The influence of adenosine triphosphate on left ventricular function and blood flow distribution during aortic crossclamping in dogs

The importance of transesophageal echocardiography during surgery of the thoracic aorta

OBJECTIVES

To assess left ventricular dimensions and cardiac output during thoracic and thoracoabdominal aortic aneurysm repair.

MATERIAL AND METHODS

Nine patients undergoing thoracic and thoracoabdominal aneurysm repair using direct cross-clamping without shunt or by-pass were studied prospectively. Prior to, during cross-clamping (XC) and after declamping left ventricular cross-sectional areas were monitored with transesophageal echocardiography. A pulmonary artery catheter was used for measurements of cardiac output with the thermodilution technique.

RESULTS

Cardiac output increased 43% from baseline during XC (p < 0.01) and was still 55% above baseline at declamping (p < 0.05). Left ventricular end-systolic inner area was reduced 32% during XC (p < 0.01). Pulmonary artery pressures and central venous pressure increased during declamping (p < 0.05). Heart rate increased 38% from 66 beats/ min to 92 beats/min (p < 0.01) and was still 30% elevated at declamping (p < 0.01).

CONCLUSION

During thoracic aortic XC, cardiac output is increased and left ventricular end-systolic dimension is reduced. TEE is a valuable supplement to pressure measurements for the evaluation of cardiac function during surgery of the thoracic aorta.

Increased left ventricular contractility during cross-clamping of the descending thoracic aorta

OBJECTIVE

To evaluate how left ventricular (LV) dimensions and contractility and proximal systemic hemodynamics respond during and after 30 minutes of cross-clamping of the descending thoracic aorta.

DESIGN

The study was prospective and controlled.

SETTING

The study was performed in a university animal laboratory.

PARTICIPANTS

Ten pigs (bodyweight: 22 to 30 kg).

INTERVENTIONS

The pigs were anesthetized with fentanyl and ketamine, and the heart and aorta were exposed through a left thoracotomy. The aortic root pressure and flow and LV dimensions were monitored with a high-fidelity pressure catheter, a precalibrated ultrasonic transit-time flow probe, and by two-dimensional ultrasound imaging, respectively.

MEASUREMENTS AND MAIN RESULTS

After 1 minute of cross-clamping, LV end-diastolic and end-systolic diameters were increased 17% and 32% above baseline (both p < 0.001), respectively, whereas LV fiber shortening was decreased by 35% (p < 0.05) corresponding to the 257% increase in wall stress (p < 0.001). After 5 minutes, LV dimensions, fiber shortening, and wall stress had returned to baseline levels. After 10 minutes, fiber shortening was increased 67% (p < 0.05), although wall stress was maintained at baseline levels. Simultaneously, the aortic mean blood pressure, heart rate, and cardiac output peaked 112% (p < 0.001), 81% (p < 0.001), and 125% (p < 0.01) above baseline, respectively.

CONCLUSIONS

Cross-clamping grossly increased systemic afterload grossly and was followed by moderate LV dilation, which resolved after 5 minutes owing to the combined effects of proximal vasodilation, increased myocardial contractility, and tachycardia. This hyperdynamic circulatory state was maintained during cross-clamping and decreased after declamping.

Effects of nifedipine on the hemodynamic response to clamping and declamping of the abdominal aorta in dogs

Clamping and declamping of the infrarenal abdominal aorta may adversely affect cardiovascular function, particularly in the presence of heart disease. This effect may be further altered by drugs used in the treatment of symptomatic coronary artery disease. The effect of nifedipine on the hemodynamic response to aortic clamping and declamping was determined in 12 dogs anesthetized with 50% nitrous oxide and 0.6% end-tidal isoflurane and monitored with aortic, left ventricular (LV), and thermodilution pulmonary artery catheters. Six dogs received a nifedipine bolus of 100 micrograms/kg followed by an infusion of 4 micrograms/kg/min. Six dogs did not receive any nifedipine and served as controls. Before clamping, nifedipine produced immediate decreases in arterial pressure, systemic vascular resistance (SVR), and LV dP/dt, and a modest increase in cardiac output (CO). During aortic clamping, nifedipine-treated dogs demonstrated marked increases in heart rate (HR), dP/dt, and CO while maintaining a low SVR. There were no significant changes upon declamping. The nifedipine-treated animals maintained a high CO and low SVR. Thus, nifedipine greatly altered the hemodynamic responses to aortic clamping and declamping. Awareness of these alterations is important when caring for patients being treated with nifedipine who are undergoing aortic surgery.