Differential response of coronary collateral channels to atrial pacing and balloon occlusion at angioplasty.

BACKGROUND

Collateral channels can protect from infarction, even in the presence of a total or sub-total occlusion. Acute re-occlusion following restoration of flow may still lead to ischaemia or infarction. It is unclear whether collaterals respond differently to tachycardia-induced stress and balloon inflation. This study compared the response of collateral-dependent viable myocardium to repetitive atrial pacing with the response to multiple balloon occlusions during percutaneous transluminal coronary angioplasty (PTCA).

METHODS AND RESULTS

Fifteen patients undergoing elective single vessel PTCA with well-developed collateral channels supplying the target vessel were recruited. Patients underwent two periods of incremental atrial pacing (P(1); P(2)) followed by two 90-s balloon inflations (I(1); I(2)). Collateral flow velocity was assessed by Doppler flow wire across the target lesion. Evidence of ischaemia was obtained from monitoring of surface ST-segments and by chest pain scores recorded on a visual analogue scale. Retrograde and 'aggregate' flow velocities were significantly lower during I(1) and I(2) than either P(1) or P(2). Reduction in flow velocity was most marked during I(1) compared with P(1) or P(2). Chest pain score was lower during P(2) than P(1) (3.8 +/- 3.5 versus 5.5 +/- 3.0, P < 0.02), although flow velocity was unchanged.

CONCLUSION

Collateral flow velocity is significantly higher during tachycardia-induced stress than balloon occlusion. Restoration of antegrade flow by balloon inflation results in a further reduction in flow during a second inflation, suggesting a functional down-regulation of the collateral channels. Ischaemic symptoms are attenuated with repetitive pacing independent of collateral flow, suggesting an additional preconditioning response.