Unexplained Cardiac Arrest Evaluation
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Source: Krahn AD, et al. Systematic assessment of patients with unexplained cardiac arrest: Cardiac Arrest Survivors With Preserved Ejection Fraction Registry (CASPER). Circulation. 2009;120:278-285.
In this paper, Krahn et al from a Canadian consortium report on the results of systematic evaluations in patients with unexplained cardiac arrest due to ventricular tachycardia or ventricular fibrillation. Patients were eligible for inclusion if they had normal left ventricular function, no severe hypertrophy, normal coronary arteries, long QT syndrome (LQTS), or if Brugada syndrome could not be diagnosed based on their resting ECG and no reversible cause for cardiac arrest had been identified. Patients were enrolled between January 1, 2004 and October 1, 2008, in eight adult and one pediatric electrophysiology center in Canada. Patients who were candidates for the study underwent continuous ECG monitoring, transthoracic echocardiography, and coronary angiography. Patients, where the cardiac arrest remained unexplained, were evaluated using a standardized testing protocol that included a signal averaged ECG, exercise testing, cardiac magnetic resonance imaging, and intravenous drug challenges with epinephrine and procainamide. Patients also underwent electrophysiologic studies with programmed ventricular stimulation using up to three ventricular extrastimuli at two drive cycle lengths. Voltage mapping, right ventricular angiography, and right ventricular biopsy were conducted if occult arrhythmogenic right ventricular cardiomyopathy (ARVC) was suspected. Finally, targeted genetic testing was performed on the basis of phenotype detection. Genetic testing was performed on culprit genes for LQTS, Brugada syndrome, ARVC, and catecholaminergic polymorphic ventricular tachycardia (CPVT).
Sixty-three patients were included in the study. The mean age was 43 ± 13 years; 29 patients were female (46%). Specific diagnoses were made in 35 of 63 patients (56%). The cardiac arrest remained unexplained in the remaining 28 patients (44%). A variety of abnormalities were detected. LQTS was detected in eight patients (23%), CPVT in eight (23%), ARVC in six (17%), early repolarization in five (14%), coronary spasm in four (11%), Brugada syndrome in three (9%) and myocarditis in one (3%). Imaging was positive in eight patients, provocation with either exercise or drug infusion in 18, and voltage mapping or ventricular biopsy in three. Coronary spasm was diagnosed in four patients who spontaneously had greater than 2 mm of ST segment elevation during inpatient telemetry. Family screening was performed in 64 family members of nine patients who had causative mutations. Fifteen of these 64 family members were found to have previously undiagnosed mutations that could lead to cardiac arrest.
Krahn et al conclude that the cause of a previously unexplained cardiac arrest can be determined in about half of all such patients with the use of systematic noninvasive and invasive testing. Drug provocation and advanced imaging modalities had the greatest yield. Positive results can direct genetic testing among family members for genetically mediated arrhythmia syndromes.
Commentary
In most series of out-of-hospital cardiac arrest survivors, about 3%-10% of patients have no apparent structural heart disease identifiable. In some of these patients, the resting ECG provides a diagnosis that can be used to guide therapy, but in others, the ECG and monitoring will be only inconclusive. In this report, Krahn and a group of investigators from nine Canadian centers show that a systematic diagnostic approach can efficiently and accurately identify the cause for cardiac arrest in about 50% of cases. The knowledge gained can then be used to guide therapy both in the patient and, perhaps more importantly, in potentially affected family members.
The greatest yield was seen with provocative tests using either exercise or drug infusions. In patients with LQTS, CPVT, and Brugada syndrome, the baseline ECG may be normal, and it is only with provocative testing that the diagnosis can be made. Electrophysiologic study is rarely helpful in patients with a normal resting ECG and normal cardiac function.
The four patients with spasm-induced arrhythmias are an interesting group. Spasm may occur both with and without a definable underlying coronary stenosis. However, spasm must be suspected and treated when chest pain precedes the arrest and no significant coronary disease is seen with angiography.
Despite the protocol followed by Krahn et al, 44% of the cardiac arrests remained unexplained. Whether these patients have a previously unrecognized condition, or the arrest was the response of a truly normal heart to some unknown irritant, will require future studies looking at this interesting group of patients.
In this paper, Krahn et al from a Canadian consortium report on the results of systematic evaluations in patients with unexplained cardiac arrest due to ventricular tachycardia or ventricular fibrillation.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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