Circadian variation in QT dispersion determined from a 12-lead Holter recording: a methodological study of an age- and sex-stratified group of healthy subjects

Greater insulin resistance indicates decreased diurnal variation in the QT interval in patients with type 2 diabetes

Circadian variations in the QT interval (QT) and QT dispersion are decreased in patients with type 2 diabetes because of cardioneuropathy. Insulin resistance has been recently identified as an independent determinant of QT prolongation in normoglycemic women. However, the relationship between QT prolongation and the degree of insulin resistance as well as circadian variation remains unclear in diabetic patients. This study was designed to assess the relationship between insulin resistance and the circadian variation in QT measurements in patients with type 2 diabetes. In 14 patients with diabetes, QT, corrected QT (QTc), QT dispersion, QTc dispersion, and RR interval (RR) were analyzed using 12-lead Holter monitoring and commercial software. The degree of diurnal variation in each measurement was defined as the amplitude between the maximum and mean values on curves fitted using the mean cosinor method (A_QT, A_QTc, A_QT dispersion, A_QTc dispersion, and A_RR). The cosine curve was fitted to all measured values in each QT measurement and RR for 24 h. Insulin resistance (glucose infusion rate (GIR)) was measured using the euglycemic hyperinsulinemic glucose clamp method. The maximum QT, QTc, QT dispersion, and QTc dispersion were >450 ms. GIR was significantly correlated with A_QT only (r = 0.59, P < 0.05). GIR was not correlated with other variables, and was dependent only on the circadian variation in QT.

Sex and gender aspects in antiarrhythmic therapy

Although cardiac arrhythmia had long been considered a predominantly male syndrome, it is now clear that arrhythmia is also a primary cause of mortality in women. Notably, the manifestation of specific arrhythmia syndromes appears to be gender specific. In particular, female sex is an independent risk factor for development of torsade de pointes (TdP) arrhythmias not only in congenital long QT syndromes but also in acquired long QT syndromes which occur as adverse effects of existing drugs. Males, on the other hand, are more likely to develop Brugada syndrome. Recent clinical and experimental studies suggest that these differences may stem from intrinsic sex differences in cardiac tissue. These include fundamental electrical differences resulting from variable ion channel expression and diverse sex hormonal regulation via long-term genomic and acute nongenomic pathways, and sex differences in drug responses and metabolisms. Undoubtedly, determining the effect of gender on cardiac function will be difficult and require sophisticated methodologies. However, gender differences underlying predilection to distinct arrhythmia syndromes must be revealed so that new therapeutic strategies that take gender into account can be applied to at-risk patients.

Cardiac conductive disturbance in patients with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is the most common endocrine abnormality of reproductive-aged women and increases the risk of cardiovascular disease. However, the effects of PCOS on electrocardiograms (ECGs) are not fully elucidated. The aim of this study was to evaluate the characteristics of ECGs in patients with PCOS.

METHODS

This study included 24 patients with PCOS and 12 patients without PCOS. The heart rate, PR interval, QRS duration, Sokolow-Lyon voltage (SV1 + RV5/6), Cornell voltage (RaVL + SV3), QT interval and QTc interval were measured in 12-lead ECGs.

RESULTS

The QRS duration was wider in patients with PCOS than those without PCOS (91 ± 8 vs. 81 ± 10 ms, p < 0.05). The heart rate, PR interval, Sokolow-Lyon voltage, product of the QRS duration times Cornell voltage combination, QT interval, QTc interval, QT dispersion and QTc dispersion were similar between the two groups.

CONCLUSIONS

PCOS is associated with a widening QRS duration, which may contribute to its increased cardiovascular risks.

Aging modulates dispersion of ventricular repolarization in the very old of the geriatric population

Aging plays an essential role in cardiac pathophysiology. Knowledge on the ventricular repolarization in very old individuals is limited. An increase of QT dispersion is associated with higher cardiovascular mortality. The purpose of this study is to investigate whether aging changes the QT dispersion in the very old. Heart rate, P wave duration, PR interval, QRS axis, QRS duration, QT interval, and QTc interval were measured from 12-lead resting ECG. QT dispersion (46 ± 21, 47 ± 17, 69 ± 31 ms, p < 0.005) was significantly increased in the age group ≧85 years (n = 29, 89 ± 4 years) than in the age group 75-84 years (n = 33, 79 ± 3 years) and the age group 65-74 years (n = 32, 68 ± 3 years). Aging modulates dispersion of ventricular repolarization, which may contribute to the cardiac mortality in the very old Asian population.

Circadian and gender effects on repolarization in healthy adults: a study using harmonic regression analysis

BACKGROUND

Sudden cardiac death and myocardial infarction have a circadian variation with a peak incidence in the early morning hours. Increased dispersion of repolarization facilitates the development of conduction delay necessary to induce sustained arrhythmia. Both QT-dispersion and T-wave peak to T-wave end (TpTe) have been proposed as markers of dispersion of myocardial repolarization.

METHODS

Forty healthy adults (20 women), age 35-67 years old, with normal EKGs, echocardiograms, stress tests, and tilt-table tests were analyzed during a 27-hour hospital stay. EKGs were done at eight different time points. QT-intervals, QT-dispersion, and TpTe were measured at each time point. Harmonic regression was used to model circadian periodicity, P < 0.05 was considered significant.

RESULTS

The composite QT-interval was longer in women than in men (416 + or - 17 msec vs 411 + or - 20 msec, respectively, P = 0.006). The QT-dispersion among all leads was greater in men than women (37 + or - 13 msec vs 30 + or - 11 msec, respectively, P < 0.0001); a similar difference was found in the precordial leads. Harmonic regression showed that QT-dispersion had a significant circadian variation, primarily in men. In men, the maximum QT-dispersion occurred at 6 AM (45 + or - 15 msec). TpTe also had a significant circadian variation that was not affected by gender in the majority of leads.

CONCLUSIONS

A circadian variation exists in the dispersion of myocardial repolarization, as measured by both TpTe and QT-dispersion. Men and women have a different circadian variation pattern. Further studies regarding the mechanisms and clinical implications are needed.

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.