Tachyarrhythmias

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  • A wide complex rhythm suggests an aberrancy in the normal conduction system and is usually the result of one of the following:

    • A preexisting or rate-related abnormality within the normal conduction system (e.g., bundle branch block).
    • An accessory pathway (e.g., Wolff–Parkinson–White syndrome [WPW]).




      Table 21.1. Classification of common tachyarrhythmias







      Presentation


      Classic presentation


      • Ironically, the “classic presentation” mostly consists of nonspecific symptoms. Patients may complain of palpitations, chest pain, lightheadedness, dyspnea, or nonspecific weakness.
      • Further evaluation will reveal a rapid heart rate on physical examination or on the electrocardiogram (ECG).

      Critical presentation


      • Patients with unstable tachyarrhythmias present with signs and symptoms of hypoperfusion and hemodynamic compromise while still maintaining a palpable pulse:

        • Hypotension
        • Altered mentation
        • Ischemic chest pain
        • Pulmonary edema.

      • Patients who do not have a palpable pulse are deemed to be in cardiac arrest and are treated according to Advanced Cardiovascular Life Support (ACLS) guidelines.

      Diagnosis and evaluation



      • Primary evaluation consists of performing an ECG with a rhythm strip.
      • Once tachyarrhythmia is confirmed, consideration should be given to whether the arrhythmia has an underlying noncardiac etiology such as a toxic ingestion or a metabolic disturbance.

        • Clinical history is useful and important. Attention should be paid to the patient’s medical history and potential use of QT-prolonging medications.
        • A chest radiograph and basic blood work may be helpful in identifying a metabolic or infectious etiology of the arrhythmia.

      • The type of arrhythmia can be determined on the basis of the ECG:

        • Sinus tachycardia:

          • Narrow-complex tachycardia.
          • Regular rate greater than 100 bpm.
          • Rates >160 bpm are not typically attributable to sinus tachycardia.
          • Each P wave is associated with a QRS complex.
          • There is a fixed P-R interval.

      • Supraventricular tachycardia (SVT):

        • Narrow-complex tachycardia.
        • Regular rate between 140 and 250 bpm.
        • P waves may be present but difficult to see due to the rate.
        • The most common cause of SVT is atrioventricular nodal reentrant tachycardia (AVNRT).
        • SVT may also present as a wide-complex tachycardia if it is associated with a rate-related or preexisting bundle branch block. This is often referred to as “SVT with aberrant conduction” and may mimic VT.

      • Atrial fibrillation:

        • Atrial fibrillation is the most common cardiac arrhythmia.
        • Usually narrow complex, but can present with a wide QRS in the presence of underlying disease of the conduction system.
        • Irregularly irregular rhythm with absent P waves and atrial rates varying from 400 to 700 bpm.
        • Ventricular response is usually 120–180 bpm.
        • Irregularly irregular rate distinguishes AF from other arrhythmias, even when the complex is wide.

      • Atrial flutter:

        • On a spectrum of sinus node dysfunction with atrial fibrillation.
        • Usually narrow complex.
        • Presents with a classic “sawtooth” pattern of P waves.
        • The atrial rate ranges between 250 and 350 bpm.
        • Atrial flutter is associated with varying degrees of AV block and can present as a regular or regularly irregular rhythm.
        • Most often, the atrial rate is regular at 300 bpm with a 2:1 block, producing a regular ventricular rate of 150 bpm.

      • Multifocal atrial tachycardia:

        • Irregularly irregular tachyarrhythmia.
        • Diagnosed by the presence of at least three different P wave morphologies with varying P-R intervals.
        • MAT is almost always seen in the elderly and those with pulmonary disease. It is also associated with hypomagnesemia, hypokalemia, and coronary artery disease.

      • Ventricular tachycardia:

        • Wide complex regular tachyarrhythmia.
        • Ventricular rate is greater than 120 bpm.
        • VT can be monomorphic or polymorphic:

          • Monomorphic VT usually presents with rates between 120 and 300 bpm.
          • Polymorphic VT usually has rates >200 bpm.
          • Torsades de pointes is a polymorphic VT with a prolonged QT. On the ECG, the QRS complex appears to be twisting around an axis. It is a subtype, not a synonym, of polymorphic VT.

      • All wide-complex regular tachycardias are potentially life threatening and should be considered VT until proven otherwise.
      • Ventricular fibrillation:

        • Wide complex irregular tachyarrhythmia.
        • Always associated with unstable or pulseless patient.

      Critical management



      • In patients with tachyarrhythmias, critical management actions include

        • Assessment of overall stability with ABCs
        • ECG and continuous telemetry
        • Intravenous access
        • Placement of pacer/defibrillation pads on the patient in anticipation of potential deterioration

      • Definitive therapy will vary depending on the underlying rhythm.
      • Commonly used medications as well as their dosage are presented in Table 21.2.

        • Sinus tachycardia

          • The primary goal with a patient in sinus tachycardia (ST) is to treat the underlying condition rather than the tachycardia itself.
          • The primary indication for rate control in ST is during acute myocardial infarction, where tachycardia is associated with worse outcomes. Nodal agents, particularly beta-blockers, are useful in this setting.

        • Paroxysmal supraventricular tachycardia

          • Generally unrelated to an underlying cause.
          • Rhythm control is the primary intervention.
          • Vagal maneuvers can be attempted prior to pharmacological therapy.
          • Adenosine is the medication of choice as it is both diagnostic and therapeutic.

            • Adenosine is metabolized quickly by nonspecific esterases in the plasma and therefore should be pushed quickly via the intravenous access closest to the heart.

        • If adenosine fails, consider synchronized cardioversion or rate control with agents that slow conduction through the AV node.
        • Atrial fibrillation and atrial flutter

          • These rhythms are modulated by sinus automaticity and, like sinus tachycardia, can be driven by underlying etiologies.
          • Rate control is the primary treatment modality

            • Nodal blockers and digoxin are reasonable options.
            • Amiodarone is an appropriate alternative.
            • Of note, rapid atrial fibrillation with a wide QRS complex suggestive of WPW should not be treated with AV nodal blocking agents. In this setting, procainamide or synchronized cardioversion should be used.

      • Multifocal atrial tachycardia

        • Initial therapy for MAT should be aimed at treating the underlying cause such as hypomagnesemia, hypokalemia, pulmonary, or cardiac disease.
        • Pharmacological therapy is indicated if the arrhythmia is causing significant symptoms such as ischemia, hypoxia, heart failure, or shock.
        • Nodal blockers can be used, though their efficacy is limited.

      • Ventricular tachycardia

        • In stable patients with monomorphic VT, procainamide or amiodarone can be used.
        • Polymorphic VT is often caused by myocardial ischemia. Diagnosis and treatment of potential myocardial infarction should be pursued.
        • Treatment of torsades de pointes is aimed at decreasing the QT interval.

          • Intravenous magnesium sulfate is the first-line treatment.
          • Overdrive pacing also shortens the QT interval and can be used if magnesium therapy is ineffective. It can be achieved by transcutaneous pacing or with pharmacological agents such as isoproterenol.

        • Ventricular fibrillation:

          • VF is an unstable rhythm that should be primarily managed by defibrillation.
          • ACLS should be initiated promptly in all patients exhibiting this rhythm.

      Feb 17, 2017 | Posted by in CRITICAL CARE | Comments Off on Tachyarrhythmias

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