Background-Cardiac arrest without evident cardiac disease may be caused by subclinical genetic conditions. Provocative testing to unmask a phenotype is often necessary to detect primary electrical disease, direct genetic testing, and perform family screening. Methods and Results-Patients with apparently unexplained cardiac arrest and no evident cardiac disease (normal cardiac function on echocardiogram, no evidence of coronary artery disease, and a normal ECG) underwent systematic evaluation that included cardiac magnetic resonance imaging, signal-averaged ECG, exercise testing, drug challenge, and selective electrophysiological testing. Diagnostic criteria were based on accepted criteria or provocation of the characteristic clinical features for long-QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, early repolarization, arrhythmogenic right ventricular cardiomyopathy, coronary spasm, and myocarditis. Sixty-three patients in 9 centers were enrolled (age 43.0Ϯ13.4 years, 29 women Key Words: heart arrest Ⅲ diagnosis Ⅲ catecholamines Ⅲ genetics Ⅲ magnetic resonance imaging C ardiac arrest in the absence of evident structural heart disease is uncommon, with a broad differential diagnosis that includes subclinical cardiomyopathy, primary electrical disorders, and idiopathic ventricular fibrillation. [1][2][3][4][5] Growing recognition of the clinical features of uncommon genetic conditions that lead to cardiac arrest has reduced the number of cases that remain unexplained.
Clinical Perspective on p 285Cardiac ion channel disorders that result in "primary electrical disease" may be difficult to diagnose unless overt ECG abnormalities are present. 6 -12 Subclinical QT prolongation, ST-segment shifts, or ventricular arrhythmias may be electrocardiographically subtle or intermittent. [13][14][15][16][17][18] Although an implantable cardioverter defibrillator (ICD) is indicated in patients who have had a cardiac arrest without a correctable cause, 19 optimal management to reduce recurrence requires a diagnosis. In addition, screening of family members is dependent on recognition of a phenotype that allows case finding, targeted genetic testing, and prophylactic intervention. We describe the yield of sequential noninvasive and invasive testing in Patients were enrolled between January 1, 2004, and October 1, 2008, in 8 adult and 1 pediatric electrophysiology center across Canada. During the recruitment period, the 9 involved centers enrolled 63 patients, during which time they implanted 1877 secondary-prevention ICDs (3.4%). On the basis of projections from the systematic data from a single year, an estimated 105 patients (5.6%) would have been excluded from enrollment because of cardiac arrest manifestly attributed to long-QT syndrome (LQTS), Brugada syndrome. and arrhythmogenic right ventricular cardiomyopathy (ARVC). 23 All patients provided written informed consent. The protocol was approved by the Health Sciences Research Ethics Board of the University of Western Ontario, as well...
