The effect of open-chest cardiac resuscitation on mitral regurgitant flow: an on-line transesophageal echocardiographic study in dogs.

INTRODUCTION We sought to determine the effect of cardiac massage on a pre-existing regurgitant mitral valve during open-chest cardiopulmonary resuscitation (OCCPR) in an animal experiment. METHODS Our study included 29 dogs that were used as experimental models. We anesthetized them and inserted a transesophageal echocardiographic (TEE) probe. Then we performed a transverse thoracotomy, attempting to produce acute mitral regurgitation (MR). In models that showed cardiac arrest we initiated OCCPR to restore cardiac function. The regurgitant area of mitral jet and left ventricular (LV) diameters and volumes were calculated before and during OCCPR using TEE. RESULTS Ventricular fibrillation and/or electromechanical dissociation occurred in 13 animals (45%). In 4 models without preexisting MR, no additional regurgitation was detected during OCCPR, while in another 5 with preexisting MR we noticed a slight increase in the regurgitant flow. The regurgitant flow area changed from 0.62 +/- 1 cm2 before to 1.1 +/- 0.36 cm2 during OCCPR (p<0.008). In the 4 animals that had severe damage to the mitral apparatus after the attempts, the regurgitant flow increased from 4.01 +/- 0.93 cm2 to 7.7 +/- 2.6 cm2 (p<0.002). The LV transverse diameter decreased from 4.39 +/- 0.62 cm to 1.54 +/- 0.5 cm and its volume from 60.5 +/- 7.14 cm3 to 17.02 +/- 4.14 cm3 (both p<0.001), thus showing the effectiveness of OCCPR. CONCLUSIONS Given the presence of preexisting mitral regurgitation, direct cardiac massage during OCCPR would probably be less effective than expected, because of an increase in the amount of the regurgitant.