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Perioperative myocardial infarction in peripheral vascular surgery

^a Peripheral Vascular Unit, Glasgow Royal Infirmary, Glasgow G31 2ER, ^b Department of Medical Cardiology, Glasgow Royal Infirmary, ^c Department of Biochemistry, Glasgow Royal Infirmary

Correspondence to: Mr Mamode.

The commonest major complication in patients undergoing peripheral vascular surgery is perioperative myocardial infarction.¹ No study in Britain has prospectively assessed this risk, but a recent retrospective study found an incidence of 6.3% in patients undergoing aortic surgery.² We report the incidence of perioperative myocardial infarction in our unit, which is a regional centre for peripheral vascular surgery.

Patients, methods, and results

We studied consecutive patients undergoing peripheral vascular surgery after excluding those who were undergoing surgery for trauma, venous surgery, and minor procedures. Patients thought to be at high risk of perioperative myocardial infarction were referred to a cardiologist for further preoperative assessment. Concentrations of creatinine kinase MB isoenzymes were measured (by Imx STAT) for the first three days after surgery, and electrocardiograms were recorded on admission, on discharge from hospital, and at doctors' discretion. Because the concentration of creatinine kinase MB isoenzyme may be raised by skeletal muscle ischaemia, myocardial infarction was diagnosed only when a raised total creatinine kinase concentration was associated with an MB subunit concentration of > 10 ng/ml and a ratio of MB subunit to total creatinine kinase of >/=5%. Cardiac death was defined as death unequivocally related to myocardial infarction, heart failure, or arrhythmia. The primary end points of our study were myocardial infarction or cardiac death within 30 days of surgery. We performed statistical analysis with the ² test or, when appropriate, Fisher's exact test.

The 191 patients included in our study (128 men, median age 65, and 63 women, median age 70) underwent 204 operations, of which 100 were elective procedures, 70 were urgent (requiring surgery within the same hospital admission), and 34 were emergency (requiring surgery within 24 hours). Ninety one of the operations were carried out for critical ischaemia, 32 were aortic procedures, and 120 patients (of the 182 in whom data were available) had preoperative evidence of ischaemic heart disease.

The overall incidence of perioperative myocardial infarction and cardiac death was 7.3%--6% for those undergoing elective or urgent procedures and 12% for those undergoing emergency surgery. Table 1 gives details of the six myocardial infarctions and eight cardiac deaths that occurred. Four of the non-fatal infarctions were clinically silent. Two patients had surgery performed under regional anaesthesia (amputation and brachial embolectomy), while the rest had a general anaesthetic. Three patients were submitted to necropsy, which showed subendocardial infarction in two patients and transmural infarction (probably preceding surgery) in the other. The factors associated with perioperative myocardial infarction were age over 70 ²=4.642, P=0.03), sex (²=3.989, P=.05), perioperative shock (Fisher's exact test ²=6.949, P=0.05), and angina (Fisher's exact test ²=7.317, P=0.008).

Table 1--Details of patients undergoing peripheral vascular surgery who sustained perioperative myocardial infarction
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                                                                                                Infarction
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Patient's age        Operation (class)                  Time*         Associated signs                         Risk factors+
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Non-fatal infarction
64                   Carotid (elective)                   1           Angina, electrocardiographic changes     High blood pressure, ischaemic heart disease
78                   Femoropopliteal (elective)           1           Silent (electrocardiographic signs of    Ischaemic heart disease, smoker, age
                                                                        bundle branch block)
65                   Ileofemoral graft and operative      0           Silent (electrocardiographic signs of    Ischaemic heart disease, cerebrovascular
                        sympathectomy (urgent)                          bundle branch block)                     accident, diabetes
69                   Below knee amputation (urgent)       2           Silent                                   High blood pressure, diabetes
81                   Below knee amputation (urgent)       0           Silent                                   Ischaemic heart disease, high blood pressure,
                                                                                                                 cerebrovascular accident, age
66                   Abdominal aortic aneurysm            0           Angina, electrocardiographic changes,    Perioperative shock, ischaemic heart disease,
                       repair (emergency)                              bradycardia                              smoker
Fatal infarction
65                   Abdominal aortic aneurysm            2           Left ventricular failure, subendocardial Ischaemic heart disease, high blood pressure,
                      repair (elective)                                 myocardial infarction on necropsy        cerebrovascular accident
63                   Abdominal aortic aneurysm           11           Left ventricular failure,                Ischaemic heart disease, high blood pressure,
                      repair (elective)                                 electrocardiographic changes             perioperative shock
73                   Femoral-femoral crossover (elective) 4           Left ventricular failure, subendocardial Ischaemic heart disease, high blood pressure,
                                                                        myocardial infarction on necropsy        age, smoker
71                   Ileofemoral graft and operative      4           Angina, electrocardiographic changes     Ischaemic heart disease, high blood pressure,
                        sympathectomy (urgent)                                                                   cerebrovascular accident, age
90                   Below knee amputation (urgent)      13           Left ventricular failure                 Ischaemic heart disease, high blood pressure,
                                                                                                                 age
72                   Abdominal aortic aneurysm            3           Left ventricular failure,                Ischaemic heart disease, perioperative shock,
                      repair (emergency)                                electrocardiographic changes             smoker, age
75                   Abdominal aortic aneurysm            0           Cardiogenic shock                        Ischaemic heart disease, perioperative shock,
                      repair (emergency)                                                                         age
89                   Brachial embolectomy (emergency)     0           Cardiac arrest, transmural myocardial    Ischaemic heart disease, smoker, age
                                                                       infarction on necropsy
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*No of days after peripheral vascular surgery.
+Age >70 years; high blood pressure; previous transient ischaemic attack or cerebrovascular accident; diabetes; current smoker; perioperative shock; ischaemic heart disease (angina,
previous myocardial infarction, or abnormal electrocardiographic results).

Comment

This is the first prospective study in Britain to assess the incidence of perioperative myocardial infarction in patients undergoing peripheral vascular surgery. Infarction is clinically silent in about 30% of patients,³ as we found, and is fatal in 50%.⁴ Perioperative cardiac events were not restricted to patients obviously at high risk: myocardial infarctions occurred in patients undergoing elective non-aortic surgery as well as in those undergoing repair of ruptured aortic aneurysm. We found angina to be a strong predictor of risk, but previous myocardial infarction was not. Reviews have confirmed age, diabetes, and heart failure at operation as the only consistent predictors of risk,⁵ but larger studies with better design might shed more light on this.

We found an overall rate of perioperative myocardial infarction of 7.3%, which remained substantial at 6% if we excluded patients undergoing emergency surgery. This implies that further attempts at risk stratification are justified. We urgently require studies to ascertain the best methods of preoperative stratification in order to minimise the risks of vascular surgery.

Funding: None. Conflict of interest: None.

1. Mamode N, Cobbe SM, Pollock JG. Infarcts after surgery. BMJ 1995;310:1215-6. [Free Full Text]
2. Kalra M, Charlesworth D, Morris JA, Al-Khaffaf H. Myocardial infarction after reconstruction of the abdominal aorta. Br J Surg 1993;80:28-3. [Medline]
3. Taylor, LM, Yeager RA, Moneta GL, McConnell DB, Porter JM. The incidence of perioperative myocardial infarction in general vascular surgery. J Vasc Surg 1991;15:52-61.
4. Mangano DT. Perioperative cardiac morbidity. Anaesthesiology 1990:72;153-84.
5. Wong T, Detsky AS. Preoperative cardiac risk assessment for patients having peripheral vascular surgery. Ann Intern Med 1992;116:743-53.

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