The value of silent myocardial ischemia monitoring in the prediction of perioperative myocardial infarction in patients undergoing peripheral vascular surgery

Real-time electrocardiographic monitoring for silent myocardial ischemia was performed on 200 patients undergoing peripheral vascular surgery to try to better define those at high risk of perioperative myocardial infarction. The patients were divided into those undergoing abdominal aortic aneurysm or lower extremity revascularization procedures (group I, n = 120) and those undergoing carotid artery endarterectomy (group II, n = 80). Silent ischemia was detected during the preoperative, intraoperative, or post-operative periods in 60.8% of group I and 67.5% of group II patients. Six group I and three group II patients suffered an acute perioperative myocardial infarction with two cardiac deaths. In both groups I and II a variety of parameters based on monitoring of silent myocardial ischemia were compared between the subgroups of patients who had myocardial infarction and those who did not. The results show that in both groups there was a significantly (p less than or equal to 0.05) greater total duration of perioperative ischemic time, total number of perioperative ischemic episodes, and total duration of perioperative ischemic time as a percent of total monitoring time in patients who suffered a perioperative myocardial infarction compared to those who did not. Multivariate logistic regression analysis of preoperative characteristics in all 200 patients showed the occurrence of preoperative silent myocardial ischemia and angina at rest to be the only significant predictors of perioperative myocardial infarction. Thus perioperative monitoring for silent myocardial ischemia might noninvasively identify those patients undergoing peripheral vascular surgery who are at increased risk for perioperative myocardial infarction, permitting implementation of timely preventive measures in selected patients.     

The influence of propofol versus sevoflurane anesthesia on outcome in 10,535 cardiac surgical procedures

OBJECTIVE: The purpose of this study was to evaluate the possible cardioprotective effect of sevoflurane versus propofol anesthesia in patients undergoing cardiac surgery. METHODS: Ten thousand five hundred thirty-five consecutive single cardiac surgical procedures from 3 cardiac centers were reported to a common registry from 1999 to 2005. The registry was established by the National Board of Health, and reporting was obligatory for all public heart centers in Denmark. The patients were stratified according to preoperative risk factors (EuroSCORE parameters). The outcome parameters were 30-day mortality, the incidence of postoperative myocardial infarction, and the incidence of postoperative arrhythmias. RESULTS: Overall, the 30-day mortality was lower after sevoflurane (2.84%) versus propofol (3.30%), although not significantly so (p = 0.18). No difference was found in the incidence of postoperative myocardial infarction (sevoflurane, 7.76%/propofol, 7.47%). Patients with preoperative unstable angina and/or recent myocardial infarction, and thus already "preconditioned," did not show any difference in mortality between anesthetic groups, whereas patients without these predictors showed a lower postoperative mortality after sevoflurane (2.28% v 3.14%, p = 0.015), which can at least partly be explained by a preconditioning-like effect. The data suggest that patients suffering relatively severe preoperative ischemic stress benefited from propofol anesthesia, which can be related to the antioxidant effects of propofol. Patients in the sevoflurane group had a higher incidence of postoperative atrial fibrillation (28.75% v 24.87%, p < 0.001), whereas patients in the propofol group showed a higher incidence of all other arrhythmias. CONCLUSION: Sevoflurane and propofol both possess some, although different, cardioprotective properties. Sevoflurane appears to be superior to propofol in patients with little or no ischemic heart disease, such as noncoronary artery bypass graft (CABG) surgery and CABG surgery without severe preoperative ischemia, whereas propofol seems superior in patients with severe ischemia, cardiovascular instability, or in acute/urgent surgery.     

Automated, continuous ST segment analysis in the ECG as a monitor of myocardial ischemia during aortocoronary bypass surgery

Patients with coronary artery disease (CAD) who are subjected to cardiac and major noncardiac surgical procedures have a high incidence of perioperative myocardial ischemia. Earlier studies in patients undergoing coronary artery bypass graft surgery (CABG) indicated the frequency of postoperative myocardial infarction to be directly proportional to the incidence and severity of pre-bypass myocardial ischemia. METHODS. We investigated the incidence of pre-bypass ischemia in 50 patients undergoing elective CABG using an automated ST segment monitoring system (Marquette 7010). Analyzing leads I, II, and V5, this device measures ST segment deviations 60 ms after the J-point. Occurrence of myocardial ischemia was defined as follows: new ST segment deviations larger than 1 mm = 0.1 mV that lasted for more than at least 10 consecutive heartbeats. RESULTS. In 19 out of 50 patients (38%) we found 96 episodes of myocardial ischemia in the pre-bypass period; 47% of all ischemic episodes were associated with significant hemodynamic changes, e.g., tachycardia, hypertension, or hypotension. The incidence of ischemia was different between population sub-groups: patients with a previous infarction had a lower incidence of ischemia (35%) than patients without infarction (44%). Patients with preoperative left ventricular end diastolic pressure (LVEDP) less than 15 mm Hg had a lower incidence of ischemia (29%) than patients with LVEDP greater than 15 mm Hg (50%). Patients treated preoperatively with beta-blockers showed a significantly lower incidence of ischemia (9%) when compared to untreated patients (46%, p less than 0.05). No difference was found between patients with or without unstable angina pectoris or between patients of NYHA classes II, III, or IV. Postoperative myocardial infarction occurred in 2 patients, both with evidence of pre-bypass myocardial ischemia. CONCLUSION. Our study confirms that automated ST segment analysis is able to detect myocardial ischemia similarly to that documented in previous studies using conventional ECG lead analysis.     

Perioperative cardiac complications of pulmonary operations in patients with/without coronary stenosis]

It has been suggested that the presence of ischemic heart disease correlates with an increased risk of cardiac infarction and fatal arrhythmia following noncardiac operations. To prevent these complications, coronary arteriographies were performed on 55 patients before pulmonary surgery for the assessment of the risk of perioperative cardiac complications. A coronary artery obstruction, with a 50% or greater reduction in the internal diameter was recognized on 21 patients (Group 1) and the other 34 patients showed no significant coronary stenotic lesions (Group 2). Discriminant analysis revealed that cardiac index (p less than 0.025), blood sugar level (p less than 0.05), hyperlipidemia (p less than 0.05) and postoperative cardiac failure (p less than 0.005) correlated independently with coronary artery stenosis. Postoperative cardiac complications were observed in the form of atrial arrhythmias (11%), ventricular arrhythmias (16%) and ischemic ECG findings (17%) in all cases. The rate of occurrence of these complications were not different between the two groups. However, the need for therapeutic procedures for perioperative circulatory failure (18%) was much greater in group 1 (p less than 0.005). This study supports the merits of preoperative coronary arterial angiography and the estimation of the left ventricular function in reducing pulmonary perioperative risk.     

Influence of allopurinol on cardiac complications in open heart operations

During cardiac operations, the heart is subjected to total ischemia and reperfusion, causing serious operative and postoperative complications such as arrhythmias, heart failure, and infarctions that may be partly due to free radical generation. Thus, allopurinol was tested to see if it could reduce cardiac complications during open heart operations. Ninety patients undergoing elective coronary artery bypass grafting were studied prospectively. Fortyfive patients were treated with allopurinol and 45 patients acted as controls. Treatment requiring arrhythmias in the allopurinol group was 6.6% compared with 33.3% in the control group (p less than 0.01). The percentage of patients requiring inotropes was significantly lower in the allopurinol group than in the control group (4.4% versus 26.6%; p less than 0.01). Perioperative myocardial infarction did not occur in the allopurinol group but was seen in 8 patients (17.7%) in the control group. Intraaortic balloon pumping was used in 5 control patients (11.1%) but not in the allopurinol group. This study shows that allopurinol decreases significantly the incidence of cardiac complications in open heart operations.     

Silent myocardial ischemia is not predictive of myocardial infarction in peripheral vascular surgery patients

Continuous ambulatory ECG (CAECG) monitoring has been advocated as an effective low-cost preoperative method for detecting silent myocardial ischemia in patients undergoing peripheral vascular surgery. In addition, silent ischemic events are associated with an increased incidence of postoperative myocardial infarctions. Ninety-six patients (mean age 73 years) admitted for elective aortic (24) or infrainguinal (72) operations over a 2-year period underwent 24-hour two- or three-lead CAECG monitoring. Results were reviewed by a single cardiologist blinded to the study. The criterion for ischemia was ST segment depressions of 1 mm or greater for 40 seconds or more 60 msec after the J point. Postoperative myocardial infarction was determined by ECG changes and/or elevated serum creatinine phosphokinase with positive MB isoenzymes. Risk factors included hypertension (71%), history of coronary artery disease (66%), smoking (61%), and diabetes mellitus (47%). Nine out of 96 patients (9.4%) had a positive CAECG test for silent myocardial ischemia. Only one patient (11.1%) developed postoperative myocardial infarction and there were no deaths in this group. The incidence of postoperative myocardial infarction in the nonischemic group was 16.1% (14/87). However, the mortality in this group was 6.9% (6/87). New and malignant arrhythmias requiring preoperative medical intervention were observed in seven patients (7.4%): two cases of ventricular tachycardia and five cases of atrial flutter/fibrillation. Contrary to previous reports, CAECG monitoring for silent ischemia was not a significant predictor of postoperative myocardial infarction or mortality in our patient population. However, we continue to recommend the preoperative use of CAECG monitoring as a diagnostic tool for unsuspected malignant arrhythmias.Presented at the Seventeenth Annual Meeting of the Peripheral Vascular Surgery Society, Chicago, Ill., June 7, 1992.     

Importance of preoperative myocardial glycogen levels in human cardiac preservation. Preliminary report.

One hundred seventeen patients undergoing elective coronary bypass were divided into four groups according to prebypass myocardial glycogen levels and the use of potassium chloride cardioplegia. Myocardial glycogen levels were enhanced with a preoperative fat loading diet and overnight glucose loading. The control group (n = 27) which had mean cardiac glycogen levels of 750 mg/100 gm heart weight and no cardioplegia, had a transmural myocardial infarct rate of 14.4%; 35% had severe atrial arrhythmias 65% had severe ventricular arrhythmias, and 31% had severe vasopressor dependence. The group (n = 30) with low cardiac glycogen (736 mg/100 gm) and with potassium chloride cardioplegia had an infarct rate of 6.4%; 6.7% had severe atrial arrhythmias, 18% had severe ventricular arrhythmias, and 16.7% had severe vasopressor dependence. However, the group (n = 26) which had high cardiac glycogen levels (1,208 mg/100 gm) and no cardioplegia had no myocardial infarctions; 3.8% had severe atrial arrhythmias, 27% had severe ventricular arrhythmias, and only 7.8% had severe vasopressor need. The group (n = 34) which had high glycogen levels (1,516 mg/100 gm) and potassium chloride cardioplegia did best of all with no myocardial infarctions or no severe atrial arrhythmias; 14% had severe ventricular arrhythmias and 2.81% severe vasopressor need. The lessening of vasopressor dependence and severe atrial and ventricular arrhythmias were significant by chi square contingency tables at p less than 0.05 and p less than 0.001, respectively. One cardiac-related death each occurred in the two groups with low glycogen and none in those with high glycogen levels. This suggests that better preoperative cardiac nutrition as represented by enhanced cardiac glycogen helps that heart tolerate anoxic stress whether cardioplegia is utilized or not and is additive to potassium chloride cardioplegia.     

Silent myocardial ischemia monitoring predicts late as well as perioperative cardiac events in patients undergoing vascular surgery.

In a previous study we have shown that perioperative monitoring for silent myocardial ischemia can noninvasively identify those patients undergoing peripheral vascular surgery who are at significantly increased risk for perioperative myocardial infarction. In the present study a group of 385 patients undergoing peripheral vascular surgery was studied long-term as well as short-term to determine whether perioperative monitoring for silent ischemia can identify those patients who are at significantly increased risk of late cardiac death or late cardiac complications as well as those patients at increased risk of perioperative myocardial infarction. All patients were monitored before, during, and after operation and were divided into two groups on the basis of results of monitoring: patients whose total duration of silent ischemia as a percentage of the total duration of perioperative monitoring was 1% or greater (group I, n = 120) and those for whom this value was less than 1% (group II, n = 265). Among patients in group I 13.3% (16 of 120) suffered a perioperative myocardial infarction in contrast to only 1.1% (3 of 265) patients in group II (p less than 0.001). Multivariate logistic regression analysis of preoperative and perioperative characteristics showed that the presence of a total perioperative percent time ischemic 1% or greater and age were the only significant predictors of perioperative myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)     

The preoperative and intraoperative hemodynamic predictors of postoperative myocardial infarction or ischemia in patients undergoing noncardiac surgery.

Among hypertensive and diabetic patients undergoing elective noncardiac surgery, preoperative status and intraoperative changes in mean arterial pressure (MAP) were evaluated as predictors of postoperative ischemic complications. Of 254 patients evaluated before operation and monitored during operation, 30 (12%) had postoperative cardiac death, ischemia, or infarction. Twenty-four per cent of patients with a previous myocardial infarction or cardiomegaly had an ischemic postoperative cardiac complication. Only 7% of those without either of these conditions sustained an ischemic complication. No other preoperative characteristics, including the presence of angina, predicted ischemic cardiac risk. Nineteen per cent of patients who had 20 mm Hg or more intraoperative decreases in MAP lasting 60 minutes or more had ischemic cardiac complications. Patients who had more than 20 mm Hg decreases in MAP lasting 5 to 59 minutes and more than 20 mm Hg increases lasting 15 minutes or more also had increased complications (p less than 0.03). Changes in pulse were not independent predictors of complications and the use of the rate-pressure product did not improve prediction based on MAP alone. In conclusion patients with a previous infarction or radiographic cardiomegaly are at high risk for postoperative ischemic complications. Prolonged intraoperative increases or decreases of 20 mm or more in MAP also resulted in a significant increase in these potentially life-threatening surgical complications.     

Perioperative myocardial ischemia: importance of the preoperative ischemic pattern

Previous studies investigating the incidence of myocardial ischemia in patients undergoing coronary-artery bypass grafting (CABG) surgery have not considered the potential significance of the preoperative ischemic pattern in the development of intra- and postoperative myocardial ischemia and infarction. Accordingly, the authors compared the frequency and severity of pre-, intra-, and postoperative ischemic episodes (ST-segment depression greater than or equal to 0.1 mV or elevation greater than or equal to 0.2 mV) in 50 men with severe coronary artery disease scheduled for elective CABG. All subjects were monitored by continuous electrocardiography (ECG) (Holter monitor) for 2 preoperative days, intraoperatively, and 2 postoperative days (total monitoring time = 4,363 h). Routine anti-anginal medications were continued until the morning of surgery, and the anesthetic management of the patient was not controlled. During the preoperative period, 42% of the patients had ECG ischemic episodes, 87% of which were clinically silent. Only 18% developed intraoperative ischemia. Postoperatively, the incidence increased to 40%. The number of ischemic episodes/hour (epis/h) of monitoring among the three monitoring periods was similar (0.09 +/- 0.12 epis/h preoperatively, 0.11 +/- 0.20 epis/h intraoperatively, and 0.05 +/- 0.08 epis/h postoperatively; P = NS). The median duration of ischemic episodes was similar pre- and intraoperatively (16 vs. 18.5 min, P = NS), but greater postoperatively (41 min, P less than 0.05). Seventy-six per cent of the perioperative ECG ischemia occurred without acute change (+/- 20% of control) in blood pressure or heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Surgical management of acute myocardial ischemia following percutaneous transluminal coronary angioplasty. Role of the intra-aortic balloon pump

Acute myocardial ischemia is a serious complication of percutaneous transluminal coronary angioplasty, often requiring emergency myocardial revascularization. Since our initial report of 17 such patients, we have encountered an additional 32 patients requiring emergency myocardial revascularization since September, 1981. The indication for emergency myocardial revascularization was ischemic chest pain in all 32 patients. Percutaneous transluminal coronary angioplasty resulted in injury to the right coronary artery in 11 patients, the left anterior descending artery in 19 patients, and the left main artery in two patients. The onset of ischemia was immediate in 26 patients but delayed up to 22 hours in six patients. Chest pain was associated with ST-segment elevation in 21 patients, hypotension in 7 patients, and cardiac arrest in 6 patients. Immediate intra-aortic balloon pumping was instituted in the angioplasty suite in 16 patients. The mean time from onset of ischemia to completed revascularization was 156 minutes with a mean of 1.6 grafts performed per patient. Seventeen patients (53%) had enzyme evidence of myocardial infarction postoperatively, with a significantly higher (p less than 0.01) incidence of myocardial infarction in those patients with preoperative ST elevation (76% versus 9%). In the 21 patients with ST-segment elevation, the incidence of Q wave infarction was 20% (3/15) with balloon pumping and 50% (3/6) without balloon pumping. Complications associated with intra-aortic balloon pumping occurred in one patient (6%). There were no hospital or late deaths with follow-up extending 16 months. The spectrum of injury resulting from percutaneous transluminal coronary angioplasty extends from chest pain alone to severe transmural ischemia with hypotension or cardiac arrest. Presentation may be immediate or delayed. Urgent emergency myocardial revascularization remains the accepted therapy for this complication. Immediate preoperative intra-aortic balloon pumping is a useful adjunct to emergency myocardial revascularization in the group of patients with acute ischemia and ST-segment elevation.     

Myocardial ischemia revisited

Does perioperative myocardial ischemia lead to postoperative myocardial infarction? By Stephen Slogoff and Arthur S. Keats. Anesthesiology 1985; 62:107-14. Reprinted with permission. To determine if a relationship exists between perioperative myocardial ischemia (ST segment depression greater than or equal to 0.1 mV) and postoperative myocardial infarction (PMI), nonparticipating observers recorded all electrocardiographic, hemodynamic, and other events between arrival of patients in the operating room and onset of cardiopulmonary bypass during 1,023 elective coronary artery bypass operations (CABG). The roles of preoperative patient characteristics, quality of the operation limited by disease as rated by the surgeon and duration of ischemic cardiac arrest as risk factors for PMI also were quantified. Electrocardiographic ischemia occurred in 36.9% of all patients, with almost half the episodes occurring before induction of anesthesia. PMI was almost three times as frequent in patients with ischemia (6.9% vs. 2.5%) and was independent of when ischemia occurred. Ischemia was related significantly to tachycardia but not hypertension nor hypotension and was frequent in the absence of any hemodynamic abnormalities. The anesthesiologist whose patients had the highest rate of tachycardia and ischemia had the highest rate of PMI. Although neither single nor multiple preoperative patient characteristics related to PMI, suboptimal quality of operation and prolonged ischemic cardiac arrest increased the likelihood of PMI independent of the occurrence of myocardial ischemia. The authors conclude that perioperative myocardial ischemia is common in patients undergoing CABG, occurs randomly as well as in response to hemodynamic abnormalities, and is one of three independent risk factors the authors identified as related to PMI. PMI is unrelated to preoperative patient characteristics such as ejection fraction and left main coronary artery disease, and its frequency will relate primarily to perioperative management rather than patient selection.     

Surgical results for mitral regurgitation from coronary artery disease

Results of coronary artery bypass grafting with and without mitral valve replacement were analyzed retrospectively in 101 patients with preoperative ischemic mitral regurgitation to determine the effects of severity and surgical treatment of mitral regurgitation on survival. Between 1980 and 1984, a total of 1,475 patients (mean age 59, 77% male) underwent coronary bypass. These patients were divided into three groups: (1) patients without ischemic mitral regurgitation who underwent isolated coronary bypass (1,374; 93%), (2) patients with ischemic mitral regurgitation who underwent isolated coronary bypass without valve replacement (85; 6%), and (3) patients with ischemic mitral regurgitation who underwent combined mitral valve replacement and coronary bypass (16; 1%). Preoperatively, patients with ischemic mitral regurgitation compared to those without regurgitation were significantly older (+6 years, p less than 0.001), had more severe coronary artery disease (p less than 0.001), a higher incidence of congestive heart failure (24% versus 5%, p less than 0.001) and recent myocardial infarction (16% versus 8%, p less than 0.01), and a lower mean ejection fraction (45% versus 61%, p less than 0.001). Operative mortality was significantly increased in patients with ischemic mitral regurgitation who underwent coronary bypass alone (p less than 0.01) and in those who underwent coronary bypass and mitral valve replacement (p less than 0.01)--11% and 19%, respectively--than in the coronary bypass patients without ischemic mitral regurgitation (3.7%). The severity of mitral regurgitation (0 to 4+) proved to be the most significant predictor of operative mortality. The actuarial survival rate at 5 years for the coronary bypass patients without ischemic mitral regurgitation was 85% compared to 91% (p less than 0.05) for the coronary bypass patients without ischemic mitral regurgitation. These results indicate that patients with ischemic mitral regurgitation have a higher prevalence of cardiac risk factors and are at an increased risk of operative mortality. Although the severity of the ischemic mitral regurgitation was strongly predictive of early survival, it proved to have an unexpectedly modest effect on long-term survival after surgical treatment.     

Does perioperative myocardial ischemia lead to postoperative myocardial infarction?

To determine if a relationship exists between perioperative myocardial ischemia (ST segment depression greater than or equal to 0.1 mV) and postoperative myocardial infarction (PMI), nonparticipating observers recorded all ECG, hemodynamic, and other events between arrival of patients in the operating room and onset of cardiopulmonary bypass during 1,023 elective coronary artery bypass operations (CABG). The roles of preoperative patient characteristics, quality of the operation limited by disease as rated by the surgeon and duration of ischemic cardiac arrest as risk factors for PMI also were quantified. ECG ischemia occurred in 36.9% of all patients, with almost half the episodes occurring before induction of anesthesia. PMI was almost three times as frequent in patients with ischemia (6.9% vs. 2.5%) and was independent of when ischemia occurred. Ischemia was related significantly to tachycardia but not hypertension nor hypotension and was frequent in the absence of any hemodynamic abnormalities. The anesthesiologist whose patients had the highest rate of tachycardia and ischemia had the highest rate of PMI. Although neither single nor multiple preoperative patient characteristics related to PMI, suboptimal quality of operation and prolonged ischemic cardiac arrest increased the likelihood of PMI independent of the occurrence of myocardial ischemia. The authors conclude that perioperative myocardial ischemia is common in patients undergoing CABG, occurs randomly as well as in response to hemodynamic abnormalities, and is one of three independent risk factors the authors identified as related to PMI. PMI is unrelated to preoperative patient characteristics such as ejection fraction and left main coronary artery disease, and its frequency will relate primarily to perioperative management rather than patient selection.     

Prophylaxis of atrial fibrillation with magnesium sulfate after coronary artery bypass grafting

Ninety-nine consecutive consenting patients were prospectively entered into a randomized, double-blind, placebo-controlled trial to determine the efficacy of postoperative magnesium therapy on the incidence of cardiac arrhythmias after elective coronary artery bypass grafting. No patient had documented or suspected arrhythmias preoperatively. Forty-nine patients received 178 mEq of magnesium given over the first 4 postoperative days, and 50 patients received only placebo. The clinical characteristics of both groups were similar. The preoperative mean serum magnesium concentration was similar in both study (1.90 mEq/L) and placebo (1.90 mEq/L) groups. The mean postoperative serum magnesium concentration in study patients was significantly elevated over postoperative days 1 through 4 when compared with preoperative levels (p less than 0.001). The postoperative mean serum magnesium concentration in control patients declined and remained significantly depressed through postoperative day 3 (p less than 0.001), but increased to preoperative levels by postoperative day 4. The mean serum magnesium concentration was significantly greater in the study patients as compared with the control patients over postoperative days 1 through 4 (p less than 0.001). Although there was no significant difference between groups with respect to episodes of ventricular arrhythmias, there was a significant decrease in the number of episodes of atrial fibrillation in the group receiving magnesium therapy (p less than 0.02). There were no recognized adverse effects of magnesium therapy. Prophylactic magnesium administration seems to lessen the incidence and severity of atrial fibrillation after coronary artery bypass grafting.     

Influence of cardiac pacing on graft flow following aortocoronary bypass surgery--comparison of ventricular and atrial pacing

To evaluate the influence of cardiac pacing on hemodynamics and graft flow dynamics following aortocoronary bypass surgery, we measured vein graft flow, systolic and diastolic graft flow volume along with blood pressure and cardiac output during atrial and ventricular pacing in 20 patients, 26 grafts. During ventricular pacing, systolic blood pressure showed a significant decline of 17% at the minimum pacing rates (101 +/- 9/min), 17% and 21% at the pacing rates of 120 and 140, respectively (p less than 0.01) in comparison with the original heart rates (96 +/- 8/min). The cardiac output also decreased significantly (p less than 0.01) during ventricular pacing. Graft flow at the original heart rates was 86 +/- 22 ml/min and the graft flow at the minimum pacing rates, at the pacing rates of 120 and 140 decreased to 73 +/- 20, 75 +/- 21, 74 +/- 23 ml/min (P less than 0.01), respectively. These reduction in the graft flow were caused by a decrease in diastolic graft flow (p less than 0.01). In the patients with a history of myocardial infarction, ventricular pacing brought about much more decrease in blood pressure, cardiac output and graft flow volume than those in patients without myocardial infarction (p less than 0.01). During atrial pacing, no significant change was observed in blood pressure and cardiac output. The graft flow was 86 +/- 21 ml/min at the original heart rates and it increased to 93 +/- 24 at the pacing rates of 120 and 95 +/- 26 ml/min at the pacing rates of 140 (p less than 0.01). These increase in graft flow during atrial pacing were attributable to an increase in diastolic graft flow (p less than 0.05). These findings suggest that the atrial pacing following aortocoronary bypass surgery brings about the beneficial effects on coronary perfusion compared with ventricular pacing.     

Determinants of cardiac failure after coronary bypass surgery within 30 days of acute myocardial infarction

Timing of coronary artery bypass grafting after acute myocardial infarction (MI) is controversial, especially if myocardial function is depressed. Early coronary artery bypass grafting may result in reperfusion injury causing cardiac failure. Delay, however, may risk a second ischemic event. This study was performed to determine if four preoperative factors--time after MI, ejection fraction, ischemia (need for intravenous administration of nitroglycerin), and failure (need for inotropic support)--independently predict postoperative cardiac failure. Postoperative failure was defined as the need for inotropic support or intraaortic balloon pumping. The study group consisted of 145 patients who underwent isolated coronary artery bypass grafting between January, 1980, and July, 1985, within 4 weeks of an acute MI. Postoperatively 38 patients (26%) had cardiac failure. Five patients, all of whom had postoperative cardiac failure, died. Univariate and stepwise logistic regression analyses showed preoperative failure (p = .0001), ejection fraction less than 45% (p = .002), and preoperative ischemia (p = .02) were predictors of postoperative cardiac failure. Time after MI was not found to be an independent predictor (p = .96). We conclude that if ischemia or threatening coronary anatomy is present early after MI and clinical improvement is not occurring, operative intervention should be strongly considered at that time, as it does not appear that delay itself reduces the risk of cardiac failure and may risk a second ischemic event.     

Impact of unstable angina on operative mortality with coronary revascularization at varying time intervals after myocardial infarction

We have performed a retrospective study of patients undergoing coronary artery bypass grafting for postinfarction angina in an effort to determine the influence of recency of myocardial infarction and unstable angina on operative mortality. Time from myocardial infarction to bypass was arbitrarily divided into five intervals. Nine hundred ninety-three patients having isolated coronary bypass for postinfarction angina were analyzed, and a significant trend of increased operative mortality with recency of myocardial infarction was found (p less than 0.001). When patients were operated on during the time interval zero to 24 hours after infarction, the operative mortality rate was 18.6%. In the interval from 1 day to 1 week after infarction, the operative mortality rate was 7.4%; 1 week to 3 weeks, 5.9%; and 3 weeks to 3 months, 2.7%. In patients operated on more than 3 months after infarction, the operative mortality rate was 3.9%. The operative mortality rate in 360 patients with postinfarction stable angina was 0.83% compared with 7.3% in 633 patients with postinfarction unstable angina (p less than 0.001). Of 18 risk factors tested, 12 were found by univariate analysis to be independent predictors of operative mortality, including recency of myocardial infarction and unstable angina. Stepwise logistic regression analysis of independent predictive variables revealed that unstable angina, previous surgical revascularization, preoperative hypotension, nonelective surgery, preoperative cardiac arrest, and female sex were the strongest predictors of mortality; recency of myocardial infarction was not a factor. When acute surgical reperfusion is not the primary treatment strategy for patients with myocardial infarction, operative mortality with coronary bypass is increased with the recency of myocardial infarction. The reason for this increase in operative mortality is a patient selection process in which those with persistent or intermittent myocardial ischemia, as reflected in the clinical syndrome of unstable angina, are selected for operation. Unstable angina is a major determinant of operative mortality after myocardial infarction. In patients with stable angina, operative mortality is not increased by the recency of myocardial infarction.     

Postoperative myocardial ischemia in patients undergoing coronary artery bypass graft surgery. S.P.I. Research Group

Cardiac morbidity and mortality after coronary artery bypass graft (CABG) surgery continue to be significant problems. To determine the prevalence, characteristics, and prognostic importance of postoperative myocardial ischemia after CABG surgery, the authors monitored 50 patients continuously for 10 perioperative days with the use of two-lead electrocardiography (ECG). ECG changes consistent with ischemia were defined as a reversible ST depression of 1 mm or greater or an elevation of 2 mm or greater from baseline, lasting at least 1 min. Baseline was adjusted for positional changes and temporal drift. All episodes were verified, with the use of the ECG monitor printout (ECG complexes), by two independent blinded investigators. Clinical care was not controlled by study protocol, and clinicians were unaware of the research data collected. Twenty-six of 50 patients (52%) had 207 episodes of perioperative ischemia (3,409 ischemic minutes). Postoperatively, ischemia developed in 48% of patients, compared with 12% preoperatively and 10% intraoperatively before bypass. Postoperative ischemia was most common in the early period (postoperative days [PODs] 0-2; 38% of patients), peaking during the first 2 h after revascularization, and less common during the late postoperative period (PODs 3-7; 24% of patients). Almost all (120 of 122; 98%) postoperative episodes (after tracheal extubation) were asymptomatic: only 9 of 70 (13%) early episodes were detected by clinical ECG monitoring. Postoperative ischemia did not appear to be related to acute changes in myocardial oxygen demand: only 39% of the postoperative episodes were preceded by a greater than 20% increase in heart rate. However, tachycardia persisted throughout the postoperative week (22-33% of all heart rates greater than 100 beats per min), and patients with postoperative ischemia (POD 0) more frequently had tachycardia (median 43% vs. 12% of the time; P less than 0.01). Five adverse cardiac outcomes occurred on the day of surgery; all five were preceded by postoperative ischemia, three by intraoperative ischemia before bypass, and none by preoperative ischemia. Patients with late postoperative ischemia did not have an adverse cardiac outcome. The authors conclude the following: 1) ischemia is more prevalent postoperatively than preoperatively or intraoperatively before bypass; 2) the incidence of postoperative ischemia peaks shortly after revascularization, during which time it is symptomatically silent, difficult to detect, and related to adverse cardiac outcome; 3) late postoperative ischemia also is silent, but it is less prevalent and not associated with in-hospital adverse cardiac outcome; and 4) a relationship between ischemia and persistently elevated postoperative heart rate may exist and warrants additional investigation.     

The Role of Myocardial Perfusion Scanning, Heart Rate Variability and D-dimers in Predicting the Risk of Perioperative Cardiac Complications after Peripheral Vascular Surgery

OBJECTIVES: To study the value of a number of proposed prognostic factors in prediction of the risk of perioperative cardiac events after vascular surgery. DESIGN AND METHODS: Two hundred and ninety-seven patients undergoing peripheral vascular surgery were prospectively studied. Patients underwent preoperative 24 h ambulatory electrocardiography, measurement of haemostatic variables, myocardial assessment of perfusion by dipyridamole-thallium scintigraphy and radionuclide ventriculography. The primary endpoint was cardiac death or nonfatal myocardial infarction within 30 days of surgery. A combined endpoint included the primary endpoint plus occurrence of cardiac failure, unstable angina or serious arrhythmias. RESULTS: The primary endpoint occurred in 21 (7%), and the combined endpoint in 41 (14%) of patients. On multivariate analysis, increased age, previous myocardial infarction, aortic surgery, impaired heart rate variability and a positive thallium scan were independent predictors of primary end-points. Preoperative atrial fibrillation and increased fibrin D-dimer were additional predictors of the combined endpoint. Construction of receiver-operator characteristic curves to examine the incremental value of predictive models showed that sensitivity and specificity of clinical data alone for primary endpoints was 71% and 72% respectively, while for the full model (incorporating heart rate variability and thallium data) this rose to 84% and 80% (p=0.0001). CONCLUSIONS: Preliminary screening using clinical data has limited value in risk assessment prior to vascular surgery but preoperative heart rate variability, D-dimers and thallium scanning provide modest incremental predictive value.