Assessment of Unexplained SCA With Focus on Idiopathic Ventricular Fibrillation

Study Questions:

In real-world practice, how often do patients with unexplained sudden cardiac arrest (SCA) receive systematic and thorough investigation?


This observational study analyzed the medical records of all patients in the Paris-SDEC (Paris Sudden Death Expertise Center) registry who survived to hospital discharge following out-of-hospital cardiac arrest. Medical investigations were conducted at the discretion of the real-world managing medical team. Data collection was standardized for all cases and included demographic characteristics, location of arrest, pre-hospital data, past medical history, final diagnoses, preventive measures implemented, and vital status and neurological outcome at hospital discharge.


Of 18,662 out-of-hospital cardiac arrests, 717 patients with a diagnosis of SCA of cardiac etiology survived to hospital discharge from May 2011 to May 2016. Diagnosis was established in 87.7% (n = 629) by electrocardiogram (ECG), coronary angiography, and echocardiogram. Additional testing yielded a diagnosis in 5.4% (n = 39) by cardiac magnetic resonance imaging, ergonovine challenge, ajmaline test, and catecholamine test. Underlying diagnosis was coronary artery disease in 525 (73.2%), cardiomyopathy in 88 (12.3%), electrical cardiac disorder in 15 (2.1%), and “other” in 40 (5.6%). Idiopathic ventricular fibrillation was the diagnosis of exclusion in 49 (6.8%) patients. Patients labelled with idiopathic ventricular fibrillation were younger and had fewer traditional cardiovascular risk factors and a greater likelihood of family history of SCA. Emergency medical service was less frequently called prior to SCA, fewer warning symptoms occurred, and time from collapse to basic life support was longer. All patients with a diagnosis of idiopathic ventricular fibrillation had a favorable neurological outcome; all were implanted with an implantable cardioverter-defibrillator. Family screening was initiated during initial hospitalization in 12 (24.5%). Additional testing was performed on patients labelled with idiopathic ventricular fibrillation; however, the types of testing performed was done inconsistently. In addition to ECG, echocardiogram, and coronary angiogram, most (n = 40; 81.6%) had cardiac magnetic resonance imaging. Many had some form of provocative challenge: ajmaline (n = 21; 42.9%) and ergonovine (n = 19; 38.8%). Several had electrophysiology study (n = 12; 24.5%), usually with isuprel infusion (n = 10; 20.4%), genetic testing (n = 9; 18.4%), 24-hour Holter monitor (n = 6; 12.2%), or right ventricular angiography (n = 5; 10.2%). Fewer had exercise testing (n = 4; 8.2%), signal-averaged ECG (n = 2; 4.1%), or cardiac scintigraphy (n = 1; 2.0%). Cardiac biopsy, adrenaline challenge, and voltage mapping were not performed. More thorough investigations were conducted on younger patients and on those admitted to university centers with dedicated electrophysiology units. During a median 48.7-month follow-up period, additional testing was performed including exercise testing, Holter-ECG, genetic testing, ergonovine challenge, and cardiac scintigraphy. These tests revealed coronary vasospasm in 2 and long QT syndrome (unmasked by exercise testing) in 1 associated with a KCNQ1 gene variant of unknown significance. During the follow-up period, 10 (21.7%) patients with idiopathic ventricular fibrillation had recurrent ventricular arrhythmia with an annual incidence rate of 5.7%.


This study shows the extent to which unexplained cardiac arrest is inadequately evaluated in the real-world setting because fewer than 20% of patients labeled with idiopathic ventricular fibrillation received a comprehensive evaluation. Previous studies have shown that systematic evaluation that utilizes provocative, exercise, and genetic testing may allow the identification of a definitive diagnosis in >50% of otherwise unexplained SCA. These results demonstrate a gap between results from tertiary specialized electrophysiology teams and unselected real-world hospitals and the importance of referring these patients to expert centers.


Findings suggest that systematic, comprehensive cardiac evaluation is significantly underutilized in the community, leading to overuse of the diagnosis of idiopathic ventricular fibrillation. These findings merit the implementation of a standardized and systematic diagnostic approach for the evaluation of unexplained SCA.

Clinical Topics: Arrhythmias and Clinical EP, Congenital Heart Disease and Pediatric Cardiology, Heart Failure and Cardiomyopathies, Invasive Cardiovascular Angiography and Intervention, Noninvasive Imaging, Stable Ischemic Heart Disease, Atherosclerotic Disease (CAD/PAD), Implantable Devices, Genetic Arrhythmic Conditions, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Congenital Heart Disease, CHD and Pediatrics and Arrhythmias, CHD and Pediatrics and Imaging, CHD and Pediatrics and Interventions, Statins, Interventions and Coronary Artery Disease, Interventions and Imaging, Interventions and Structural Heart Disease, Angiography, Magnetic Resonance Imaging, Nuclear Imaging, Chronic Angina

Keywords: Out-of-Hospital Cardiac Arrest, Ventricular Fibrillation, Electrophysiology, Coronary Angiography, Coronary Artery Disease, Defibrillators, Implantable, Ajmaline, Isoproterenol, Epinephrine, Coronary Vasospasm, Ergonovine, Electrocardiography, Exercise Test, Long QT Syndrome, Cardiomyopathies, Emergency Medical Services, Hospitalization, Radionuclide Imaging, Magnetic Resonance Imaging

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