Procedures which require general anaesthesia may stress the heart, producing cardiac arrhythmias, particularly in the presence of ischaemic heart disease.
More frequently, the electrocardiographic recording performed at pre-assessment or during procedures reveals pre-existing rhythm disturbances that have not previously been diagnosed.
Arrhythmias diagnosed at the time of anaesthesia may have prognostic importance and most are fully correctible.
The diagnosis of atrial fibrillation (AF) or flutter may permit referral for anticoagulation, which in turn may prevent stroke.
If the risk of bradycardia is sufficient to require perioperative pacing, it almost always requires permanent pacing. The perioperative use of temporary pacing has therefore declined almost to the point of disappearance.
Screening in the pre-assessment clinic may identify cardiac pathology which may constitute a threat to the life of the patient and to the successful completion of the elective procedure. This risk may be small, but because it may be mitigated, it is worthy of much attention.
The anaesthetist in pre-assessment may seek electrophysiology expertise and input to assess arrhythmias and delineate their risk. These arrhythmias include both tachyarrhythmias and bradyarrhythmias. Tachycardias are now most often treated by ablation but occasionally using antiarrhythmic drugs. The treatment of symptomatic or potentially hazardous bradycardia consists of reversing the cause if possible, and implanting a pacemaker in all other cases. Many patients attending for elective procedures have arrhythmias, have had arrhythmias in the past or are at risk of arrhythmias. Guidelines are available to aid the anaesthetist in managing these patients (Kristensen et al., 2014), and this chapter aims to summarise and explain the more important practical aspects of these.
The concept of cardiac electrophysiology as a matter of electronics divorced from the simple mechanics of coronary flow and cardiac valves is of course a false one. Life-threatening arrhythmias usually occur as a consequence of severe structural heart disease, and most decisions on treatment in electrophysiology are made on simple structural criteria, not esoteric electrophysiological ones.
Arrhythmic Risks of the Perioperative Period
The stress of surgery may provoke myocardial ischaemia. In a conscious patient, ischaemia is manifest first as chest discomfort. If ischaemia occurs during anaesthesia, there is no such warning; the features are first electrical, later haemodynamic. Early recognition of the electrical features is vital. The sequence of events is observed daily in patients presenting to cardiology with acute myocardial infarction (MI) or undergoing angioplasty: the ST segments become elevated or depressed, ventricular ectopic beats occur and occasionally trigger ventricular fibrillation (VF) or, less often, ventricular tachycardia (VT). If the occlusion persists and the ischaemia involves a large proportion of the myocardium, haemodynamic deterioration progresses from hypotension and raised left atrial pressure to cardiogenic shock and pulmonary oedema. Early recognition permits treatment of the ischaemia, but ideally the risk should be avoided by recognising the risk before surgery is performed, and treating it by revascularisation.
Because patients fast before surgery and sometimes are not able to take oral medications for many hours during and immediately after it, elective medications can be omitted for long periods. This can usually be avoided by administration of necessary medications orally as close as possible before and after the procedure. All of the common antiarrhythmic agents can be given intravenously if oral administration is impossible for a substantial period.
It is important to instruct the patient with absolute clarity on preoperative fasting: all vital medications including antiarrhythmic agents should be taken with a minimum of water even if their time of administration falls within the preoperative fasting period.
Most arrhythmias are intermittent, so the history is more likely than examination to hint at a problem. Minor arrhythmias generally manifest as palpitation, life-threatening ones as syncope or pre-syncope. The investigation of any of these symptoms rests on obtaining an electrographic record of the heart rhythm at the time of the symptoms, ideally a continuous recording of sufficient duration to encompass the onset and termination of the event. The frequency and duration of the symptoms dictates the type of device required to obtain a recording that meets these criteria.
In the asymptomatic patient, the only rhythm disturbances that are commonly encountered are atrial fibrillation (AF), atrial tachycardia and ectopic beats. All of these may be detected on clinical examination, but more often are noted on a routine ECG or on ambulatory ECGs done for other purposes.
A routine preoperative ECG is fast and free of risk. It has therefore become routine in many settings. Although the yield of information of immediate importance is low, the ECG performed in this relaxed setting often forms a baseline that is valuable in subsequent years. As there is some cost involved, ECG screening has become more selective and is now recommended to subsets of patients, but this still constitutes a large proportion of those requiring general anaesthesia.
ECG screening is recommended in patients aged over 65 years undergoing high-risk surgery and in all patients with heart failure or ischaemic heart disease, with renal impairment, diabetes requiring insulin or a history of transient ischaemic attack or stroke. ESC guidelines recommend against it in younger patients undergoing low-risk procedures, but this still leaves a substantial grey area where ECG screening is permitted but not necessarily recommended (Kristensen et al., 2014).
The immediate benefits of ECG screening pertain more to ischaemic and structural heart disease than to arrhythmias. The ECG may identify abnormalities that require further investigation by exercise stress testing, stress echo, coronary angiography or other modes of cardiac imaging to determine whether the patient is fit for the intended procedure or whether revascularisation is required either as an enabling procedure before the planned surgery or for the long-term welfare of the patient.
AF, atrial flutter and isolated ectopic beats of either atrial or ventricular origin are frequently found on the resting ECG of asymptomatic patients.
Exercise Stress Electrocardiogram
An exercise stress test is normally performed to observe ventricular repolarisation during myocardial stress to exclude the presence of prognostically important ischaemia. It is also useful in excluding the presence of exercise-induced arrhythmia or observing how an arrhythmia will behave in circumstances of stress and thus predicting whether it is likely to cause problems in the perioperative period.
The ambulatory ECG recorder developed by Norman Holter has been a cornerstone of clinical electrophysiology for decades. The 24-hour period documented in most recordings is an arbitrary one, but as it covers the entirety of the most important of the cycles that govern our lives, it gives an excellent representation of the long-term electrical behaviour of the heart. For most purposes, particularly in the asymptomatic patient, this 24-hour recording is sufficient provided that the patient undertakes a normal spread of activities during the period of recording.
In patients complaining of symptoms that occur less frequently than once per day, a longer recording is required. Variants on the traditional Holter monitor have been developed to fill this niche. For continuous recordings of up to 1 week, a reasonable level of tolerability can be achieved by using more compact devices and fewer electrodes compared to those designed for 24-hour recordings.
When symptoms occur only a few times per year or less frequently, an implanted loop recorder (ILR) is the only convenient way of obtaining a recording that encompasses an episode from start to finish. Several models of ILR are available, all of which may be implanted through an incision as little as 1 cm in length, are minimally obtrusive and well tolerated and remain active for 2 years or more after implantation.
Event recorders give a less complete recording of an event as the recording can be started only after the patient notices the symptoms and applies the device. Many models of event recorders are available, and smartphones can be adapted to this function with appropriate attachments and software applications.
Atrial and ventricular ectopic beats occur in a substantial majority of healthy individuals in any given 24-hour period. In the presence of structural heart disease, the frequency of ectopic beats is greater, as is the variety of morphologies of the ventricular ectopics (Gallagher et al., 2007). Ventricular ectopics can produce left ventricular dysfunction if the frequency exceeds 10,000 beats per day over a period of years (Baman et al., 2010). Because of its status as a marker of risk, the presence of ectopic beats on a routine screening ECG should prompt referral for echocardiography and a 24-hour Holter monitor.
From around 40 years of age, most patients will display one or more runs of atrial tachycardia in any 24-hour Holter recording (Figure 3.1). In children and young adults such runs of atrial beats are less common, and may merit further investigation, at least echocardiography. In older patients no investigation or treatment is required.