Transesophageal echocardiography to assess mitral valve movement and flow during long term cardiopulmonary resuscitation: How cardiac effects fade with time.

Background: Although the cardiac pump and the thoracic pump are the two main theories, the actual mechanisms of blood flow during Cardiopulmonary Resuscitation (CPR) in humans are still unclear. The aim of this study was to explore the relationship between the pump mechanism and time after cardiac arrest.

Results: 20 patients with non-traumatic cardiac arrest were enrolled in this study. Transesophageal two-dimensional and pulse-doppler echocardiography were used during CPR. The duration of CPR was 60-80min if there was no return of spontaneous circulation (ROSC). We found: (1) The mechanisms of blood flow during CPR varied with time: the thoracic pump took the place of the cardiac pump after prolonged CPR in the same patient. (2) Peak transmitral flow (TMF) decreased (p<0.05) after prolonged CPR in patients with mitral valve closure during chest compressions. (3) Longer elapsed time from collapse to CPR and TEE was correlated to lower peak TMF in CPR (Both p<0.05). (4) Peak TMF(p<0.01), mitral valve time-velocity integrals(p<0.05), left ventricular stroke volume (p<0.05) and end-tidal carbon dioxide tension (p<0.05) is higher in the group of patients with mitral valve closure during chest compressions. This group of patients had a shorter time from collapse to CPR (p<0.01), shorter time from collapse to TEE (p<0.01) and had overall better outcomes.

Conclusions: The pump mechanism changes over the course of prolonged CPR. Cardiac effect is an essential part of the pump at the beginning of cardiac arrest, but it faded with time, making the thoracic pump the dominate mechanism after prolonged CPR.