Comparison of adenosine, dobutamine and bicycle exercise on intracoronary physiological indices in patients with myocardial bridges

Abstract Background We have recently demonstrated that patients with angina and nonobstructive coronary arteries (ANOCA) with myocardial bridges (MBs) exhibit maladaptive exercise physiology, due to abnormal wave energies arising at the tunnelled segment (1). Intracoronary pressure-derived indices in response to dobutamine and adenosine are used to identify an ischaemic substrate in these patients in clinical practice (2). However, it remains unknown if the changes induced by dobutamine and adenosine are comparable with physical exercise. Methods Patients with ANOCA and a MB in the left anterior descending artery underwent simultaneous acquisition of intracoronary pressure and flow sequentially during rest, supine bicycle exercise and intravenous adenosine and dobutamine infusion. We compared coronary perfusion efficiency (accelerating energy/total energy flux) and changes in specific wave energies in response to these three stressors. Results Twenty-five patients were enrolled (36% females, 59±9 years old). Patients had a high symptom burden (88% CCS II-IV) and myocardial bridge muscle index (79±30). Fractional flow reserve and coronary flow reserve were 0.86±0.05 and 2.5±0.5. Microvascular resistances during adenosine, dobutamine and exercise were 2.0±0.7, 3.4±1.4 and 4.3±1.3 mmHg.cm-1.s-1 respectively (p<0.001). There was a reduction in coronary perfusion efficiency in response to adenosine (64±8% to 51±12%), dobutamine (65±9% to 53±13%) and exercise (66±10% to 56±9%) (all p<0.001), with no between stressor differences in delta perfusion efficiency (ANOVA p=0.641). However, the impact of each stressor on the wave energy arising from the tunnelled segment was different whereas no such difference (between stressors) was observed in the wave energies arising from the microcirculation. There was no difference in tunnelled-segment derived delta wave energies between dobutamine and exercise (Figure 1). Conclusions Adenosine, dobutamine and exercise have different effects on coronary microvascular resistance and cardiac coronary coupling in patients with myocardial bridges. Our findings provide novel mechanistic insights into the pathophysiology of ANOCA in combination with MB, and suggest that dobutamine (but not adenosine) could be used as a surrogate for physical exercise during intracoronary physiological assessment.Figure 1.