Relationship between cardiac autonomic tone and left ventricular dysfunction in dilated cardiomyopathy

In recent years, evaluation of cardiac autonomic activity by means of heart rate variability (HRV) determination and baroreflex sensitivity (BRS) test ing has become readily available. The results of the ATRAMI (Autonomic Tone and Reflexes After Myocardial Infarction) study showed that both diminishe d HRV and baroreflex sensitivity are associated with poor outcome in patien ts after myocardial infarction. In contrast to patients with coronary disea se little information is available concerning cardiac autonomic activity in idiopathic dilated cardiomyopathy (IDC). Therefore, HRV and BRS were asses sed in 160 patients with IDC and preserved sinus rhythm in order to investi gate the relationship between HRV, BRS, and left ventricular ejection fract ion. Time domain indices of HRV were computed from 24-hour digital Holter r ecordings. BRS testing was performed using the noninvasive phenylephrine: m ethod. Mean standard deviation of all normal RR intervals (SDNN) of the who le study population was 112 +/- 46 ms, A well preserved HRV (SDNN > 105 ms) was found in 74 patients (46%), a moderately decreased HRV (SDNN 70-105 ms ) in 59 patients (37%), and a severely decreased HRV (SDNN < 70 ms) in 27 p atients (17%). Mean BRS was 7.5 +/- 5.0 ms/mm Hg. A well preserved BRS (> 6 ms/mm Hg) was present in 78 patients (57%), a moderately decreased BRS (3- 6 ms/mm Hg) was present iu. 38 patients (28%), and a severely decreased BRS (< 3ms/mm Hg) in 21 patients (15%). There was only a weak correlation betw een SDNN and BRS (r = 0.19; p < 0.05). A weak correlation was Found for SDN N and left Ventricular ejection fraction (r = 0,29: p < 0.05). There was no significant correlation between BRS and left ventricular ejection fraction (r = 0,14). In summary, there was only a weak correlation between the HRV, BRS, and left ventricular ejection fraction in patients with IDC suggestin g that these 3 variables may be independent predictors of sudden death in I DC. The relative prognostic value of these variables and other potential ri sk predictors including the presence of arrhythmias on Holter, microvolt T wave alternans, QTc dispersion, and signal-averaged ECG is currently under investigation in a large prospective observational study (Marburg Cardiomyo pathy Study (MACAS)) during 5-year follow-up at our institution.