QTC AND NOT QTC DISPERSION BEHAVIOR AFFECTS THE OCCURRENCE OF VENTRICULAR EXTRASYSTOLE DURING EXERCISE IN INFARCTED PATIENTS

Both a long QTc and a large QTc dispersion (QTcd) can predispose infar cted patients to ventricular arrhythmias. The former simply reflects a general prolongation of ventricular recovery time, whereas QTcd is us eful for revealing regional inhomogeneities of ventricular repolarizat ion. The aim of our study was to evaluate QTc and QTcd behavior during exercise in 50 patients (all men) with previous myocardial infarction , and its possible correlation with the occurrence of exercise-induced premature ventricular complexes (EIPVC). Our patients underwent ergom etric stress test with a load increase of 25 W, every 2 min, until the maximal age-related heart rate or symptoms were obtained, followed by a 10-min recovery phase. QTc and QTcd measurement was performed at re st (BS) and during exercise at two progressively increasing heart rate steps: 100-115 beats/min (T1) and 116-130 beats/min (T2). The patient s were divided into two groups according to the absence (group A; n = 22) or presence (group B; n = 28) of EIPVC. In terms of QTcd, no signi ficant difference was found between the two groups at BS, T1, and T2. As for the mean QTc (QTcm), it was significantly longer in group B at BS (416 +/- 22 ms versus 395 +/- 19 ms: P = 0.001) and at T1 (431 +/- 24 ms versus 310 +/- 8 ms; P = 0.0001). When group B was further diffe rentiated into two subgroups - Bx and Bz - according to the severity o f EIPVC, we noted that patients with the most severe arrhythmic respon se (group Bz; n = 12) showed a persisting, significantly longer QTcm t han group A (BS, 426 +/- 28 ms versus 395 +/- 19 ms; P < 0.05; T1, 445 +/- 24 ms versus 410 +/- 8 ms; P < 0.05; T2, 427 +/- 17 ms versus 412 +/- 14 ms; P < 0.05), and group Bx (n = 16) (BS, 426 +/- 28 ms versus 409 +/- 15 ms; P < 0.05; T1, 445 +/- 24 ms versus 420 +/- 19 ms; P < 0.05; T2, 427 +/- 17 ms versus 410 +/- 17 ms; P < 0.05). Group Bx show ed a significantly longer QTcm than group A only at BS (409 +/- 15 ms versus 395 +/- 19 ms; P < 0.05). No significant difference in QTcd was found between the three groups at BS, T1, and T2. We also noted that the relationship between QTcm and QTcd was modified by the exercise, c hanging from a trend of direct relation at BS, towards an inverse one during effort, which reached significance at T2 (r = -0.319; P = 0.037 ). Based on our data, EIPVC occurrence seems to be more affected by th e total duration rather than by regional inhomogeneities of the ventri cular recovery time. In those patients with the most severe arrhythmic response, the autonomic modifications generated by the exercise succe ed in attenuating only the regional inhomogeneities, but do not elimin ate the differences in total duration of the repolarization period.