Transeosophageal echocardiograph assessment of mitral valve position during prolonged cardiopulmonary resuscitation and in moderate hypothermia

Abstract

Two competing hypotheses have been put forward for the mechanism of blood flow during closed chest cardiopulmonary resuscitation (CPR): the cardiac pump theory and the thoracic pump theory [1Niemann J.T. Rosborough J.P. Hausknecht M. et al.Pressure synchronized cineangiography during experimental cardiopulmonary resuscitation.Circulation. 1981; 164: 985Crossref Scopus (122) Google Scholar, 2Kouwenhoven W.B. Jude J.R. Knickerbocker G.G. Closed chest cardiac massage.J. Am. Med. Assoc. 1960; 173: 1064Crossref PubMed Scopus (1310) Google Scholar]. Transeosophageal echocardiographic assessment of mitral valve position during chest compression offers an opportunity to distinguish between these theories [[3]Higano S.T. Oh J.K. Ewy G.A. Seward J.B.: The mechanism of blood flow during closed chest cardiac massage in humans: transesophageal echocardiographic observations.Mayo Clin. Proc. 1990; 65: 1432-1440Abstract Full Text Full Text PDF Scopus (60) Google Scholar]. Hypothermic patients in many ways differ from normothermic patients. To evaluate a possible difference between normothermic and hypothermic patients and changes during CPR, we have performed transoesophageal echocardiography (TEE) in six patients (age 62–75 years) at 10 min intervals during prolonged CPR which was finally unsuccessful. The cause of cardiac arrest was primarily cardiac in all patients. CPR was performed according to the European Resuscitation Council guidelines. Four patients were normothermic at the time of CPR, in two patients the tympanic temperature was 31.9 and 30.4°C due to prolonged exposure to cold air. The median time between beginning of CPR and the start of TEE was 18 min (range 9–30 min). The mitral valve was observed to be closed during chest compression at this time in six of six patients. Ten min later, the valve was closed in only two of six patients (the two hypothermic patients) and at 20 min it was not closed in any of the six patients. Previous studies have demonstrated, that the cardiac pump theory is the main mechanism in CPR because the mitral valve is closed during compression in patients with a short interval between collapse and CPR [4Redberg R.F. Tucker K.J. Cohen T.J. Dutton J.P. Callaham M.L. Schiller N.B. Physiology of blood flow during cardiopulmonary resuscitation. A transesophageal echocardiographic study.Circulation. 1993; 88: 534-542Crossref Scopus (70) Google Scholar, 5Pell A.C. Guly U.M. Sutherland G.R. Steedman D.J. Bloomfield P. Robertson C. Mechanism of closed chest cardiopulmonary resuscitation investigated by transesophageal echocardiography.J. Accid. Emerg. Med. 1994; 11: 139-143Crossref Scopus (23) Google Scholar]. In contrast the mitral valve remains open or even dilates in patients with a prolonged delay [[6]Ma M.H. Hwang J.J. Lai L.P. Wang S.M. Huang G.T. Shyu K.G. Ko Y.L. Lin J.L. Chen W.J. Hsu K.L.: Transesophageal echocardiographic asssessment of mitral valve position and pulmonary venous flow during cardiopulmonary resuscitation in humans.Circulation. 1995; 92: 854-861Crossref Scopus (54) Google Scholar]. Our data support the conclusion that the cardiac pump is the predominant mechanism at the beginning of CPR and is replaced by the thoracic pump after prolonged CPR. Furthermore our findings suggest that possibly the time for which direct cardiac compression during CPR is the predominant mechanism for forward blood flow is prolonged in hypothermic patients.