The Anatomic Conventional Paradigm In Clinical Practice

As outlined in both the 1991 and the 2004 CABG Guidelines, left main coronary artery stenosis of greater than 50% is a class I indication for CABG in stable patients with either asymptomatic, mild angina or moderate angina, regardless of the level of LV function, regardless of whether myocardial ischemia has been documented, and without mention of any form of medical therapy. The same applies for greater than 70% narrowing of all three major vascular territories.

Further extension of the anatomic approach includes application to two-vessel disease, by separating those patients with or without proximal narrowing greater than 70% in the LAD. The complex formulas and figures, especially the control or "medical therapy" arms displayed in the 1991 Guideline, were derived primarily from the VA Cooperative Stable Angina Study, which was completed by the early 1970s and did not routinely include any of the four categories of medications subsequently shown to have survival benefit.

Acute MI was divided into Q and non-Q types in the 1991 CABG Guideline, and, in general, early post-MI CABG was proscribed. Nevertheless, specific direction was not given (beyond coronary anatomy) regarding which, if any, MI patients would be better served with PCI than with CABG.

By the 2004 CABG Guideline Update, clinical patient subgroups were expanded to include asymptomatic or mild angina, stable angina, unstable angina/NSTEMI, STEMI, poor LV function, and life-threatening arrhythmias, to be consistent with both the PCI Guidelines, the MI Guidelines, and the Stable and Unstable Angina Guidelines.

As outlined in the 1988 PCI Guideline, the first major "cut-point" in PCI Guidelines was between single-vessel and multivessel CAD; multivessel disease referred to greater than 70% diameter stenoses in two more major epicardial vessels. Particularly given the possibility of acute occlusion with attendant acute MI and need for emergency CABG, each category of recommendation was accompanied by an estimate of the likelihood of success and the likelihood of acute occlusive syndrome based on an anatomic scheme introduced in that Guideline. The ACC/AHA lesion classification was for balloon-only angioplasty, because stents had not yet become available. Type A lesions were said to be associated with greater than 85% success and a low risk of acute complications. Type A lesions were discrete (<10 mm), concentric, readily accessible, nonangulated, smooth lesions with little or no calcification that were less than totally occlusive, not ostial, not bifurcated, and free of thrombus. Type B anatomic lesions were said to be associated with 60% to 85% success and a moderate risk of complications. Type B lesions included those that were 10 to 20 mm in length, eccentric, of moderate tortuosity, with moderate angulation, irregular contour, moderate to heavy calcification, total occlusion of less than 3 months' duration, ostial location, presence of bifurcation necessitating two guidewires, and containing thrombus. Class C anatomic features were said to be associated with less than 60% acute success and a high risk of acute complications. Class C features included greater than 2 cm length, excessive tortuosities, angulation of greater than 90 degrees, total occlusion of longer than 3 months' duration, inability to protect major side branches, and degenerated saphenous vein graft lesion.

For purposes of illustration, consider two hypothetical 74-year-old patients (male or female; diabetic or not), one stable and the other unstable, in whom coronary angiography was completed and showed 50% left main narrowing and 70% proximal circumflex and right coronary artery stenoses. In the stable patient, the LAD has an additional high-grade, discrete stenosis, whereas in the unstable patient, there is a 100% thrombotic occlusion. The unstable patient is suffering an acute anterior MI with ST elevation and has a blood pressure of 80 mm Hg on high-dose dopamine (>20 jjg/kg/min), despite a pulmonary wedge pressure of 22 mm Hg. In other words, this patient has anterior STEMI with cardiogenic shock. The stable patient has Canadian Cardiovascular Society Class II angina, is receiving no medical therapy, and has not had a provocative test for ischemia. The ACC/AHA CABG Guidelines suggest that both patients should receive CABG as a class I recommendation, based on level of evidence "A" (multiple trials and or meta-analysis).1-5 Perusal of the reference list shows that the multiple trials are the five CABG versus medical therapy trials alluded to previously, although later publications of longer follow-up are cited (see Table 4-1).3,4

Regarding our unstable patient with acute STEMI, this patient would not have been excluded by the more than 20 trials of thrombolytic therapy versus primary PCI that supported revascularization, more than 90% of which was accomplished by PCI (see Table 4-4).5,28,29 However, all five CABG versus medical therapy trials excluded patients who were hemody-namically unstable, within 30 days of an MI, and older than 70 years of age and therefore would have excluded our patient with STEMI and shock (see Table 4-1).3,4 The SHould we emergently revascularize Occluded Coronaries in cardiogenic shocK? (SHOCK) trial of cardiogenic shock would provide support for the decision to revascularize our unstable patient, but, because there was no randomization between CABG and PCI in that trial (two thirds of revascular-izations were by PCI), it does not help with the choice of revascularization method.2,5 Given the speed of reperfusion and its importance, many operators and hospitals would use primary PCI to care for this STEMI patient. Facilities without PCI, or operators without sufficient experience and comfort, might use thrombolytics and an intra-aortic balloon pump (IABP), and the SHOCK trial provides support for this approach. The CABG Guidelines' own caveats regarding the timing of surgery relative to MI might be used to declare CABG a "prohibitive risk" in many settings.3

For our stable patient, the ACC/AHA Guidelines would give a class I recommendation for CABG, based on class A evidence. Nevertheless, based on the patient's age, he or she would have been excluded from the three CABG versus medical therapy trials (see Table 4-1).1-4 The patient would likely undergo CABG at most hospitals. In fact, in many communities, radio and television advertisements extol the importance of using calcium scores to guide asymptomatic and untreated subjects to coronary angiog-raphy; patients with three-vessel CAD go on to provide testimonials as to having their lives "saved" by CABG.

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