Difference In QTc Interval Research Articles

Sex differences in QTc interval and QT dispersion: Dynamics during exercise and recovery in healthy subjects

Background Sex differences have been described in resting cardiac repolarization and susceptibility to torsade de pointes in humans. This study compares the QT-interval and QT-dispersion dynamics during exercise and recovery between healthy men and women.Methods Twenty healthy subjects (10 males aged 30 ± 4 years, 10 females aged 31 ± 11 years) underwent symptom-limited bicycle ergometry followed by a 10-minute recovery period. Digital 12-lead electrocardiograms (ECG) were recorded every 10 seconds during exercise and recovery. For each lead, the QTp interval (Q onset to T peak) was automatically measured by use of QT Guard (GE Marquette, Milwaukee, Wis). QTp dispersion was defined as the difference between the maximum and minimum QTp for each ECG. To quantify QT dynamics, we fit the QTp in lead V3 (QTpV3) versus cycle length (CL) relationship to a quadratic function during exercise and recovery with nonlinear regression analy- sis. Similar regression analysis was performed for the QTp dispersion versus CL relationship.Results At baseline, QTpcVs was longer in women than in men (338 ± 25 vs 278 ± 15 ms, P < .0001), but QTp dispersion was similar (35 ± 18 vs 41 ± 19 ms). At peak exercise, QT dispersion decreased compared with baseline in both men and women. During exercise and recovery, women had a steeper QTpVs-CL relationship. QTpVs hysteresis, a measure of the exercise and recovery QTpVs-CL curve separation, was greater in women than in men when measured 1 minute into recovery (33 ± 20 vs 6 ± 8 ms, P < .001). No sex difference in QTp-dispersion-rate adaptation was observed during exercise or recovery.Conclusions Healthy women exhibit greater QT-interval-rate adaptation during both exercise and recovery than men, resulting in more QT-interval hysteresis. Greater QT prolongation during decelerating heart rates in recovery may play a role in increasing proarrhythmia risk in women.

Can the assessment of dynamic QT dispersion on exercise electrocardiogram predict sudden cardiac death in hypertrophic cardiomyopathy?

Premature sudden cardiac death (SD) is a critical event in the natural history of hypertrophic cardiomyopathy (HCM), and occurs during or just after physical exertion in approximately 60% of instances. Abnormalities in ventricular repolarization may not be present at rest in some patients but may become apparent under certain conditions. This study was performed to examine whether dynamic QT dispersion during exercise is associated with SD in HCM. Twenty-four HCM patients with catastrophic events (group I; 18 SD, 6 ventricular fibrillation) and 24 event-free survivors (group II) were studied. The two groups were pair-matched for age, gender, and maximum left ventricular wall thickness. QT intervals were manually measured from 12-lead exercise electrocardiogram (ECG) with a digitizing board. A custom-developed program was used to calculate QT and JT dispersion. The QT/RR relationship was evaluated by the slope of linear regression analysis. Before exercise, significant differences in heart rate and JT dispersion were found between group I and II. During exercise, heart rate increased and QT decreased significantly in both groups. QT and JT dispersion decreased in both groups, though the magnitude of reduction was greater in group I than in group II. No significant differences in QTc interval and QT or JT dispersion were found between the groups at any stages. At 3 minutes of recovery, heart rate had decreased but remained higher than before exercise, and all measurements of QT components remained shorter compared with those made before exercise in both groups. There was a strong correlation between QT and RR interval during exercise in all study patients (r = 0.95). No difference in the slope of QT against RR intervals was found between the groups (0.317 vs 0.319). In conclusion, exercise reduced QT dispersion in patients with HCM. The dynamic changes in QT dispersion examined by this method on exercise ECG did not make additional contributions in their risk stratification.

Long-term effect of epalrestat on cardiac autonomic neuropathy in subjects with non-insulin dependent diabetes mellitus

To evaluate the effect of long-term administration of an aldose reductase inhibitor on diabetic cardiovascular autonomic neuropathy, 22 subjects with non-insulin dependent diabetes mellitus (NIDDM, 11 men and 11 women, mean age; 64.8±7.8 years, duration of diabetes; 18.3±5.6 years) were administered epalrestat, one type of aldose reductase inhibitor, for 36 months. The changes in the coefficient of variation of the R-R interval (CV R R) during rest and the QTc interval were compared with 43 age-matched NIDDM (controls). During the study, the CV R R value gradually decreased in the controls, while it slightly increased in subjects treated with epalrestat. After 36 months, the CV R R value (2.31±1.09%) in subjects treated with epalrestat was significantly ( P<0.05) higher than that (1.84±0.75%) in the controls. There were no significant differences in QTc intervals in both groups. These results suggest that long-term administration of an aldose reductase inhibitor may be available for cardiac autonomic neuropathy in even relatively older diabetic subjects with long duration.

CHARACTERIZATION OF THE QT INTERVAL DURING UPRIGHT EXERCISE IN CHILDREN

The QTc interval which reflects ventricular activation/repolarization has not been characterized in children during exercise. We studied 60 children (ages 5-18 years) who underwent upright cycle ergometry according to a standard James protocol. These children were without known cardiac or medical problems. The QT interval was measured at rest (R); maximal exercise (MAX); immediate post exercise (IPE); and 1 (IPE1), 3 (IPE3) and 5 (IPE5) minutes post exercise. This interval was corrected for heart rate and QTc calculated with Bazett's formula. All patients demonstrated a normal QRS duration (<0.08 sec.). Patients were assigned to one of four groups on the basis of body surface area (BSA) and sex (M, F). There were no significant differences in QTc interval on the basis of body size or sex at each level of exercise. In all out the smallest children, the QTc interval was longer at 5 min. post exercise than at rest. This suggests that there is a modest prolongation of ventricular repolarization following exercise which is an integral part of a normal exercise response.