Hemodynamic changes during cardiac manipulation in off-CPB surgery: relevance in brain perfusion

The recent introduction of various cardiac stabilization and positioning devices, alone or in combination with deep pericardial traction sutures, has greatly increased the ability to perform beating heart surgery to accomplish multi-vessel coronary revascularization without the need for cardiopulmonary bypass (CPB), with its associated risks. However, positioning the heart for anastomosis of the circumflex (Cx) and the posterior descending artery poses a risk of inducing hypotension, impaired cardiac output, and generalized hemodynamic instability with risk of cerebral compromise. This report discusses clinical studies suggesting that compromised right ventricular diastolic filling as a result of direct ventricular compression, rather than impaired contractility or ischemia, may be the primary mechanism for producing hemodynamic instability during OPCAB surgery. Foremost among measures to minimize ventricular compression is optimal placement of the myocardial stabilization device. Secondary measures include steep Trendelenburg positioning, fluid loading, right-sided pleuro-pericardial window that allows rotation of the heart by partial herniation into the right pleural cavity, and possibly certain pharmacological agents. This report also analyzes the effect that variable degrees of hemodynamic disturbance accompanying displacement of the heart for OPCAB surgery has on endorgan perfusion and considers the effects of hypotensive agents, direct cerebral dilators, and patient-specific factors on cerebral blood flow. The role of the partial aortic occlusion clamp and risk of stroke is also considered. We conclude that for cardiac surgery patients considered at increased risk of adverse central nervous system events, direct monitoring of cerebral function and avoidance of aortic manipulation is strongly recommended.