[QT dispersion in DDD and VVI paced patients after myocardial infarction or with left ventricular hypertrophy]

The aim of this study was to assess the alterations of stroke volume (SV) on the QT dispersion (QTD) as a result of different pacing modes and programmed AV delays in patients (pts) after myocardial infarction (MI) or with left ventricular hypertrophy (LVH). We studied 14 MI pts (9 M, 5 F) in mean age 72.3 +/- 3.7 yrs (Group I) and 12 pts with LVH (7 M, 5 F) in mean age 67.3 +/- 5.9 yrs (Group II), in whom DDD pacemakers were implanted due to complete atrioventricular block. The control group (Group III) consisted of 9 pts without MI or LVH. In all cases basic rate of the pacemaker was programmed at 70/min. Resting ECG showed all atrial and ventricular complexes captured. AV delay optimization was based on the measurements of SV by Doppler echocardiography. QT intervals (QTi) were measured from 12-lead ECG at 50 mm/s speed. QTD was calculated as the difference between maximal and minimal QTi. It was measured at optimal (opt. DDD, with highest SV) and "unoptimal" (unopt. DDD) programmed AV intervals and then in VVI mode (with lowest SV) after following reprogramming of the pacemaker. In Group I and II, a strong correlation between SV and QTD was found (R = 0.816 and -0.897, respectively). In control group, it was insignificant (R = -0.339). In VVI mode SV was significantly lower than in unopt. DDD (in Mi pts: 56.1 ml vs 71.1 ml, respectively, p < 0.01; in LVH pts: 64.1 ml vs 96.7 ml, respectively, p < 0.005) and QTD was significantly greater (74.8 ms vs 66.8 ms, respectively, p < 0.005 and 70.0 ms vs 53.5 ms, respectively, p < 0.005). In LVH pts or MI pts programming of different AV intervals and pacing modes significantly influences QTD.