Ischemic Preconditioning Protects Heart During Surgery

Shutting off the blood supply to an arm or leg before cardiac surgery protects the heart during the surgical procedure, according to a new study.

Researchers at the Norwegian University of Science and Technology (NTNU; Trondheim, Norway) and St. Olavs Hospital (Trondheim, Norway) randomized 60 patients undergoing coronary artery bypass graft (CABG) to a remote ischemic preconditioning (RIPC) group or to a control group. All patients had a blood pressure cuff applied preoperatively; while the cuff remained deflated in the control group, RIPC was performed via three cycles of cuff inflation for 5 minutes, separated by 5 minute deflation intervals. The researchers also obtained left ventricular biopsies both before and 15 minutes after aortic declamping.

The primary outcome of the study was mitochondrial respiration; secondary outcomes included activation of protein kinase Akt and expression of microRNAs, as assessed by array and real-time polymerase chain reaction (PCR). The results showed that mitochondrial respiration was preserved during surgery in those receiving RIPC, and reduced by 15% in the controls. RIPC also activated protein kinase Akt before aortic clamping, followed by increased phosphorylation of Akt substrates at reperfusion. No differences were observed in microRNA expression. The study was published online on October 14, 2014, in the International Journal of Cardiology.

“During heart surgery we have to stop the blood supply to the heart to be able to operate on it. After some time without fresh blood, the heart will reduce its ability to produce energy because it doesn't get oxygen,” said lead author Katrine Hordnes Slagsvold, MD, of St. Olavs Hospital. “When we shut off the blood flow to another large muscle, such as an arm or a leg, the body prepares for an upcoming challenge by mobilizing its defense system.”

“The heart muscle of the patients who had restricted blood flow to their arm before surgery were able to maintain the same level of energy production during the whole operation, while heart muscle from the other patients' hearts was not,” added Dr. Slagsvold, who is also a PhD candidate at NTNU. “This may be important because heart tissue is dependent on energy to survive, as well as to repair injuries the cells may have endured during surgery.”

RIPC is a phenomenon whereby brief episodes of cyclic ischemia and reperfusion applied in distant tissues or organs render the myocardium resistant to a subsequent sustained episode of ischemia. The concept has been translated to patients undergoing planned ischemic events, such as elective abdominal aortic aneurysm repair, angioplasty, and CABG surgery.

Related Links:
Norwegian University of Science and Technology
St. Olavs Hospital