[Hypokinetic arrhythmia, paradoxical chronotropic reaction and hypotension during dobutamine stress test]

The aim of this study was to evaluate the incidence of hypokinetic arrhythmias, bradycardiac (BR) and hypotensive reactions in a population of 775 patients during dobutamine stress test (DST): 281 patients (36.2%, group I) were symptomatic for thoracic pain without any history of coronary artery disease (CAD); 494 patients (63.8%, group II) were evaluated 3-4 weeks after an acute myocardial infarction (AMI) to stratify ischemic risk. None of these patients was receiving coronarodilating therapy.

DST was performed using an infusion of 5, 10, 20, 40 micrograms/kg/min for 5 minutes during the first two stages and for 3 minutes during subsequent stages, and was accompanied by EKG and echocardiographic monitoring. BR was defined as severe when heart rate diminished more than 40 b/min, moderate when the decrease ranged between 20 and 39 b/min, and mild when the decrease was less than 20 b/min.

A total of 34 (4.38%) BR were observed, 19 (55%) in group I and 15 (45%) in group II. BR were severe in 12 patients (35.9%), 3 with recent AMI (2 inferior and 1 anterior) and 9 without a history of CAD. Fifteen (45%) presented moderate BR, 8 with recent AMI (6 inferior and 2 anterior); 7 cases were in group I. Mild BR was observed in 7 patients (20%), 2 with recent AMI (1 inferior, 1 anterior), of which 5 were in group I. Episodes of junctional rhythm were also observed in 10 patients (29.4%) and 1 patient (2.9%) presented 2nd degree AV block during DST positive for ischemia. The mean duration of bradycardic episodes was 89.6 seconds (+/- 29.8) and only 3 patients (8.8%) presented significant hypotension. In 13 patients (38.2%) arrhythmia was observed during dobutamine-induced ischemia. In spite of the often severely diminished heart rate, no significant hypotension was evident during the bradycardiac episode in 19 patients (55%). Only one patient (2.9%) showed a decrease of more than 40 mmHg.

In conclusion, we found that the incidence of BR during DST (4.38%) is higher than that reported in the literature; moreover, patients with recent inferior AMI showed a higher incidence of BR compared to patients with AMI in other sites (9 vs 4, p = n.s.). We feel that ischemia alone may not be responsible for hypokinetic arrhythmia during DST, but that dobutamine-induced neurovegetative reflexes may also contribute to the pathophysiological mechanisms underlying the phenomenon.