Re: In vivo model for reversal of pulmonary blood flow in canines.

Abstract

It is with interest I read a Letter to the Editor titled `In vivo model for reversal of pulmonary blood ow in canines' by Dan Abramov, Boris Orlov, and Yoram Abramov in your journal of August 1999 [1]. I must congratulate the authors in reviving an interest in this subject. We published an article in International Research Communication System entitled `Reversed pulmonary circulation ± possible clinical application in single ventricle deformity' in 1979 [2]. In the article we described two in vivo canine models that we developed to show that satisfactory oxygenation could be achieved by reversing the blood ow in the lungs. Ten dogs were used in this study. In the ®rst four dogs, on cardio-pulmonary bypass and cardioplegic arrest the right atrium was opened and both the atrio-ventricular valves were sutured closed after excising the atrial septum and the right atrium closed. The blood returning towards the right ventricle through the pulmonary arteries was redirected through a valved conduit in to the left ventricle through the apex (see Fig. 1 in original article). The dogs were weaned off bypass and kept alive for 2 h on ventilation with room air. One dog failed to come off bypass because of air embolus into the coronaries. In the second group of six dogs, we developed a model without using any prosthetic material. On bypass, the right atrium was opened and the atrio-ventricular valve was closed. The atrial septum was detached from its right border and sutured posterior to the right pulmonary veins. The left lung was excluded by snaring the hilum. The left atrium was anastamosed to the left pulmonary artery at the appendage thus redirecting the blood returning from the right lung through the right pulmonary artery in to the left atrium and then on to the aorta (see Fig. 2 in original article). All the six dogs survived the surgery with good oxygenation for over 2 h when the experiment had to be terminated, as we were not licensed to conduct survival experiments. This study reinforced the belief that normal life is possible with the blood circulating the wrong way around in our lungs. We used this haemodynamic turn-about to suggest a new operative procedure for single ventricle deformity in children. The proposed operation carried out with cardio-pulmonary bypass with or without circulatory arrest consists of closing both or single atrio-ventricular valve, as the individual anatomy requires after excising the interatrial septum. The pulmonary valve is then excised with a cuff of pulmonary artery and resutured upside down so that the single ventricle can now eject only through the aorta. A bioprosthetic conduit may have to be used in rare anatomical situations. The advantages that one can see in this operation are (a) the operation can be carried out without damaging the ventricle and (b) in most cases, no prosthetic material is needed.