The effects of cardioplegia on coronary pressure-flow velocity relationships during aortic valve replacement

Objective: The acute physiological response of the coronary circulation to aortic valve replacement (AVR) has not been fully elucidated. This study ai med to characterize the changes in coronary perfusion pressure-flow velocit y relationships, and to test whether this relationship is affected by cardi oplegic method. Methods: Nineteen patients (mean age 67 +/- 12 (SD) years, 9 males) undergoing aortic valve replacement who received either cold blood cardioplegia (CBC, n = 9) or warm blood cardioplegia (WBC, n = 10), were p rospectively studied before and 30 min after the operation, using transesop hageal Doppler echocardiography combined with high fidelity left ventricula r (LV) and aortic pressures. We thus determined: (1) Diastolic flow velocit ies in proximal anterior descending coronary artery (LAD), and simultaneous aorta to LV pressure differences. (2) The slope (LAD proximal linear resis tance) and pressure intercept (zero flow pressure) of this relationship. (3 ) Overall LAD linear resistance as the ratio of mean diastolic flow velocit y to mean pressure difference between aorta and left ventricle. (4) LV myoc ardial stroke work. Results: Following operation, myocardial stroke work fe ll from 5.2 +/- 2.7 to 3.0 +/- 1.7, mJ cm(-3) (P = 0.001), LAD mean diastol ic flow velocity increased from 47 +/- 19 to 74 +/- 21, cm s(-1) (P = 0.000 2). LAD overall linear cm resistance fell (0.75 +/- 0.24 vs. 1.26 +/- 0.26, mmHg cm(-1) s, P = 0.001). LAD proximal linear resistance, however, remain ed unchanged (P = 0.21), but the zero flow pressure fell (18 +/- 12.6 vs. 2 7 +/- 12.2, mmHg above LV end diastolic pressure, P = 0.013). With similar fall in myocardial work postoperatively, there was a greater fall in zero f low pressure after WBC than CBC (48 +/- 28 vs. 19 +/- 13,% of pre-op, P = 0 .012), and a greater increase in flow velocity time integral (127 +/- 81 vs . 53 +/- 59,%, P = 0.039). Conclusion: instantaneous diastolic LAD pressure -flow velocity relations in the early postoperative period can be explained more satisfactorily in terms of zero flow pressure and proximal linear res istance than simple resistance alone. The fall in zero flow pressure alone explains the increase in LAD flow velocity immediately after aortic valve r eplacement. The extent of this fall is greater after warm rather than cold blood cardioplegia. (C) 1999 Elsevier Science B.V. All rights reserved.