Absence of heart rate increase during inferoposterior left ventricular hypoperfusion caused by dipyridamole infusion.

BACKGROUND: Stimuli such as inferoposterior myocardial infarction and right coronary injection with radiographic contrast media evoke a vasodepressor reflex characterized by bradycardia and hypotension (Bezold-Jarisch reflex). Dipyridamole acts by adenosine-mediated coronary vasodilation to disclose myocardial perfusion heterogeneity for thallium-201 scintigraphy. OBJECTIVE: To determine whether there is a relationship between the site of left ventricular hypoperfusion and the heart rate response to dipyridamole. DESIGN: One thousand eight hundred consecutive dipyridamole-thallium studies performed between 1985 and 1993 were reviewed to identify 48 subjects who met prespecified selection criteria. SETTING: Nuclear cardiology laboratory of a university teaching hospital. PATIENTS: Group 1 (n=26) had less than 5% pretest likelihood of coronary artery disease and normal thallium perfusion, group 2 (n=10) had isolated, completely reversible anterior perfusion abnormalities, and group 3 (n=12) had analogous inferoposterior perfusion abnormalities. INTERVENTIONS: Heart rate and blood pressure were recorded at baseline and each minute of supine dipyridamole infusion. MAIN RESULTS: After 4 mins of dipyridamole infusion, a significant increase in heart rate was observed in group 1 (+12 beats/min, P<0.05) and group 2 subjects (+12 beats/min, P<0.05) but not in group 3 subjects (+3 beats/min, not significant; P=0.016 compared with responses in the other two groups). Blood pressure was not affected by dipyridamole infusion in any group. CONCLUSIONS: Isolated, moderate or severe inferoposterior hypoperfusion in response to dipyridamole is not accompanied by an increase in heart rate, suggesting that the chronotropic response to dipyridamole is modulated by the presence and location of myocardial perfusion abnormalities. This observation is consistent with the concept that inhibition of adenosine reuptake by dipyridamole, leading to local increases of adenosine concentration, exerts direct and/or reflex effects on heart rate that are site specific. The absence of a rise in heart rate during dipyridamole infusion may be a marker of impaired coronary flow reserve in the inferoposterior left ventricular wall.