Syncope and Ventricular Tachycardia: Revisiting the Evidence Base

Area of Science:

• Cardiology
• Electrophysiology
• Syncope Evaluation

Background:

• Syncope is a common symptom in cardiac disorders, often with misattributed arrhythmic causes.
• Sustained ventricular tachyarrhythmias (VT) are typically non-self-terminating, challenging their role in transient loss of consciousness.

Purpose of the Study:

• To clarify the role of ventricular rhythms in causing brief, self-limited syncope.
• To differentiate between self-terminating and non-self-terminating ventricular arrhythmias in syncope etiology.

Main Methods:

• Synthesis of evidence from community emergency department cohorts, implantable loop recorder (ILR) registries, and implantable cardioverter-defibrillator (ICD) trials.
• Analysis of the characteristics of sustained and nonsustained ventricular tachyarrhythmias in relation to syncope.

Main Results:

• Sustained monomorphic or polymorphic VT typically persist or degenerate, requiring intervention and rarely causing transient syncope.
• Torsades de pointes (TdP) is the primary exception, a self-terminating ventricular arrhythmia associated with prolonged repolarization that can present as syncope.
• Nonsustained VT (NSVT) can indicate underlying cardiac disease severity but is rarely a direct cause of syncope.

Conclusions:

• The evaluation of syncope should prioritize bradyarrhythmic and hypotensive/reflex mechanisms over VT.
• A VT hypothesis for syncope should be reserved for narrowly defined contexts, such as TdP.
• Real-world data indicate malignant ventricular arrhythmias are an infrequent cause of syncope.