Update on mechanical intervention in acute myocardial infarction

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<ul><li><p>Update on mechanical intervention in acute myocardial infarction </p><p>The role of pharmacologic interventions in acute myocardial infarction (i.e., a combination of intravenous nitroglycerin, intravenous @-blocker, oral aspirin, and intravenous thrombolysis), has become more standardized, whereas the role of mechanical intervention remains to be defined. Mechanical intervention includes percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting. The number of carefully controlled, randomized trials is limited, particularly with surgery. Nevertheless, in optimal circumstances, when performed within the first few hours of myocardial infarction, surgery can be beneficial in reducing mortality, especially with anterior location of infarct. Surgery may not prevent reinfarctlon. However, the results of nonrandomized surgical trials done 10 years ago are difficult to compare with modern-day treatment of myocardial infarction with the availability of new agents and PTCA. Angloplasty can be performed safely in the acute phase of myocardial infarction but may not be the ideal choice for all patients. The results may be more optimal if performed when the patient is stable. Clinical factors associated with favorable and unfavorable outcomes have been identified. Mortality is not significantly affected by early versus late PTCA. Certain selected patients benefit from PTCA, particularly those in cardiogenic shock, in whom PTCA has made a dramatic improvement in outcome. To achieve maximal benefit, intervention should be performed early, within the first hours of symptoms. Further well-designed studies may help clarify the role mechanical techniques will play in future combinations of interventional therapy. (AM HEART J (1990;120:734.) </p><p>Stephen C. Vlay, MD. Stony Brook, A? Y. </p><p>The number of therapeutic options for the treatment of acute myocardial infarction has increased greatly during the past decade and now includes mechanical and surgical interventions-percutaneous translu- minal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG)-as well as medical treatments. Few cardiologists today would hesitate to initiate individual or combination therapy with in- travenous nitroglycerin, aspirin, intravenous meto- prolol, or thrombolysis in the typical patient with myocardial infarction meeting the standard criteria and having no contraindications to these treatments. However, the role of coronary angioplasty and bypass surgery is more controversial, as was the role of P-blockers and thrombolysis just a short time ago. The comparative efficacy of surgical and medical treatments continues to be assessed in large-scale studies, the results of which will form the basis for treatment recommendations. Of particular interest is </p><p>From the Division of Cardiology, Department of Medicine, State University of New York Health Sciences Center, Stony Brook. </p><p>Reprint requests: Stephen C. Vlay, MD, Associate Professor of Medicine and Director, CCU, Health Sciences Center T-17 020, SUNY at Stony Brook, Stony Brook, NY 11794-8171. </p><p>410122236 </p><p>whether the timing of surgical intervention or PTCA (acute or elective) affects the outcome in specific subsets of the myocardial infarction population. This article presents current views on the role of mechan- ical interventions in the treatment of acute myocar- dial infarction. </p><p>ROLE OF SURGERY (CABG) </p><p>Some insights into the comparative efficacy of CABG versus medical management may be gained by reviewing the results of a long-term study conducted in Spokane, Wash. 1, 2 This investigation involved 387 patients with myocardial infarction managed either medically or surgically who were followed for up to 13 years. Baseline variables, such as age, gender, infarct location, number of diseased vessels, and Killip clas- sification, were comparable between the two groups. </p><p>Overall mortality. The in-hospital mortality rate was 5.8% in the surgical group and 11.5% in the medical group (p &lt; 0.07). Long-term mortality rates (as- sessed at 10 to 13 years) were 27 % and 41% , respec- tively (p &lt; 0.0007). In both instances, the differences between the two groups were highly statistically sig- nificant. In addition, the surgical and medical groups had significantly different rates of sudden cardiac </p><p>734 </p></li><li><p>Volume 120 </p><p>Number 3 CABG and PTCA in acute myocardial infarction 735 </p><p>death-7.4% versus 17.5%) respectively (p &lt; 0.01). The mortality data were also analyzed according to </p><p>whether CABG was performed early (within 6 hours of symptom onset) or late (after 6 hours). The results revealed that patients who underwent surgery during the late phase of acute myocardial infarction had a mortality rate similar to that in the medically man- aged group. On the other hand, the mortality rate was only 2% among patients who underwent CABG within the first 2 hours. These data suggest that out- come can be improved if intervention is accom- plished early in the course of myocardial infarction and if the infarct-related artery is successfully opened. </p><p>Reinfarction rates. The analysis of reinfarction rates revealed no significant difference between the med- ical and surgical groups. This confirms the well- established observation that CABG does not prevent myocardial infarction. Among only subjects who ex- perienced recurrent myocardial infarction, the mor- tality rate was lower in the surgical arm of the study (p = 0.04). One explanation for the latter finding may be that surgery afforded more complete revascular- ization of vessels other than the infarct-related artery and thereby protected a greater area of myocardium. </p><p>Anterior versus inferior wall infarction. Analysis by location of infarction showed that mortality was sig- nificantly greater among patients with large amounts of jeopardized myocardium who were initially treated medically. The mortality rate was 50% among pa- tients with anterior wall Q wave infarctions com- pared with 3% among those with inferior wall in- farctions. </p><p>Anterior wall infarction. In patients with anterior wall infarctions, surgical therapy was associated with a better outcome in both in-hospital mortality and 13-year mortality. In addition, whether surgery was performed early or late made a significant difference. The 13-year mortality rate was 30% for patients re- ceiving early surgical intervention compared with 54% for patients treated medically (p = 0.0006). </p><p>Global ejection fraction was higher by 7 % to 10 % in patients receiving surgery than in patients treated medically. The ejection fraction was not significantly different in patients receiving early versus late surgi- cal intervention. </p><p>Inferior wall infarction. Overall in-hospital mor- tality was not significantly different for patients with inferior wall infarctions treated medically or surgi- cally (6.1% vs 4.6%), nor was there a significant dif- ference overall between the medical and surgical treatment groups in 13-year mortality. However, the Xl-year mortality rate was greatly affected by the timing of surgery; it was 19% for patients treated </p><p>with early surgery and 47% for late surgery, com- pared with a 32% mortality rate in the medical treatment group. In-hospital mortality was not as dramatically affected by early or late surgery. </p><p>The benefit of early surgery in the patients with inferior wall infarctions was also seen in the ejection fraction, which was 56% for patients treated with early surgery compared with 47 % for those receiving medical treatment (p &lt; 0.01). </p><p>Clinical implications. The results of this study sug- gest that surgical intervention may offer benefit in a specific subset of patients with acute myocardial in- farction. One must keep in mind, however, that these data were collected in 1979 before many of the cur- rently available medical therapies (most notably, thrombolysis) had been introduced. Consequently, the results cannot be extrapolated to the present medical armamentarium. A further consideration is the fact that this investigation was nonrandomized and uncontrolled. In light of these limitations, one may conclude that CABG may be performed safely and may substantially improve outcome but only in a carefully selected segment of the myocardial in- farction population. </p><p>ROLE OF ANGIOPLASTY (PTCA) </p><p>Over the past few years, several major studies have attested to the fact that PTCA can be performed safely and successfully during the acute phase of myocardial infarction. Various studies have com- pared outcomes from immediate and delayed PTCA and have evaluated the use of PTCA in conjunction with thrombolytic therapy and in special patient groups. Study end points include reocclusion and re- infarction as well as mortality. </p><p>Efficacy and mortality with PTCA. In a 1988 Duke University study, PTCA resulted in successful reper- fusion of the infarct-related artery in 94% of 342 patients.3 The procedure-related mortality rate was low (1.2 % ), and the in-hospital mortality rate (11% ) was similar to that which would be expected with medical management. The l-year survival rate was 87% among the overall study population and was 98% among patients who survived the hospitaliza- tion period. In addition, 84 % of patients had a l-year survival free of cardiac events, and 94 % experienced a l-year infarct-free survival. </p><p>Information on longer-term outcome emerged from work conducted at the University of Michigan in Ann Arbor. When performed within 4 hours of onset of symptoms, PTCA was associated with an in-hospital mortality rate of 11%.4 Among 293 patients (mean age, 55 years) who survived the hospitalization phase, the mean ejection fraction was 48%) multiple-vessel </p></li><li><p>736 Vlay September 1900 </p><p>American Heart Journal </p><p>disease was present in 53 % , and half had received thrombolytic therapy in addition to angioplasty. The l-year survival rate in this group was 96 % , and the 2-year survival rate was 94%. </p><p>Predictors of successful PTCA. A study reported by Ellis et a1.5 examined the results of PTCA in terms of factors that were associated with a favorable or un- favorable outcome. In this study population of mid- dle-aged men, 6 % of the patients were in cardiogenic shock. The mean ejection fraction was 46 % . The an- gioplasty procedure was associated with a success rate of 80%) which was slightly lower than in other University of Michigan studies. </p><p>Several factors were judged to be predictive of a favorable outcome: ejection fraction &gt;30 % , absence of anatomical features that might complicate the procedure (such as an arterial bend at the PTCA site), fewer than three diseased vessels, absence of total occlusion, and absence of additional stenoses. Angioplasty should be avoided if there is well-main- tained coronary flow and no reason to expect imme- diate reocclusion. </p><p>Features associated with a poor prognosis included the presence of coronary flow classified as less than TIM1 grade 1 or more than two risk factors for PTCA failure (i.e., poor ejection fraction, a bend at the pro- posed dilation site, or triple-vessel disease). When these factors are present, bypass surgery may be considered, if the patient is an otherwise suitable surgical candidate. </p><p>Acute versus elective PTCA. In a follow-up of pa- tients in a Duke University study who underwent PTCA on an acute or elective basis,6 the in-hospital reocclusion rate was notably higher when PTCA was performed in the acute phase than when it was done on an elective basis (p &lt; O.OOOl), whereas late re- stenosis (at 28 to 30 weeks) was slightly more com- mon after the elective procedure (p &lt; 0.0006). </p><p>PTCA after thrombolysis. The results of two large studies analyzing the use of PTCA in patients treated with tissue plasminogen activator (tPA) have greatly influenced trends in the management of patients with myocardial infarction. One of these was the Throm- bolysis and Angioplasty in Myocardial Infarction (TAMI) trial.7 Of the 386 patients treated, 288 were successfully reperfused by way of thrombolysis with tPA, 197 of whom were suitable candidates for PTCA. This latter group was randomized to undergo angioplasty either immediately or 7 to 10 days after admission to the hospital. </p><p>The reocclusion rates associated with immediate and delayed PTCA were 11% and 13 % , respectively, a difference that was not statistically significant. Neither group experienced a significant improve- </p><p>ment in left ventricular ejection fraction. Emergency PTCA was required in 16% of the patients who had been randomized to the elective procedure and in 5 % of those randomized to the immediate procedure. Among those assigned to delayed PTCA, 14% were judged not to require the procedure when they were reassessed at 7 to 10 days, probably because their thrombi had largely resolved. On the basis of these findings, the study team concluded that immediate angioplasty in the acute phase of myocardial infarc- tion offers no clear advantage over delayed angio- plasty. </p><p>Some observers have criticized this study because of the fact that the 96 patients who failed thrombol- ysis were not randomized. The investigators none- theless attempted immediate angioplasty in 86 of these individuals. Angioplasty was successful (de- fined as </p></li><li><p>Volume 120 </p><p>Number 3 CABG and PTCA in acute myocardial infarction 737 </p><p>differences were apparent with regard to infarct size or left ventricular ejection fraction. </p><p>In a 1989 report on a German study, Erbel et al.l described findings in patients who received intra- coronary streptokinase either alone or followed by immediate PTCA. The combined approach yielded an overall success rate of 69%; 9% of patients required repeat angioplasty, which was successful in 100% of cases. Among the patients treated with streptokinase alone, 21% required elective PTCA, which was successful in 86%. The incidence of re- occlusion and reinfarction and the 3-year mortality rate were similar in the two groups, again suggesting that immediate angioplasty is not warranted in most patients treated with thrombolytic therapy. </p><p>In yet another investigation at the University of Michigan, early PTCA was associated with a success rate of 73% in patients who had received throm- bolytic therapy; half this group had anterior wall infarctions.12 </p><p>In summary, the cumulative experience from these many trials has demonstrated several factors that correlate with in-hospital mortality associated with PTCA, specifically, ejection fraction of </p></li><li><p>738 Vlay </p><p>ries. The rate is higher in the elderly. The procedure carries a low mortality rate but is associated with some risk of complications, such as hypotension, ventricular fibrillation, bleeding, and the need for urgent surgery. </p><p>Patients do benefit from the present standard treatment for acute myocardial infarction, which in- cludes oxygen, morphine, sedation, and drug therapy with nitroglycerin, aspirin, P-blockers, and throm- bolytic agents. Mechanical intervention cannot be considered until a patient with hemodynamic com- promise has bee...</p></li></ul>