Dispersion of the QT interval and autonomic modulation of heart rate in hypertensive men with and without left ventricular hypertrophy

Regression of left ventricular hypertrophy results in improvement of QT dispersion in patients with hypertension

OBJECTIVES

Increased QT dispersion has been considered as predisposing to ventricular arrhythmias in hypertrophic cardiomyopathy, congestive heart failure, and coronary artery disease. An increased QT dispersion has also been found in hypertensive patients with left ventricular hypertrophy (LVH). The data on the effect of LVH regression on QT dispersion are limited.

METHODS AND RESULTS

To assess the relation of LVH regression and QT dispersion decrease, 68 patients (42 men and 26 women, mean age 56.3+/-9.5 years) with uncomplicated essential hypertension were studied. All underwent full electrocardiographic and echocardiographic studies at baseline and after 6 months of monotherapy, 29 with angiotensin-converting enzyme inhibitors and 39 with calcium antagonists. QT dispersion was calculated by subtracting the shortest QT from the longest QT, in absolute value (QTmax - QTmin). It was also corrected with Bazett's formula (QTc dispersion). Left ventricular mass index was assessed according to the Devereux formula. After treatment, LVH decreased with both angiotensin-converting enzyme inhibitors (from 155 to 130 g/m2, P < .001) and calcium antagonists (156 to 133/92/m2, P < .001). QT dispersion decreased both after angiotensin-converting enzyme inhibitor treatment (from 82 to 63 ms) and calcium antagonist treatment (from 77 to 63 ms, both P < .001 ). There was a significant correlation of QT dispersion and left ventricular mass after therapy (r = 0.36, P < .005). There was a correlation of the degree of LVH and QT dispersion decrease (r = 0.27, P < .05).

CONCLUSIONS

It is concluded that LVH regression influences AQT favorably. Its prognostic value has yet to be determined.

Electrocardiographic measures of ventricular repolarisation dispersion in patients with coronary artery disease susceptible to ventricular fibrillation

OBJECTIVE

To study electrocardiographic measures of ventricular repolarisation dispersion in patients prone to ventricular fibrillation compared with controls matched for the extent of coronary heart disease and the use of beta blockers.

DESIGN

A case-control study.

SETTING

Cardiovascular laboratory of a tertiary referral centre.

PATIENTS

Fifty patients with documented ventricular fibrillation not associated with acute myocardial infarction, and their controls matched for sex, age, number of diseased coronary vessels, left ventricular ejection fraction, previous myocardial infarction and its location, and the use of beta blockers.

MAIN OUTCOME MEASURES

Electrocardiographic measures of QT, JT, and Tend interval dispersions in a 12 lead electrocardiogram.

RESULTS

The ventricular fibrillation patients compared to controls showed increased mean (SD) QTapex dispersion (53 (18) ms v 44 (18) ms, respectively; p < 0.01) and mean (SD) Tend dispersion (46 (17) ms v 38 (15) ms, respectively; p < 0.05).

CONCLUSIONS

Increased QTapex and Tend dispersions are associated with a susceptibility to ventricular fibrillation even when the extent of the coronary heart disease and use of beta blockers are taken into consideration. However, because of a considerable overlap between the groups, measures of QT dispersion assessed from a 12 lead electrocardiogram do not provide clinically useful information for identification of patients at risk of sudden cardiac death.

Significance of QTc prolongation on ventricular arrhythmias in patients with left ventricular hypertrophy secondary to essential hypertension

The present study was designed to detect the arrhythmogenic effect of left ventricular hypertrophy, QTc prolongation and the relationship between the QTc duration and ventricular arrhythmias in patients with left ventricular hypertrophy secondary to essential hypertension. Sixty-eight hypertensive patients (51 male and 17 female, mean age 52+/-6 years) and 30 healthy normotensive subjects (22 male and eight female, mean age 49+/-6 years) were enrolled in the study. The frequency of ventricular arrhythmias was investigated with 24-h ambulatory electrocardiographic monitoring and grade 3 and 4 ventricular arrhythmias according to a modified Lown and Wolf classification were accepted as complex arrhythmias. The echocardiographic features of the patients were divided into five groups as follows: (1) normal left ventricular diameter and wall thickness, (2) concentric left ventricular hypertrophy, (3) asymmetric septal hypertrophy, (4) dilated left ventricle, (5) dilated and hypertrophic left ventricle. The frequency of complex ventricular ectopia and the QTc duration were estimated for each group and compared with Student's t-test. Left ventricular hypertrophy was detected in 38 of 68 patients (56%) with essential hypertension. In patients with left ventricular hypertrophy, the incidence of complex ventricular arrhythmias was two- and fivefold higher compared with patients without left ventricular hypertrophy and with controls, respectively. All of the patients with echocardiographic left ventricular dilatation had experienced complex ventricular arrhythmias. QTc duration correlated positively with left ventricular mass index and left ventricular internal diastolic dimension. The highest QTc intervals were detected in patients with left ventricular hypertrophy and complex arrhythmias. In patients with left ventricular hypertrophy, a QTc duration longer than 380 ms had a sensitivity of 74% and a specificity of 89% for detecting complex ventricular arrhythmias. It is concluded that patients with left ventricular hypertrophy have a higher incidence of complex ventricular arrhythmias and QTc prolongation in those patients can be a good marker for the increased risk of arrhythmias.

Effect of exercise rehabilitation on heart rate variability in hypertensives after myocardial infarction

OBJECTIVE

The aim of the study was to find out whether the presence of hypertension affects heart rate variability in patients rehabilitated after myocardial infarction.

DESIGN

Echocardiography, exercise testing and 24 h Holter monitoring were performed before and after 27 days of early postdischarge cardiac rehabilitation.

PATIENTS

The study population consisted of 64 patients aged 34-65 years (mean+/-SD 51.6+/-6.6) discharged from hospital after a first myocardial infarction who were subdivided into two groups, group A comprising 34 patients with arterial hypertension which had lasted 4.8+/-2.1 years and group B comprising 30 normotensives.

MAIN OUTCOME

We expected exercise rehabilitation to affect heart rate variability, exercise tolerance and myocardial ischemia in patients after myocardial infarction with and without arterial hypertension.

RESULTS

At baseline no intergroup differences were seen in the duration of exercise, workload and heart rate variability parameters. All parameters increased significantly after cardiac rehabilitation (P < 0.01): SD of all normal RR intervals 123.4+/-30.0 versus 123.8+/-30.0 ms; SD of the averages of normal RR intervals in all 5-min segments of the entire recording 115.1+/-30.5 versus 116.3+/-28.3 ms; mean of the SD of all normal RR intervals for all 5-min segments of the entire recording 49.0+/-12.5 versus 48.3+/-11.8 ms; square root of the mean of the sum of the squares of differences between adjacent RR intervals 29.7+/-9.1 versus 28.0+/-8.5 ms; percentage of differences between adjacent RR intervals > 50 ms 7.9+/-6.0 versus 7.1+/-6.1% (group A versus group B, respectively, NS). The duration of exercise and the workload were significantly increased (the rise was higher in normotensives). No differences were seen in the frequency and severity of silent myocardial ischemia.

CONCLUSIONS

Early stationary exercise rehabilitation after myocardial infarction improves heart rate variability parameters and exercise tolerance both in hypertensives and in normotensives.

Precordial QT dispersion and inducible ventricular tachycardia

We compared the performance of precordial QT dispersion, late potentials on the signal-averaged electrocardiogram (ECG), and reduced left ventricular ejection fraction for identification of inducible ventricular tachycardia (VT) in 162 patients undergoing electrophysiologic study (EPS). QT(apex) dispersion in 56 patients with inducible VT (72 +/- 55 msec) was greater than that in 106 patients without inducible VT (55 +/- 36 msec, p < 0.01); dispersion was greater in both groups than in 144 normal subjects (33 +/- 19 msec). A QT(apex) dispersion partition of more than 68 msec, the upper ninety-fifth percentile in normal subjects, identified inducible VT with a specificity of 75% and a sensitivity of 45%. Although the performances of late potentials (specificity 82%, sensitivity 59%) and reduced ejection fraction (specificity 86%, sensitivity 54%) were each stronger than QT dispersion alone for identification of inducible VT, abnormal QT(apex) dispersion remained a significant additional predictor of inducible VT in a logistic regression model that included the three variables (specificity 78%, sensitivity 75%).