Unexplained cardiac arrest (idiopathic ventricular fibrillation): clinical and genetic characteristics

AIM: The study was to evaluate the clinical and genetic characteristics of inherited arrhythmias in patients who survived unexplained cardiac arrest. MATERIALS AND METHODS: 20 patients (10 male and 10 female) aged 15 to 55 years (median age 36 [28; 44] years) with documented VT/VF on ECG were observed for 3 years. The clinical and instrumental study included registration of 12-lead ECG, 24-hour Holter ECG, genealogical history collection and family history of sudden cardiac death with ECG assessment of all family members, transthoracic echocardiography, 2D Speckle Tracking echocardiography and cardiac magnetic resonance imaging to exclude structural myocardial changes. High-throughput sequencing (NGS) was utilized to search for mutations in genes linked to the onset of channelopathies and other inherited rhythm disorders. RESULTS: In 4 (20 %) of the 20 probands included in the study, likely pathogenic variants were identified (pathogenicity class IV), and in 7 (35 %) patients, variants with unknown clinical significance (pathogenicity class III) in 10 genes associated with channelopathies (KCNQ1, KCNH2, SCN5A, AKAP9, ANK2, SCN10А, RYR2) and cardiomyopathies (MYH7, JPH2, RBM20). Several genetic variants were found in 3 cases. No significant genetic changes were detected in 9 (45 %) probands. The clinical diagnosis was established during the follow-up period and was verified due to the genetic testing in 5 (25 %) patients. From their ECGs, a prolonged QTc 460 ms was found in 1 patient, Brugada pattern in 2 individuals, and a shortening of QTc up to 323 ms in 1 proband. Subclinical structural changes associated with cardiomyopathies were revealed in 2 patients. In 15 (75 %) patients, it was unfeasible to establish a distinct clinical phenotype. In 6 (30 %) probands, the diagnosis was clarified due to detected genetic variants. CONCLUSION: Clinical manifestations and diverse genetic variants have been studied in patients who have survived unexplained cardiac arrest. In the course of genotyping patients who suffered unexplained cardiac arrest, genetic changes associated with LQTS were detected in 30 % of cases, while the QTc in most cases did not exceed 440 ms, which makes it difficult to establish a diagnosis at an early stage before the development of life-threatening arrhythmic events. The data from our study confirm the idea that in patients with idiopathic ventricular fibrillation, who have suffered unexplained cardiac arrest, cardiac channelopathy or subclinical manifestations of cardiomyopathy are commonly the cause. This phenomenon imposes a need for genetic testing in this category of patients.