Effects of cardiovascular autonomic function tests on QT dispersion in the 12-lead electrocardiogram of healthy patients

The effect of different stressors on the QT interval and the T wave

Prolonged QT interval is associated with the generation of life-threatening arrhythmias and sudden death. However, neither the relation between QT duration and heart rate, nor the association between mental stress and QT time has been clarified. Aim: The relationship between QT duration and smoking, cardiovascular reactivity, and mental stress as well as newer methods of QT correction were studied. Methods: In six laboratory experiments 166 volunteers were studied. Smoking, treadmill exercise, mental arithmetic and videogame were applied as stressors. Besides fixed formulae, study and subject-specific QT correction methods were also used. Results: 1. Bazett formula is not appropriate to compare QT durations. 2. Acute smoking has no effect on QT time. 3. QT changes are related to cardiovascular reactivity. 4. Mental stress may induce QT prolongation. 5. Bifid T waves often develop during mental and isometric stress. Conclusions: New methods for QT correction are more reliable than preformed formulae. QT prolongation and bifid T waves may be the links between mental stress and life threatening arrhythmias.

Mental stress may induce QT-interval prolongation and T-wave notching

BACKGROUND

The effects of active and passive mental stress (PMS) on the QT interval were studied by using an intraindividual regression method of QT-interval correction for heart rate.

METHODS

Thirty healthy males (age 21.2 +/- 1.8 years) performed a mental arithmetic for 1 minute, which was considered as active mental stress (AMS) because of the performance requirement. A 1-minute unpleasant video clip was used for PMS. Two baseline and two (an early and a late) ECGs were prepared in both mental stress periods. The individual QT-RR relationship was assessed by linear regression analysis of 7-15 (11.0 +/- 1.9) controlled QT-RR data pairs, also obtained from ECGs gained during a successive set of 9 isometric stretching exercises.

RESULTS

Heart rate has increased significantly at both measurements in response to AMS (P < 0.0001), but not in response to passive stress. QTc significantly prolonged early in AMS (P = 0.0004), then normalized by the end of the period. During PMS, no significant QTc changes were observed. The evolution of bifid T waves was noted in 14 subjects: 8 presented bifid T waves during both AMS and exercise, and 6 during only exercise.

CONCLUSIONS

AMS and PMS elicit different cardiovascular reactions. Our results indicate that changes in the autonomic tone, probably abrupt sympathetic predominance, may cause QTc prolongation and bifid T waves. This suggests that besides stress quality and intensity, the dynamics of stress application and perception also influence repolarization.

[Prognostic value of Poincare plot as nonlinear parameter of chaos theory in patients with myocardial infarction]

INTRODUCTION

There are different proofs about association of autonomic nervous system dysfunction, especially nonlinear parameters, with higher mortality after myocardial infarction.

OBJECTIVE

The objective of the study was to determine predictive value of Poincaré plot as nonlinear parameter and other significant standard risk predictors: ejection fraction of the left ventricle, late potentials, ventricular arrhythmias, and QT interval.

METHOD

The study included 1081 patients with mean follow-up of 28 months (ranging from 0-80 months). End-point of the study was cardiovascular mortality. The following diagnostic methods were used during the second week: ECG with commercial software Schiller AT-10: short time spectral analysis of RR variability with analysis of Poincaré plot as nonlinear parameter and late potentials; 24-hour ambulatory ECG monitoring: QT interval, RR interval, QT/RR slope, ventricular arrhythmias (Lown > II); echocardiography examinations: systolic disorder (defined as EF < 40%).

RESULTS

There were 103 (9.52%) cardiovascular deaths during the follow-up. In univariate analysis, the following parameters were significantly correlated with mortality: mean RR interval < 800 ms, QT and RR interval space relationship as mean RR interval < 800 ms and QT interval > 350 ms, positive late potentials, systolic dysfunction, Poincaré plot as a point, ventricular arrhythmias (Lown > II). In multivariate analysis, the significant risk predictors were: Poincaré plot as a point and mean RR interval lower than 800 ms.

CONCLUSION

Mean RR interval lower than 800 ms and nonlinear and space presentation of RR interval as a point Poincaré plot were multivariate risk predictors.

[Early risk predictors of sudden cardiac death after myocardial infarction: results of follow up of 881 patients]

INTRODUCTION

It has been shown that depolarization disorders, autonomic dysfunction, and systolic dysfunction of the left ventricle are associated with sudden cardiac death after myocardial infarction.

OBJECTIVE

The objective of study was to examine the prognostic value of the most important predictors in the first week after myocardial infarction.

METHOD

Study included 881 patients who were followed up from 1 to 60 months. During the first week after myocardial infarction, following examination were performed: ECG with standard leads and X, Y, Z orthogonal leads, vectorcardiogram, QT interval, late potentials, short-time spectral analysis of RR variability, nonlinear (Poincaré plot) analysis and echocardiogram.

RESULTS

In univariate analysis, the following parameters measured on the first day were important predictors of sudden cardiac death: lower LF/HF ratio (<1.5) (p = 0.000), T wave inversion in X lead (p = 0.000), high P wave in D2 lead (p=0.030), and diminished systolic function (p = 0.000). In multivariate analysis, the following parameters were significant risk predictors: T wave inversion in X lead, lower LF/HF ratio, positive late potentials and the left ventricle systolic dysfunction.

CONCLUSION

The parameters of the left ventricle systolic disfunction with sympathicovagal imbalance and electric instability are the key risk predictors in the first few days after myocardial infarction.

Acute reduction of ventricular volume decreases QT interval dispersion in elderly subjects with and without heart failure

To evaluate the effects of acute reduction in ventricular volume (VV) on QT interval dispersion (QTd), 14 men with heart failure (HF; 74.5 ± 2 yr of age) and 11 healthy male control subjects (68 ± 2 yr of age) were studied. For 15 min, lower body negative pressure (LBNP) was applied at −15 and −40 mmHg to reduce venous return. At baseline and during LBNP application, QTd was measured with an 87-lead, body-surface-mapping device; chamber volumes were assessed by radioisotope ventriculography; blood pressure (BP) and heart rate (HR) were continuously monitored; and blood samples were obtained for assessment of norepinephrine (Nor) levels. At −15 mmHg, LNBP application induced a significant decrease in VV but did not change BP and HR in both groups. In addition, Nor levels increased significantly ( P ≤ 0.05) in the control group (from 286.7 ± 31.5 to 388.8 ± 41.2 pg/ml) and in HF patients (from 405.8 ± 56 to 477.6 ± 47 pg/ml), and QTd was significantly ( P ≤ 0.05) decreased in the control group (57.2 ± 3.8 vs. 49.1 ± 3.4 ms) and in HF patients (67.8 ± 6 vs. 63.7 ± 5.9 ms). No additional decreases in VV or QTd were produced by −40 mmHg LNBP, but Nor levels did increase in both groups and reach 475.5 ± 34 and 586.5 ± 60 pg/ml ( P < 0.05) in the control and HF groups, respectively; BP did not change, but HR also increased in both groups. In conclusion, an acute LBNP-induced reduction in VV caused a decrease in the QTd of elderly men regardless of the existence of HF. Because increased sympathetic activity with more intense LBNP was not accompanied by additional changes in QTd, altered QTd may be better related to changes in VV than to autonomic nervous system activity.