The Significance of Cardiac Sympathetic Nervous System Abnormality in the Long-Term Prognosis of Patients with a History of Ventricular Tachyarrhythmia

Severe left ventricular dysfunction or cardiac sympathetic nervous system (SNS) abnormality predicts cardiac death in various heart diseases, including arrhythmogenic disorders. However, it is not clear whether SNS abnormality predicts sudden cardiac death during long-term follow-up in patients with a history of ventricular tachyarrhythmia. We hypothesized that SNS abnormality would be associated with recurrent ventricular arrhythmic events. Methods: I-123-metaiodobenzylguanidine (MIBG) scintigraphy was performed on 86 patients (mean age +/- SD, 46 +/- 19 y, 65.1% men) with a history of ventricular tachycardia or fibrillation. I-123-MIBG (111 MBq) was intravenously administered under resting conditions, and planar images were obtained 15 min and 4 h later (anterior view for 6 min; 512 x 512 matrices; zoom ratio, 1.0). SNS activity was assessed using the heart-to-mediastinum ratio on delayed imaging. Results: During about 11 y of follow-up (mean +/- SD, 5.2 +/- 3.7 y), 3 patients (3.5%) had sudden cardiac death and 21 patients (24.4%) had sustained ventricular tachyarrhythmic events. SNS abnormality, defined as a heart-to-mediastinum ratio of less than 2.8, and left ventricular dysfunction, defined as a left ventricular ejection fraction of less than 50%, were associated with sudden cardiac death or recurrent ventricular tachyarrhythmic events (18/40 patients [45%] with SNS abnormality, vs. 6/46 patients [13%] without, P = 0.004; 9/15 patients [60%] with left ventricular dysfunction, vs. 15/71 patients [21.1%] without, P = 0.008). After adjustment for potential confounding variables such as age, sex, coronary risk factors, medication use, history of structural heart disease, and left ventricular function, SNS abnormality was a powerful predictor of recurrent arrhythmic events, with a hazard ratio of 3.6 [95% confidence interval, 1.4-9.2, P = 0.007]). Further, SINS abnormality had incremental and additive prognostic power in combination with left ventricular dysfunction, with an adjusted hazard ratio of 4.4 [95% confidence interval, 1.9-9.9, P < 0.0001]). Conclusion: SNS abnormality predicted recurrent ventricular tachyarrhythmic events during long-term follow-up. I-123-MIBG scintigraphic evaluations for SNS abnormality may be an option for screening patients at high risk for sudden cardiac death.