The Role of Electrophysiology Testing in Survivors of Unexplained Cardiac Arrest
The Role of Electrophysiology Testing in Survivors of Unexplained Cardiac Arrest
Sudden cardiac death (SCD) remains a major cause of mortality within developed nations
 despite aggressive efforts to reduce its societal burden. Despite extensive clinical and
 genetic investigations, a subgroup of cardiac arrests remain unexplained, highlighting the
 potential contribution of additional cardiac conditions that may not be identified with
 contemporary diagnostic algorithms. The EPS ARREST study aims to evaluate the role of
 invasive electrophysiology study within this patient population.
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