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 studie s 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 ar tery disease and normal thallium perfusion, group 2 (n=10) had isolated, co mpletely reversible anterior perfusion ab-normalities, and group 3 (n=12) h ad 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 nor 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, s uggesting that the chronotropic response to dipyridamole is modulated by th e presence and location of myocardial perfusion abnormalities. This observa tion is consistent with the concept that inhibition of adenosine reuptake b y dipyridamole, leading to local increases of adenosine concentration, exer ts direct and/or reflex effects on heart rate that are site specific. The a bsence of a rise in heart rate during dipyridamole infusion may be a marker of impaired coronary flow reserve in the inferoposterior left ventricular wall.