39.4 Cardiac syncope

Cardiac syncope accounts overall for about 10% of the presentations of syncope but it is common in older patients and relatively rare in the young. Diagnosis is by the initial evaluation as proposed by the European Society of Cardiology Guidelines on syncope. Many patients present at the emergency department (ED) where they are seen by ED physicians whose approach is different from cardiologists. ED physicians are concerned with short-term outcome and cardiologists with diagnosis and appropriate treatment. Excellent risk stratification systems are lacking. The result is that admission rates of patients are too high, inflating healthcare costs, and optimal care is not administered. Syncope management units are proposed to address this situation. The pathophysiology of syncope in structural cardiac disease is complex as it depends on the underlying condition and possible coincidence of reflex and arrhythmic syncope. The diagnostic approach must be aligned to the findings of the initial evaluation and many diagnostic tools are available; each has its best deployment. Therapy depends on the diagnosis and includes cardiac pacing for bradycardias, implanted cardioverter defibrillators, ablation, and drugs for tachyarrhythmias. Structural heart diseases are treated according to the cause identified.

Syncope is a common condition; it represents about 1% of emergency department (ED) attendances¹ and around 40% of people sustain at least one syncope in their lives.² The most frequent cause is reflex, of which vasovagal syncope is numerically the greatest.¹ Cardiac syncope, where the cause can be attributed solely to the heart and its related vasculature, accounts for only around 10% of all syncope but these cardiovascular conditions are potentially life-threatening in the majority of cases, demanding precise diagnosis and prompt treatment.

Cardiac syncope should be considered in two main groups: arrhythmic and structural (see Chapter 39.1, Figure 39.1.1). Arrhythmic syncope is either bradycardic including asystole or tachycardic. Bradycardias are caused by conduction tissue disease involving the sinoatrial node, atrioventricular node, or His–Purkinje system. Sinus node disease may precipitate syncope through a pause in beats or also by a fast tachyarrhythmia. Atrioventricular block, caused usually by His–Purkinje disease of unknown aetiology, is associated in the Mobitz II and complete atrioventricular block forms with episodic asystole. When a device implanted to combat one of these conditions malfunctions, bradycardia and asystole may re-emerge. Tachycardias are supraventricular including congenital abnormalities, such as Wolff–Parkinson–White syndrome, and acquired arrhythmias, dominantly atrial fibrillation. Ventricular arrhythmias are considered in two categories: firstly, structural mainly related to myocardial ischaemia and infarction but also to cardiomyopathies and, secondly, related to channelopathies, which are genetically determined. These include long QT and Brugada syndromes as the best known examples. Many arrhythmias in this category are precipitated by drugs, prescribed either for cardiac or more frequently for non-cardiac conditions, acting on vulnerable cardiac channels in the transmembrane electrolyte exchange in depolarization and repolarization.^3,4,5 Again, implanted device malfunction may be responsible.

The second main category is structural cardiovascular. Diseases affecting the heart which obstruct outflow and/or inflow of blood may restrict increases in cardiac output on exercise rendering this insufficient to maintain the circulation. This effect is enhanced by the vasodilation associated with exercise. Examples are left ventricular hypertrophy caused by hypertension, aortic stenosis, or accompanying hypertrophic cardiomyopathy, or external limitation of inflow by pericardial effusion or tamponade. Pulmonary hypertension or pulmonary embolism act by a similar mechanism to limit rises in cardiac output. Other obstructive lesions such as atrial myxoma, atrial ball thrombus, and stenosed prosthetic valves tend to impede the circulation at the level of the atrioventricular valves. Aortic dissection is a condition which acutely obstructs outflow and may also be very painful. Finally, myocardial ischaemia and infarction may precipitate syncope. Rarely, congenital coronary artery abnormalities may cause syncope, usually on the basis of ischaemia and arrhythmia. It is necessary to bear in mind that any of these conditions may be associated with arrhythmias or reflex syncope triggered, for example, by pain or palpitation. Thus, the cause of syncope in structural cardiac syncope may be complex.

Rhythm disturbances adversely affect cardiac function leading to a reduction in cardiac output and blood pressure. In structural heart disease, circulatory demand outstrips supply by the heart due to limitation of inflow and/or outflow of blood which limit cardiac output in the context of the vasodilatation of exercise. The role of a vasovagal type of reflex, by adding further vasodilatation and bradycardia is incompletely understood but it may be triggered by pain in acute structural heart disease and by palpitation in tachyarrhythmias (see Chapter 39.1, Figure 39.1.2).

Cardiac syncope is the third most common cause of syncope after reflex and orthostatic hypotension. In the ED, cardiac syncope amounts to 5–21% of syncope.⁶

It is noteworthy that cardiac syncope increases with advancing age implying that the older the patient is at presentation, the more likely is cardiac syncope.^7,8 Over the age of 60 years, cardiac syncope becomes the second most common cause of syncope after reflex causes. Cardiac syncope causes less than 1% of syncope in youth (<40 years) and 11–34% in those over 60 years of age.^6,8

Emergency physicians are concerned about correct management of syncope on presentation and whether hospital admission is required. Many of the causes of cardiac syncope are life-threatening. The risk was high (odds ratio 1.31) for death following attendance in the ED in the Framingham study.⁸

Another important consideration in the ED is risk of recurrence of syncope⁹ together with the ability of the patient to self-care after discharge from the ED. The best predictor of recurrence is the number of previous episodes of syncope. In the case of four to six previous episodes, 51% recurrence in 2 years can be expected.¹⁰ Gender is not a useful predictor of recurrence.¹¹ Associated trauma in the presenting episode is minor in 29.1% and major in 4.7%. Morbidity is higher in older people especially when institutionalization is required.⁷

Thus, many attempts have been made to create risk stratification schemes to help in deciding whom should be admitted to hospital but, at present, it must be accepted that none is successful.¹² The checklists from the European Society of Cardiology (ESC) Guidelines of low-risk and high-risk features at initial evaluation are shown in Table 39.4.1. High-risk patients are more likely to have cardiac syncope. Structural heart disease and primary electrical disease are major risk factors for sudden cardiac death and overall mortality in patients with syncope. Low-risk patients are more likely to have reflex syncope and have an excellent prognosis.

Patients frequently present in the ED where they will be seen by emergency physicians who are less concerned about diagnosing the cause of syncope than cardiologists. Their concern is, if the patient is discharged, what is the risk of death and recurrence of syncope within a short period. At present, this concern leads to more admissions to hospital (approximately 50%) of patients with syncope than is really desirable as they may remain several days as in-patients undergoing investigation and some are discharged without a diagnosis.^13,14 The implication is unsatisfactory for good patient care and expensive in terms of the healthcare budget. The ESC has recently proposed the creation of specialized syncope management units that will offer the possibility of reducing the admission rate and expense.¹⁵ The 2018 ESC Guidelines on syncope suggest following the risk stratification chart shown in Figure 39.4.1.

The 2018 ESC Guidelines on syncope have identified the diagnostic tests, procedures, and interventions that may require admission for patients with high-risk features; these are listed in Table 39.4.2.

When diagnosis of cardiac syncope is suspected, yet not established, at the initial evaluation, this prompts appropriate tests. Monitoring, which is required to be long term in the case of syncope, will be valuable in bradycardias. Electrophysiological studies are seldom required but may occasionally be diagnostic in tachycardias. False positives occur. Echocardiography may be indicated in structural heart disease when suggested by the initial evaluation. Exercise testing is only warranted if the patient’s symptoms occur in relation to exercise. Tilt testing should be interpreted with caution in patients with suspected cardiac syncope owing to the possibility of false-positive responses; however, if positive, it must be considered as revealing a hypotensive tendency which may not yield a diagnosis.¹⁶

The criteria for appropriate indication and interpretation of diagnostic tests are listed in the tables of recommendations of the 2018 ESC Guidelines on syncope (see Chapter 39.7).

For bradycardias, cardiac pacing offers a solution to many patients’ needs but there are recurrences even in atrioventricular block.^17,18 Device malfunction is nowadays rare and requires reprogramming or device/lead replacement.

Tilt-positive patients are more likely to experience recurrence of syncope¹⁹ when paced for any indication except atrioventricular block. Thus, using tilt as a risk of recurrence stratification tool seems to have value in all bradycardia patients except atrioventricular block.

Ablation is now a well-established therapy for many supraventricular tachycardias offering a complete cure in Wolff–Parkinson–White syndrome and potentially good rhythm control in atrial fibrillation. In ventricular tachyarrhythmias of ischaemic or myopathic origin, implantable cardioverter defibrillators (ICD) are usually indicated according to current guidelines¹⁹ but the role of ablation is gaining ground to reduce the number of shocks needed over the lifetime of an ICD. Device malfunction may allow recurrence of arrhythmia, which is addressed by programming or, if necessary, by device/lead replacement.

Bilateral bundle branch block or trifascicular block remains an unresolved issue when presenting with syncope. Trials, so far, have been inconclusive and it is well known that syncope in these electrocardiogram (ECG) abnormalities can be due to atrioventricular block, where permanent pacing is indicated but also can be ventricular tachycardia or vasovagal syncope. One approach is to insert an ECG loop recorder and await a further syncope in order to make a definitive diagnosis and offer appropriate treatment. This course of action does not appear to endanger the patient. Further trials are awaited.

Specific causes of ventricular tachyarrhythmias deserve mention. Arrhythmogenic ventricular cardiomyopathy may require an ICD and ablation is less effective than in ischaemic aetiology, while long QT syndrome in the majority of cases is approached by use of beta blockers with ICD implantation at any suggestion of lack of arrhythmia control. Brugada syndrome has not been addressed successfully by drugs so an ICD is used in failed sudden cardiac death¹⁹ but considerable conservatism is justified when the cause of syncope is undocumented and the patient is young. This conservatism is on grounds of the high rate of complications of ICDs in these patients and the seemingly high rate of reflex syncope among them.²⁰

The criteria for the choice of the appropriate therapy are listed in the tables of recommendations of the 2018 ESC Guidelines on syncope (see Chapter 39.7).

Cardiac syncope has multiple and diverse causes contributing to about 10% of those episodes of syncope which reach medical attention. The percentage rises much among older patients and is relatively very low in the young. Presentation in the ED raises the problem that a diagnosis is necessary as early as possible so that only the patients needing admission to hospital are admitted. The approach by ED physicians who are obliged to see these patients first is not identical to that of cardiologists. The ED physicians are more concerned with immediate outcome on discharge while cardiologists seek a diagnosis and appropriate treatment. The present high rate of admission is an area of potential improvement in patient management and cost reduction. Treatment of cardiac syncope depends on its identified cause, which is the province of cardiologists.