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

The acute physiological response of the coronary circulation to aortic valve replacement (AVR) has not been fully elucidated. This study aimed to characterize the changes in coronary perfusion pressure-flow velocity relationships, and to test whether this relationship is affected by cardioplegic method.

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 prospectively studied before and 30 min after the operation, using transesophageal Doppler echocardiography combined with high fidelity left ventricular (LV) and aortic pressures. We thus determined: (1) Diastolic flow velocities in proximal anterior descending coronary artery (LAD), and simultaneous aorta to LV pressure differences. (2) The slope (LAD proximal linear resistance) and pressure intercept (zero flow pressure) of this relationship. (3) Overall LAD linear resistance as the ratio of mean diastolic flow velocity to mean pressure difference between aorta and left ventricle. (4) LV myocardial stroke work.

Following operation, myocardial stroke work fell from 5.2 +/- 2.7 to 3.0 +/- 1.7, mJ cm(-3) (P = 0.001), LAD mean diastolic flow velocity increased from 47 +/- 19 to 74 +/- 21, cm s(-1) (P = 0.0002). LAD overall linear resistance fell (0.75 +/- 0.24 vs. 1.26 +/- 0.26, mmHg cm(-1) s, P = 0.001). LAD proximal linear resistance, however, remained unchanged (P = 0.21), but the zero flow pressure fell (18 +/- 12.6 vs. 27 +/- 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 flow 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).

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 resistance than simple resistance alone. The fall in zero flow pressure alone explains the increase in LAD flow velocity immediately after aortic valve replacement. The extent of this fall is greater after warm rather than cold blood cardioplegia.