Prolonged QT interval is associated with blood pressure rather than left ventricular mass in spontaneously hypertensive rats

QT interval is prolonged in hypertensive individuals, although the factors responsible for this increase are not completely understood. We questioned whether enhanced left ventricular mass (LVM) or increased systemic blood pressure represents the principal factor determining QT prolongation in the period of development of hypertension and left ventricular hypertrophy (LVH) in spontaneously hypertensive rats (SHR). In 12-and 20-week-old SHR (SHR12 and SHR20) and age-matched normotensive Wistar-Kyoto rats (WKY12 and WKY20), arterial systolic blood pressure (sBP) was measured using tail-cuff technique. Orthogonal Frank ECG was registered in anaesthetized animals in vivo, and bipolar ECG was measured in spontaneously beating isolated hearts in vitro. Progressive increase of sBP and LVM resulted in significant QT prolongation in SHR20 as compared to WKY12, WKY20, and also to SHR12 in vivo (WKY12: 82 +/- 9 ms, WKY20: 81 +/- 9 ms, SHR12: 88 +/- 15 and SHR20: 100 +/- 10, respectively; p < 0.05) but not in isolated hearts (WKY20: 196 +/- 39 ms and SHR20: 220 +/- 55, respectively; NS). In whole animals, QT duration was positively related to sBP (r = 0.6842; p < 0.001) but not to LVM (r = 0.1632, NS) in SHR20. The results suggest that QT prolongation in SHR developing hypertension and LVH depends on blood pressure rather than increase in LVM. In this period, myocardial hypertrophy is probably the predisposition for QT prolongation, but the significant change manifests only in the presence of elevated systemic factors.