The Role of Electrophysiology Testing in Survivors of Unexplained Cardiac Arrest

The majority of cases of SCD in older individuals occur secondary to coronary and structural
heart disease, while genetic channelopathies and cardiomyopathies are prominent contributors
in young adults. Among individuals that suffer aborted cardiac arrests in the absence of
overt coronary and structural heart disease, diagnostic algorithms that screen for cardiac
channelopathies and more subtle forms of structural heart disease have been established.
Despite the extensive investigations currently utilized, a significant proportion of aborted
cardiac arrests remain unexplained.

Although invasive electrophysiology studies are a cornerstone for diagnosis and management of
arrhythmia disorders, they are not invariably included in the workup of cases of unexplained
aborted cardiac arrest. This is largely driven by initial studies suggesting that the
diagnostic yield in this context is low, however these investigations often used invasive
electrophysiology studies indiscriminately in all cases of aborted cardiac arrest. Since
these earlier studies, our insight and approach to SCD has evolved and it has become clear
that the majority of patients do not require an invasive electrophysiology study for
diagnosis. However an invasive electrophysiology study may still have an important role among
these individuals when the initial workup is negative. Notably, arrhythmias that require
invasive electrophysiology for diagnosis, including bundle branch reentrant ventricular
tachycardia and supraventricular tachycardias associated with hemodynamic collapse, have been
identified as arrhythmic culprits in this patient population.

The goal of the EPS ARREST study is to evaluate the diagnostic yield of a standardized
invasive electrophysiology study among survivors of SCD when initial investigations fail to
identify an underlying etiology.

Inclusion Criteria:

1. Unexplained cardiac arrest requiring cardioversion or defibrillation

2. Willing and able to sign informed consent

Exclusion Criteria:

1. Coronary artery disease (stenosis > 50%) and clinical findings consistent with an
ischemic arrest

2. Reduced left ventricular function (left ventricular ejection fraction < 50%) on
echocardiogram or cardiac MRI.

3. Persistent resting QTc > 460 msec for males and 480 msec for females

4. Resting QTc < 350 msec

5. Type I Brugada ECG with >/= 2 mm ST elevation in V1 and/or V2 (Spontaneous or
Drug-Induced)

6. Polymorphic or bidirectional ventricular tachycardia observed with exertion on
exercise treadmill testing

7. Clinical, electrocardiographic, and/or imaging findings consistent with a diagnosis of
arrhythmogenic right ventricular cardiomyopathy

8. Myocarditis

9. Reversible cause of cardiac arrest such as marked hypokalemia (<2.8 mmol/l) or drug
overdose sufficient in severity without other cause to explain the cardiac arrest.

10. Arrhythmic mitral valve prolapse syndrome

11. Documented ventricular fibrillation initiated by a short-coupled premature ventricular
contraction