Minimally Invasive Heart Surgery

Fritz Baumgartner

The advent of laparoscopic cholecystectomy in the late 1980s conceptually changed surgeons' perceptions of operative procedures. The impact of these new perceptions affected not only general surgery, but most surgical specialties, and thoracoscopy was a natural extension of laparoscopic procedures. Cardiac surgery, however, was considered by most to be insulated from a general acceptance of these new "minimally invasive" procedures. This concept has radically changed in the last several years.

A primary question regards the very definition of "minimally invasive" with respect to cardiac surgery. Extrapolated from laparoscopic surgery, "minimally invasive" cardiac surgery implied a small incision. However, limited exposure incisions in cardiac surgery can lead to dire consequences if a misadventure occurs. The end result of a small, cosmetic incision does not justify turning a routine cardiac procedure into a risk to the patient's well being, or inordinately prolonging the length of time to complete the procedure.

Furthermore, endoscopic gallbladder surgery compared to open cholecystec-tomy is a physiologically poor analogy when applied to cardiac surgery because the heart-lung machine adds a new level of physiologic derangement. Cardiopulmonary bypass (CPB) and ischemic arrest are nonphysiologic as attested to by systemic inflammation, coagulopathy, low vascular resistance, and low-output postpump states. Furthermore, neuropsychiatric events and outright stroke are known risk factors of CPB which increase markedly with age. Adverse cerebral outcomes from CPB occur in about 6% of all patients undergoing coronary artery bypass (CABG), with 3% being Type I events (strokes, transient ischemic attacks) and 3% being Type II events (deterioration of intellectual function or seizures). However, when the specific subgroup of patients greater than 80 years of age undergoing CABG with CPB is examined, the adverse cerebral complication rate increases to about 16%, with about 8% each for Type I and Type II events. There are therefore compelling reasons to limit CPB time in the elderly population.

Besides the elderly, other subgroups who have a higher incidence of adverse outcomes from CPB include patients with profound ventricular dysfunction, prior stroke, and pulmonary and renal dysfunction. In patients such as these, a smaller incision may have less importance in the definition of "minimally invasive" than does limiting the crossclamp and pump times. If a smaller incision means that these times are prolonged, then these "minimal incision" procedures should not necessarily be deemed as "minimally invasive."

It is for these reasons that another school of thought maintains that "minimally invasive" for heart surgery should be viewed in terms of total-body trauma

rather than local in terms of incision size. These surgeons generally maintain that the key element in "minimally invasive" heart surgery is reducing, or eliminating, the use of CPB rather than using small incisions. For coronary bypass surgery, this means performing grafts on coronary vessels while the heart is beating. Valve surgery, which by its very nature requires entry into the cardiac chambers, requires CPB, and some would therefore consider "minimally invasive" valve surgery to be a misnomer. Some of the more common "minimally invasive" cardiac procedures follow.

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