Left Main Coronary Artery Stenosis

Abstract

Although most patients with left main coronary artery stenosis undergo urgent coronary artery bypass grafting, limited information is available regarding the risk factors that might lead to cardiac events between angiographic diagnosis and surgery.

We retrospectively reviewed 1,731 cases of coronary artery bypass grafting at our institution, 97 of which were performed in patients with significant (≥50%) left main coronary artery stenosis. These patients were placed in 1 of 2 groups: eventful waiting or uneventful waiting. We analyzed multiple preoperative variables, and the incidence of serious cardiac events (death, myocardial infarction, unstable angina, left ventricular failure, and life-threatening ventricular arrhythmias) during the waiting period between angiography and surgery.

Four patients (4.1%) experienced serious cardiac events while awaiting surgery (1 had non-ST-elevation myocardial infarction; 3 had life-threatening ventricular arrhythmias); none died. All the events occurred more than 24 hours after cardiac catheterization. Of the preoperative variables analyzed (acute coronary syndrome, age, history of diabetes, hypertension, hyperlipidemia, smoking, renal failure, severity of left main stenosis, right coronary artery involvement, ejection fraction, and use of intra-aortic balloon pump), only acute coronary syndrome predicted the incidence of preoperative cardiac events (P =0.001).

The occurrence of severe cardiac events while patients await coronary artery bypass grafting is rare. Carefully selected patients with severe left main coronary artery stenosis can safely await surgery. Concomitant acute coronary syndrome and severe left main coronary artery stenosis indicate a high risk for cardiac events. Therefore, in patients with these conditions, emergency coronary artery bypass may be preferable.

Left main coronary artery (LMCA) stenosis is a relatively infrequent but important cause of symptomatic coronary artery disease.¹ Multiple studies have found LMCA stenosis to be an independent indicator of increased morbidity and mortality rates among patients with coronary artery disease.^2,3

Patients who have LMCA stenosis experience a high rate of complications during or shortly after catheterization.^4–8 Although percutaneous angioplasty has been performed for unprotected LMCA stenosis,^9–14 surgery is the preferred treatment^8,15,16 and improves the likelihood of survival, as shown by the Coronary Artery Surgery Study (CASS)^17,18 and the Veterans Administration Cooperative Study.¹⁹

Coronary artery bypass grafting (CABG) is performed as urgent surgery in most patients with LMCA stenosis, with the intent to lower the incidence of postoperative ischemic complications. Because of the logistical constraints associated with cardiac surgery, however, some patients undergo CABG less urgently. Limited information is available regarding the optimal time interval between angiographic diagnosis of LMCA stenosis and CABG.

We performed this study in patients with angiographically documented LMCA stenosis who were awaiting CABG, in order to determine the incidence of severe cardiac events after coronary angiography and to identify the risk factors that might predict the occurrence of such events before CABG was performed.

Patients and Methods

We retrospectively reviewed the records of all patients with an angiographically confirmed diagnosis of significant LMCA stenosis who underwent CABG at our institution from January 2000 through August 2002. Significant LMCA stenosis was defined as a reduction of at least 50% in the luminal diameter of the LMCA. Patients who underwent any associated procedure (such as repair or replacement of a valve or repair of the ascending aorta) were excluded from the analysis.

Of the 1,731 patients who underwent CABG during the designated period, 97 required the procedure because of significant LMCA stenosis. These 97 patients were placed into 2 groups. The 1st group, called the eventful waiting group, comprised 4 patients who experienced cardiac events during the waiting period between angiographic diagnosis of LMCA stenosis and CABG. The 2nd group, called the uneventful waiting group, comprised 93 patients who did not experience any cardiac events during this waiting period. Events were defined as the occurrence of recurrent ischemia or myocardial infarction as evidenced by electrocardiographic changes or by an increase in cardiac enzyme activity, the occurrence of symptomatic ventricular arrhythmia, or the occurrence of congestive heart failure during the waiting period.

Data Collection.

Detailed demographic, clinical, angiographic, and surgical data were collected for each patient. These included age; sex; indications for angiography; degree of LMCA stenosis; the presence of hypertension, diabetes, hyperlipidemia, peripheral vascular disease, renal failure requiring dialysis, significant right coronary artery (RCA) stenosis, or stroke; and left ventricular ejection fraction. Particular emphasis was placed on recording the time interval between cardiac catheterization and CABG and on the occurrence of cardiovascular events during that interval.

Statistical Analysis.

Categorical variables were expressed as frequencies and percentages for each variable and were analyzed by the χ² test. Continuous variables were presented as means ± SD and were analyzed with the paired Student's t-test. A P value of <0.05 was considered statistically significant.

Results

Four (4.1%) of the 97 patients with angiographically documented LMCA stenosis experienced nonfatal cardiac events while awaiting surgery (1 had non–ST-segment elevation myocardial infarction and 3 had life-threatening ventricular arrhythmias) (Table I). All events occurred within the first 3 days after coronary angiography; no complications occurred during the first 24 hours after the diagnostic procedure.

Table I. Clinical Characteristics of the Study Groups^a

Between the patients who experienced events and those who did not, there were no statistically significant differences in age, sex, risk factors for coronary artery disease, left ventricular ejection fraction, severity of LMCA stenosis, RCA involvement, or preoperative use of an intra-aortic balloon pump. In addition, there was no significant difference in the average period between angiography and CABG (eventful waiting group, 2.25 days; uneventful waiting group, 8.1 days; P =0.26).

All patients who experienced events had acute coronary syndrome (defined as unstable angina or acute myocardial infarction) before they underwent cardiac catheterization for angiography. Comparison of the 2 groups showed that only the presence of acute coronary syndrome when the patient presented at the hospital predicted the occurrence of cardiac events among the patients awaiting CABG (eventful waiting group, 100%; uneventful waiting group, 17%; P =0.001).

Discussion

The results of this study indicate that patients with LMCA stenosis rarely experience complications during the first 24 hours after coronary angiography. Results also suggest that similar patients who arrive at the hospital with symptoms of unstable angina or myocardial infarction are at very high risk of experiencing cardiac events while awaiting CABG after angiography.

Morton and colleagues⁶ found patients with LMCA stenosis to be at high risk for adverse cardiac events during cardiac catheterization or within the 1st few hours thereafter. Similarly, Miller and associates,⁷ in their study of 83 patients with LMCA stenosis, found that 3.6% of the patients died during or shortly after coronary angiography. None of the patients in our study experienced any cardiac events during the first 24 hours after angiography. This finding may indicate that coronary angiography has become a much safer procedure, even for high-risk patients with LMCA stenosis. In addition, awareness of the high complication rate in such patients has changed the diagnostic procedure: cannulation of the LMCA is performed with more caution, and fewer angiographic views are obtained when the patient has LMCA disease.

Although cardiologists and cardiac surgeons commonly perform urgent CABG in most patients with LMCA stenosis, there is no consensus regarding the ideal interval between the angiographic diagnosis and surgery. Urgent CABG is associated with poor surgical outcomes.²⁰ Furthermore, performing urgent CABG on all patients with LMCA stenosis may burden the resources of a cardiac surgery practice. For these reasons, we decided to evaluate which patients with LMCA stenosis are more likely to experience a cardiac event while awaiting CABG.

Previous retrospective studies from Maziak and coworkers²¹ and Sharareh and colleagues²² found a low incidence of severe cardiac events among patients with significant LMCA stenosis who were awaiting surgery. Maziak's group also determined that patients with LMCA stenosis of 75% or more, those in New York Heart Association (NYHA) functional class IV heart failure, and those who had experienced a preoperative myocardial infarction were more likely to undergo CABG early (≤10 days after coronary angiography). Of interest, the extent of RCA stenosis did not influence perioperative outcomes. In our study, we found that the severity of the LMCA stenosis, the involvement of the RCA, and the ejection fraction did not predict the occurrence of cardiac events among patients with LMCA stenosis.

In 2003, da Rocha and associates²³ reported that unstable angina independently predicted severe adverse cardiac events. Indeed, the risk was 5 times greater in patients whose indication for coronary angiography was unstable angina, even in those whose clinical condition had stabilized. In our study, 4 patients experienced an adverse cardiac event more than 24 hours after cardiac catheterization, while awaiting surgery. All four of these patients had required coronary angiography because of unstable angina or myocardial infarction at the time of admission to the hospital. On the basis of these findings, we believe that such patients should be treated with greater vigilance and should perhaps be considered as candidates for urgent CABG.

This study has some limitations. Because of its retrospective design, we could not adequately evaluate all of the clinical and angiographic variables that might influence the incidence of preoperative adverse cardiac events. In addition, the small number of events limited the power of the study, especially in terms of evaluating several different risk factors. Finally, our data were derived from the experience at our university hospital alone, which may not be representative of experiences at other institutions. Prospective randomized controlled trials are needed to further clarify the importance of each of these variables.

Conclusions

Serious cardiac events occur infrequently in patients with angiographically confirmed significant LCMA stenosis who are awaiting CABG. We conclude that carefully selected patients with significant LMCA stenosis can safely await surgery without undergoing emergency CABG. The association of acute coronary syndrome with significant LMCA stenosis indicates a high risk of cardiac events; therefore, patients with these conditions should be considered for emergency CABG.