Diurnal variation in QT dispersion in patients with chronic heart failure

Disruption of cardiovascular circadian rhythms in mice post myocardial infarction: relationship with central angiotensin II receptor expression

Angiotensin II (Ang II) is well known to participate in the abnormal autonomic cardiovascular control that occurs during the development of chronic heart failure (CHF). Disrupted cardiovascular circadian rhythm in CHF is also well accepted; however, the mechanisms underlying and the role of central Ang II type 1 receptors (AT1R) and oxidative stress in mediating such changes are not clear. In a post myocardial infarction (MI) CHF mouse model we investigated the circadian rhythm for mean arterial pressure (MAP), heart rate (HR), and baroreflex sensitivity (BRS) following MI. The cardiovascular parameters represent the middle 6‐h averages during daytime (6:00–18:00) and nighttime (18:00–6:00). HR increased with the severity of CHF reaching its maximum by 12 weeks post‐MI; loss of circadian HR and BRS rhythms were observed as early as 4 weeks post‐MI in conjunction with a significant blunting of the BRS and an upregulation in the AT1R and gp91^phox proteins in the brainstem. Loss of MAP circadian rhythm was observed 8 weeks post‐MI. Circadian AT1R expression was demonstrated in sham animals but was lost 8 weeks following MI. Losartan reduced AT1R expression in daytime (1.18 ± 0.1 vs. 0.85 ± 0.1; P < 0.05) with a trend toward a reduction in the AT1R mRNA expression in the nighttime (1.2 ± 0.1 vs. 1.0 ± 0.1; P > 0.05) but failed to restore circadian variability. The disruption of circadian rhythm for HR, MAP and BRS along with the upregulation of AT1 and gp91^phox suggests a possible role for central oxidative stress as a mediator of circadian cardiovascular parameters in the post‐MI state.

Increases in central angiotenisn II signaling provide a driving force for sympatho‐excitation in heart failure. In this study, we show a loss of circadian variability in angiotensin type 1 receptor expression in the brainstem of mice post myocardial infarction. These changes correlate with a loss of cardiovascular circadian variability. These data suggest that sympatho‐ excitation may be increased in the post‐MI state at times when sympathetic outflow is normally reduced.

Lack of diurnal variation of P-wave and QT dispersions in patients with heart failure

BACKGROUND

P-wave dispersion (PWD) is a new parameter for the assessment of risk of atrial fibrillation and has been reported to be increased in heart failure. Diurnal variation of the PWD has been reported in patients with coronary artery disease (CAD). QT dispersion (QTD) has also a circadian variation. In this study we aimed to search diurnal variation of PWD and QTD in patients with heart failure.

METHODS

Fifty-three clinical heart failure patients having left ventricular ejection fraction (LVEF) <40% were divided into two groups according to presence of CAD. Twelve-lead ECGs were obtained in the morning (07:00-08:00 hours), at noon (12:00-14:00 hours), and at night (22:00-24:00 hours).

RESULTS

All the patients were in New York Heart Association class II except one in class I. beta-blocker and angiotensin-converting enzyme inhibitor or angiotensin receptor blocker usage was over 80% and spiranolactone usage was around 75% in the study group. PWD and QTD were not significantly different between patients with (n = 27) and without (n = 26) CAD. There was no significant diurnal variation of P wave and QT parameters.

CONCLUSIONS

We found that PWD and QTD do not show diurnal variation in patients having either ischemic or nonischemic origin of heart failure treated with optimal drug therapy.

QT intervals and QT dispersion determined from a 12-lead 24-hour Holter recording in patients with coronary artery disease and patients with heart failure

BACKGROUND

QT dispersion is considered an index of spatial inhomogeneity of repolarization duration and increased dispersion of ventricular repolarization is supposed to increase the risk of ventricular arrhythmia. Circadian variation in QT dispersion was investigated.

METHODS

Three different modes of lead selection was used: all 12-leads (QTdisp 12), only precordial leads (QTdisp 6), and one pair of preselected leads (QTdisp 2) in a 24-hour Holter recording every fourth hour each comprising 10 consecutive measurements in 54 healthy subjects, 29 patients with coronary artery disease (CAD), and 29 patients with heart failure (HF).

RESULTS

A significant circadian variation was observed in healthy subjects when modes QTdisp 12 and QTdisp 6 were used (Mean +/- SD 35.58 +/- 16.48 ms; P < 0.0001; and 28.82 +/- 16.02 ms; P < 0.0001, respectively), and in patients with CAD (Mean +/- SD 37.86 +/- 17.87 ms; P < 0.01; and 28.72 +/- 17.06 ms; P < 0.0001, respectively), whereas no circadian variation was observed in QTdisp 2. No circadian variation was observed in patients with HF irrespectively of lead selection. Patients with CAD without myocardial infarction (MI) had a circadian variation in QTdisp 12 (Mean +/- SD 33.13 +/- 14.86 ms; P < 0.05), whereas no circadian variation was observed in patients with MI (Mean +/- SD 40.35 +/- 18.80 ms; P = NS).

CONCLUSIONS

Circadian variation of QT dispersion was detected in healthy subjects and in patients with uncomplicated CAD, but not in those who had suffered a previous MI and in patients with HF. The number of leads among which selection of the longest and shortest QT intervals took place was critical for the disclosure of circadian variation of QT dispersion.