Reversing or Avoiding Acidosis in Heart Tissue During Cardiac Surgery Improves Long-Term Patient Survival
In a study published this month in the Journal of Thoracic and Cardiovascular Surgery, a group of surgeons reported 10-year follow-up data on adult patients undergoing cardiac surgery with cardiopulmonary bypass. They found that pH levels in the myocardium (heart tissue) before aortic cross-clamping, during aortic cross-clamping, or after aortic cross-clamping, were independently associated with long-term patient survival. Aortic cross-clamping refers to the time during which the heart is deprived of its natural blood supply while the patient is placed on the heart-lung machine.
In the study, cardiac surgeons at the VA Boston Healthcare System followed a total of 496 adult patients who underwent valve replacement, coronary bypass surgery, or both for an average of 10 years. During the surgery, they monitored pH levels in the myocardium. Analysis of the data identified three significant thresholds that affected long-term mortality: pH less than 6.63 before aortic cross-clamp, pH less than 6.73 at the end of cardiopulmonary bypass, and integrated mean pH of less than 6.34 during the period of aortic cross-clamp.
Raising the pH level from lower than threshold before aortic cross-clamp to higher than threshold during clamping increased the median survival by 40.2%.
"This is the first documentation of the adverse impact of intraoperative myocardial acidosis, and thus myocardial ischemia, on long-term patient survival,” explained Shukri Khuri, lead author of the study. Myocardial acidosis, as measured with tissue pH electrodes, has been repeatedly shown to be reflective of myocardial ischemia.
The study's authors hypothesize that because intraoperative myocardial acidosis accelerates apoptosis (premature cell death) in the myocardium, it may also contribute to post-operative congestive heart failure, one of the leading causes of late mortality after cardiac surgery. They hope to elucidate further the relationship between acidosis, apoptosis, and congestive heart failure in ongoing studies.
"The degree of myocardial acidosis that is encountered during cardiac surgery varies widely from one patient to the next, and in most cases is unpredictable,” states Dr. Khuri. "If the surgical team is monitoring myocardial pH during the surgery, the surgeon can employ a number of different protocols and maneuvers to reverse or avoid ischemic conditions.”
Dr. Khuri has developed an intraoperative pH monitoring system in cooperation with Terumo Cardiovascular Systems Corporation. The Khuri Myocardial pH Monitoring System is available worldwide. For more information, visit www.terumo-cvs.com/khuriph.
Khuri and coauthors published the study, "Intraoperative regional myocardial acidosis and reduction in long-term patient survival,” in the Journal of Thoracic and Cardiovascular Surgery 2005;129:372-81.
Terumo Cardiovascular Systems Corporation manufactures and markets products for the cardiac surgery, interventional, and neurovascular markets. It is headquartered in Ann Arbor, Michigan with American manufacturing operations in Ann Arbor, as well as Elkton, Maryland; Ashland, Massachusetts; Tustin, California; and Matamoros, Mexico. It is one of several subsidiaries of Terumo Corporation of Japan that are focused exclusively on the cardiac and vascular markets, including: Vascutek, Ltd., developer of vascular grafts; and Terumo Heart, developer of a ventricular assist device. Terumo Corporation is a premier global medical company with 2003 annual sales in excess of $1.9 billion. Terumo Corporation develops, manufactures, and markets a wide range of medical products including syringes, needles, catheters, and blood bags. For more information, visit www.terumo-cvs.com.