gms | German Medical Science

Objective: Ventricular repolarization instability as quantified by the index of QT interval variability (QTVI) is one of the best predictors for risk of malignant ventricular arrhythmias and sudden cardiac death. Because it is difficult to appropriately monitor early signs of organ dysfunction at high altitude, we investigated whether high resolution advanced electrocardiogram (HR-ECG) analysis might be helpful as a non-invasive and easy-to-use tool for evaluating the risk of cardiac arrhythmias during exposure to acute hypoxia.

Material/Methods: 19 non-acclimatized healthy trained alpinists (age 37,8±4,7 years) participated in the study. Five-minute 12-lead HR-ECGs (Cardiosoft) were recorded in each subject at rest in the supine position breathing room air and then after breathing 30 min of 12.5% oxygen. For beat-to-beat RR interval and QT interval variability (RRV and QTV, respectively), the program of Starc was utilized to derive standard time domain measures such as root mean square of the successive interval difference (rMSSD) of RRV and QTV, the corrected QT interval (QTc) and the QTVI in lead II. Changes were evaluated with paired-samples t-test with p-values <0.05 considered statistically significant.

Results: As expected, the RR interval and its variability both decreased with increasing altitude, with p=0.000 and p=0.005, respectively. Significant increases were found in both the rMSSDQT and the QTVI in lead II, with p=0.002 and p=0.003, respectively. There was no change in QTc interval length (p = non significant).

Conclusion: QT variability parameters may be useful for evaluating changes in ventricular repolarization caused by hypoxia. These changes might be driven by increases in sympathetic nervous system activity at ventricular level.