Duration and dispersion of QT interval in smokers

Cigarette Smoking Is Associated with Prolongation of the QTc Interval Duration in Patients with Type 2 Diabetes Mellitus

Aims. Aim of the study was to evaluate the effect of smoking on autonomic nervous system (ANS) activity and QTc interval duration in patients with Type 2 diabetes mellitus (T2DM). Methods. A total of 70 patients with T2DM (35 chronic smokers, 35 nonsmokers) treated with oral antidiabetic medications underwent continuous ECG Holter monitoring for 24 hours and analysis of time- and frequency-domain measures of heart rate variability (HRV). HRV over short time was also assessed using the deep breathing test. In addition, baroreflex sensitivity (BRS) was evaluated using the spontaneous sequence method. The mean QTc interval was measured from the 24-hour ECG recordings. Results. Smokers had lower body mass index (BMI) and exhibited higher 24-hour mean heart rate. There was no difference regarding all measures of ANS activity between the two groups. Smokers showed increased mean QTc duration during the 24 hours (439.25 ± 26.95 versus 425.05 ± 23.03 ms, P = 0.021) as well as in both day (439.14 ± 24.31 ms, P = 0.042) and night periods (440.91 ± 32.30 versus 425.51 ± 24.98 ms, P = 0.033). The association between smoking status and mean QTc interval persisted after adjusting for BMI. Conclusions. Cigarette smoking is associated with prolongation of the QTc interval in patients with T2DM by a mechanism independent of ANS dysfunction.

Association between ventricular repolarization and main cardiovascular risk factors

OBJECTIVE

To assess the association between QT interval, QT dispersion and main cardiovascular risk factors in Tallinn women population aged 50-69 years.

DESIGN

A random sample of Tallinn population, 302 women underwent 12-lead rest ECG, echocardiography and laboratory tests. Corrected QT interval and QT dispersion were calculated.

RESULTS

The significant correlation coefficients for corrected QT interval and dispersion were observed with systolic, diastolic, pulse pressure, blood pressure value grade, heart rate, left ventricular mass index, and total cardiovascular risk grade. According to the data of multiple logistic regression, risk factors independently associated with prolonged QTc and QTD were arterial hypertension: OR 2.69, p < 0.001 and OR 3.29, p < 0.001, pulse pressure ≥ 60 mm Hg: OR 2.62, p < 0.001 and OR 3.04, p < 0.001, age > 65 years: OR 2.44, p < 0.001 and OR 1.91, p < 0.01, family history of cardiovascular disease: OR 2.02, p < 0.01 and OR 2.48, p < 0.001, left ventricular hypertrophy: OR 2.78, p < 0.001 and OR 5.29, p < 0.001. Multivariable linear regression data showed an independent association between corrected QT interval, QT dispersion and systolic blood pressure: β = 0.32, p < 0.001 and β = 0.39, p=0.003, pulse pressure: β = 0.21, p = 0.004 and β = 0.27, p < 0.001, blood pressure value grade: β = 0.35, p < 0.001 (for QT dispersion only), heart rate: β = 0.21, p < 0.001 and β = -0.19, p = 0.001, left ventricular mass index: β = 0.23, p < 0.001 and β = 0.27, p < 0.001.

CONCLUSION

In Tallinn women population, electrocardiographic parameters reflecting ventricular repolarization are associated with systolic blood pressure, pulse pressure, blood pressure value grade, heart rate and left ventricular hypertrophy.

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.