Objective-To examine the circadian variation in the signal averaged electrocardiogram (saECG) and heart rate variability and investigate their relations in healthy subjects. Methods-24 hour ECGs were obtained with a three channel recorder using bipolar X, Y, and Z leads in 20 healthy subjects. The following variables were determined hourly: heart rate, filtered QRS (f-QRS) duration, low and high frequency components of heart rate variability (LF and HF), and the LF/HF ratio. Results-Heart rate, f-QRS duration, HF, and the LF/HF ratio showed significant circadian rhythms, as determined by the single cosinor method. Heart rate and the LF/HF ratio increased during daytime, and f-QRS duration and HF increased at night. f-QRS duration was negatively correlated with heart rate (r = 0.95, p < 0.001) and the LF/HF ratio (r = 0.94, p < 0.001) and positively with HF (r = 0.93, p < 0.001). Conclusions-f-QRS duration has a significant circadian rhythm in healthy subjects and is closely related to the circadian rhythm of autonomic tone. (Heart 1998;79:493-496) Keywords: signal averaged ECG; f-QRS duration; circadian rhythm; heart rate variability Signal averaged electrocardiography (saECG) is a non-invasive method of detecting the substrate for malignant ventricular arrhythmias and is widely used to identify individuals at high risk for such arrhythmias and for sudden cardiac death. [1][2][3][4][5] Although the saECG has been assumed to measure fixed parameters, several studies have shown that these are altered by changes in factors such as heart rate and autonomic tone.6-8 Analysis of heart rate variability has been used to evaluate cardiac autonomic tone. 9-11Heart rate, heart rate variability, cardiac autonomic tone, and ventricular arrhythmias are known to have a circadian rhythm, [12][13][14][15][16] but information on the possibility of a circadian rhythm of the saECG and on the contribution of circadian fluctuations in autonomic function to the saECG is limited. We investigated whether the saECG has a circadian rhythm in healthy subjects and examined the relation between circadian fluctuations of the saECG and heart rate variability. Methods STUDY POPULATIONWe analysed 24 hour ECG recordings obtained in 44 healthy volunteers (28 men and 16 women, mean age (SD): 28.2 (3.3) years) in whom no abnormalities were detected by the medical history, physical examination, biochemical profile, 12 lead ECG, echocardiogram, or chest x ray. No subjects were on drug treatment. ANALYSIS OF 24 HOUR ECG RECORDINGSThe 24 hour ECG recordings were made with a three channel recorder (model 459, Del Mar Avionics, Irvine, California, USA) using bipolar leads X, Y, and Z. saECG analysisSignal averaging was performed on the data obtained from the first 500 seconds of every hour over the 24 hour period and filtered with a bidirectional filter at 40 to 250 Hz. The filtered leads were combined to form a vector as: √X 2 +Y 2 +Z 2 . The QRS onset and oVset were determined by a computer algorithm. The computer determined QRS oVset point w...

on behalf of the J-RHYTHM Registry Investigators* Background--To clarify the influence of hypertension and blood pressure (BP) control on thromboembolism and major hemorrhage in patients with nonvalvular atrial fibrillation, a post hoc analysis of the J-RHYTHM Registry was performed.

Our objective was to examine the autonomic influence on QT interval dispersion using the head-up tilt test in healthy subjects. RR and QT intervals, heart rate variability, and plasma norepinephrine concentration were measured in the supine position and tilting to 70 degrees for 20 minutes using a footboard support in 15 healthy male volunteers (mean age +/- SD: 28.0 +/- 4.5 years). The rate-corrected QT interval (QTc) was calculated using Bazett's formula, and QT and QTc dispersions were defined as the maximum minus minimum values for the QT and QTc, respectively, from the 12-lead ECG. Spectral analysis of the heart rate variability generated values for the low- and high-frequency powers (LF and HF) and their ratio (LF/HF). Compared with values obtained in the supine position, tilting significantly increased QT (P < 0.05) and QTc dispersion (P < 0.01), the LF/HF ratio (P < 0.0001), and plasma norepinephrine concentration (P < 0.0001), and significantly decreased HF (P < 0.0001). QTc dispersion was positively correlated with the LF/HF ratio and plasma norepinephrine concentration, and negatively correlated with HF. These results suggest that head-up tilt testing increases QT dispersion by increasing sympathetic tone and/or decreasing vagal tone in healthy subjects.

The results of this preliminary study indicate that the presence of WML was associated with the microalbuminuria and insulin resistance in these Japanese patients with type 2 DM; larger cohort studies are warranted to confirm these findings.

The present study demonstrated that pioglitazone can restore the nocturnal BP declines in parallel to reductions in the HOMA index, suggesting that insulin resistance may play an important role in the genesis of circadian BP rhythms. TZD-based treatment may thus have the additional therapeutic advantage of reducing the risk of cardiovascular complications by transforming the circadian rhythm of BP.