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Pharmacological radionuclide ventriculography for detection of myocardial contractile reserve in patients after myocardial infarction: head-to-head comparison of low dose dobutamine and low dose dipyridamole.

BACKGROUND
Low dose pharmacological stress echocardiography with either dobutamine or dipyridamole infusion has been proposed for recognition of myocardial viability. However, dependence on adequate acoustic window, observer experience, and the mild degree of wall motion changes make the viability assessment by stress echocardiography especially bothersome. The objective of the study was to evaluate the ability of low dose dobutamine and low dose dipyridamole radionuclide ventriculography to detect contractile reserve in patients after myocardial infarction and functional recovery after coronary angioplasty.


METHODS
The study group consisted of 20 consecutive patients (52 +/- 10 years, 17 male, 3 female) with previous myocardial infarction and resting regional dyssynergy, in whom diagnostic cardiac catheterization revealed significant one-vessel coronary artery stenosis suitable for angioplasty. Each patient underwent equilibrium 99m-Tc radionuclide ventriculography which was performed at rest and during low dose dipyridamole (0.28 mg/kg over 2 minutes) and low dose dobutamine infusion (up to 10 mcg/kg/min). Left ventricular global and regional ejection fractions were determined. Increase of regional ejection fraction for > 5% (inferoapical and posterolateral regions) or > 10% (anteroseptal regions) during low dose dobutamine and dipyridamole in infarcted regions, as well as in the followup period, was considered as index of contractile reserve. After 8 weeks of successful angioplasty, resting radionuclide ventriculography was repeated in all patients in order to identify functional recovery of the infarct zone.


RESULTS
Out of the 180 analyzed segments (20 x 9), 90 regional ejection fractions have shown depressed contractility. The mean of the regional ejection fractions showing depressed contractility increased from the resting value of 34 +/- 12% to 42 +/- 14% in the follow-up period (p = 0.06). Of the 90 with baseline dyssynergy, 46 were responders during low-dose dobutamine (51%), whereas 32 segments were responders (36%, p = 0.05 vs. dobutamine) during low dose dipyridamole. Positive predictive value of dobutamine and dipyridamole for predicting functional recovery was 72% and 75% (p = ns), respectively. Negative predictive value of dobutamine and dipyridamole was 48% and 69% (p = 0.05), respectively. In the group of patients with most severe dyskinesia (regional ejection fraction < 35%, 42 segments) positive predictive value was 73% and 82%, while negative predictive value was 42% and 64% for low dose dobutamine and low dose dipyridamole respectively (p = ns).


CONCLUSION
Although low dose dobutamine induced higher rate of positive responses during radionuclide ventriculography imaging, dipyridamole radionuclide ventriculography has shown superior, particularly negative, prognostic value for predicting functional recovery of infarcted regions.