Discussion
Both stress modalities are safe. The occurrence of life threatening complications is rare. Data from the International Stress Echo Complication Registry reports a rate of 1 of 6574 patients undergoing exercise stress Echo and 1 of 557 patients undergoing dobutamine stress Echo.
In our study no death, myocardial infarction, ventricular fibrillation or high conduction disturbances were observed. Several studies reported an incidence of 0.002%, 0.02%, 0.04% and 0.23% respectively with the use of dobutamine as stressor. We registered 1 case of sustained ventricular tachycardia in the dobutamine group, the reported incidence is 0.15%. The clinical significance of Dobutamine stress echo induced ventricular tachycardia has not been clarified. Previous studies failed to establish a relationship between this ventricular rhythm disturbance and inductile myocardial ischemia. Elhendy et al., in a series of 286 patients who underwent dobutamine stress echo and subsequent coronary angiography, reported that tachyarrhythmia during dobutamine stress were not predicted by the presence or the extent of coronary artery disease on angiography nor by the induction of ischemia during the stress echo. The arrhythmia may be attributed to beta 1-receptor stimulation, to dobutamine induced reduction in ventricular refractory period or to a dobutamine-induced reduction in plasma potassium.
In the presented study, supraventricular tachycardia occurred in 2 (1.8%) dobutamine tests. Similar results were reported by Secknus et al. (1.7%), Pezzano et al. (1.6%) and Tsutsui et al. (1.6%). Supraventricular arrhythmias seem to be more frequent in older patients.
Minor rhythmic complications were observed in both stress modalities with a statistically higher incidence in the dobutamine group. Minor events included premature ventricular beats and nonsustained ventricular tachycardia NSVT, the reported incidence is 33.7% and 2.1% respectively. In a previous study, the prognostic significance of NSVT during dobutamine stress echo was explored, there was no difference in survival over the 3 years follow-up between the NSTV and the no NSTV groups in patients without inducible ischemia and with an ejection fraction > 0.45.
Severe hypotension occurred in 3.7% of dobutamine tests, the reported incidence is 20%. Although hypotensive response during exercise has strongly been associated to myocardial ischemia and poor cardiac prognostic, hypotension during dobutamine infusion cannot be consider as a specific indicator of cardiac anomalies. The mechanism of hypotensive response during dobutamine infusion remains unclear, vigorous myocardial contraction around a small chamber may trigger sympathoinhibition and increased parasympathetic discharge, leading to a systemic hypotension. The prognostic significance has been widely discussed, most studies did not reported a significant association with cardiac complications occurrence, while Dunkelgrun et al. in a retrospective study of 3381 patients showed that severe hypotension during dobutamine infusion is an independent predictor of cardiac death and non-fatal myocardial infarction.
Atropine co administration in dobutamine stress echocardiography is a safe and effective strategy in patients who had inadequate chronotropic response. Atropine adjunction was first reported by Mc Neill et al., if 85% of maximal predicted heart rate was not achieved at the end of the last stage, atropine was administered in doses of 0.25 mg each minute to a maximum of 1.0 mg while maintaining a continuous infusion of dobutamine. Recently, new protocols have been developed including the early injection of atropine at the dose of 20 μ/Kg/min when the heart rate is < 100 beats per minute. The early injection of atropine during dobutamine stress echo has been demonstrated to reduce the duration and dose of dobutamine infusion, to reduce dobutamine related adverse events, while at the same time preserving a similar diagnostic accuracy.
In our study, we used the early atropine protocol. Atropine administration was not associated to higher incidence of adverse events.
Stress modalities are safe but not equally safe, exercise tests are safer. The most common adverse events are the rhythmic disturbances and are usually minor and well tolerated.