regard, a short‐acting agent such as esmolol may offer a larger margin of safety. The use of intravenous (IV) class IC agents such as propafenone and flecainide has been reported, but these drugs have not been studied extensively for JET [44–46]. The natural history of perioperative JET is that it resolves within 2–5 days after the surgical intervention. Long‐term anti‐arrhythmic therapy is usually not necessary. Rarely, extracorporeal membrane oxygenator (ECMO) support may be necessary for incessant hemodynamically significant JET not responding to other therapies.
    Schematic illustration of junctional ectopic tachycardia.

    Figure 22.9 Junctional ectopic tachycardia. Fifteen‐lead electrocardiogram in a postoperative patient with junctional ectopic tachycardia after corrective surgery for tetralogy of Fallot. The tachyarrhythmia is characterized by a narrow QRS complex and atrioventricular dissociation.


  • Cardioversion is generally considered ineffective in terminating JET.
  • Catheter ablation of the junctional focus should be considered only as a last resort, because it can result in complete AV block, given that postoperative JET is usually transient [47, 48].

Reentrant supraventricular tachycardias

Reentry, also known as “circus” movement or reciprocation, implies that a single stimulus or excitation wave front returns and reactivates the same site or tissue from which it originated. Reentrant forms of SVT may or may not involve accessory pathways.


Atrial flutter

Atrial flutter is a rhythm disturbance confined to the atrial myocardium. The electrophysiologic basis for this arrhythmia involves reentry within the atrium itself. The typical or classic form of atrial flutter is characterized by a negative sawtooth P‐wave pattern and atrial rates that exceed 300 bpm (Figure 22.10). This form of atrial flutter is occasionally seen in otherwise healthy neonates but is relatively uncommon in children. In patients with CHD, slower atrial rates and varying P‐wave morphologies are more frequently seen than in those without CHD. This is due to anatomic abnormalities related to suture lines, scars, or fibrosis from a previous surgery involving atrial tissue. This form of “scar flutter” is commonly termed intra‐atrial reentrant tachycardia (IART) [49]. It is one of the most common arrhythmias in postoperative patients with structural heart disease and is considered the cause of significant morbidity after certain types of surgical interventions [50]. Procedures that involve extensive atrial suture lines, such as atrial redirection procedures (Senning or Mustard operations) and those associated with atrial dilation (Fontan surgery) pose a particularly high risk of atrial flutter. The possibility of atrial flutter is suggested by the abrupt onset of a rapid atrial rhythm that remains relatively regular over time. AV nodal conduction accounts for variability in the ventricular response rate. Rapid clinical deterioration is likely; fast ventricular rates frequently require prompt intervention.

Schematic illustration of atrial flutter.

Figure 22.10 Atrial flutter. Surface electrogram showing the typical features of atrial flutter: sawtooth flutter waves and 4:1 atrioventricular conduction.


Management principles for atrial flutter


  • Adenosine will not terminate tachycardia but may assist in confirming the diagnosis by uncovering flutter waves during AV block.
  • Atrial overdrive pacing is a safe and effective way to rapidly terminate atrial flutter by using a transesophageal or transvenous pacing catheter or epicardial wires [51]. After the atrial cycle length is assessed, rapid atrial stimulation is performed in short bursts to attempt an interruption of the reentry circuit.
  • Synchronized cardioversion is the treatment of choice in any patient with unstable hemodynamics. Placement of the cardioversion pads over the front and back of the hemithorax may be necessary to provide a shock vector through the entire atrium, which is usually thickened in patients with CHD.
  • Pharmacologic agents such as digoxin, procainamide, sotalol, and amiodarone can be used in urgent situations. Drugs for controlling the ventricular response in atrial flutter include ß‐blockers and calcium‐channel blockers. Important considerations regarding drug selection are patient age, underlying ventricular function, and whether there is sinus node dysfunction (a concomitant problem in patients with recurrent atrial flutter). Ibutilide and sotalol are available for rapid termination of atrial flutter and have been used in postoperative pediatric and adult patients with CHD [52–55].
  • Long‐term drug therapy is frequently necessary in patients with CHD because of the potential for recurrence and associated rapid AV conduction.
  • Pacemaker therapy, atrial anti‐tachycardia pacing, and radiofrequency ablation are additional modalities often used for long‐term management of atrial flutter.

Atrial fibrillation

Atrial fibrillation is a complex arrhythmia that can be due to either multiple reentrant circuits or focal points within the pulmonary veins. In the majority of cases, it originates in the left atrium (in contrast to atrial flutter, which is generally considered a disease of the right atrium). In children, this tachyarrhythmia is less frequent than atrial flutter. The atrial rates are rapid and irregular, ranging from 400 to 700 bpm. Ventricular response rates are variable but generally range between 80 and 150 bpm. Patients at potential risk for atrial fibrillation include those with an enlarged left atrium (e.g., rheumatic heart disease, severe AV valve regurgitation), pre‐excitation syndromes, structural heart disease (Ebstein anomaly, tricuspid atresia, ASDs), and cardiomyopathies.


Management principles for atrial fibrillation


  • Its management principles are similar to those for atrial flutter except that atrial overdrive pacing is not effective in terminating the arrhythmia.
  • Cardioversion is more likely to be required, and higher amounts of energy may be needed. As in the case of atrial flutter, the placement of cardioversion pads should be optimized by using a front and back configuration over the chest. Anticoagulation and consideration of transesophageal echocardiography for evaluating intracardiac thrombi are recommended before cardioversion if atrial fibrillation has been present more than 48 hours [56, 57].

Atrioventricular reentrant tachycardia and atrioventricular nodal reentrant tachycardia

Atrioventricular reentrant tachycardia (AVRT) is the most common type of SVT in infancy and childhood. It is mediated by an accessory pathway between the atrium and ventricle. The tachycardia circuit typically consists of conduction from the atrium, down the AV node, through the bundle of His and ventricles, and then up the accessory connection back to the atrium. This form of SVT is referred to as orthodromic SVT and occurs in patients with Wolff–Parkinson–White syndrome (WPW; Figure 22.11), concealed accessory pathways, and permanent junctional reciprocating tachycardia. In contrast, in antidromic SVT, conduction travels from the atrium, down the accessory connection, through the ventricles, up the AV node, and back to the atrium. The QRS complex in this form of SVT is wide. Antidromic tachycardia can occur in patients with WPW and other pre‐excitation variants (Mahaim tachycardia).


Atrioventricular nodal reentrant tachycardia (AVNRT), or reentry within the AV node, is most likely in adolescents or young adults. In AVNRT, the AV node has two physiologically distinct components, designated the “slow” and “fast” AV nodal pathways. The typical form of AVNRT consists of antegrade conduction (from the atrium to the ventricle) via the slow pathway, followed by retrograde conduction (back to the atrium) via the fast pathway.


Both AVRT and AVNRT have clinical characteristics typical of reentrant tachycardia mechanisms as listed in Table 22.1. The two can often be distinguished by closely evaluating the surface ECG during sinus rhythm and tachycardia. In orthodromic AVRT, the P wave can be seen immediately after the QRS complex or in the ST segment or T wave (Figure 22.12). The reason for this P‐wave location is that a set time is necessary for conduction to proceed from the ventricles through the accessory pathway back to the atrium. In contrast, in AVNRT, the P wave is buried in the QRS complex and is often not discernible (Figure 22.13). This is the case because the tachycardia circuit is within the AV node, and the atria and the ventricles are activated almost simultaneously. Patients with structurally normal hearts, as well as those with CHD, can have either AVRT or AVNRT. Ebstein malformation of the tricuspid valve is frequently associated with AVRT secondary to one or multiple accessory pathways. The accessory connections in this condition are usually right‐sided. Congenitally corrected transposition can be associated with an Ebstenoid left‐sided AV valve, and left‐sided accessory pathways can be identified in a subset of patients.

Schematic illustration of wolff–Parkinson–White syndrome.

Figure 22.11 Wolff–Parkinson–White syndrome. Surface electrocardiogram depicting the shortened PR interval and characteristic delta wave (slurring and slow rise of the initial upstroke of the QRS complex) in the Wolff–Parkinson–White pre‐excitation syndrome during normal sinus rhythm.

Schematic illustration of atrioventricular reentrant tachycardia.

Figure 22.12 Atrioventricular reentrant tachycardia. Electrocardiogram showing a narrow‐complex tachycardia with a regular rate and a distinct retrograde P wave approximately 80 ms after the QRS complex.

Schematic illustration of atrioventricular nodal reentrant tachycardia.

Figure 22.13 Atrioventricular nodal reentrant tachycardia. Electrocardiogram showing a narrow‐complex tachycardia. There is no evidence of a retrograde P wave because it is obscured by the QRS complex, secondary to simultaneous atrial and ventricular activation.


Management principles for AVRT or AVNRT


  • Direct current synchronized cardioversion (0.5–1.0 J/kg) should be performed in hemodynamically unstable patients. A lower energy setting is adequate if paddles are used directly on the heart (epicardial paddles). Cardioversion should also be considered in stable patients when potential rapid clinical deterioration is anticipated or after an unsuccessful conventional therapy.
  • In stable patients, tachycardia can be rapidly terminated with vagal maneuvers (Valsalva maneuver, coughing, gag reflex stimulation, ice to the face, Trendelenburg position), which enhance parasympathetic influences [58].
  • Adenosine is the first‐line drug therapy for SVT [59–62]. Other agents (digoxin, edrophonium, ß‐blockers, calcium‐channel blockers, phenylephrine, dexmedetomidine, sotalol) have been used in acute treatment with variable results; however, serious adverse effects can be seen. Continuous ECG monitoring is recommended, as well as the availability of atropine and other emergency drugs is ensured, because transient bradycardia may follow tachycardia termination (Figure 22.14). During short‐term pharmacologic therapy, backup pacing may be appropriate, depending on the drug and clinical status of the patient.
    Schematic illustration of adenosine treatment of supraventricular tachycardia.

    Figure 22.14 Adenosine treatment of supraventricular tachycardia. Tracings showing effects of an adenosine bolus administered during supraventricular tachycardia (upper panel). Upon termination of the tachycardia, several ventricular beats are seen (right half of upper panel), followed by just atrial beats (middle panel) and restoration of sinus rhythm (lower panel).


  • Rapid atrial pacing can be performed with a transesophageal electrode catheter or via temporary atrial pacing wires. Beforehand, one must ensure that there is no ventricular capture by the catheter or temporary wires at the desired output site. Rapid atrial pacing is performed by pacing the atrium at 10–20% faster than the SVT rate for a period of up to 15 seconds, which typically terminates the tachycardia. In a patient with a high catecholamine state, SVT can be successfully terminated but rapid recurrence is possible. In this case, a higher level of patient sedation and limiting catecholamine stimulation should be considered.
  • Anti‐arrhythmic medication can be instituted once the tachycardia has terminated or if it terminates and then reinitiates. For perioperative patients unable to take oral medications, parenteral therapy may include procainamide, sotalol, or amiodarone. β‐blockers and calcium‐channel blockers may be less desirable in such cases because of their negative effects on myocardial contractility; a short‐acting agent, such as esmolol, may offer a larger margin of safety.
  • Transcatheter ablation may be warranted in patients with a history of SVT who would prefer not to take medications, or in those with incessant tachycardia that cannot be controlled with medications. Success rates for transcatheter ablation exceed 95%.
Jun 21, 2023 | Posted by in ANESTHESIA | Comments Off on 22: Arrhythmias: Diagnosis and Management

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