Concepts in assisted circulation

Assisted circulation by extracorporeal and extracardiac bypass techniques must be based on the requirements of the heart and of the total body, though these may differ. The cardiac problem in cardiogenic shock is more likely to be a biventricular problem demanding decompression of both sides. Extra pulmonary oxygenation should be avoided because of complexity in long-term use. Principles of assisted circulation may be applied in an extra-thoracic temporary manner or as an intracorporeal long-term device without removal of the heart. We have compared a number of extracorporeal mechanical bypass techniques (left ventricular bypass, left atrial bypass, right atrial plus left ventrical bypass, and right atrial plus left atrial bypass) in dogs at different flow rates with control groups (nitroprusside, metabolic substrates, and no therapy) for survival during and after 4-hour treatment periods in a standard severe myocardial infarction preparation with biventricular failure. The left ventricle was cannulated in a retrograde manner. Right atrial bypass was mixed with oxygenated left ventricular blood before return without oxygenation. Results in 50 dogs revealed that without treatment 20% survived; left ventricular plus right atrial bypass provided 100% survival during the 4-hour treatment, whereas left ventricular bypass and nitroprusside were intermediate with approximately 70% survival. Respiration and acid-base balance were not significantly altered by right atrial bypass, which provided adequate decompression of the right ventricle. Flow rates of 50% of control levels were adequate to provide normal or increased peripheral circulation as well as decompression of both ventricles and maintenance of sinus or nodal rhythm. Left atrial or left ventricular bypass alone was unable to support the heart or circulation in severe failure. Hemodynamics, including total body perfusion, atrial pressures, and dP/dt were improved significantly only by left ventricular plus right atrial bypass, even though reduced rates of flow were used. Similar findings were seen in lactic acid, CPK, and oxygen consumption. The addition of metabolic substrates currently does not improve survival though they appear to act as metabolic modulators. We conclude that the principle of a low flow left ventricular plus right atrial bypass without an oxygenator offers a technique for long- or short-term assistance.