Perioperative risk of MI

During the perioperative period, major physiologic changes occur that may alter the myocardial oxygen supply/demand balance. Surgery induces a catecholamine surge that increases myocardial oxygen demand and stimulates the release of inflammatory cytokines that increase thrombotic risk. Fluid shifts may contribute to hypotension, or alternatively increased myocardial wall stress. Pain, in conjunction with all of the aforementioned issues, may cause tachycardia and hypertension. The risk of perioperative MI classically peaks within the first 3 postoperative days when these factors are most pronounced. The Badner study below suggests that this risk might actually be highest on post-op days 0 and 1. The pathophysiology of perioperative MI is not fully understood, but may involve both acute plaque disruption and prolonged ischemia in the setting of underlying CAD.

In 1999, Lee et al derived the Revised Cardiac Risk Index to help predict those at greatest risk for an event. They reviewed many possible risk factors and used regression analysis to determine factors most predictive of a “major cardiac complication” (MI, Pulmonary Edema, VT, cardiac arrest, complete heart block). Factors included high risk surgery, CAD, CHF, DM on insulin, CKD (Creatinine > 2), and history of TIA or CVA. The percentage experiencing major cardiac complication by # of risk factors in their validation cohort were:

0 – 0.4% 1 – 0.9% 2 – 6.6% 3 or more – 11%

Aldesanya reviewed the literature and concluded that the following may be associated with increased risk of perioperative infarction: major abdominal, thoracic and head and neck surgery (especially vascular), CAD, PVD, recent CHF, intraoperative blood loss and transfusion, >20-30 min of ST segment depression, cumulative ST depression length of >1-2 hours, and postoperative hypotension. It has also been well established that surgery after recent PCI adds increased risk (< 2 weeks post angioplasty, <4-6 weeks after BMS , and <1 year following DES).