Displacement of the Beating Heart Induces an Immediate and Sustained Increase in Myocardial Reactive Oxygen Species

Abstract

isplacement of the heart during beating heart surgery can reduce coronary blood flow and cardiac output (CO) 1 and to normalize hemodynamics the Trendelenburg position is often employed with or without fluid and pharmacological intervention. 1 Methods to reestablish coronary flow could be deemed reperfusion therapy and cardiac reperfusion after a brief ischemic insult can increase reactive oxygen species (ROS), 2 which may promote cardiac dysfunction and/or arrhythmias. 3-5 However, no studies have investigated the effects of dislocating the beating heart on possible associated reperfusion and free radical production. Thus, the aim of the present study was to examine heart dislocation and its re-positioning on myocardial ROS generation in dogs.The AEC National University of Singapore approved the experimental protocols. Seven male dogs (17-21 kg) were fasted overnight and anesthetized via intramuscular injection of ketamine (20 mg/kg) and intravenous thiopentone (30 mg/kg), intubated and ventilated. Anesthesia was maintained via 1.5 L oxygen/air and 1.5-2% isoflurane. Ventilation rate (20 strokes/min), tidal volume and FiO2 were adjusted to maintain arterial PO2 >100 mmHg. A left thoracotomy was performed in the fifth intercostal space and the heart was suspended in a pericardial cradle. A catheter was inserted into the coronary sinus for blood sampling of venous effluent.After 20-min stabilization, the heart was displaced by 90 degrees (dislocation) manually until the apex pointed upward to expose the left circumflex coronary artery (LCx). After 10 min each dog was placed in the Trendelenburg position (20 degrees head down) for 15 min without changing the position of the displaced heart. The operating table was then returned to horizontal and the heart returned to its anatomical position. ROS measurements began immediately after the heart was replaced in its normal position.Dogs were instrumented for hemodynamic measurements during heart displacement. Intra-aortic pressure was measured by inserting a fluid-filled 20 g Huber point needle cannula into the ascending aorta. CO and flow for the left anterior descending coronary artery (LAD), right coronary artery (RCA) and LCx was measured via ultrasonic probes (Power Lab/4S).ROS were measured in blood samples prior to heart dislocation procedures (control) and at 3, 30 and 60 min after the heart had been replaced in its anatomical position. A 2-ml sample of venous blood from the coronary sinus was collected in a 5-ml syringe pre-filled with 1 ml ofphenyl-N-tert-butylnitrone (PBN, 50 mmol/L) and gently mixed with brief periods of exposure to room air for 1 min and then immediately frozen in liquid nitrogen. For EPR measurements, samples were thawed on ice and transferred into glass tubes containing 1.5 ml spectroscopic-grade toluene, gently shaken and centrifuged for 5 min at 4,000 rpm Background Heart manipulation and displacement are common maneuvers during beating heart surgery to expose coronary arteries for revascularization. Effects of heart displacement on fr...

Protein Kinase A Catalytic Subunit Alters Cardiac Mitochondrial Redox State and Membrane Potential Via the Formation of Reactive Oxygen Species

“…8 The ROS production in the mitochondria contributes to pathological process such as cardiomyopathy, 32 aging, 33 apoptosis, 34 hypoxia, 35 and ischemia/reperfusion. 36,37 The complexes I and III of the mitochondrial electron transport chain (ETC) are regarded as the major sites of ROS production. It has been reported that PKAcat activates the respiratory chain complex I and/or III, and decreases the generation of ROS in isolated mitochondria.…”