Cardiac risk stratification prior to vascular surgery

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CARDIAC RISK STRATIFICATION PRIOR TO VASCULAR SURGERY Howard H. Weitz, MD

Patients who undergo peripheral vascular surgery have an increased risk of cardiac complication and death in the days, months, and years following surgery. Approximately 40% to 60% of early postoperative deaths following peripheral revascularization surgery are owing to a cardiac etiology.5, 22, 23, 28, 56, 58 For patients with symptomatic or severe large vessel peripheral arterial disease the 10-year risk of death owing to coronary heart disease is 10 to 15 times greater than for those free of large vessel arterial disease. 8 A variety of clinical schemes as well as laboratory studies have been described to aid in the identification of the patient at risk for cardiac complication in relation to peripheral vascular surgery. This article attempts to put these modalities in perspective and in doing so answer the following questions: Why is the risk of cardiac complication increased in the patient who undergoes vascular surgery? How may the patient at risk be identified? Are there any methods to decrease risk in the high risk patient? WHY IS THE RISK OF CARDIAC COMPLICATION INCREASED IN THE PATIENT WHO UNDERGOES VASCULAR SURGERY?

The incidence of coronary artery disease (CAD) is significantly increased in the patient with peripheral vascular disease who requires a revascularization procedure. Pooled data from 50 series representing From the Division of Cardiology, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania MEDICAL CLINICS OF NORTH AMERICA VOLUME 77' NUMBER 2 • MARCH 1993

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more than 10,000 patients who underwent surgery for repair of abdominal aortic aneurysms, carotid artery disease, or lower limb ischemia demonstrated clinical evidence of CAD in approximately 50% of patients. Although the indications for coronary angiography as well as the definition of significant CAD varied among the series pooled, significant CAD was found in approximately 60% of patients who underwent preoperative coronary angiography.23 In a classic study, coronary angiography was performed in 1000 consecutive patients who were referred to the Cleveland Clinic for elective vascular surgery. Only 8% of the patients had normal coronary arteries. Thirty-two percent had CAD classified as mild to moderate (demonstrable CAD but no lesion exceeding 70% stenosis); and 28% had advanced but compensated CAD (greater than 70% stenosis of one or more coronary arteries but involved myocardium supplied by collateral vessels or replaced by scar). Therefore, 60% of patients had CAD but did not have myocardium at risk of ischemia or infarction. In 31 % of the group, CAD was thought to be severe enough to either require surgical revascularization or be inoperable. Of the total patient group, 446 patients had no clinical or electrocardiographic evidence of CAD. Importantly, 14% of this group had severe correctable CAD, and in 1% coronary disease was severe and inoperable. 20 Based on these findings, preoperative cardiac catheterization was recommended for all patients with clinical evidence of CAD before peripheral vascular surgery. Noninvasive cardiac screening tests were suggested for patients with no cardiac symptoms, and normal electrocardiograms were suggested to identify those with occult ischemic heart disease. In a study of 59 patients who underwent aortic reconstruction for aneurysmal or occlusive disease Orecchia49 found that 64% of patients with no preoperative clinical indication of CAD had at least a 70% stenosis of one major coronary artery and 29% of these unsuspected patients had either triple vessel or left main CAD. There are varied reasons for the absence of cardiac symptoms in patients with coronary artery and peripheral vascular disease. Myocardial ischemia may be silent in 50% to 60% of patients who undergo vascular surgery. 34, 51 Also, many patients with peripheral vascular disease are sedentary with physical activity limited by claudication. This reduction of activity, with its associated decreased demand for myocardial oxygen delivery and cardiac output, may make the degree of cardiac dysfunction less apparent. IS Vascular surgery is associated with significant hemodynamic stress and increased demands for myocardial oxygen delivery that may not be satisfied in the patient with obstructive CAD. There are five periods when significant hemodynamic changes may occur. During anesthetic induction, transient hypotension may occur as a result of alteration of vasomotor regulation. During the operation when posterior peritoneal traction is applied, autonomic responses may result in bradycardia and hypotension. Aortic cross-clamping may lead to elevation of blood pressure, systemic vascular resistance, and pulmonary capillary wedge pressure in the patient with CAD. Release of the aortic clamp may result in hypotension as the distal vascular bed is reexpanded and

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demand for blood flow to this bed provoked by tissue hypoxia and acidosis is increased. Finally, re sorption of interstitial or "third space" fluids 24 to 48 hours following surgery leads to further reexpansion of intravascular volume. 2, 19,65 In carotid surgery the hemodynamic changes are less problematic. Changes in afterload as well as the size and tone of the vascular bed during and following vascular clamping are minor, and there is significantly less change in intravascular volume. The hemodynamic stress associated with lower extremity vascular repair without aortic manipulation falls somewhere between these extremes. Traditional views regarding the etiology of perioperative myocardial ischemia have recently been challenged. In a study using intraoperative electrocardiographic ischemia monitoring as well as transesophageal echocardiography, KrupskP4 found that intra operative myocardial ischemia was likely to occur randomly and not in relation to placement of aortic clamps. Fifty percent of adverse cardiac events occurred after the third postoperative day, a time when hemodynamics are relatively stable, suggesting that delayed factors play a role in postoperative myocardial ischemia. IS CARDIAC RISK RELATED TO THE TYPE OF REVASCULARIZATION PROCEDURE?

It has been suggested that patients with CAD who undergo distal vascular procedures, i.e., carotid artery endarterectomy or femeropopliteal bypass, are probably subjected to less cardiac risk than patients whose surgical site involves the aorta. 16, 70 A contrary view was presented by KrupskP4 who in a comparison of cardiac morbidity between aortic and infrainguinal revascularization procedures found that although more patients experienced intra operative myocardial ischemia, as detected by transesophageal echocardiography during aortic surgery, the incidence of postoperative cardiac events (nonfatal myocardial infarction [MIl, unstable angina, ventricular tachycardia, congestive heart failure) was similar among both groups. These findings are clouded by the fact that the patients who underwent infrainguinal revascularization procedures had a higher prevalence of preoperative cardiac risk factors including diabetes mellitus, angina pectoris, congestive heart failure, and cardiac arrhythmias, 34 In a recent series of patients who underwent elective aortic reconstruction for either abdominal aortic aneurysm or aortoiliac occlusive disease, Cambria6 found a higher cardiac complication rate in the patients whose surgery was for aortoiliac disease. The reason for this difference was not explained by a difference in the prevalence of clinical markers of CAD. Finally, in a review of patients who underwent general vascular surgery, Taylor62 found that all operative deaths and the majority of perioperative MIs that occurred were associated with surgery that was performed on an urgent or emergent basis. The most common surgical procedure that was associated with cardiac morbidity or mortality was re vascularization for lower limb ischemia,

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HOW MAY THE PATIENT AT RISK BE IDENTIFIED?

A variety of stratification methods have been described to delineate cardiac risk before vascular surgery. They include clinical risk indexes, coronary angiography, radionuclide ventriculography, exercise electrocardiography, pacing electrocardiography, radionuclide myocardial imaging, vasodilator myocardial imaging, silent ischemia monitoring, and techniques using echocardiography. The selection of an appropriate risk stratification method may be confusing and is occasionally controversial. The use of studies that provide redundant information may increase the cost of the risk stratification evaluation without further enhancing the estimate of risk. These modalities and their role in patient evaluation before vascular surgery will be discussed in the following sections. Clinical Risk Stratification Indexes

One of the most widely used risk stratification indexes is the multifactorial index of cardiac risk described by Goldman in 1977. This index is based on data of 1001 patients who underwent noncardiac surgery. Univariate and multivariate analysis was used to identify risk factors that correlated with an increased incidence of perioperative cardiac complication or death (Table 1). Risk points were tabulated allowing assignment of patients to one of four risk classes (class I, 0 to 5 points; class II, 6 to 12 points; class Ill, 13 to 25 points; and class IV > 25 points). Risk of perioperative cardiac complication or cardiac death ranged from less than 1 % in low-risk class I to approximately 78% in Table 1. COMPUTATION OF THE MULTIFACTORIAL CARDIAC RISK INDEX Variable

Points

Age >70 Myocardial infarction in previous 6 months S3 or jugular venous distention Important valvular aortic stenosis Rhythm other than sinus or the presence of PACs on preoperative electrocardiogram >5 VPCs/min at any time before operation Poor general medical status PO, <60 or Peo, >50 mm Hg K + <3.0 or HC0 3- <20 mEq/L BUN >50 or Cr >3.0 mg/dL Abnormal SGOT, chronic liver disease, or patient bedridden owing to noncardiac cause Intraperitoneal, intrathoracic, or aortic surgery Emergency surgery TOTAL

5

10 11

3

7 7

3

3

4

53

From Goldman L, Caldera DL, Nussbaum SR, et al: Multifactorial index of cardiac risk in noncardiac surgical procedures. N Engl J Med 297:845, 1977.

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high-risk class IV. Although aortic surgery was found to be a risk factor, the presence of chronic stable angina as well as the presence of peripheral atherosclerotic vascular disease was not found to increase cardiac risk in the perioperative period. In applying the results of this study to the patient who is to undergo a revascularization procedure it is important to realize that only 16.2% of the patient group underwent abdominal aortic aneurysm repair or lower extremity revascularization and only 27% had clinical evidence of CAD.17 Zeldin,71 in a prospective study of 1140 patients over age 40 who underwent noncardiac surgery, validated the multifactorial risk index but found that the risk of perioperative cardiac complication of the class IV patient was only 30%, which was less than half that found by Goldman. Risk for other groups was similar. Importantly, only 7.5% of the patients studied underwent vascular surgery. Because of this relatively small number of patients, we are unable to extend the results of this study to the patient who is to undergo vascular surgery. When applied specifically to patients undergoing abdominal aortic aneurysm repair, the multifactorial risk index has been found to underestimate the incidence of perioperative cardiac complication in patients initially thought to be at "low" risk. 29,46 The multifactorial cardiac risk index was also evaluated in a prospective study of men at either high risk for or documented CAD who underwent noncardiac surgery. Vascular surgery was performed in 37% of patients in this study, which failed to show correlation between the multifactorial cardiac risk index and the incidence of perioperative cardiac complications. Interestingly, the presence of postoperative myocardial ischemia was the most important risk factor for the prediction of postoperative cardiac death, nonfatal MI, or unstable angina. 43 Detsky et apo have modified the original multifactorial index by incorporating additional variables (Canadian Cardiovascular Society angina classes 3 and 4, unstable angina, and a history of pulmonary edema [Table 2].10 In a recent assessment of the usefulness of multivariate clinical models to predict the occurrence of perioperative MI or cardiac death in relation to vascular surgery, Lette et aP8 found that the only feature of the clinical risk indexes that correlated with the incidence of perioperative cardiac complications was the total point score of the Detsky modified risk index. 38 Based on the shortcomings of clinical risk factor indexes to identify the patient at risk for cardiac complications, a variety of diagnostic studies have been proposed to aid the clinician in risk assessment. Coronary Angiography

Routine preoperative coronary angiography to define coronary anatomy and facilitate coronary artery revascularization before peripheral vascular surgery, if indicated, was initially advocated in the 1980s for all patients with clinical evidence of CAD.20 This approach often does not reflect the impact of CAD on coronary blood flow as well as

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Table 2. COMPUTATION OF THE MODIFIED MULTIFACTORIAL RISK INDEX Variable

Points

MI within 6 months MI more than 6 months Canadian cardiovascular society angina Class 3 Class 4 Unstable angina within 3 months Pulmonary edema within 1 week Pulmonary edema ever Suspected critical aortic stenosis Age >70 Rhythm other than sinus or the presence of PACs on last preoperative electrocardiogram >5 VPCs/min at any time before operation Poor general medical status P0 2 <60 or Pco 2 >50 mm Hg K + <3.0 or HC03 - <20 mEq/L BUN >50 or Cr >3.0 mg/dL Abnormal SGOT, chronic liver disease, or patient bedridden owing to noncardiac cause Emergency operation

10 5

10 20 10 10

5

20

5 5 5 5

10

From Detsky AS, Abrams HB, McLaughlin JR: Predicting cardiac complications in patients undergoing noncardiac surgery. J Gen Intern Med 1 :211-219,1986.

the extent of viable myocardium in jeopardy. It is also expensive and associated with a small degree of risk. For these reasons we typically reserve coronary angiography for the patient who, by clinical evaluation or noninvasive laboratory study, is suspected to be at high risk for a perioperative cardiac complication.

Estimate of Left Ventricular Ejection Fraction

Although reduced ejection fraction has been shown to be a predictor of decreased long-term survival following vascular surgery, controversy exists regarding the usefulness of determination of left ventricular ejection fraction at rest by radionuclide ventriculography to determine perioperative risk. 30, 45 Although one review using rest radionuclide ventriculography has shown that resting left ventricular ejection fraction was inversely correlated to the incidence of perioperative MI in patients who underwent lower extremity revascularization procedures, a similar study of patients undergoing lower extremity revascularization procedures failed to show this relationship. 33, 52 Similarly, there is no consensus regarding the predictive usefulness of resting left ventricular ejection fraction in the patient who undergoes abdominal aortic aneurysm repair despite the fact that several studies have documented an increased incidence of perioperative cardiac complications or death in patients whose preoperative ejection fraction is less than 35%.14, 15, 30,

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33,48 This controversy as well as the fact that critical CAD may exist in conjunction with preserved resting left ventricular ejection fraction has led us to favor functional estimates of myocardial perfusion rather than static evaluation of left ventricular function for risk stratification before vascular surgery.

Exercise Electrocardiography

Exercise electrocardiography is advantageous because it enables assessment of the functional status of coronary perfusion. Unfortunately, it is infrequently of help in risk stratification of patients with peripheral vascular disease because lower-extremity vascular disease often limits adequate exercise. McPhail,47 assessing the value of preoperative exercise testing before vascular surgery, found that only 30% of patients were able to achieve 85% of their predicted maximum heart rate. In the patient who is able to exercise, a negative exercise study, after achieving the targeted heart rate blood pressure product, has been associated with a low risk of cardiac complication in peripheral vascular surgery. Similarly, an exercise study that demonstrates inducible ischemia suggests an increased risk for perioperative cardiac events, particularly if the iscemia is induced at a low level of exercise. I, 9 Arm Ergometry

Arm exercise has been proposed as a diagnostic modality for the patient who cannot perform conventional lower-extremity exercise. Arm exercise-thallium imaging has shown in small studies to have an 83% sensitivity and 78% specificity for detecting the presence of CAD. Physiologic responses of normal subjects have been standardized to allow development of reproducible upper extremity exercise protocols.3, 4 In the only reported experience where this technique was used to stratify risk in vascular surgery, a normal study was associated with an uncomplicated perioperative course (negative predictive value 95%) whereas an abnormal result was not helpful in predicting which patients would develop perioperative cardiac complications owing to a low number of abnormal results (positive predictive value 12%).41 Many patients who cannot perform lower-extremity exercise are also unable to perform enough upper-extremity work to yield a valid study, further limiting the usefulness of this diagnostic test. Pacing Electrocardiography

Atrial pacing using either a transvenous pacing catheter advanced to the right atrium or a transesophageal pacing catheter has been shown to have a sensitivity and specificity for detection of CAD similar to that

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of conventional stress testing. Protocols evaluating this technique require that peak heart rate be 85% to 100% of the age predicted maximal heart rate or 170 beats per minute. Addition of thallium 201 scintigraphy, two-dimensional echocardiography, or radionuclide ventriculography improves the sensitivity and specificity of the study. 59 Strattmann applied this technology to the vascular surgery patient in a cohort of patients with known or suspected CAD but who were classified on clinical grounds as being at low risk for perioperative cardiac complications by the multifactorial risk index. A normal atrial pacing thallium 201 study or one demonstrating a fixed defect was associated with a low incidence of perioperative cardiac complications. Small patient numbers precluded outcome assessment of the patient who demonstrated inducible myocardial ischemia. 60 Drawbacks of pacing electrocardiography include the risks of transvenous pacemaker insertion, patient intolerance of the transesophageal pacemaker catheter, and physiologic development of Mobitz I AV block before target heart rate is achieved even in the absence of intrinsic conduction system disease or use of medications that may lead to impairment of atrioventricular conduction (digoxin, ~-blocking agents, calcium channel antagonists). At the current time we use pacing electrocardiography for risk assessment of the patient who is unable to exercise and also has contraindications to vasodilator myocardial imaging. Vasodilator Myocardial Imaging

Vasodilator myocardial imaging has emerged as an ideal test to aid the assessment of cardiac risk in the patient who cannot exercise. 69 The most commonly used agent is intravenous dipyridamole, which reduces inactivation of endogenous adenosine by adenosine deaminase therefore increasing the sensitivity of the coronary artery to adenosine, a potent coronary vasodilator. Dipyridamole also inhibits the phosphodiesterase enzyme, resulting in an increase of cyclic adenosine monophosphate, which is a coronary vasodilator. Coronary blood flow in normal coronary arteries is increased three to five times following coronary vasodilation and is unchanged in vessels that are severely stenotic or occluded. Study protocols have used dipyridamole 0.56 mg/ kg infused over 4 minutes with thallium 201 injected 3 to 5 minutes later. Thallium myocardial scanning is done immediately after thallium injection with delayed scanning done 3 to 4 hours later. A normal scan suggests that myocardial blood supply is preserved. The presence of initial myocardial defects that redistribute on delayed scans indicates viable but ischemic myocardium, and the presence of a fixed defect on initial and delayed scans represents myocardial scar. McEnroe 46 found that up to 20% of fixed defects seen on delayed scans performed at 4 hours may indicate viable but intensely ischemic myocardium and has suggested that delayed thallium imaging at 18 to 72 hours, or reinjection of thallium, and then delayed imaging be performed in patients with

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fixed defects to decide whether these defects indicate myocardial scar or ischemia. Because the effect of dipyridamole is antagonized by xanthines, patients must avoid theophylline-containing medications for at least 36 hours before the test and must refrain from caffeine intake for at least 4 hours before the study. 36 Transient side effects are common. In a study of 3911 patients the most common side effects were chest pain (19.7%), headache (12.2%), and dizziness (11.8%).55 In this large clinical study, four patients sustained acute MIs attributed to dipyridamole; two cases were fatal. Bronchospasm may be precipitated in the patient with a history of asthma. It is usually immediately reversed by the administration of intravenous aminophylline, which blocks adenosine receptors. Because myocardial ischemia may occur, intravenous dipyridamole should be avoided in the patient with unstable angina or in the acute phase of an MI. The safety of intravenous dipyridamole was further confirmed in a multicenter study of 16,000 patients in 10 Canadian and US hospitals. There was a 0.01% coronary death rate, 0.04% MI rate, and no strokes. 38 Before intravenous dipyridamole was readily available, several investigators documented the efficacy of oral dipyridamole-thallium imaging. 61 Major drawbacks to this modality are the unpredictable absorption and onset of action of oral dipyridamole and the prolonged duration of effect. Since Food and Drug Administration approval has made dipyridamole available for intravenous infusion, the role of oral dipyridamole-thallium imaging has decreased. Adenosine-thallium scanning has been advocated as another vasodilator myocardial imaging technique. Adenosine-thallium single photon emission computed tomography (SPECT) imaging has been shown to have diagnostic accuracy similar to exercise thallium scanning for the diagnosis of CAD. A major advantage of adenosine, however, is that although side effects (chest pain, flushing, headache, dyspnea, heart block) are frequent, they are transient, lasting only 1 to 2 minutes after discontinuation of the adenosine infusion owing to the rapid metabolism of adenosine. 68 Adenosine-thallium imaging has not yet been studied in large scale randomized trials evaluating perioperative risk in vascular surgery, but we suspect that its diagnostic usefulness will be similar to the dipyridamole-thallium technique. Pooled data indicate that the presence of a normal scan or one with a fixed defect has a negative predictive value for a perioperative cardiac event of 98%, whereas the presence of a redistribution abnormality has a positive predictive value of 28% .16 Therefore, a negative scan is quite helpful in clinical decision making, whereas a positive result often is not. To enhance the usefulness of vasodilator myocardial imaging, consideration of clinical risk variables as well as semiquantitative analysis of thallium scans has been advocated. Eagle et al ll have identified clinical variables that when used to select patients for preoperative dipyridamole-thallium imaging can significantly improve the specificity and positive predictive value of the study. They found that the following were predictors of cardiac risk relating to vascular surgery: Q waves on the electrocardiogram, angina,

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history of ventricular ectopy that has required treatment, diabetes mellitus that has required treatment, and age greater than 70 years. In a study of 200 patients who underwent vascular surgery (69% of the procedures were associated with aortic manipulation, i.e., AAA repair, aortofemoral, aortoiliac bypass) patients with none of the above risk factors had only a 3.1 % incidence of perioperative cardiac complication, whereas those with three or more risk factors had a 50% incidence of cardiac events. The usefulness of dipyridamole-thallium scanning was demonstrated primarily for patients with one or two risk factors. The patient with no evidence of thallium redistribution had a cardiac complication incidence of 3.2%, similar to the low-risk patient with no risk factors. In contrast, the patient with one or two risk predictors and evidence of redistribution on the dipyridamole-thallium scan was found to be at high risk with a cardiac complication rate of 30%. Use of these risk predictors increased the positive predictive value of the study from 30% when the results of the thallium scan were used alone to 43% when the clinical variables were included. Therefore, the dipyridamolethallium scan is most helpful in risk stratification of the patient found clinically to be at intermediate risk of caridiac complication. Semiquantitative analysis of the thallium scan has helped to further define risk (Table 3). In the patient with demonstable ischemia in less than or equal to 3 of 15 myocardial segments, the incidence of cardiac events in a study by Levinson et aP9 was only 12% in contrast to a 38% cardiac event rate when redistribution was seen in 2: 4 myocardial segments. Similarly, patients with thallium redistribution in only one coronary artery territory had a lower rate of cardiac complication when compared to those with redistribution in two or three coronary territories. 40 Lette37 has proposed an alternate three-stage stratification protocol using dipyridamole-thallium scanning with simplified semiquantitative analysis along with clinical parameters (Fig. 1). In this model, myocardial scan interpretation considers only three myocardial regions; the Table 3. SEMIQUANTITATIVE ANALYSIS OF DIPYRIDAMOLE-THALLIUM SCANS* Extent of Thallium Redistribution None $3 segments 2:4 segments One coronary territory Two or three coronary territories

Cardiac Eventt Predictive Value (%)

o

12 38 13 43

*Scoring was based on analysis of thallium scan in three standard views with each view divided into 5 segments for a total of 15 segments. tPerioperative cardiac events: unstable angina, 2-two episodes of symptomatic ischemic electrocardiographic changes, ischemic pulmonary edema, myocardial infarction, cardiac death. From Levinson J, Boucher C, Coley C, et al: Usefulness of semiquantitative analysis of dipyridamolethallium-201 redistribution for improving risk stratification before vascular surgery. Am J Cardiol 66:406410,1990.

Extent of thallium redistribution

o

Segments

1 to 2 Segments

3 Segments or LV dilation

Figure 1. Semiquantitative thallium imaging based on evaluation of three myocardial regions (anterior, inferior, and posterolateral) and clinical factors. Cardiac event rate is shown for each subgroup. (Adapted from LeUe J, Waters D, Cerino M, et al: Preoperative coronary artery disease risk stratification based on dipyridamole imaging and a simple three-step, three-segment model for patients undergoing noncardiac vascular surgery or major general surgery. Am J Cardiol 69:15531558, 1992; with permission.) YJ

00

'I

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anterior, inferior, and posterolateral segments. Patients whose dipyridamole-thallium scans demonstrated normal anterior, inferior, and posterolateral myocardial perfusion had only a 1.3% incidence of perioperative cardiac complications and were considered to be at low risk. Patients with suggestion of left main, triple vessel, or high risk two vessel CAD (reversible defects of all three segments, left ventricular cavity dilation during the study) had a 52% incidence of perioperative cardiac events and were considered to be at high risk. The remaining patients were at intermediate risk and were further stratified using the number of cardiac segments that displayed reversible defects, age greater than 70, and the presence or absence of diabetes mellitus in patients who were younger than 70. The incidence of complications ranged from 5% (age less than 70, no history of diabetes, myocardial redistribution involving one of the three myocardial segments) to 36% (age greater than or equal to 70, myocardial thallium redistribution involving two of three myocardial segments)Y This approach differs from that of Eagle,11 which advocated a selective approach to dipyridamole-thallium scanning based on initial consideration of clinical risk factors. Further studies will be necessary to decide which approach is superior. Despite much support in favor of selective dipyridamole-thallium scanning, KrupskP4 found, in a study of patients who underwent aortic as well as infrainguinal arterial revascularization, that dipyridamolethallium scanning was not a predictor of postoperative cardiac complications. The author indicated, however, that this result might reflect bias in that only one third of patients who underwent vascular surgery had preoperative dipyridamole-thallium scanning. Other Modalities

Clinically silent myocardial ischemia has been postulated as a marker of perioperative complications. Raby,54 in a prospective study of patients who underwent elective vascular surgery, found that 24 to 48 hours of electrocardiographic ischemia monitoring within 9 days preceding surgery was helpful in predicting the likelihood of perioperative adverse cardiac events. An important finding was that the absence of preoperative myocardial ischemia was associated with a very low likelihood of perioperative cardiac events (negative predictive value, 99%). The clinical significance of preoperative silent myocardial ischemia was less clear in that it was associated with a 37% incidence of postoperative cardiac events. In an expansion of this study preoperative ischemia was found to not only predict postoperative cardiac events but also to correlate with intraoperative and postoperative myocardial ischemia. 53 Pasternack50 found that 61 % of patients who underwent vascular surgery had silent myocardial ischemia in the perioperative period. There was a direct correlation between the duration and frequency of ischemic episodes and the incidence of perioperative MI.

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In the absence of perioperative myocardial ischemia, no patients sustained Mt highlighting the clinical importance of a negative ischemia monitoring study. Although a correlation between perioperative ischemia and infarction was demonstrated, the low incidence of perioperative MI (7.3%) makes the positive predictive value of perioperative ischemia monitoring quite low. In a study of patients who underwent vascular surgery, Cambria6 found the presence of intraoperative myocardial ischemia to be a univariate predictor of major postoperative cardiac complications. Confusing the issue are the findings of Mangan0 43 who, in a group of men with either known CAD or high risk for it (36% of whom underwent vascular surgery) found that postoperative myocardial ischemia, not ischemia that was identified before or during surgery, was the most significant marker of risk of postoperative cardiac complication. Finally, in up to 15% of patients who undergo continuous perioperative electrocardiographic monitoring the electrocardiogram is inadequate for the detection of myocardial ischemia. The most common limiting factors are left bundle branch block, left ventricular hypertrophy, digoxin effect, and artifact. 12 These discrepancies regarding the clinical significance of preoperative, intraoperative, and postoperative myocardial ischemia, low-positive predictive value, and technical limitations of the study lead us to refrain from recommending perioperative silent ischemia monitoring as a primary method to assess risk before vascular surgery until further more definitive studies are performed. Dobutamine and dipyridamole echo cardiography have been evaluated in small pilot studies as modalities to assess perioperative cardiac risk. In a study of 38 patients who underwent noncardiac surgery (65% underwent vascular surgery) the presence of dobutamine-induced wall motion abnormalities detected by echocardiography identified a group of patients with a 21 % incidence of perioperative cardiac complication. There were no perioperative cardiac complications in patients who did not have inducible myocardial abnormalities. 35 Similarly, in a study of 109 patients who underwent vascular surgery, dipyridamole echocardiography had a sensitivity and specificity of 88% and 98%, respectively, for predicting perioperative cardiac events. The positive and negative predictive values were 78% and 99%. If these results are reproduced, preoperative dipyridamole echocardiography promises to be an important study for preoperative risk stratification. 63 THE PATIENT WHO HAS UNDERGONE A CORONARY ARTERY REVASCULARIZATION PROCEDURE

It has been suggested that prior coronary artery bypass surgery is protective for the patient with CAD who is to undergo peripheral vascular surgery.6, 21, 25, 42, 56, 64 Using pooled data, Hertzer23 found that operative mortality in 1237 patients who underwent vascular surgery was 1.3% in patients without clinical evidence of CAD, 1.5% in patients with CAD who had previously undergone coronary artery bypass

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surgery, and 6.8% in patients who were suspected to have CAD but had not undergone a coronary revascularization procedure. In a nonrandomized retrospective study of 50 patients judged clinically to be at high risk for perioperative cardiac complications (52% of whom underwent vascular surgery) percutaneous transluminal coronary angioplasty of critical coronary artery stenoses was done a median of 9 days before surgery. A lower than expected incidence of perioperative MI (5.6%) and cardiac death (1. 9%) was found. 26 , 27 Although these reports suggest that coronary artery re vascularization is beneficial in risk reduction before vascular surgery, we believe that additional prospective randomized trials are required to better assess the impact of coronary artery re vascularization before a peripheral revascularization procedure. While awaiting further data and in consideration of the fact that atherosclerosis of native coronary arteries as well as saphenous vein bypass grafts is progressive with occlusion of 12% to 20% of saphenous vein bypass grafts at 1 year, 20% to 30% at 5 years, and 40% to 50% at 10 years, it is our practice to perform a noninvasive myocardial perfusion study, e.g., exercise electrocardiogram and vasodilator myocardial imaging, in the patient who presents for vascular surgery with a history of prior coronary artery bypass surgery. 7, 13 Our approach is similar for the patient who has undergone percutaneous transluminal coronary angioplasty given that coronary restenosis occurs in approximately 25% to 35% of patients within 6 months of angioplasty.44 If noninvasive evaluation demonstrates significant myocardium at risk of ischemia or infarction, we then usually proceed to coronary angiography to further define coronary anatomy. OUR APPROACH

Carotid endarterectomy morbidity and mortality are low enough that for most patients, except those with angina with daily activity, unstable angina, or recent MI, carotid revascularization may proceed without specialized studies to assess coronary anatomy (Fig. 2).40,57,70 In patients who have angina with low levels of activity, unstable angina, or recent MI we usually perform coronary angiography to define coronary anatomy and consider a combined carotid-coronary artery revascularization procedure if the patient has left main coronary disease, or in the setting of left ventricular dysfunction, triple vessel coronary disease, or double vessel coronary disease when one of the involved vessels is the proximal left anterior descending coronary artery. For the patient who undergoes aortic or femeropopliteal revascularization, we use the criteria identified by Eagle ll to estimate perioperative cardiac risk (age greater than 70, history of angina, Q waves on electrocardiogram, history of ventricular premature contractions that have required treatment, diabetes mellitus). The patient who is moderately physically active and has none of these factors is considered to be at low risk and proceeds to vascular surgery without specialized

Assess risk factors: age > 70, angina, waves, VPCs, diabetes

a

o Risk factors, physically active

1 to 2 Risk factors or sedentary

I

T

I

Surgery

I

~

One of the following: Vasodilator myocardial imaging, exercise thallium scan, atrial pacing scan, arm ergometry scan

I

No thallium redistribution

I

I

Surgery

I

Low risk

I

Surgery

I

I Avoid surgery. If surgery unavoidable, coronary angiography to define coronary anatomy. Coronary revasc. if indicated

Thallium redistribution

I

11

I

Moderate to high risk

I

I

Coronary angiography. Coronary revasc. if indicated

VJ \0

......

.~

Semiquantitative evaluation

1

3 Risk factors or unstable angina or recent MI

Figure 2. Approach to the patient.

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cardiac evaluation. The patient with one or two of these factors undergoes noninvasive assessment of myocardial perfusion (vasodilator myocardial imaging, exercise-thallium scan) with semiquantitative evaluation of the thallium scan. We also perform vasodilator myocardial imaging in patients who are sedentary, even if risk factors are absent, as they may have coronary artery disease but no angina owing to limited activity. For the patient who cannot undergo vasodilator myocardial imaging or exercise electrocardiography we attempt an atrial pacing study, arm ergometry thallium scan, or preoperative ischemia monitoring, taking into account the prognostic benefit of a negative study as well as the difficulty in clinical interpretation of a positive study. Following vasodilator myocardial imaging the patient with a normal study or demonstration of a fixed thallium defect is considered to be at low risk and then undergoes peripheral vascular surgery. Coronary angiography is performed if the patient demonstrates reversible thallium defects and is judged to be at moderate to high risk. The patient with three or more risk factors, unstable angina, or recent MI is considered to be at high risk. Elective vascular surgery is avoided, if possible, but if it is necessary antecedent coronary angiography is performed to define the need for a coronary revascularization procedure. Although randomized, prospective clinical trials have not yet been done to assess the protective effect of coronary revascularization before vascular surgery, we do perform coronary revascularization if the patient has angina despite a maximal medical antianginal regimen, unstable angina, or in a setting in which coronary revascularization has been shown to decrease long-term mortality, i.e., critical left main coronary stenosis, left ventricular dysfunction in the setting of triplevessel coronary disease, two-vessel coronary disease if there is severe proximal stenosis of the left anterior descending coronary artery, or severe proximal stenosis of a large left anterior descending coronary artery with demonstrable myocardial ischemia. 32 There are no widely accepted methods to decrease perioperative risk. Although many patients undergo invasive hemodynamic monitoring during and after surgery it has not been definitively proven to lower the risk of perioperative cardiac complication. 66 [3-Blockers were shown in one study to decrease the frequency and duration of perioperative ischemic episodes; however, a beneficial effect on outcome has not yet been proven. 50 Finally, in a recent study comparing the effects of epidural anesthesia and analgesia on outcome after major vascular surgery in a group of patients with a relatively high incidence of CAD or at risk for CAD, Tuman67 found that the incidence of cardiovascular complications was lower in patients receiving combined epidural anesthesia-analgesia than in patients receiving general anesthesia alone. The reason for this difference is not clear, but it has been postulated that patients with atherosclerotic vascular disease are hypercoagulable and that epidural anesthesia and analgesia attenuated the hypercoagulable state by blocking postoperative stress responses, thereby reducing mediators of platelet activation, limiting synthesis of fibrinogen, and enhancing fibrinolytic activity by increasing the concentration of

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the endogenous fibrinolytic agent, plasminogen activator. This exciting observation and its impact on the vascular surgery patient await further study. References 1. Arous El, Baum PL, Cutler BS: The ischemic exercise test in patients with peripheral vascular disease. Arch Surg 119:780-783, 1984 2. Attia R, Murphy JO, Snider M, et al: Myocardial ischemia due to infrarenal aortic crossclamping during aortic surgery in patients with severe coronary artery disease. Circulation 53:961-965, 1976 3. Balady Gl, Weiner OA, Rose L, et al: Physiologic responses to arm ergometry exercise relative to age and gender. J Am ColI Cardiol 16:130-135, 1990 4. Balady Gl, Weiner OA, Rothendler JA, et al: Arm exercise-thallium imaging testing for the detection of coronary artery disease. J Am ColI Cardiol 9:84-88, 1987 5. Blombery PA, Ferguson I, Rosengarten 0, et al: The role of coronary artery disease in complications of abdominal aortic aneurysm surgery. Surgery 101:150-155, 1987 6. Cambria R, Brewster 0, Abbott W: The impact of selective use of dipyridamole thallium scans and surgical function on the current morbidity of aortic surgery. J Vasc Surg 1992(15):43-51, 1992 7. Campeau L, Enjalbert M, Lesperance l, et al: Atherosclerosis and late closure of aortocoronary saphenous vein grafts: Sequential angiographic studies at 2 weeks, 1 year, 5 to 7 years, and 10 to 12 years after surgery. Circulation 68(suppl 2):1, 1983 8. Criqui M, Langer R, Fronek A, et al: Mortality over a period of 10 years in patients with peripheral arterial disease. NEJM 326:381-386, 1992 9. Cutler BS, Wheeler HB, Paraskos JA, et al: Applicability and interpretation of electrocardiographic stress testing in patients with peripheral vascular disease. Am J Surg 141:501-506, 1981 10. Oetsky AS, Abrams HB, McLaughlin JR: Predicting cardiac complications in patients undergoing noncardiac surgery. J Gen Intern Med 1:211-219, 1986 11. Eagle KA, Coley Cc, Newell JB, et al: Combining clinical and thallium data optimizes preoperative assessment of cardiac risk before major vascular surgery. Ann Intern Med 110:859-866, 1989 12. Elliott BM, Robison l, Zellner l, et al: Oobutamine-201 T1 Imaging: Assessing cardiac risks associated with vascular surgery. Circulation 84(suppl 3):54-60, 1991 13. FitzGibbon GM, Leach Al, Kafka HP, et al: Coronary bypass graft fate: Long-term angiographic study. J Am Coli Cardiol 17:1075-1080, 1991 14. Fletcher JP, Antico VF, Gruenewald S, et al: Risk of aortic aneurysm surgery as assessed by preoperative gated heart pool scan. Br J Surg 76:26-28, 1989 15. Freeman WK, Gersh Bl, Gloviczki P: Abdominal aortic aneurysm and coronary artery disease: Frequent companions, but an uneasy relationship. J Vasc Surg 12:73-77, 1990 16. Gersh B, Charanjit S, Rooke T, et al: Evaluation and management of patients with both peripheral vascular and coronary artery disease. J Am ColI Cardiol 18:203-214, 1991 17. Goldman L, Caldera 0, Nussbaum S, et al: Multifactorial index of cardiac risk in noncardiac surgical procedures. NEJM 297:845-850, 1977 18. Goldman L, Cook EF, Mitchell N, et al: Pitfalls in the serial assessment of cardiac functional status: How a reduction in "ordinary" activity may reduce the apparent degree of cardiac compromise and give a misleading impression of improvement. J Chronic Ois 35:763-771, 1982 19. Gooding JM, Archie JP: Hemodynamic response to infrarenal aortic crossclamping in patients with and without coronary artery disease. Crit Care Med 8:382-385, 1980 20. Hertzer N, Beven E,'Young l, et al: Coronary artery disease in peripheral vascular patients: A classification of 1000 coronary angiograms and results of surgical management. Ann Surg 199:223-233, 1984

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