Cardiac assessment with thallium scanning prior to aortic aneurysm repair

Cardiovascular Surgery, Vol. 7, No. 6, pp. 640–644, 1999  1999 The Society for Cardiovascular Surgery. Published by Elsevier Science Ltd All rights reserved. Printed in Great Britain 0967–2109/99 $20.00 ⫹ 0.00

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Cardiac assessment with thallium scanning prior to aortic aneurysm repair F. G. Quigley, D. Clark and J. Avramovic 39 Fulham Road, Pimlico, Queensland, Australia Coronary artery disease occurs commonly in patients with aortic aneurysms and is a major cause of morbidity and mortality. The role of screening and intervention for cardiac disease prior to aneurysm repair is controversial. The outcome after cardiac screening with thallium scanning and/or angiography in 102 consecutive patients undergoing aortic aneurysm repair was documented. Significant coronary artery disease was found in 34 (33%) patients and two patients had either coronary artery bypass or angioplasty prior to aneurysm repair. There was no cardiac mortality after aneurysm repair and the overall mortality on an intention-to-treat basis was 2%. There was good correlation between prior history of cardiac events, electrocardiography (ECG) and the results of screening with thallium scanning and angiography. There was no correlation between cardiac history, ECG and the incidence of cardiac events in the postoperative period. Significant coronary artery disease was found in 33% of patients without a cardiac history or abnormal ECG. Cardiac screening with thallium scanning confirmed a high incidence of significant coronary disease in patients with aortic aneurysm. In this study, cardiac intervention followed by expedient aneurysm repair in 20 patients was associated with zero mortality. The short-term benefit of such a policy is difficult to prove and its main advantage may be better long-term survival.  1999 The Society for Cardiovascular Surgery. Published by Elsevier Science Ltd. All rights reserved Keywords: aneurysm, cardiac assessment, thallium scanning

Introduction The mortality for elective repair of aortic aneurysms has improved but still remains at a significant level of ~5% [1]. Cardiac causes are recognized as the major cause of mortality and a significant cause of morbidity [2, 3], and this has motivated many attempts to improve the outcome of elective surgery for aortic aneurysm by preoperative recognition and treatment of cardiac disease. A basic assessment of cardiac risk entails taking the patient’s history of cardiac disease and interpretation of an electrocardiography (ECG). The Goldman Cardiac Risk Index [4] determines the risk of perioperative cardiac event. This assessment identifies nine independent significant correlates of lifethreatening and fatal cardiac complications and can be calculated on the basis of history, ECG, routine biochemistry and blood gas analysis, and echocardiogram where necessary. This test has proved to be 640

a good predictor of cardiac events in the general surgical population but is of less use when applied to the higher risk vascular population. The most aggressive or invasive approach to cardiac assessment is to obtain coronary angiography on all patients prior to aortic surgery. In a Cleveland Clinic Study of 263 patients with aortic aneurysm who underwent coronary angiography, severe correctable coronary artery disease was found in 31%, 70 of 250 (28%) patients subsequently having coronary artery grafting prior to aneurysm repair, for a combined coronary artery bypass grafting and aortic aneurysm mortality of 3.9% [5]. Only one death occurred following abdominal aortic aneurysm repair in a patient who had prior coronary artery bypass grafting, but four of 76 patients undergoing coronary artery bypass grafting died prior to aneurysm repair. The American College of Physicians has recently recommended that any patient undergoing vascular CARDIOVASCULAR SURGERY

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Cardiac assessment with thallium scanning prior to aortic aneurysm repair: F. G. Quigley et al.

surgery with more than one risk factor as determined by their modified cardiac risk index should have further evaluation with either thallium scanning or stress echocardiography [6]. Echocardiography and thallium scanning represent a more practical approach to cardiac assessment. A thallium scan with a stress component will delineate areas of non-perfused myocardium that correlate with previously infarcted muscle. It will also show areas of underperfused myocardium, which might represent the greatest risk for perioperative events. Thallium behaves in much the same way as potassium and, injected intravenously, will be taken up by myocardium with an intact blood supply. At rest, the difference in blood flow through stenotic and normal vessels may be minimal but, during stress, myocardium supplied by normal vessels will receive more thallium than regions supplied by stenotic vessels. The areas of myocardium supplied by stenotic vessels will accumulate thallium over a longer period but, on delayed images, will appear the same as those areas with normal perfusion. Dobutamine stress echocardiography shares some features of thallium scanning: it is designed to detect areas of myocardium that behave abnormally during stress and to show evidence of previous infarction. It also provides an assessment of left ventricular function and valvular heart disease but is probably more operator-dependent than thallium scanning The main arguments for coronary angiography (or any cardiac evaluation) are that there is a high incidence of unsuspected critical coronary artery disease and that the correction or identification of the disease will improve perioperative results, although this is yet to be proven in a randomized trial. For every study that shows good results with aggressive cardiac screening there is another with similar results with selective use of investigations. Previous reports on this topic are predominantly from either tertiary referral centres, such as the Cleveland Clinic, or large metropolitan hospitals. As such they may treat a population with a greater proportion of complex or sicker patients. The aims of this study were to document the incidence of significant cardiac disease in patients undergoing elective aortic aneurysm repair in a non-metropolitan setting using a combination of thallium scanning and angiography. Furthermore, the incidence of perioperative cardiac events was established, and comparisons were made of the incidence of cardiac abnormalities on testing with those patients suspected on the grounds of history and ECG.

Methods All patients scheduled for elective aortic aneurysm repair underwent cardiac screening with either thalCARDIOVASCULAR SURGERY

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lium scanning or angiography unless the attending physician refused, or the tests were unavailable. Data were collected prospectively and analysed after 100 consecutive repairs. Thallium scanning A thallium stress test has three phases: a standard cardiac stress test using a treadmill or stationary bicycle, during which the thallium is injected at peak stress. This is followed by nuclear imaging, and a wait of about 3 h before resting nuclear imaging. Imaging of the heart is at three angles by single photon emission tomography, which provides similar sectional images to a CT scan. Thallium scan results were classified as normal, showing a fixed defect, or having a reversible defect. A fixed defect was reported where there was an area of decreased thallium uptake on the initial image, which remained on the delayed study. A reversible defect was reported when an area that initially showed decreased perfusion showed perfusion on delayed images. Results of coronary angiography were classified according to the treatment recommendations of the cardiologist. The catagories used were normal or no significant disease, abnormal but not requiring intervention, and significant disease. Demographic data recorded for each patient included age, sex, presence or absence of hypertension, diabetes, elevated creatinine and history of smoking (Table 1). Particular note was made of history of prior cardiac problems including angina, myocardial infarction, cardiac failure, prior cardiac intervention and the presence of abnormal ECG recording. When results of either thallium scanning or angiography showed significant disease, patients were considered for either coronary artery surgery or angioplasty prior to aneurysm repair. Patients that had bypass surgery prior to aneurysm repair were generally kept in hospital after bypass surgery and had aneurysm repair at about 7 days after cardiac surgery unless they suffered a complication such as respiratory infection. Patients treated with angioplasty or a stent usually waited 1 month before aneurysm repair as most took the anti-platelet agent Ticlopidine for 1 month following the cardiac intervention. Morbidity and mortality were recorded prospecTable 1 Demographic data Hypertension Diabetes Smoking Cardiac disease Male sex Age

75 (72%) 9 (9%) 74 (71%) 66 (63%) 87 (84%) Median 71 years (57–89)

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Cardiac assessment with thallium scanning prior to aortic aneurysm repair: F. G. Quigley et al. Table 2 Incidence of cardiac events compared with results of preoperative cardiac investigations

None Normal Thallium or angio fixed defect signif. disease

tively. A patient was considered to have suffered cardiac morbidity if a cardiac event occurred that required therapeutic intervention or delayed discharge. Cardiac enzyme tests and ECG recordings were not carried out routinely.

Results Of 102 consecutive patients, 94 patients had either thallium 201 scanning and/or coronary angiography. Patients who did not have these tests either did not have a positive cardiac history or abnormal ECG, had their operations when thallium scanning was unavailable for a short time (six patients), or because their treating physician did not feel it necessary (two patients). One-third of patients (34/94) had significant areas of reperfusion on thallium scanning (28) or had significant disease on angiography (six). Of these patients, 20 had cardiac intervention prior to aneurysm repair (coronary artery bypass 14, angioplasty ⫾ stent six). No cardiac mortality occurred following aneurysm repair but there were 10 cardiac complications. In the patients who demonstrated significant disease preoperatively there were three postoperative cardiac complications: one cardiac arrest occurred 7 days postoperatively with no subsequent ECG or enzyme changes to suggest infarction. This patient had coronary angioplasty 1 month prior to aneurysm repair and subsequently recovered without further troubles. One patient who had bypass surgery developed atrial fibrillation at day 4 post-aneurysm repair and one other patient who did not have cardiac intervention had an episode of atrial fibrillation. Of the eight patients who did not have cardiac screening preoperatively there was one episode of failure without ECG or enzyme evidence of infarction and one episode of atrial fibrillation. Only two of 36 patients with normal cardiac investigations had any cardiac morbidity: both arrhythmias. There was a higher incidence (3 of 23) of cardiac events in those with a fixed defect on thallium scanning, one episode of failure and two with significant arrhythmias (Table 2). Non-cardiac morbidity is documented in Table 3. There was good correlation between cardiac history, ECG results and the findings on coronary angi642

Number

Cardiac morbidity

8 36

2 (25%) 2(6%)

23 34

3 (13%) 3 (9%)

Table 3 Non-cardiac morbidity Respiratory infection Lymph fistula Ileus Gastrointestinal bleeding Increased creatinine Colonic ischaemia Strangulated hernia Urinary tract infection Pulmonary embolism Reoperation for bleeding Epilepsy Central line sepsis Epidural abscess Wound infection Transfusion reaction a

10 3 3 2 2 1a 1 1 1 1 1 1 1 1 1

Patient mortality

ography and thallium scanning (Table 4). A positive cardiac history and/or abnormal ECG had a positive predictive of 82% for a thallium or angiographic abnormality. There was good correlation between coronary angiography and thallium scanning in the 22 patients who had both investigations: 19 of 22 had significant coronary disease confirmed on angiography. The three patients who had abnormal thallium scans but normal coronary angiography had defects on thallium scanning that were artefacts caused by diaphragmatic attenuation. Of the 19 positive coronary angiograms after thallium scanning 15 patients had coronary intervention prior to aneurysm repair. The four patients who did not have intervention prior to aneurysm repair had significant comorbid conditions and were judged to be inappropriate for inclusion by a cardiologist, cardiac surgeon and an anaesthetist. Cardiac history and ECG findings were not a good predictor of cardiac events (Table 5). The sensitivity and positive predictive value of a cardiac history and/or abnormal ECG for a cardiac event were 60% and 10%, respectively. History and ECG alone would have missed 20% of patients with an abnormal scan or angiogram and 10% who were thought to require intervention prior to abdominal aortic aneurysm repair. There was one death among the 101 patients who had aneurysm repair. This was a morbidly obese CARDIOVASCULAR SURGERY

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Cardiac assessment with thallium scanning prior to aortic aneurysm repair: F. G. Quigley et al. Table 4 Comparison of history, ECG and cardiac screening Thallium or angiographic abnormality (total 94) Yes

No

51 12

11 20

Yes

No

6 4

57 34

+ ve ECG or cardiac history Yes No

Table 5 Comparison of history, ECG and incidence of cardiac events Cardiac event

+ ve ECG or cardiac history Yes No

patient who had a normal thallium scan preoperatively. The patient required a large transfusion for blood loss and subsequently developed colonic ischaemia and then multiorgan failure. There was no mortality in patients who underwent cardiac intervention and subsequent aneurysm repair, but one patient did have coronary artery bypass surgery and did not have abdominal aortic aneurysm repair because of a rapid decline in health and death 3 months after coronary surgery. The patient had a cathectic appearance, which is consistent with a malignant process, but extensive investigation by the patients’ physician found no cause prior to death. On an intention-to-treat basis this increases mortality for the study group from 1 to 2%.

Discussion This study did not prove or disprove an advantage for aggressive cardiac screening prior to aortic aneurysm repair. It confirms the high incidence of significant cardiac disease in this population and demonstrated that correction of significant coronary artery disease prior to aortic aneurysm repair allowed aneurysm repair to be carried out with minimal cardiac morbidity. All patients with an aortic aneurysm of ⱖ 5 cm were considered for repair unless there was a coexistent condition such as malignancy that was associated with a life expectancy of ⬍ 2 years. All aneurysm repairs for the district were carried out at the study centres, so these results should reflect the true incidence of cardiac disease in patients with aortic aneurysm. The authors of some papers have stated a favoured policy of delayed or interval repair of the aneurysm CARDIOVASCULAR SURGERY

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after cardiac surgery [5, 7]. In previous studies there have been a number of deaths after coronary artery surgery because of aneurysm rupture [7, 8]. Alternative approaches are synchronous coronary artery bypass and aneurysm repair or, as in this study, repair of the aneurysm during the same hospital admission. The authors favour the last approach as it is logistically easier and decreases the risk of perioperative aneurysm rupture while avoiding bleeding and other morbidity associated with a long operating time within two body cavities. Although in this study no patient with significant uncorrected coronary artery disease died in the postoperative period, others have demonstrated a high cardiac complication rate in that group. In a report by Bayazit, when severe coronary artery disease was found but not corrected prior to aortic aneurysm repair, three of seven patients died following abdominal aortic aneurysm repair compared with two of 118 patients who had either cardiac intervention prior to repair or no significant coronary artery disease on angiography [9]. In this study there was good correlation between history of cardiac disease, ECG findings and results of thallium scanning and angiography. However, a cardiac assessment based on history and ECG findings would still have missed 20% of those with a significant abnormality on thallium scanning and angiography. Schueppert found a similar incidence of significant abnormality on thallium scanning in patients undergoing vascular procedures (44%), and that a history of angina or myocardial infarction was of limited use in predicting the presence of significant abnormalities on thallium scanning [10]. Starr et al. found only a low incidence of critical coronary 643

Cardiac assessment with thallium scanning prior to aortic aneurysm repair: F. G. Quigley et al.

artery disease on angiography when there was no prior history of angina or myocardial infarction and the ECG was normal [11]. Without a randomized trial it is difficult to show whether an aggressive or conservative cardiac evaluation is optimal, but it would seem to the authors that the approach adopted in this study has at least raised the awareness of those treating these patients of the high incidence of coexistent cardiac disease and aortic aneurysm. In a hospital where there is a high turnover of junior staff doctors and anaesthetic staff such an approach may be better than assuming an expert knowledge of cardiovascular intervention in all staff caring for such patients. Another impression was that this approach led to improved understanding between the vascular surgeon, cardiologist and cardiac surgeon, which had the benefit of an improved perspective and management of other patients with both cardiac and vascular disease. The benefit of coronary artery bypass grafting or angioplasty prior to abdominal aortic aneurysm repair may be better long-term survival, as the perioperative cardiac event rate is low even in patients suspected or proven to have serious coronary artery disease who do not have intervention prior to abdominal aortic aneurysm repair. Starr found that late survival for all patients was primarily related to age, serum creatinine level and the presence of coronary artery disease at time of surgery [11], whereas Schueppert also found thallium abnormality was a good predictor of late cardiac morbidity [10]. Patients who have cardiac intervention prior to aortic aneurysm repair have the same long-term survival as those who have only mild cardiac abnormality on preoperative testing [11]. It is clear there has been a consistent improvement in perioperative mortality for abdominal aortic aneurysm repair over the last 30 years. Preoperative cardiac intervention is a probable but unproven reason for this improvement.

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This study has confirmed a high incidence of coronary artery disease in patients undergoing surgery for infrarenal aortic aneurysm, even when this is not suspected on the basis of history and ECG. It has also found that coronary revascularization prior to aortic surgery can be done safely. Previous experience suggests that this approach can lead to better long-term outcome.

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