Abstract 19777: How Physiological is Adenosine-Induced Hyperaemia? Insights From Exercise in the Catheterisation Laboratory

Introduction: Fractional flow reserve during adenosine-induced hyperaemia (FFR) is frequently considered a surrogate for inducible myocardial ischaemia on exercise; however it is unclear whether the stresses are comparable. Hypothesis: The mechanism of flow augmentation with exercise is different to that of adenosine. Methods: Patients undergoing coronary angiography were assessed with a dual pressure-flow sensing intracoronary wire at rest, whilst performing on-table supine bicycle ergometry and during adenosine-induced hyperaemia. Aortic pressure (P a ) , distal coronary pressure (P d ) and flow velocity were recorded at peak exercise and hyperaemia. Mean P d /P a was calculated for both stresses (FFR, exercise P d /P a ). Wave intensity analysis was used to investigate the mechanisms governing flow. Results: Forty-two patients performed the protocol, attaining a mean heart rate of 75% of age predicted maximum. Rate pressure product (reflecting myocardial work) rose from 11x10 3 ±3x10 3 bpm.mmHg at rest to 13x10 3 ±3x10 3 bpm.mmHg with adenosine and 21x10 3 ±7x10 3 bpm.mmHg with exercise. Mean FFR and exercise P d /P a were similar (0.88±0.08 vs. 0.90±0.09, p=0.131), but only moderately correlated (Spearman’s rho 0.57) (figure 1). Doppler flow velocity was assessed throughout in 18 patients. Mean velocity increased from 18.1±6.3cms -1 at rest to 38.7±16.8cms -1 with adenosine and 28.1±7.4cms -1 with exercise. Coronary perfusion was more efficient during exercise (84±6% of total wave energy accelerating flow) than adenosine hyperaemia (77±12%, p = 0.02). This was due to augmentation of diastolic suction, with the backward expansion wave contributing 58±11% of total wave energy during exercise compared with 50±10% during adenosine (p = 0.02). Conclusions: Adenosine decreases microvascular resistance but does not reproduce the complex cardiac-coronary coupling that occurs with exercise. This may explain why FFR does not correlate well with P d /P a during exercise.