Significance of new Q waves after aortocoronary bypass surgery. Correlation with changes in ventricular wall motion

Serum cardiac troponin I after conventional and minimal invasive coronary artery bypass surgery

We evaluated myocardial release of cardiac troponin I (cTnI) in patients treated with conventional coronary artery bypass grafting (CABG), which employs extracorporeal circulation, and different kinds of minimal invasive coronary artery bypass grafting (MICABG), a surgical technique where the operation is performed without extra-corporeal circulation. Furthermore, we evaluated the usefulness of serum cTnI measurement to detect perioperative myocardial infarction (PMI) after coronary artery bypass surgery. Thirty-one patients were included: sixteen underwent CABG, fifteen underwent different MICABG and five patients had PMI. Blood specimens for cTnI measurements were collected up to 72 hours after opening the graft. Aortic cross-clamping time was a minor determinant of myocardial damage; on the other side, the trauma during surgery correlated with the number of involved arteries and with the manoeuvre employed to obtain heart dislocation, and appeared a more important determinant of myocardial damage. In patients with PMI, the cumulative release of cTnI was higher than in patients free from PMI; however, only after 24-72 hours we observed significant differences in serum cTnI values, because the increased perioperative values of cTnI complicated the interpretation of the myocardial status and a single cut-off could not be used to exclude PMI.

Comparison of some criteria for diagnosing a myocardial infarction after aorto-coronary bypass grafting (CABG)

The incidence of myocardial infarction during a 1-year follow-up period after coronary bypass surgery (CABG), i.e. a recent myocardial infarction (RMI), was studied in 86 patients. Different criteria for the diagnosis of a RMI were compared. Clinical observation, including ECG and serum enzyme analysis, diagnosed RMI in 8% of patients. Specific ECG changes indicating RMI (ECGsp) occurred in 12% of cases, and if less specific ECG changes were also taken into account (ECGsp+nonsp) RMI was found in 30% of cases. Asynergy, detected by two-plane ventriculography, indicated RMI in 24% of the patients, and was probably the most valid of the criteria examined. The differences in diagnostic accuracy of the various criteria highlight the importance of defining diagnostic criteria.

Infusion of nifedipine after coronary artery bypass grafting decreases the incidence of early postoperative myocardial ischemia

We performed a randomized study on patients undergoing elective coronary bypass grafting to examine whether postoperative infusion of nifedipine (n = 25) could reduce the incidence of isolated transient myocardial ischemia, myocardial infarction, or both. The control group (n = 25) received nitroglycerin. Hemodynamic and Holter monitoring and serial assessment of enzymatic and electrocardiographic changes were performed for all patients. Both groups showed comparable preoperative and operative data. The incidence of myocardial infarction was significantly lower in the nifedipine group (n = 1) as compared with the control group (n = 4), whereas the number of patients with isolated transient myocardial ischemia was similar in both groups (nifedipine, 3; control, 4). At the time of peak activity, levels of creatine kinase (350 +/- 129 versus 511 +/- 287 IU/mL), creatine kinase-MB (8.4 +/- 5.4 versus 17.1 +/- 11.0 IU/mL), and glutamate-oxaloacetate-transaminase (30.4 +/- 4.4 versus 41.0 +/- 7.9 IU/mL) were markedly lower in the nifedipine group (p less than 0.05). We conclude that infusion of nifedipine after elective coronary artery bypass grafting effectively decreases the incidence of myocardial infarction and the extent of myocardial necrosis during the early postoperative period.

Preoperative myocardial ischaemia: its relation to perioperative infarction

One hundred consecutive patients undergoing coronary artery bypass surgery were randomly allocated to a preoperative (24 h) intravenous infusion of isosorbide dinitrate (1.5-15 mg/hr) (50 patients) or to placebo (50 patients). The characteristics of the two groups were similar. Evidence of acute myocardial ischaemia was sought by continuous electrocardiographic Holter recordings and acute myocardial infarction by the appearance of new Q waves and increased activity of the creatine kinase MB isoenzyme. Episodes of acute myocardial ischaemia were found in 18% of patients in the control group and in none of those who received isosorbide dinitrate. None the less, the frequency of perioperative myocardial infarction was similar (22% and 18% respectively) in the two groups. Perioperative infarction was significantly more common in women, in patients with unstable angina or poor left ventricular function, in those who had coronary endarterectomy, and in those in whom the aortic clamping time was greater than 50 minutes. These factors may have obscured any effect that prevention of preoperative ischaemia had on perioperative infarction. Preoperative infusion of isosorbide dinitrate eliminated preoperative ischaemia but did not influence the occurrence of perioperative infarction. The probable benefits of prevention of preoperative ischaemia on postoperative left ventricular function, which is a determinant of long term survival, remain to be established.

Mechanisms of the development and resolution of paradoxical interventricular septal motion after uncomplicated cardiac surgery

Of 16 patients with normal preoperative left ventricular (LV) function studied by simultaneous two-dimensional and M-mode echocardiography before and after uncomplicated cardiac surgery, M-mode interventricular septal motion remained normal in seven (group I) and was paradoxical in nine (group II) 7 to 13 days postoperatively, but was normal in all 12 patients (7 group II) studied 3 to 18 months later. An abnormal systolic increase in normalized septal curvature, the essential feature of truly paradoxical septal motion, was not observed in either group during any study period (mean = 0.92 +/- 0.08), nor were significant differences found in septal thickening, LV fractional shortening, or fractional area change. In contrast, systolic anterior motion of the LV center increased from -0.1 +/- 1.6 mm preoperatively to 4.8 +/- 2.5 mm postoperatively in group II (p less than 0.001), and the LV posterior wall motion:thickening ratio increased from 1.10 +/- 0.33 to 2.16 +/- 0.45 (p less than 0.01), but both parameters had returned to preoperative levels at the follow-up study. Both parameters remained stable in group I during all study periods. In addition, direct intraoperative M-mode recordings (n = 14) demonstrated normal septal motion in both groups before chest closure, but esophageal echocardiograms (n = 10) demonstrated exaggerated anterior systolic LV motion within 2 hours of surgery in those from group II. Thus, early after uncomplicated cardiac surgery, apparently paradoxical septal motion relative to a fixed reference point is an artifact due to exaggerated cardiac mobility that resolves with the progressive restraining effect of postoperative adhesions.

Early results and complications of coronary artery bypass surgery. A consecutive series of 441 patients

The mortality rate and early complications of coronary artery bypass surgery were assessed for the first 441 consecutive patients operated on at Turku University Hospital. The overall hospital mortality rate was 2.5%. Perioperative myocardial infarction (PMI) accounted for more than half of the deaths, cerebral thromboembolism and sudden coronary death each for one-fifth and left ventricular failure for one-tenth. Postoperative complications occurred in 17.7% of the patients. Bleeding and postpericardiotomy syndrome were the most common complications (in 5.2 and 3.6% of the patients). Sternal resuture was needed in 3.2% of the patients, and PMI occurred in 2.9%. PMI had a 46% mortality rate, with two-thirds of the deaths occurring in the operating theatre. Only PMI reached statistical significance as sole cause of death. Mode of myocardial protection, completeness of revascularization and severity of coronary disease did not influence the PMI rate. Graft patency overall was 92.8% on average 3 months after surgery. The respective patency rates for internal mammary artery grafts and vein grafts were 90.3 and 92.9%.

Quantitative two-dimensional echocardiographic analysis of regional wall motion in patients with perioperative myocardial infarction

Regional left ventricular wall motion was evaluated by two-dimensional echocardiographic techniques with fixed- and floating-axis analytical algorithms in three groups of subjects: normal subjects (n = 15), patients undergoing uncomplicated coronary artery bypass graft surgery (CABG) (n = 10), and patients suffering perioperative myocardial infarction (n = 27). In patients undergoing uncomplicated CABG, fixed-axis analysis in the apical four-chamber view produced septal hypokinesis indistinguishable from the septal hypokinesis seen in patients with anterior myocardial infarction. In addition, fixed-axis analysis enhanced lateral wall motion so that patients with lateral myocardial infarction were classified as normal. Floating-axis analysis corrected these limitations by (1) producing regional left ventricular wall motion in the patients undergoing uncomplicated CABG, which was identical to that in normal subjects, and (2) producing regional left ventricular wall motion in patients with myocardial infarction that was hypokinetic in segments corresponding to the electrocardiographic area of involvement. In patients with new Q waves, fixed-axis analysis detected abnormalities of regional left ventricular wall motion in 24 of 34 (71%) electrocardiographically involved regions but also classified 44 of 100 segments in uncomplicated patients as abnormal. Floating-axis analysis detected regional left ventricular wall motion abnormalities in 30 of 34 patients (88%; p less than .05 vs fixed-axis analysis) and only 15 of 100 segments in patients undergoing uncomplicated CABG were classified as abnormal (p less than .001 vs fixed-axis analysis). We conclude that floating-axis analysis is a more accurate and clinically relevant method of evaluating regional left ventricular wall motion in patients undergoing CABG who suffer myocardial infarction as a perioperative complication.

Myocardial infarction related to coronary artery bypass graft surgery

Fifty consecutive patients undergoing coronary artery bypass grafting for chronic stable angina were assessed by serial electrocardiography, preoperative and postoperative myocardial scanning with technetium-99m pyrophosphate, gated radionuclide ventriculography, and serial measurement of creatine kinase, aspartate aminotransferase, urea stable lactic dehydrogenase, and creatine kinase isoenzyme (MB) to assess the incidence of perioperative myocardial infarction and identify the most appropriate diagnostic techniques. The correlation between myocardial scanning and the measurement of peak enzyme and isoenzyme activity was excellent in the diagnosis of perioperative infarction, although electrocardiography proved less helpful. There appeared to be no advantage in measuring creatine kinase MB rather than the more routinely measured enzymes. There were two deaths and evidence of myocardial infarction in five other patients, an incidence of 14%. Perioperative infarction was associated with a significant reduction in resting ejection fraction in two cases. In those patients without evidence of perioperative infarction the mean increase in ejection fraction of 7.8% was statistically significant.

Graft patency in patients with coronary artery bypass operation complicated by perioperative myocardial infarction

Coronary artery bypass graft patency was examined by contrast-enhanced computed tomography in 18 patients with perioperative myocardial infarction soon after surgery to determine the role of graft occlusion. Preoperative coronary angiograms were reviewed to assess native coronary disease and visible collateral channels in the distribution of the myocardial infarction. Perioperative myocardial infarction was diagnosed if creatine kinase-MB was elevated, characteristic electrocardiographic changes occurred and, in the majority of cases, the pyrophosphate scan was positive. Fourteen patients (78%) had patent grafts and perioperative myocardial infarction in the distribution of the grafted vessel. Four patients had an occluded graft with infarction in the distribution of the grafted vessel. Among the 14 patients with patent grafts, there was a significant difference (p less than 0.0005) in the degree of the mean (+/- standard deviation) diameter stenosis of 80 +/- 11% in native coronary vessels supplying the perioperatively infarcted myocardium versus a 55 +/- 12% mean diameter stenosis in the 23 bypassed native coronary vessels supplying noninfarcted myocardium. It is concluded that the majority of perioperative myocardial infarcts associated with coronary artery bypass operations are not caused by graft occlusion. The severity of coronary obstruction in the grafted vessel and the lack of collateral vessels to the region of perioperative infarction in patients with patent grafts suggests that an island of jeopardized myocardium exists that is subject to inadequate intraoperative preservation.

Relation between QRS changes and left ventricular function after coronary artery bypass grafting

Preoperative and serial postoperative electrocardiograms (ECGs) were reviewed in 104 patients undergoing rest and exercise radionuclide angiocardiography before and 1 to 12 months after coronary artery bypass grafting (CABG). Five patient groups were defined by ECG findings before and after CABG: Group I--normal ECG before and no ECG change after CABG; Group II--prior myocardial infarction by ECG before but no QRS change after CABG; Group III--all patients with a minor QRS change (less than 0.04-second Q wave, loss of R-wave amplitude) after CABG; Group IV--all patients with a major QRS change (greater than or equal to 0.04-second Q wave) after CABG; Group V--all patients without new Q waves or loss of R-wave amplitude but with a major QRS change (conduction disturbance) after CABG. Mean resting ejection fraction changed little after CABG in all groups, although the 0.03 increase in Group I was significant (p less than 0.05). Group IV had the largest decrease in resting ejection fraction after CABG (0.04), but this was not statistically significant. Mean exercise ejection fraction increased significantly (p less than 0.0001) in Groups I, II and III but not in Groups IV and V. QRS changes do not consistently reflect impairment of left ventricular (LV) function after CABG.

The definition of myocardial infarction during aortocoronary bypass surgery

In a study of 392 aortocoronary bypass (CABG) patients, we found 16 patients with a postoperative new Q wave, 29 patients with new intraventricular conduction disturbance, 17 patients with cardiogenic shock, and 14 patients with excessive CK-MB activity. Those criteria were considered as diagnostic of perioperative acute myocardial infarction (AMI). Listing the 392 patients in a Venn diagram: five patients had three positive criteria, eight had two, 43 had one, and 336 had none. Ventricular arrhythmia, supraventricular arrhythmia, or ST-T changes occurred in decreasing frequency in patients with a decreasing number of positive criteria. Five patients died postoperatively and in four a postmortem examination was available. Diagnostic criteria partly predicted autopsy findings. We conclude that the diagnostic criteria of perioperative myocardial infarction have a low diagnostic performance.

Use of survival analysis to determine the clinical significance of new Q waves after coronary bypass surgery

There are few data on the long-term effects of new Q waves on survival and morbidity after coronary bypass graft surgery (CABG). We followed 1340 patients who underwent CABG in 1978 at 10 hospitals participating in the Coronary Artery Surgery Study (CASS). The incidence of perioperative Q-wave infarction was 4.76% (range 0.0-10.3% by hospital). The rate of infarction was higher in patients who had an increased left ventricular end-diastolic pressure or cardiomegaly on the preoperative chest radiograph. Patients who received more grafts or who had longer cardiopulmonary bypass time were also at higher risk of infarction. In a stepwise discriminant analysis of 44 clinical, angiographic and surgical variables, cardiopulmonary bypass time, topical cardiac hypothermia and cardiomegaly entered the stepwise selection of variables. Long-term survival was adversely affected by the appearance of new postoperative Q waves. The hospital mortality was 9.7% in the 62 patients who had new postoperative Q waves and 1.0% in the 1278 patients who did not (p less than 0.001); the 3-year cumulative survival rates were 85% and 95%, respectively (p less than 0.001). In patients who survived to hospital discharge, the presence of new postoperative Q waves did not adversely affect 3-year survival (94% and 96%, respectively). The survival rates were worse in patients who had a history of infarction or who had impaired left ventricular function preoperatively. The number of readmissions to hospital after CABG among the patients who had a transmural perioperative infarction was similar to to that among patients who did not. We conclude that the appearance of new Q waves after CABG adversely affects survival. The major impact on mortality occurs before hospital discharge. Patients who are destined to have a perioperative infarct cannot be predicted from commonly measured preoperative and angiographic variables.

Effect of perioperative myocardial infarction on late survival in patients undergoing coronary artery bypass surgery

From the Seattle Heart Watch angiography registry, the baseline characteristics and late survival of 77 patients who sustained operative infarction (new Q waves) with myocardial revascularization were compared with 1790 patients who underwent coronary artery bypass without perioperative infarction. With the exception of coronary collateral vessels, which were less frequently seen in the patients with perioperative infarction, no baseline or operative characteristic distinguished between the two groups. Late survival was clearly adversely affected by perioperative infarction. Five-year survival was 76% in patients with perioperative infarction, compared with 90% in those with no perioperative infarction.

Serum CK-MB activity during and after aortocoronary bypass surgery

Frequent serum sampling of CK-MB and total CK levels was carried out in 100 patients during and up to 48 hours following aortocoronary bypass surgery. Using an ion exchange chromatography method for CK-MB determination, significantly higher serum CK-MB levels (peak 46.1 +/- 5.2 cf. 31.3 +/- 2.2 u/L), but not total CK levels were present 6 to 16 hours postoperatively in those with new Q waves in the ECG. Serum levels of CK-MB in those patients with uncomplicated surgery were defined. New post-operative Q waves were seen in only one half of cases with frankly abnormal CK-MB curves and seriously underestimated the incidence of perioperative infarction. Peak levels of CK-MB in patients with new Q waves occurred within 16 hours of surgery suggesting that infarction is usually an intraoperative or early post-operative event.

Predictors of perioperative myocardial infarction in coronary artery operation

Postoperative graft patency and thirteen perioperative variables were evaluated as potential risk factors for perioperative myocardial infarction (MI) in 102 consecutive patients undergoing coronary artery bypass grafting. Also, the incidence of perioperative MI and the amount of CK-MB released in the postoperative period were compared in three groups of patients selected according to the myocardial preservation technique employed: (1) topical hypothermia with and (2) without aortic cross-clamping and (3) cardioplegia. A perioperative MI as detected by electrocardiogram, enzymes, and myocardial scintigraphy with technetium 99 developed in 15 patients. Most important predictors of perioperative MI were found to be (1) left main and triple-vessel coronary artery disease, (2) a left ventricular end-diastolic pressure greater than or equal to 15 mm Hg, (3) a decreased ejection fraction (p < 0.05), and (4) cardiopulmonary bypass time > 120 minutes (p < 0.01). The incidence of perioperative MI was 50% in patients with three or more risk factors and 7% in those with less than three risk factors (p < 0.001). Graft patency was similar in patients with or without perioperative MI. Differing myocardial preservation techniques did not influence CK-MB release or the incidence of perioperative MI. Thus, the severity of ischemic heart disease and the length of the cardiopulmonary bypass time were important predictors of perioperative MI while graft patency and myocardial preservation technique did not appear to be related to its incidence in this study.

Diagnostic criteria for acute myocardial infarction in patients undergoing coronary artery bypass surgery

Current techniques for diagnosing perioperative myocardial infarction were studied in 58 patients who underwent coronary bypass surgery. All patients had preoperative and postoperative ECGs and technetium-99m stannous pyrophosphate myocardial scintigrams; serum CK-MB was measured immediately after surgery and daily for 3 days. Postoperative bypass graft visualization and left ventriculography were performed before hospital discharge in every patient. Nine patients (16%) had new Q waves postoperatively. Five of these nine patients had positive pyrophosphate scintigrams, postive CK-MB and new wall motion abnormalities, and the remaining four had negative CK-MB, negative phyrophosphate scintigrams and no new wall motion abnormalities. Seven patients (12%) had newly positive postoperative pyrophosphate scintigrams, positive CK-MB and new wall motion abnormalities on postoperative ventriculography, but only four had new Q waves postoperatively. Eight patients (14%) had new wall motion abnormalities; seven had positive pyrophosphate scintigrams and all had positive CK-MB, but only five had new Q waves. Sixteen patients (28%) had positive CK-MB, including all patients with either positive pyrophosphate scintigrams or new wall motion abnormalities, Eight patients had positive CK-MB without other evidence of perioperative infarction. A newly positive postoperative pyrophosphate scintigram is more senstive and specific than the development of new postoperative Q waves for the diagnosis of hemodynamically significatn perioperative myocardial in farction. CK-MB is highly sensitive, but too nonspecific to be useful for the diagnosis of perioperative infarction.

Perioperative myocardial infarction: a diagnostic dilemma

Patients undergoing coronary bypass grafting were studied for incidence of perioperative myocardial infarction (MI) using three modalities: serial electrocardiograms (ECG), serial creatine phosphokinase isoenzymes (MB-CPK), and serial technetium 99m-labeled pyrophosphate scans. A definite perioperative MI was diagnosed if the results were positive in two of the three variables studied. The perioperative infarction rate for the entire group was 8%. The operative mortality was 2.9%. Seven of 8 perioperative MIs were diagnosed by the use of scanning alone. The combination of isoenzyme and ECG analysis diagnosed 5 of 8 perioperative MIs. The MB-CPK and ECG studies were associated with a higher incidence of false-positive diagnoses than myocardial scanning. Patients with perioperative MI had a benign clinical course. Justification for performing three routine 99mTc-pyrophosphate scans on all patients undergoing aortocoronary bypass operation is still to be determined.

Relief of angina by periarterial muscle resection of myocardial bridges

A 47-year-old man presented with exertional angina. Selective coronary arteriography showed complete systolic segmental occlusion of the left anterior descending coronary artery producing milking effect. Permanent relief of symptoms was achieved by surgical excision of myocardial bridges. Postoperative angiography performed 11 months later was normal. Periarterial muscle resection should be considered in symptomatic patients with this rare anomaly.

Myocardial infarct imaging after cardiac surgery

One hundred and nineteen patients undergoing cardiac surgery had postoperative myocardial imaging performed with technetium pyrophosphate in order to assess the incidence of perioperative myocardial infarction. Fifty-six patients had only coronary artery bypass graft (CABG) surgery, of whom 13(23%) had a positive scintigram. Thirteen patients had CABG with other cardiac surgery and six (46%) had a positive scintigram. Fifty patients had other cardiac surgery but no CABG, and of these eight (16%) had a positive scintigram. The overall incidence of positive scintigrams was 23%, whereas definite or probable ECG diagnosis of infarction was present in 14 patients (12%). Serum levels of cardiac enzymes were higher in patients with positive scintigrams, but this finding did not consistently reach statistical significance. The use of a left ventricular vent during surgery did not correlate with a positive scintigram, nor did the total time on cardiopulmonary bypass or aortic cross-clamping. Patients having cardiac surgery, including CABG and valve replacement, have a 23% overall incidence of positive scintigrams. This suggests that the incidence of infarction after cardiac surgery is higher than can be recognized from the conventional criteria of ECG and enzyme changes.

Aortocoronary bypass grafting in the management of patients with coronary artery disease

There is widespread agreement that aortocoronary bypass grafting generally lessens the symptoms and functional limitations of patients with angina pectoris. Evidence for prolongation of life or prevention of myocardial infarction, arrhythmias and ventricular dysfunction is inconclusive. Harmful effects associated with surgical management of coronary artery disease can be documented in terms of operative mortality, perioperative myocardial infarction, graft occlusion and progression of occlusive disease in the native circulation. In this review of published experience, the accomplishments and the limitations of myocardial revascularization are considered in various clinical settings. Critical assessment of evolving information leads to the conclusion that widespread application of this procedure beyond the alleviation of symptoms refractory to medical therapy is not justified by present data.

The detection of perioperative myocardial infarction in aortocoronary bypass surgery

The incidence of myocardial infarction associated with aortocoronary bypass is difficult to determine because of widespread disagreement in evaluating the criteria for its detection. A prospective study consisting of 100 consecutive patients undergoing surgery for aortocoronary bypass was initiated. All patients were evaluated before and after surgery with electrocardiograms, heart scans of the infarct, and determinations of the level of the MB isoenzyme of creatine phosphokinase. A figure determined to be the upper limit of the expected rise in the level of the isoenzyme resulting from cardiac manipulation was selected, and 20 percent of the patients had more than the expected rise in the enzymatic level. Approximately one-half of these patients had abnormal ECGs or scans (or both) as well. The determination of the level of isoenzyme is very sensitive, and a normal level would exclude infarction. Elevations of concentrations of the enzyme due to minor myocardial cellular alterations are frequent. For this reason, in addition to an elevation of the concentration of the enzyme above the expected rise, the presence of an abnormal scan or ECG (or both) is necessary to make the diagnosis of perioperative infarction.

Haemodynamics during maximal exercise after coronary bypass surgery

Fifty patients underwent an objective measurement of physical working capacity by means of a multistage test of maximally tolerated exertion before and after coronary bypass surgery; 29 patients also had haemodynamic measurements during maximal exercise before and after coronary bypass surgery. The patients were divided into 3 groups according to the degree of revascularisation: adequate (n = 20), partial (n = 17), or none (n = 13). Adequate revascularisation induces a large increase in physical working capacity because of an increased maximal heart rate and maximal cardiac output; stroke volume during maximal exercise and ejection fraction at rest were not modified, suggesting no major changes in left ventricular function. After unsuccessful coronary bypass surgery, the physical working capacity was unchanged despite an increased maximal heart rate; maximal cardiac output was unchanged and stroke volume during maximal exercise was significantly lower. These undesirable results are often associated with perioperative myocardial infarction and are attended by a decreased ejection fraction at rest; these data suggest an impaired left ventricular function after unsuccessful coronary bypass surgery. The results of partial revascularisation are intermediate but appear to be determined by the incidence of partial graft failure which is also often associated with perioperative myocardial infarction. From individual changes in data collected during maximal exercise testing, it is often impossible to predict the degree of revascularisation.

Significance of new Q waves after bypass grafting: correlations between graft patency, ventriculogram, and surgical venting technique

New postoperative electrocardiographic Q waves have been described in eight of 40 per cent of patients undergoing bypass grafting for coronary artery disease. Various theories have been proposed to explain these new Q waves. Correlations of new Q waves to vein bypass occlusion, prolonged pump time or aortic cross-clamping time are controversial. Indeed, whether or not the appearance of new postoperative Q waves means real transmural myocardial infarction is not clear. We report herein our experience with postoperative Q waves in 56 patients with vein bypass grafts and the relationship of new Q waves to ventricular venting, graft patency, and the postoperative ventriculogram. Our observations indicate that: (1) Not all Q waves are due to occlusion of the saphenous bypass grafts (as noted by others). (2) A certain percentage of new Q waves may not reflect true transmural myocardial infarction, especially when all the vein grafts are patent and the postoperative ventriculograms show improvement. (3) Some new Q waves reflect true transmural infarction due to occlusion of grafts or of distal coronary arteries with deteriorated left ventriculograms. (4) The high incidence of new Q waves in patients with ventricular vents is probably due to direct myocardial trauma at the apex of the left ventricle.

Physiologic improvement following coronary artery bypass surgery

In this study the effects of coronary artery bypass surgery on ventricular function were evaluated at rest by quantitative analysis of segmental wall motion on cineventriculography, and during maximal treadmill exercise by measurement of serial cardiac outputs (Fick method) with the use of indwelling pulmonary artery and radial artery catheters. The patient had single vessel coronary disease and exertional angina. Following placement of a bypass graft to the proximally occluded left anterior descenting coronary artery, and despite the presence of arterial hypoxemia secondary to interstitial pulmonary fibrosis, a striking increase in maximal cardiac output occurred, mediated by a rise in both maximal heart rate and stroke volume. In this patient, resting ventricular volumes and ejection fraction were normal both before and after surgery, but preoperative abnormalities in extent of segmental wall motion, identified quantitatively, were restored to normal after bypass grafting. These investigations indicate that bypass surgery can provide substantial physiologic benefits in addition to providing subjective relief of anginal symptoms.

The application of radionuclide infarct scintigraphy to diagnose perioperative myocardial infarction following revascularization

To evaluate the application of radionuclide infarct scintigraphy to diagnose myocardial infarction after revascularization, we obtained postoperative technetium 99m pyrophosphate myocardial scintigrams, serial electrocardiograms and CPK-MB isoenzymes in ten control and 51 revascularized patients. All control patients had negative electrocardiograms and scintigrams, but eight had positive isoenzymes. Eight revascularized patients had positive electrocardiograms, images and enzymes and two had positive scintigrams and enzymes with negative electrocardiograms. Thirty-four patients with negative electorcardiograms and scintigrams had positive isoenzymes; in only seven patients were all tests negative. Our data suggest radionuclide infarct scintigraphy is a useful adjunct to the electrocardiogram in diagnosing perioperative infarction. The frequent presence of CPK-MB in postoperative patients without other evidence of infarction suggests that further studies are required to identify all factors responsible for its release.

Pathophysiologic significance of S-T and T wave abnormalities in patients with the intermediate coronary syndrome

The frequent association of new ST-T wave changes without Q waves in the surface electrocardiogram of patients with the intermediate coronary syndrome necessitates a better understanding of the pathophysiologic significance of this finding. A previous study in patients with stable coronary artery disease indicated that the surface electrocardiogram is insensitive in detecting epicardial Q waves. This relation was evaluated in 21 patients with the intermediate syndrome, characterized by recurrent chest pain at rest associated with significant new S-T or T wave abnormalities, or both, and no new Q waves in the surface electrocardiogram at the time of open heart coronary bypass surgery. Unipolar electrograms were recorded from the epicardial surface of the left ventricle before the bypass procedure. In 19 patients, epicardial electrograms revealed initial R waves over areas of the left ventricle in which the acute S-T and T wave abnormalities were evident in the surface electrocardiogram. Two patients had epicardial Q waves (one laterally and one inferiorly). In seven patients, a transmural biopsy specimen was also obtained from the ischemic area. All showed histologically normal myocardium without evidence of early inflammatory or necrotic tissue. Of the 19 patients discharged, only one demonstrated new postoperative Q waves that had been detected by epicardial recordings before bypass. In summary, patients with the intermediate syndrome exhibiting S-T or T wave abnormalities, or both without new Q waves in the surface electrocardiogram generally do not have Q waves either in the intraoperative epicardial or postoperative surface electrocardiogram. In addition, no histopathologic abnormalities are apparent in biopsy specimens taken from the ischemic area.

Detection of perioperative myocardial damage after coronary artery bypass graft surgery

In order to evaluate methods for detecting peri-operative myocardial damage we studied 41 patients before and serially following coronary artery bypass graft surgery utilizing the 12-lead ECG, serum MB-CPK measurements, and 99mTc pyrophosphate myocardial scans. Six of the 41 patients (15%) developed persistent new Q waves after surgery. Six other patients demonstrated ischemic ST-T wave changes that persisted for 48 hours or more. Mean total MB-CPK released was highest for the group with new Q waves [1598+/-545 (SE) I.U./L-hr] as compared to the group with ischemic ST-T wave changes 708+/-65 I.U./L-hr) or the group with no ECG changes (262+/-47 I.U./L-hr). Ten patients (24%) has positive postoperative pyrophosphate scans consistent with myocardial infarction. The three techniques were compared in these 41 patients utilizing 465 I.U./L.-hr as the upper limit of normal MB-CPK released after uncomplicated coronary bypass surgery (no ECG changes, negative scan). Five patients with ischemic ECG changes had a positive scan and high MB-CPK; six patients with no ECG changes had high MB-CPK but a negative scan; and one patient with high MB-CPK and new Q wave had a negative scan. We conclude 1) new Q waves on ECG underestimate the incidence of myocardial damage after coronary artery surgery; 2) MB-CPK alone overestimates the incidence of infarction; and 3) a combination of the three techniques is the best means for detecting myocardial damage after coronary artery bypass graft surgery.