Surgical Management of the Preinfarction Syndrome

Transcription

1 Surgical Management of the Preinfarction Syndrome Ernest A. Traad, M.D., Parry B. Larsen, M.D., Thomas 0. Gentsch, M.D., Arthur J. Gosselin, M.D., and Paul S. Swaye, M.D. ABSTRACT The indications for coronary reconstruction have been extended to include those patients with the preinfarction syndrome who have failed to respond to medical therapy. Preinfarction syndrome is characterized by: (1) rapidly progressive angina; (2) exacerbation of previously stable angina; and (3) recurrent bouts of coronary insufficiency. During a three-year period 60 patients with this syndrome ranging in age between 30 and 72 years underwent urgent or emergency bypass procedures. Twenty showed electrocardiographic evidence of previous myocardial infarction. Single-vessel disease (> 75% obstruction) was demonstrated by coronary angiography in 18, double-vessel disease in 14, and triple-vessel involvement in 28. The operative technique is described. Eight sustained an early and 5 a late myocardial infarction with 1 and 3 deaths, respectively. A detailed analysis of these patients is presented including restudies and pathological findings. Of the 56 survivors, only 2 continue to have incapacitating angina. From this experience we conclude that the surgical management of a selected group of patients with the preinfarction syndrome is associated with a lower mortality and an improved functional result when compared with the natural history of the syndrome. C oronary reconstructive surgery is currently employed for the treatment of patients with chronic coronary insufficiency. It provides relief of anginal symptoms in the majority of patients and is associated with a relatively low morbidity and mortality [S, 5, 11, 12, 16, 191. The indications for this procedure have now been extended to include a selected group of patients presenting with the preinfarction syndrome. The preinfarction syndrome may be defined as: (1) rapidly progressive angina of recent onset; (2) exacerbation of previously stable angina; and (3) recurrent bouts of protracted anginal pain unresponsive to nitroglycerin therapy and often associated with electrocardiographic changes of ischemia without significant enzyme elevation. The natural history of the syndrome is From the Department of Surgery and the Cardiopulmonary Laboratory, Miami Heart Institute, Miami Beach, Fla. Presented at the Nineteenth Annual Meeting of thc Southern Thoracic Surgical Association, Port of Spain, Trinidad, Nov. 2-4, We thank Dr. Minor Diiggan for his editorial assistance, Mr. Ted Bollrnann for his skilled help with the illustrations, and Mrs. Klara Soos and Mrs. Yvonne Kosenblatt for their secretarial assistance. We also wish to acknowledge Drs. Thomas Noto and Cesar Castillo of the Cardiopulmonary Laboratory, Mercy Hospital, Miami, for their assistance with the clinical material. Address reprint requests to Dr. Traad, Miami Hmrt Institute, 4701 N. Meridian Avc., Miami Beach, Fla VOL. 16, NO. 3, SEPTEMBER,

2 TRAAD ET AL. now receiving careful scrutiny; however, recent studies [lo, 13, 211 indicate that a high percentage of patients who experience it ultimately suffer an acute myocardial infarction followed by death. Patients with the preinfarction syndrome who come under our care are admitted to a coronary care unit, where immediate medical management is instituted by bed rest, narcotics, nasal oxygen, coronary vasodilators, sedatives, and anticoagulants [ 181. If the classic electrocardiographic and enzyme changes of acute myocardial infarction are not present, coronary cineangiography is performed on those individuals who fail to respond to medical therapy. It should be recognized, however, that many of these patients may have had a small myocardial infarction which we were unable to establish. Those who present with lesions suitable for a bypass procedure and who have adequate ventricular function undergo urgent or emergency operation, and such patients constitute the basis for this report. A critical analysis of the morbidity and mortality in these patients is presented below. Clinical Material Between late 1968 and July of 1972, we performed coronary reconstructive operations on approximately 650 patients. During this period a selected group of 60 required an urgent or emergency surgical procedure for the preinfarction syndrome. (Fewer than 5y0 of patients admitted with the syndrome were believed not to be candidates for operation on the basis of angiographic findings.) Our group comprised 47 men and 13 women ranging in age from 30 to 72 years (Table 1). Coronary cineangiography by the Sones technique demonstrated single-vessel lesions in 18 patients, doublevessel lesions in 14, and triple-vessel disease in 28. These lesions were mostly segmental and were considered significant if there was a 75y0 or greater obstruction of the lumen. Ventricular function was evaluated as satisfactory in 26, fair in 31, and poor in 3. None of these patients were in clinical congestive heart failure or had significant mitral valve dysfunction at the time they were studied. Preoperative electrocardiograms were interpreted as normal in 33 patients; there were nonspecific ST-T segment changes of myocardial ischemia in 7 instances and evidence of a previous old myocardial TABLE 1. SEX AND AGE DISTRIBUTION OF 60 PATIENTS WITH PREINFARCTION SYNDROME TREATED SURGICALLY Male Age Female or > 262 THE ANNALS OF THORACIC SURGERY

3 Surgical Management of Preinfarction Syndrome TABLE 2. FUNCTIONAL AND MORPHOLOGICAL DATA IN 60 PATIENTS WITH SURGICALLY MANAGED PREINFARCTION SYNDROME Ventricular Function Good (26 patients) Vessels Involved 1 vessel, 14 pts. 2 vessels, 5 pts. 3 vessels, 7 pts. Fair (31 patients) 1 vessel, 4 pts. 2 vessels, 8 pts. 3 vessels, 19 pts. Poor (3 patients) 1 vessel, 0 pts. 2 vessels, 1 pt. 3 vessels, 2 pts. AB = abnormality; MI = myocardial infarction; pts. = patients. Preoperative ECG Normal, 21 pts. ST-T AB, 4 pts. Old MI, 1 pt. Normal, 10 pts. ST-T AB, 4 pts. Old MI, 17 pts. Normal, 0 pts. ST-T AB, 1 Pt. Old MI, 2 pts. infarction in 20. Three patients developed electrocardiographic changes of evolving infarcts while awaiting operation and subsequently were found at operation to have areas of cyanotic, noncontractile myocardium (Table 2). Opwative Technique A single large right atrial cannula and ascending aortic inflow cannula were used to institute cardiopulmonary bypass employing a Bentley disposable bubble oxygenator with hemodilution and moderate hypothermia. After left ventricular decompression was established with a catheter passed through the mitral valve and through the right superior pulmonary vein, ventricular fibrillation was induced electrically. The distal saphenous vein-to-coronary artery anastomosis was then carried out with continuous 6-0 Tevdek during periods of ischemic cardiac arrest of less than 15 minutes duration. The proximal aortocoronary vein bypass anastomosis was performed with partial or total aortic occlusion using a triangular aortotomy and a running suture of 5-0 Tevdek. Extreme care was taken not to twist the vein graft, to determine its appropriate length, and to prevent kinking or undue tension. A Y-graft was usually constructed when the left anterior descending and circumflex arteries had to be revascularized, but more recently separate aortic origins have been the rule. When the left internal mammary artery-to-coronary artery anastomosis was created, 7-0 Tevdek was employed. To obtain a good outflow, mechanical endarterectomy in conjunction with a vein bypass was employed when necessary. Optical magnification was used during all these procedures. TYPEOFPROCEDURE Eighteen patients received a single aortocoronary vein bypass graft, 13 received double-vein bypass grafts, and 23 were provided with three or more vein bypass grafts. Mechanical endarterectomy of the distal right coronary artery was carried out in 6 individuals, and imbrication of significant left VOL. 16, NO. 3, SEPTEMBER,

4 TRAAD ET AL. TABLE 3. SURGICAL PROCEDURES WITH POSTOPERATIVE MYOCARDIAL INFARCTIONS AMONG 60 PATIENTS WITH PREINFARCTION SYNDROME No. of Procedure Patients Early MI Late MI Aortocoronary vein bypass Single 18 3 (1)b 2 Double (1) Triple Quadruple Left internal mammary bypass LIMA to LAD LIMA to LAD plus vein grafts Total Plus endarterectomy or repair or both; ventricular aneurysm was present in 10 patients. bnumbers in parentheses are deaths. LIMA = left internal mammary artery; LAD = left anterior descending coronary artery; MI = myocardial infarction. ventricular scars or aneurysm was also necessary in 6 patients. Left internal mammary artery-to-left anterior descending coronary artery anastomosis was carried out in 6 patients, and in 2 of them vein bypass grafts to the right coronary artery or the circumflex coronary artery or both were performed concurrently (Table 3). Results Mortality. There was 1 early death secondary to a massive anteroseptal myocardial infarction which occurred on the operating table after a saphenous vein bypass graft to the right coronary artery was performed. Three late deaths after discharge were also secondary to acute myocardial infarctions and occurred at 17 days, one month, and two months, respectively (Table 4). TABLE 4. DEATHS AMONG 60 PATIENTS WITH SURGICALLY MANAGED PREINFARCTION SYNDROME Time of No. of Causes & Death Patients Remarks Early 1 Late Total 4 Operative and secondary to undiagnosed lesion 17 days IWMI secondary to undiagnosed PDCA lesion 1 mo. IWMI; HRF 2 mo. IWMI secondary to vein graft occlusion (SFH) with patent LIMA to LAD Acute MI ~ ~ ~ IWMI = inferior wall myocardial infarction; PDCA = posterior descending coronary artery; HRF = high-risk factor; SFH = subintimal fibrous hyperplasia; LIMA = left internal mammary artery; LAD = left anterior descending coronary artery; MI = myocardial infarction. 264 THE ANNALS OF THORACIC SURGERY

5 Surgical Management of Preinfarction Syndrome TABLE 5. RESTUDIES AMONG 60 PATIENTS WITH SURGICALLY TREATED PREINFARCTION SYNDROME Ventricular Function No. of Patients No. of No. Unchanged or Restudied Grafts Patent Improved Worse 15 (7)" (4)" 3 (3)" "Numbers in parentheses are patients who suffered myocardial infarction postoperatively. Morbidity. An early myocardial infarction occurred in 8 patients (1 of whom died), while a late infarction was sustained by 5 patients (3 of whom died). The 3 individuals who showed evolving infarcts on their preoperative electrocardiograms had the process aborted; their postoperative tracings demonstrated only nonspecific ST-T changes. Other nonfatal complications occurred in 17 patients: arrhythmias in 4; congestive heart failure and lowoutput syndrome in 3; acute toxic brain syndrome in 2; pulmonary complications in 2; postcardiotomy syndrome in 3; and miscellaneous complications including wound sepsis, renal failure, and cardiac tamponade, respectively, in 3. Of the 56 survivors 43 are asymptomatic and well. Six have experienced a mild residual angina (New York Heart Association Functional Class 11), while 2 have had incapacitating angina. Adequate follow-up information is not available for the remaining 5 patients. Restudy. Fifteen patients were restudied. Only 7 were asymptomatic; the rest either had residual chest pain or had developed a postoperative myocardial infarction. Ten of these restudies were carried out from one week to one year after operation and 5 from one year to two years after operation. Out of a total of 25 grafts restudied, 17 were found to be patent. With 1 exception, each patient had at least one patent graft. In all but 3, ventricular function was either unchanged or showed improvement as determined by ventriculogram and ventricular end-diastolic pressures (Table 5). Postoperative Acute Myocardial In farctions Thirteen postoperative myocardial infarctions occurred in this series of 60 patients. Eight of the infarctions took place during the first 24 hours following operation, and 5 developed after discharge from the hospital. Seven patients were restudied, and 3 deaths were followed by postmortem examination. Table 6 summarizes the analysis of this group of patients with postoperative myocardial infarction. ILLUSTRATIVE CASE REPORTS Patient D. C. A 36-year-old woman with a history of three months of crescendo angina was found on cardiac catheterization to have a single, 90% localized stenosis of the proximal left anterior descending coronary artery with no collaterals between the right and left coronary arteries. She had good VOL. 16, NO. 3, SEPTEMBER,

6 TRAAD ET AL. TABLE 6. ANALYSIS OF POSTOPERATIVE ACUTE MYOCARDIAL INFARCTIONS AMONG 60 PATIENTS WITH SURGICALLY TREATED PREINFARCTION SYNDROME Cause of MI Time of MI Results Undiagnosed lesions Pt. W.G. Early Died Pt. H.K. Late (2 wk.) Died Pt. J. A. Late (3 mo.) Asymptomatic Complete occlusion of Y-vein bypass graft Pt. A.B. Early Mild angina (Class 11) Occlusion of secondary branch 01 Y-vein bypass graft Pt. M. F. Late (2 mo.) Mild angina (Class 1-11) Occlusion of single-vein graft Pt. D.C. Early Severe angina (Class 111) Pt. R. P. Late (2 mo.) Died Pt. E.R. Late (2 mo.) Asymptomatic Infarction with patent graft Pt. I. D. Early Asymptomatic Pt. M. B. Early Mild angina (Class 1-11) Poor-risk patients Pt. N.W. Early Died Pt. R. B. Early Asymptomatic Pt. W. B. Early Mild angina & CHF MI = myocardial infarction; CHF = congestive heart failure. left ventricular function (Fig. 1). Following insertion of a saphenous vein bypass graft to the left anterior descending coronary artery, the patient developed an acute anterior wall myocardial infarction and now has Class I11 angina. Repeat cardiac catheterization two months after operation revealed total occlusion of the vein graft with an unchanged underlying coronary artery and a residual anterior apical ventricular aneurysm (Fig. 2). A 13 FIG. 1. Patient D. C. (A) Severe localized obstruction involving proximal anterior descending coronary artery. (B) Left ventriculogram, end systole, demonstrating normal contractility. 266 THE ANNALS OF THORACIC SURGERY

7 Surgical Management of Preinfurction Syndrome A FIG. 2. Patient D. C. (A) Postoperative angiogram demonstrating previous severe lesion of anterior descending coronary artery with total obstruction of vein bypass graft. (B) Postoperative ventriculogram demonstrating anterior apical ventricular aneurysm. B Patient E. R. A 48-year-old man with a history of six weeks of crescendo angina had had a previous myocardial infarction in Cardiac catheterization revealed severe proximal stenotic lesions of the left anterior descending and circumflex arteries with an aneurysm of the lateral wall of the left ventricle. There was poor left ventricular function. This patient underwent emergency vein bypass grafting to the left anterior descending artery with imbrication of the left ventricular aneurysm. Three weeks after operation restudies were carried out because of persistent anginal pain. These revealed a filling defect in the middle third of the graft with a patent distal anastomosis. Two months postoperatively the patient developed an acute anterior wall myocardial infarction that was presumably due to complete occlusion of the partially stenosed vein graft. Patient 1. D. A 47-year-old man had a history of one month of crescendo angina. Despite intensive medical management, he experienced recurrent bouts of acute coronary insufficiency which prompted cardiac catheterization. The study revealed a 90% segmental stenotic lesion of the proximal anterior descending artery with normal left ventricular function (Fig. 3). There were no collaterals between the right coronary and left anterior descending arteries. He underwent an emergency myocardial revascularization approximately 10 hours after the onset of severe, continuous substernal chest pain that was unresponsive to narcotics. The classic electrocardiographic and enzyme changes of acute myocardial infarction were not present. A left internal mammary artery-to-anterior descending coronary artery anastomosis was carried out. An uncomplicated acute anteroseptal myocardial infarction was recognized immediately after operation. Five months later cardiac catheterization showed a patent left internal mammary-to-left anterior descending coronary artery graft and a VOL. 16, NO. 3, SEPTEMBER,

8 TRAAD ET AL. A FIG. 3. Patient I. D. (A) Severe lesion involving proximal anterior descending coronary artery. (B) Preoperative ventriculogram demonstrates normal contractility. small anterior apical ventricular aneurysm (Fig. 4). There was no progression of the underlying coronary disease. At present the patient is completely asymptomatic. ANALYSIS OF INFARCTIONS Analysis of these infarctions reveals several points. These include: B 1. The timing of surgical intervention in patients with acute coronary insufficiency is difficult. 2. It is essential that coronary cineangiography be done immediately preoperatively in all patients with acute coronary insufficiency because of the possibility of rapid progression of lesions. 3. Current diagnostic methods for recognizing early acute myocardial infarctions have limitations which must be recognized. A FIG. 4. Patient I. D. (A) Patent left internal mammary artery bypass to anterior descending vessel. (B) Small anterior apical left ventricular aneurysm. B 268 THE ANNALS OF THORACIC SURGERY

9 Surgical Management of Preinfarclion Syndrome 4. Despite evolving infarctions, patency of grafts and preservation of the myocardium can be accomplished. 5. The incidence of failure of Y-grafts may be higher than that of individual vein grafts arising from separate aortic origins. Except for 3 patients in whom coronary vascular occlusive disease was underestimated and bypass not performed, infarction was secondary to graft closure. 6. Early reoperation should be considered in those patients who continue to have symptoms postoperatively and who have angiographic evidence of graft occlusion and preserved ventricular function. 7. Unpredictable early and late subintimal fibrous hyperplasia of vein grafts can occur and lead to total occlusion of the graft. Recently in patients undergoing elective bypass grafting we have been using both internal mammary arteries more frequently for direct anastomosis with the coronary arteries. This technique may also be feasible and desirable for patients with preinfarction angina because of the proved greater functional durability of such grafts [9]. Comment Prodromal symptoms often provide time for medical management, diagnostic catheterization, and operation in patients who subsequently sustain a myocardial infarction. The reported incidence of patients with an acute myocardial infarction who have experienced preinfarction angina varies from 39 to 45y0 [22, 231. Hochberg [lo] and Solomon, Edwards, and Killip [21] have reported the presence of prodromal pain for a week or more in 65 and goyo, respectively, of patients who ultimately developed an acute myocardial infarction. Krauss, Hutter, and DeSanctis [ 131 recently reviewed 100 consecutive patients with acute coronary insufficiency who were followed for twenty months. The overall mortality in this group was ZZyo (13 sudden deaths presumably of cardiac origin and 9 due to myocardial infarction). Of those who survived the initial attack, 14yo had acute myocardial infarction and only 17y0 were asymptomatic. In this study 36 patients with exacerbation of preexisting angina or intractable anginal pain following 12 hours of hospitalization were at an even greater risk of developing acute myocardial infarction and dying. Other studies have been reported [7, 201 and confirm the high morbidity and mortality associated with the preinfarction state. It is this group of high-risk patients who most closely resemble our operative cases. The Charleston Heart Study [Z] examined the death rate in 795 patients with acute myocardial infarction who were followed for one year. The in-hospital mortality in this group was 18.6y0. The total mortality rate VOL. 16, NO. 3, SEPTEMBER,

10 TRAAD ET AL. for one year, including in-hospital deaths, was 30.5y0. Obviously with this rate of attrition it is well worthwhile to try to prevent the first infarction. The Framingham Study [S] showed that nearly one-half of deaths from an initial coronary attack are sudden and unexpected. While half of all the persons who died suddenly had no prior clinical manifestation of heart disease, most of the coronary deaths that were not sudden were preceded by indications of clinical cardiac disease. In many instances the pathology first became apparent shortly before the final episode. This fact emphasizes once again the importance of prodromal coronary insufficiency. If the natural history of severe proximal coronary artery disease is considered [ 171, single left anterior descending coronary artery lesions have a 4 to 5% one-year mortality; double-vessel involvement has a 6.5y0 one-year mortality; and triple-vessel lesions have a 10% one-year mortality. Single left anterior descending artery lesions have a lower but significant annual attrition rate, and a poor collateral blood supply to the totally occluded left anterior descending vessel appears to decrease chances for survival [ 171. Our series consists of patients with preinfarction syndrome who failed to respond to medical management. After every effort had been made to rule out acute myocardial infarction, coronary cineangiography and subsequent coronary bypass grafting were carried out. Most of these patients had multiple-vessel disease (42 out of a total of 60) while only 18 had critical single proximal lesions, of which 12 involved the left anterior descending artery without evidence of adequate collateral circulation. Ventricular contractility was poor in only 3 patients. Because we believed that our patients constituted a high-risk population, correction of the existing myocardial perfusion deficit by a coronary bypass procedure was therefore carried out to reduce the high mortality associated with the preinfarction state. Our overall mortality of 4 deaths among 60 patients is lower than that ascribed to the natural history of the syndrome. However, our experience, in contrast to that of others [l, 4, 6, 14, 151, is associated with a high incidence of postoperative myocardial infarction. The analysis presented above leads us to believe that this incidence can be reduced significantly if special attention is paid to the following points. 1. Coronary cineangiography should be obtained in patients with acute coronary insufficiency immediately prior to a bypass operation, even though past studies may be available. 2. Special efforts should be made to improve the interpretation and assessment of the existing anatomical lesions as visualized on the cineangiog-rams. 3. Careful selection of patients should be made; their hearts should have good distal runoff' and adequate ventricular contractility. 270 THE ANNAIS OF THORACIC: SURGICKY

11 Surgical Management of Preinfarction Syndrome 4. The bypass procedure should be carefully timed. 5. Use of Y-grafts with single aortic origins should be avoided. 6. Grafting to diffusely diseased or small secondary coronary branches should be avoided. 7. Vein grafts should be carefully harvested, and those that appear to be grossly diseased should be rejected. 8. Internal mammary artery grafts should be used more often, and their use is appropriate in patients whose clinical condition during operation permits the lengthy dissection necessary with this procedure. Refeyences 1. Colin, L. H., Fogarty, T. J., Daily, P. O., and Shumway, N. E. Emergency coronary artery bypass. Surgery 10:821, Death rate among 795 patients in first year after myocardial infarction. J.A.M.A. 197:906, Favaloro, R. G. Saplienous vein graft in the surgical treatment of coronary artery disease. J. Thorac. Cardiovasc. Szirg. 58: 178, Favaloro, K. G., Effler, D. R., Cheanvechai, C., Quint, R. A., and Sones, F. M., Jr. Acute coronary insufficiency (impending myocardial infarction and myocardial infarction): Surgical treatment by the saphenous vein graft technique. Am. J. Cardiol. 28:598, Favaloro, R. G., Effler, D. B., Groves, L. K., Sheldon, W. C., and Sones, F. M.,.Jr. Direct myocardial revascularization by saphenous vein graft: Present operative technique and indications. Ann. Thorac. Sztrg. 10:97, Flemma, R. J., Johnson, W. D., Tector, A. J., Lepley, D., Jr., and Blitz, J. Surgical treatment of Preinfarction angina. Arch. Intern. Med. 129:828, Fulton, M., Lutz, W., Donald, K. W., Kirby, 13. J., Duncan, B., Morrison, S. L., Kerr, F., and Julian, D. G. Natural history of unstable angina. Lancet 1:860, Gordon, T., and Kannel, W. B. Premature mortality from coronary heart disease: The Framingham Study. J.A.M.A. 215: 1617, Green, G. E. Internal mammary artery-to-coronary artery anastomosis: Tliree-year experience with 165 patients. Ann. Thorac. Surg. 14:260, Hochberg, H. M. Characteristics and significance of prodromes of coronary care unit patients. Chest 59:10, Johnson, W. D., Flemma, R. J., and Lepley, D., Jr. Direct coronary surgery utilizing multiple-vein bypass grafts. Ann. Thorac. Surg. 9:436, Johnson, W. D., Flemma, R. J., Lepley, D.,.Jr., and Ellison, E. H. Extended treatment of severe coronary artery disease: A total surgical approach. Ann. Swg. 170:460, 19G Krauss, K. R., Hutter, A. M., Jr., and DeSanctis, R. W. Acute coronary insufficiency: Course and follow-up. Arch. Intern. Med. 129:808, Lambert, C. J., Adam, M., Geisler, G. F., Verzosa, E., Nazarian, M., and Mitchel, B. F., Jr. Emergency myocardial revascularization for impending infarctions and arrhythmias. J. Thorac. Cardiovasc. Surg. 62:522, Lambert, C. J., Mitchel, B. F., Adam, M., and Geisler, G. F. Emergency myocardial revascularization for impending myocartlial infarctions. ~hesl 61:479, VOL. 16, NO. 3, SEPTEMIIER,

12 TRAAD ET AL Mitchel, B. F., Adam, M., Lambert, C. J., Sungu, U., and Shiekh, S. Ascending aorta-to-coronary artery saphenous vein bypass grafts. J. Thorac. Cardiovasc. Surg. 60:457, Moberg, C. H., Webster, J. S., and Sones, F. M., Jr. Natural history of severe proximal coronary disease as defined by cineangiography (200 patients, 7 year followup) (abstract). Am. J. Cardiol. 29:282, Nichol, E. S., Phillips, W. C., and Casten, G. G. Virtue of prompt anticoagulant therapy in impending myocardial infarction: Experiences with 318 patients during a 10-year period. Ann. Intern. Med. 50:1158, Reul, G. J., Morris, G. C., Jr., Howell, J. F., Crawford, E. S., and Stelter, W. I. Current concepts in coronary artery surgery: A critical analysis of 1,278 patients. Ann. Thorac. Surg. 14:243, Sachs, R. G. Prognosis of suspected acute myocardial infarction without acute ECG changes. Circulation 44 (Suppl. 11):11-220, Solomon, H. A., Edwards, A. L., and Killip, T. Prodromata in acute myocardial infarction. Circulation 40:463, Vakil, R. J. Preinfarction syndrome-management and follow-up. Am. J. Cardiol. 14:55, Wood, P. Acute and subacute coronary insufficiency. Br. Med. J. 1:1779, THE ANNALS OF THORACIC SURGERY