Syncope pp 261-274 | Cite as

Unexplained Syncope in Patients with High Risk of Sudden Death

  • David S. CannomEmail author


Syncope is a clinical measure of increased risk for sudden death in the genetic diseases being considered in this chapter. Distinguishing a syncopal episode that is due to an arrhythmic cause from benign causes of syncope can be difficult. Nonetheless, the clinician needs to make that distinction as the therapy for arrhythmic syncope is entirely different from a case of syncope due to an autonomic cause.

In the patient with known hypertrophic cardiomyopathy (HCM), syncope is a major predictor of sudden death. Other well described risk factors contribute to the overall risk of sudden death. By employing all clinical modalities of treatment in hypertrophic cardiomyopathy patients the risk of death due to complications of the disease, including sudden death, can be reduced to less than 1% per year.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) patients who present with syncope are candidates for an implantable cardioverter defibrillator (ICD) in the ACC/AHA/HRS syncope guidelines. The ESC guidelines recommend an ICD only if the syncope is shown to be due to a ventricular arrhythmia. Implantable loop recorders are recommended for ARVC syncope patients without ventricular tachycardia. Precise risk stratification is difficult in the ARVC patient.

The long QT syndrome (particularly Types 1 and 2) has benefited from large clinical reports in the literature and risk stratification is clear. The patient with long QT (>460 ms) is treated with a beta blocker even if asymptomatic. If syncope occurs an ICD is recommended by both European and ACC/AHA/HRS guidelines.

Brugada syndrome may be both difficult to diagnose and difficult to risk stratify. A sudden cardiac death (SCD) survivor is a candidate for an ICD. Syncope alone without a cardiac arrest is a class IIa recommendation for an ICD in the AHA/ACC/HRS guidelines whereas the ESC guidelines recommend a loop recorder. Genetic testing and electrophysiology studies are not recommended as adding to clinical features for risk stratification.

Catecholaminergic polymorphic tachycardia (CPVT) patients who have a cardiac arrest or multiple syncopal spells without a cardiac arrest are recommended for an ICD. Flecainide can be given to reduce frequent defibrillator shocks. Genetic testing is useful in making the diagnosis of CPVT.


Syncope Sudden death ICDs Cardiomyopathy Genetic heart disease 


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© Springer Nature Switzerland AG 2020

Authors and Affiliations

  1. 1.Division of Cardiovascular MedicineKeck School of Medicine at USCLos AngelesUSA

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