Deep hypothermia and aortic regurgitation without left ventricular venting, an animal model.

OBJECTIVE: Omitting ventricular decompression in resternotomy during cardiopulmonary bypass with deep hypothermia and circulatory arrest in patients with aortic regurgitation (AR) has recently been reported. The consequences of the dilated and non-dilated heart in conjunction with rapid and profound cooling were further studied in this randomized animal model.

METHODS: In five pigs (group A) AR was induced before cooling to 15°C and circulatory arrest of 30 minutes without left ventricular decompression. The animals were rewarmed with a competent valve, and weaning off bypass was attempted. In another five pigs (group B) the protocol was repeated with left ventricular decompression. Hemodynamics and the extent of myocardial infarction were evaluated.

RESULTS: During cooling in group A mean arterial and left atrial pressures were equalized and all animals suffered massive pulmonary edema. Only one animal could be weaned off bypass. The remaining four suffered considerable biventricular failure and succumbed when weaned off bypass. The animals in group B were stable throughout the experiment and easily weaned off bypass. Myocardial infarction was significantly more extensive in group A, 22 (6-36)% of left ventricular area, compared to group B; 3 (3-11)%, p = 0.016.

CONCLUSIONS: In our experimental model aortic regurgitation without left ventricular venting in deep hypothermia and circulatory arrest has damaging effects on the myocardium.