Frequency and significance of early postoperative silent myocardial ischemia in patients having peripheral vascular surgery

Frequency and Significance of Early Postoperative Silent Myocardial Ischemia in Patients Having Peripheral Vascular Surgery Pamela Ouyang, MD, Gary Gerstenbiith, MD, William R. Furman, MD, Peter J. Golueke, MD, and Sidney 0. Gottlieb, MD

cereMrydiseasecausesthemajorityefperieperatlve cemphbw after petiphsral vascular surgery. Twenty-fellr patknts with stabk cerenary disease undergperipheral revascuMzation WM83StldidUSlng celhwuseleetroeardiegraphk monitaringtodeterminethsin&lencaofperioperatlve asymptomatk myocardial ischemia and its relath te pestqmative dlnkal ischemk events. Patient!BweremlBnitoredpreopsrativety(17*1 hews), intraoperatively and postoperattvety (29 f 2 hews) ushag 4-chamwl calibrated amplitudsmedulaMunlts.Flfteenpatknts(63%)hadeady posbperattve silent ischsmia; 3 ako had preoperative slknt lschemlb ad 5 intraoperative transient i-a. Patients with and without silent ischemia had simitar diikal charactefistks, periopsfative antianglnal medkatiens and postoperative episodes of hemodynamk instability. However, 8 of 15 patknts (53%) with dknt ischemia had postoperative chkal ischemll events (2 had myocardiil infarction, 2 had new congestive heart failure and 4 had

newrestaqgina),ve!rsusonly1of9pa~(ll%) without stlent itiia who had angina (p
oronary artery disease, identified by coronary angiography, is present in >30% of patients undergoing surgery for peripheral vascular diseaseIT and accounts for the majority of perioperative mortality in these patients. Myocardial &hernia has been found during induction of anesthesiain patients with coronary artery disease3and is an independentrisk factor for perioperative myocardial infarction.4 Preoperative identification of high risk patients appears possible.5-10However, screening for myocardial ischemia may be limited by the inability of patients with peripheral vascular diseaseto provide adequatetreadmill exercise stress tests, by the inability of older patients and women to perform adequate arm exercisetests and the lack of availability of preoperative dipyridamole-thalliurn scintigraphy. Continuous electrocardiographic monitoring has been used to identify asymptomatic myocardial ischemia in patients with stable exertional and unstable angina. Our study was undertaken to determine the frequency of transient perioperative ischemia, identified by continuous electrocardiographic monitoring, and its relation to subsequentpostoperativemyocardial ischemic events.

C

METHODS

Between January 1986 and March 1988, approximately 100 patients underwent peripheral vascular surgery at Francis Scott Key Medical Center and were consideredfor participation in the study. Exclusion criteria were as follows: no clinical evidence of coronary artery diseaseby history or electrocardiogram; digoxin therapy; baselineelectrocardiographic abnormalities including left bundle branch block, left ventricular hypertrophy with repolarization abnormalities or baselineSTsegmentdepressionor elevation >1 mm. Twenty-seven patients were eligible and approachedto participate; 3 refusedto consentand the remaining 24 patients signed an informed consentform approvedby the’ hospital’s institutional review board. The 24 patients were monitored using 2 amplitude-modulated reel-to-reel 2-chanFrom the Division of Cardiology, Departments of Medicine, Surgery nel calibrated Holter units (Delmar Avionics, model and Anesthesiology, Francis Scott Key Medical Center, and Johns Hopkins Hospital, Baltimore, Maryland. This study was supportedin 445). Two modified inferior and 2 modified anterior part by a grant from Pfizer PharmaceuticalCo., New York, New York. leadswere recorded.The ambulatory electrocardiogram Manuscript received April 27, 1989;revised manuscript received and was recorded preoperatively for 17 f 1 hours after the acceptedJuly 31, 1989. Addressfor reprints: Pamela Ouyang, MD, Division of Cardiology, patient was admitted to the hospital on the day before Francis Scott Key Medical Center, 4940 Eastern Avenue, Baltimore, surgery. Electrocardiographic monitoring was continued intra- and postoperatively (29 f 2 hours). A 1Zlead Maryland 21224. THE AMERICAN JOURNAL OF CARDIOLOGY NOVEMBER 15. 1989

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MYGCARMAL ISCREMIA AlTER PERIPHERAL VASCULAR SURGERY

TABLE I Clinical Characteristics of Patients with (Group 1) And Without (Group 2) Silent lschemia Detected by Ambulatory Electrocardiographic Monitoring

AgeWs) M:F Cardiac risk factor Cigarette smoking Systemic hypertension Diabetes mellitus Prior MI Angina Prior CABG p Blockers Calcium antagonists Nitrates +ElT* Goldman risk index

Group 1 Silent lschemia (n = 15) (%)

Group 2 No Silent lschemia (n = 9) (%)

62f2 11:4

66zt2 6:3

11 (73) 9 w9 6 W) 10 (67) 7 (47) l(7) 7 (47) 7 (47) 7 (47) 6/g (67) 1.5zto.3

6 (67) 5 (56) 101) 7 (78) 5 (56)

2 (22) 2 cm 6 (67) 3 (33) O/4 (0) 1.4zto.3

$a&o.o5, group1 vs group2. myocardial

= coronary infarction.

artery

bypass grafting:

Eli

= exercise

TABLE II Ambulatory Electrocardiographic from the 15 Patients with Silent lschemia Preoperative Holter Duration of ambulatory ECG (hrs) No. with SI No. of SI episodes Total duration of SI. median (range) in minutes Duration/episode (minutes) HR at onset (beats/min) lntraoperative Holter No. with SI No. of ischemic episodes Total duration of SI, median (range) in minutes Duration/episode (minutes) HR at onset (beats/min) Postoperative Holter No. with SI No. of ischemic episodes Total duration of SI, median (range) in minutes Duration/episode (minutes) HR at onset (beats/min)

tolerance

test; MI =

Monitoring Data

16&l 3 4.0 20(19-38) 19 107f4 5 8 58 (6-101) 32 107 f 12 15 45 63 (5-542) 41 104zt3

HR = heart rate; SI = silent ischemia.

electrocardiogram and creatine kinase with MB isoenzyme levels were obtained postoperatively. Clinically evident myocardial ischemic events were defined as rest angina, new congestive heart failure, myocardial infarction or death. Congestiveheart failure (newly heard pulmonary rales with pulmonary vascular congestion on chest x-ray) was felt to be caused by acute myocardial ischemia in the absenceof a prior history of heart failure and when failure was associated with ischemic ST changes on a 1Zlead electrocardiogram that resolvedrapidly with diuretic and antianginal therapy. Myocardial infarction was defined as a persistent changein the postoperativeelectrocardiogramassociated with an increasein creatine kinase to >2 X normal with an MB isoenzyme fraction of >4% of total creature kinase. The continuous electrocardiogram tapes were scanned in a blinded fashion by 1 technician experiii

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THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 64

enced in identifying episodesof ST-segmentchange. A printout was prepared of each episodethat included the onset and end of each episode of ST-segment change and the maximum change observed. These printouts were reviewedby 2 investigators who were blinded as to the identity of the patient. Each episodeof ST-segment shift of >l mm below the baseline lasting for >2 minutes was noted. The heart rate at the onset and the total duration of each episodewere recorded.The continuous electrocardiographicmonitoring data were not available to the clinicians and use of perioperative pressorsor antianginal medicationswas at the discretion of the surgeon. Perioperative hemodynamic changeswere noted using the anesthesiologist’shemodynamic record and the postoperative record from the intensive care unit. The duration of each episodeof hypertension (systolic blood pressure >180 mm Hg), hypotension (systolic blood pressure>90 mm Hg) or tachycardia (heart rate >lOO beats/mm) was consideredto be from the time when it was first noted on the hemodynamic flow chart to the time a different pressureor rate was recorded. Data analysis: Data are expressedas mean f standard error of the mean. Categorical data were analyzed using the Fisher exact test. Continuous variables were analyzed using unpaired t tests of significance. Data without a normal distribution were compared using a Mann-Whitney rank test. RESULTS Patknt popdath graphic monitodng:

and ambulatory

ekcbcardio-

Seventeenmen and 7 women were studied. The mean age was 64 f 5 years. Seventeen patients had prior myocardial infarction, 12 had angina pectoris and 3 had undergone coronary artery bypass surgery. Sevenpatients underwent carotid endarterectomy, 11 underwent aortic revascularization and 6 underwent infrainguinal bypass procedures.Twenty patients receivedgeneral, 1 patient receivedspinal and 3 patients receivedepidural anesthesia.The clinical characteristics of the patients are listed in Table I. Fifteen of the 24 patients (63%), group 1, had silent perioperative ischemia detected by continuous electrocardiographic monitoring. All 15 patients had postoperative transient ischemia. Of these 15 patients, 2 also had preoperative silent ischemia, 4 also had intraoperative silent ischemia and 1 patient also had ischemia both pre- and intraoperatively. The number and duration of ischemic episodes,and the heart rate at onset of transient ischemia during the pre-, intra- and postoperative periodsare listed in Table II. Nine of 24 patients (37%), group 2, had no ischemia on continuous electrocardiographic monitoring. The 2 groups did not differ with regard to clinical characteristics (Table I) or in the number of patients with a history of previous myocardial infarction, angina, coronary artery bypasssurgery or congestiveheart failure. Only 13 patients (9 in group 1 and 4 in group 2) had exercisestresstesting within the year before the vascular surgery. No group 2 patient had a stress test that was positive for inducible ischemia whereas 6 of the 9

stress tests were positive in the group 1 patients (p <0.05). Among the 24 patients, 1 of 7 patients who had a negative treadmill test before surgery had perioperative clinical ischemia, whereas 4 of 6 patients with a positive exercise test had clinical ischemia (p = 0.08). Among the 9 group 1 patients who had preoperative exercisetreadmill testing, 0 of 3 with negative treadmill tests had a clinical outcome whereas4 of 6 with a positive treadmill test had a clinical outcome (p = 0.12). Pehperative hemodynamics and mediions: The 2 groups did not differ in the frequency or duration of hypotension, hypertension or sinus tachycardia or in the use of pressors,intravenous nitroglycerin, nitroprusside and antianginal medications. Clinical outcomes: Nine patients had overt clinical evidenceof myocardial ischemia in the later postoperative period. Eight of the 9 patients had transient ischemia during continuous electrocardiographic monitoring. Thus, 8 (53%) of the group 1 patients had in-hospital ischemic events; 2 suffered myocardial infarction, both of whom also developed congestive heart failure and 1 of whom had new angina at rest; 2 had new congestive heart failure, 1 of whom also had angina at rest, and 4 patients had new angina at rest. Among the group 2 patients only 1 (11%) had new angina at rest during the in-hospital postoperativeperiod (p <0.05 vs group 1). The clinical ischemic eventsoccurred 52 f 16 hours postoperatively. In all patients, silent or transient ischemic episodeswere noted before the clinical ischemit event, occurring 31 f 18 hours (range 30 minutes to 144 hours) before the clinical event. Two patients had additional silent ischemic episodesafter the clinical event. DISCUSSION Continuous electrocardiographic monitoring detected transient myocardial ischemia, which was largely asymptomatic, in 63% of the study patients during the early postoperativeperiod. Patients with silent ischemia had a 53% incidence of postoperative clinical ischemic events compared to 11% incidence for those without transient ischemia. Approximately 30% of patients requiring vascular surgery have severe coronary artery disease.ll It has been suggestedthat patients felt to be in a high-risk group should undergo coronary angiography and coronary revascularization before elective peripheral vascular surgery.l1 Whether the benefits outweigh the risk and expenseof such an approach is not clear. Hertzer et al* found that patients with significant coronary diseasehad a very low cardiac morbidity when peripheral vascular surgery was performed after coronary revascularization. However, the cardiac surgical mortality was 5.3%in thesepatients. This mortality rate is not untoward for older patients who have multiple medical problems.l2 Many investigators have attempted to identify those patients at increasedrisk for cardiac complications after vascular surgery.5-*oJ3Intravenous dipyridamole-thalliurn-201 scintigraphy may identify patients likely to have a perioperative ischemic event.9A large single oral dipyridamole dose may provide similar information to

intravenous dipyridamole.l4 However, these screening tests may still fail to identify patients who developtransient ischemia as a result of intra- and postoperative stresses. Ambulatory electrocardiographicmonitoring can de tect myocardial ischemia in patients with stable and unstable angina and in the periinfarction period.15-2* Transient asymptomatic ischemia noted on ambulatory monitoring has been associatedwith similar functional abnormalities as symptomatic ischemia and has been associatedwith an increasedincidence of cardiovascular morbidity and mortality. However, this technique has not been widely used to identify perioperative ischemia. Studies have shown that 39% of patients with coronary artery disease may demonstrate transient myocardial ischemia on single-leadelectrocardiographic monitoring during induction of anesthesiaand intraoperatively, but this has not beencorrelated with postoperativeischemic events.3*22 We used pre-, intra- and postoperative continuous electrocardiographic monitoring in a relatively small number of patients to identify those patients at increased risk of perioperative myocardial ischemic events.Only patients with documentedcoronary artery diseasewere studied to reduce the incidence of falsepositive changes on continuous electrocardiographic monitoring. However, no patient had unstable myocardial ischemia. Despite this, a high incidence of postoperative myocardial ischemia (63%) was found that was not suspectedin the majority of patients and transient myocardial ischemia was significantly associatedwith clinical ischemic events, which occurred up to 6 days postoperatively. Becausepatients were approached for consentafter admission before surgery, monitoring was performed for only 17 hours preoperatively. Although only 3 patients (13%) had preoperative silent ischemia, more prolonged periods of preoperative ambulatory monitoring might identify more patients. Alternatively, a greater frequency of transient ischemia may occur early postoperativelyas a result of intra- and postoperative stresses.An abnormal exercise stress test before surgery was associatedwith transient perioperative ischemia but was performed in only 54% of the study patients and, in this small number of patients, did not predict clinical ischemic outcomes. Peripheral vascular surgery is often associatedwith perioperative swings in blood pressurethat could result in transient myocardial ischemia. However, no differencewas noted in the amount of hemodynamic instability between patients with or without silent ischemia in this small group of patients. These results suggest that aggressive antiischemic managementduring the postoperativeperiod may benefit selected patients. Continuous electrocardiographic monitoring cannot provide information sufficiently rapidly to be useful in postoperativepatient management. However, identification of ischemic episodes“on line” using computerized devicescould allow immediate recognition of transient myocardial ischemia and appropriate institution of antiischemic therapy that may reduce the incidence of subsequentmorbid events.

THE AMERICAN JOURNAL OF CARDIOLOGY NOVEMBER 15, 1989

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MYOCARDIAL ISCREMIA AFIER PERIPRERAL VASCULAR SURGERY

AWe are grateful to Carol A. Hewitt and Valerie Williams for secretarial assistance and to Renita C. Patton for technical assistance.

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