V-shaped trough in autonomic activity is a possible precursor of life-threatening cardiac events.

BACKGROUND: No reliable precursor of sudden cardiac death is known. METHODS AND RESULTS: Holter electrocardiograms of 34 patients experiencing a cardiac event (event group, 20 deaths) were compared with 191 controls (no event group). The event group included 25 patients with ventricular fibrillation or acute myocardial infarction (AMI), and 9 with cardiac arrest due to complete atrioventricular block. The logarithms were calculated of the moving average of 5 successive values for the low-frequency component (LF), the high-frequency component (HF), and the ratio LF/HF of heart rate variability: ln(LF), ln(HF) and ln(LF/HF). A V-shaped trough appeared in the curve of ln(LF/HF) [sV-trough] or ln(HF) [pV-trough] before such an event in 31 patients in the event group. The V-trough was marked by a small variation lasting 2 h, an abrupt descent lasting 30 min, and a sharp ascent for 40 min. An sV-trough was observed in 22 patients before the onset of ventricular fibrillation or AMI. A pV-trough was observed in all 9 patients before the onset of complete atrioventricular block. In the no event group, an sV-trough and a pV-trough were observed in 10 subjects (5%) and 20 subjects (10%), respectively. The positive predictive accuracy of an sV-trough for ventricular fibrillation or AMI and that of a pV-trough for complete atrioventricular block was 88% and 100%, respectively. CONCLUSIONS: A previously unidentified V-trough of autonomic activity is a potential precursor of lethal events.

Application of heart rate variability analysis to electrocardiogram recorded outside the driver's awareness from an automobile steering wheel.

BACKGROUND: Approximately 5% of motor vehicle deaths are assumed to be occur because of a cardiac event thought to be triggered by multiple factors. One important factor is an imbalance of sympathetic and parasympathetic nervous activities, which can be measured by analyzing heart rate variability (HRV). Therefore, a system has been developed to make electrocardiographic (ECG) recordings outside the driver's awareness from the steering wheel (steering-ECG) with an algorithm to remove noise. METHODS AND RESULTS: Steering-ECG and ECG from a chest lead (chest-ECG) were recorded simultaneously in 10 normal subjects while they were driving for 90 min. For each of 4 parameters (instantaneous heart rate, low- and high-frequency components of HRV, and the ratio of these components in all subjects), mutual information was used to examine whether the fluctuation from the steering-ECG resembled that from the chest-ECG. The mutual information of each parameter was larger than 0.047 with 95% confidence interval (mutual information values vary from 0 to 1; threshold of significance: 0.047). Hence, the fluctuation of each steering-ECG parameter resembled its chest-ECG counterpart. CONCLUSIONS: This system heralds a new driver-safety strategy by reporting alteration of autonomic nervous activity during driving.