Effect of aortic valve replacement on coronary flow velocity during metabolic stress in a patient with aortic stenosis

In Vitro Investigation of the Impact of Aortic Valve Stenosis Severity on Left Coronary Artery Flow

Patients with aortic valve stenosis (AS) may experience angina pectoris even if they have angiographically normal coronary arteries. Angina is associated with a marked increase in the risk of sudden death in AS patients. Only a few in vitro models describing the interaction between the left ventricular and aortic pressures, and the coronary circulation have been reported. These models were designed for specific research studies and they need to be improved or modified when other specific studies are required. Consequently, we have developed an in vitro model that is able to mimic the coronary circulation in presence of aortic stenosis. First, we have validated the model under physiological conditions. Then, we have examined and quantified the hemodynamic effects of different degrees of AS (from normal to severe AS) on the coronary flow using a model of the normal left coronary artery. In the coronary in vitro model without AS (normal valve), the amplitude and shape of coronary flow were similar to those observed in in vivo measurements obtained under physiological conditions, as described by Hozumi et al. (1998, “Noninvasive Assessment of Significant Left Anterior Descending Coronary Artery Stenosis by Coronary Flow Velocity Reserve With Transthoracic Color Doppler Echocardiography,” Circulation, 97, pp. 1557–1562). The presence of an AS induced an increase in the maximum and mean coronary flow rates (97% and 73%, respectively, for a very severe AS). Furthermore, when AS was very severe, a retrograde flow occurred during systole. This study allowed us to validate our coronary in vitro model under physiological conditions, both in the absence and presence of AS. These changes could explain the fact that even if patients have angiographically normal epicardial coronary arteries, we can observe the occurrence of angina pectoris in these patients in the presence of an AS.

Effect of mechanical aortic valve orientation on coronary artery flow: comparison of tilting disc versus bileaflet prostheses in pigs

OBJECTIVE

Orientation for optimal systolic performance of tilting disc and bileaflet aortic valves was defined in previous studies. The present study investigates the influence of valve orientation on coronary artery flow in an animal model.

METHODS

A rotation device holding either a Medtronic Hall tilting disc (n = 4; Medtronic, Inc, Minneapolis, Minn), a St Jude Medical bileaflet (n = 4; St Jude Medical, Inc, St Paul, Minn), or a Medtronic Advantage bileaflet (n = 3) aortic valve was implanted. The device allowed rotation of the valve without reopening the aorta. Flow through the left anterior descending coronary artery was measured preoperatively and at normal versus high cardiac output after weaning from extracorporeal circulation. Measurements were performed at the best and worst hemodynamic position, as defined previously.

RESULTS

Coronary flow rates were similar in all animals preoperatively (26 +/- 4.1 mL/min). After aortic valve replacement, left anterior descending flow increased significantly to 58.2 +/- 10.6 mL/min. Highest flow rates at normal cardiac output were found in the optimum orientation, especially for the Medtronic valves (Medtronic Hall, 64 +/- 8.7 mL/min; Medtronic Advantage, 64.6 +/- 11.6 mL/min; St Jude Medical, 48.3 +/- 10.3 mL/min), whereas the worst position demonstrated significantly lower left anterior descending flow, with no differences among valves (Medtronic Hall, 37.5 +/- 1.3 mL/min; St Jude Medical, 35.7 +/- 10.7 mL/min; Medtronic Advantage, 39.8 +/- 10 mL/min). Left anterior descending artery flow increased significantly with higher cardiac output.

CONCLUSIONS

Coronary blood flow was significantly influenced by mechanical aortic valve implantation and the orientation of prostheses. For both valve designs, the previously defined optimum orientation with respect to pressure gradients and turbulence demonstrated the highest left anterior descending flow rates. Even in its optimum orientation, the St Jude Medical valve showed significantly lower coronary flow than the other valves.