Cardiac autonomic tone and its relation to nonsustained ventricular tachyarrhythmias in idiopathic dilated cardiomyopathy

Background: In contrast to postinfarct patients, little is known about card iac autonomic tone and its relation to spontaneous ventricular tachyarrhyth mias in idiopathic dilated cardiomyopathy (IDC). Both heart rate variabilit y (HRV) and baroreflex sensitivity (BRS) are indices of autonomic innervati on of the heart. Hypothesis: The aim of the present study was to determine the relation betw een cardiac autonomic tone assessed by HRV and BRS and spontaneous nonsusta ined ventricular tachycardia (NSVT) on Holter in a large patient population with IDC. Methods: 24-h digital Kelter recordings including HRV analysis and BRS test ing were prospectively performed in 137 patients with IDC and preserved sin us rhythm Mean age was 48 +/- 12 years, and mean left ventricular (LV) ejec tion fraction was 32 +/- 9%. The HRV analysis on Holter included the mean R R interval (RRm), the standard deviation of all normal RR intervals (SDNN), the square root of the mean of the squared differences between adjacent no rmal RR intervals (rMSSD), and the proportion of adjacent normal RR interva ls differing more than 50 ms (pNN50). Testing for BRS was performed noninva sively using the phenylephrine method. Results: Of 137 study patients, 32 (31%) had spontaneous NSVT on 24-h Kelte r. compared with patients without NSVT, patients with NSVT on Holter had a higher New York Heart Association (NYHA) functional class (HYHA III: 40 vs. 18%, p<0.01), a lower ejection fraction (29 +/- 9 vs. 34 +/- 9%, p = 0.01) , and an increased LV end-diastolic diameter (69 +/- 8 mm vs. 66 +/- 7 mm, p = 0.03). The HRV variables rMSSD, pNN50, RRm, and BRS did not differ sign ificantly between patients with and without spontaneous NSVT. Only SDNN on Holter was slightly lower in patients with versus without NSVT(106 +/- 45 v s. 121 +/- 46 ms, p = 0.08). Conclusions: Patients with IDC and spontaneous NSVT on Holter are character ized by a higher NYHA functional class, a lower LV ejection fraction, an in creased LV end-diastolic diameter, and a tendency toward a lower SDNN value compared with patients without NSVT. The remaining measures of HRV includi ng rMSSD and pNN50 reflecting primarily tonic vagal activity, as well as BR S reflecting predominantly reflex vagal activity, were similar in patients with and without NSVT The prognostic significance of these findings in pati ents with IDC is currently under investigation in the Marburg Cardiomyopath y Study (MACAS) at our institution.