Exercise testing early after myocardial infarction: historic perspective and current uses

Cocaine effects on digital blood flow and diffusing capacity for carbon monoxide among chronic cocaine users

PURPOSE

To determine the acute effects of intravenous (i.v.) cocaine on primarily digital skin blood flow and diffusion capacity for carbon monoxide (CO), and secondarily on subjective and cardiovascular measures.

PATIENTS AND METHODS

A double-blind, Latin-square, placebo-controlled, dose-response study was conducted in an inpatient general clinical research center and clinical pharmacology unit of a university teaching hospital. Twelve adult males with histories of illicit drug use including i.v. cocaine received 0, 25, and 50 mg of i.v. cocaine given as 1-minute infusions, on 3 consecutive test days. Digital cutaneous blood flow was determined via laser doppler flowmetry and skin temperature. Diffusing capacity for carbon monoxide (DCO) was measured with standard techniques. Subjective responses were measured by oral report of a numerical ranking of strength of drug effect. Heart rate and blood pressure responses were measured by electronic sphygmomanometer.

RESULTS

A maximal decrease in skin blood flow occurred at 2 to 3 minutes after infusion, and was not distinguished among drug conditions. Blood flow returned to baseline more rapidly after placebo than after cocaine: 7 minutes (placebo), 35 minutes (25 mg cocaine), 50 minutes (50 mg cocaine). Skin temperature decreased by 1.25 degrees C after placebo and by 2.75 and 3.25 degrees C after 25 and 50 mg of cocaine, respectively. DCO changed by -1.02 (mean) +/- 0.25 (standard deviation), 0.16 +/- 1.22, and 0.21 +/- 1.63 ml/min/mm Hg following placebo, 25, and 50 mg of cocaine, respectively. Typical subjective, chronotropic, and pressor responses to cocaine were demonstrated, and these occurred in close temporal relationship to digital blood flow and skin temperature responses.

CONCLUSIONS

The digital cutaneous circulation is highly sensitive to vasoconstrictor effects of cocaine. Pulmonary blood volume tends to be preserved after i.v. cocaine. Subjective effects and cardiovascular responses occur in concert with peripheral blood flow changes. The peripheral vasoconstrictor effects have implications for cocaine users with concurrent vasospastic or vasculopathic disorders.

Early discharge in the thrombolytic era: an analysis of criteria for uncomplicated infarction from the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries (GUSTO) trial

OBJECTIVES

This study sought to readdress the definition of uncomplicated myocardial infarction and to apply clinical criteria for early discharge of such patients in the thrombolytic era.

BACKGROUND

Previous studies proposed early hospital discharge at day 7 to 10 after acute myocardial infarction. The potential for earlier discharge of patients with uncomplicated infarction after thrombolysis remains undemonstrated.

METHODS

We defined "uncomplicated infarction" a priori as the absence of death, reinfarction, ischemia, stroke, shock, heart failure (Killip class > 1), bypass surgery, balloon pumping, emergency catheterization or cardioversion or defibrillation in the first 4 hospital days. We applied this definition to 41,021 patients in the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries (GUSTO-I) trial. We examined death at 30 days and 1 year and rates of in-hospital reinfarction, heart failure, recurrent ischemia, shock and stroke in the uncomplicated and complicated groups created by application of our definition. We also assessed lengths of hospital and cardiac care unit stay.

RESULTS

Application of our clinical criteria yielded 23,497 (57.3%) patients in the uncomplicated group at day 4 with a very low risk of death and in-hospital complications: 30-day mortality 1%, reinfarction 1.7%, heart failure 2.6%, recurrent ischemia 6.7%, shock 0.4% and stroke 0.2%. One-year mortality was 3.6%. The median hospital stay was 9 days (7, 12 [25th, 75th percentiles, respectively]), and the median cardiac care unit stay 3 days (3, 5).

CONCLUSIONS

Simple clinical characteristics can identify a very low risk post-myocardial infarction population by hospital day 4. Use of these criteria for early discharge planning could substantially reduce length of stay for patients with uncomplicated acute myocardial infarction.

Left ventricular function in myocardial infarction. Predictive value during negative low-level exercise three weeks postinfarction

To evaluate whether the response of left ventricular pump function during low-level exercise in the early postinfarction period can anticipate its change during the first year after acute myocardial infarction (MI), global and regional ejection fractions (EF) were investigated using radionuclide angiography in 52 consecutive patients with negative predischarge exercise test. The changes in left ventricular EF and regional EF of the noninfarcted area during the early exercise test had a good linear relation with the changes during the first year after MI (r = 0.86, p less than 0.001 and r = 0.81, p less than 0.001, respectively). Our results indicate that the mobilization of the Frank-Starling mechanism and myocardial contractility were the important factors related to the change of left ventricular EF, and that the changes of left ventricular EF during exercise in the patient with a negative predischarge exercise test can predict the direction of change (concordant rise or fall) during the first year after MI.

The predictive value of silent ischemia at an exercise test before discharge after an episode of unstable coronary artery disease. RISC Study Group

The prognostic value of silent ischemia during a symptom-limited predischarge exercise test (ET) was evaluated in 740 men after an episode of unstable angina or non-Q wave myocardial infarction. The 51% of patients with ST depression at the ET had a higher rate of myocardial infarction or death after 1 year (18%) compared with those without ST depression (9%; p less than 0.01). This increased risk was not influenced by the presence or absence of pain at the ET: 18.3% in patients with painful ischemia compared with 18.1% in patients with silent ischemia. However, ST depression combined with pain at the ET predicted a higher incidence of class III or IV angina at follow-up (43.9% compared with 16.7% in the group with asymptomatic ST depression; p less than 0.001). Because revascularization in addition to alleviating symptoms also enhances the prognosis in certain groups of patients, selections for coronary angiography and possible revascularization should not be made only on the basis of symptoms but also on the presence of myocardial ischemia, whether symptomatic or not.

Should the exercise test (ET) be performed at discharge or one month later after an episode of unstable angina or non-Q-wave myocardial infarction?

The diagnostic and prognostic value of symptom limited exercise tests (ET) performed before discharge and after one month were compared in men admitted to hospital after an episode of unstable angina or a non-Q-wave myocardial infarction (MI). A 'Positive ET' was defined as either a maximal work load below 100 W or ST-depression greater than or equal to 0.1 mV in 1-2 leads below 130 W or ST-depression greater than or equal to 0.1 mV in more than 2 leads at any load at the ET. During follow-up, severe angina was the only indication for coronary angiography and revascularization. There were no significant differences in diagnostic findings between the tests--Positive ET in 47% and Negative ET in 25% at both ETs. The occurrence of MI or death and the need of revascularization were related to signs of ischemia at both ETs. There were no differences in prognostic value between the early and late tests regarding MI or death or future severe angina during the 11 months' follow-up after the one month ET. However, half (10%) of the overall event rate (20%) during the one year follow-up occurred during the first months. The risk of these events could be identified by the predischarge but, for obvious reasons, not by the one month ET. Therefore, the present study suggests that a symptom limited ET should be performed before discharge in men stabilized after an episode of unstable angina or non-Q-wave MI.

Management of the patient following coronary thrombolysis

Myocardial salvage can be maximized by the early institution of thrombolytic therapy and aspirin. Certain patients may benefit from the administration of intravenous heparin, beta blockers, or nitroglycerin. The routine use of percutaneous transluminal coronary angioplasty (PTCA) or calcium-channel blockers does not appear to be warranted. Recurrent myocardial ischemia should be vigorously treated with medical therapy and there may be value in cardiac catheterization, followed by PTCA or bypass surgery, depending upon the extent of myocardium at risk and the underlying coronary anatomy. Long-term morbidity and mortality may be reduced by instituting aspirin and beta blockers as well as by modifying risk factors. There is no evidence for the long-term benefit from any calcium-channel blocker. Oral anticoagulation may be warranted in those patients with a mural thrombus, congestive heart failure, or atrial fibrillation. ACE inhibitors may be of value in the presence of left ventricular dysfunction and certainly in the presence of symptomatic congestive heart failure. Antiarrhythmic therapy is generally indicated only for symptomatic or life-threatening arrhythmias. Residual myocardial ischemia should be sought by exercise testing, and those patients with poor exercise tolerance generally warrant cardiac catheterization in consideration for revascularization.

Safety and characteristics of exercise testing early after acute myocardial infarction

Five hundred and seventy physicians, researchers and clinicians (42% response) responded to a mailed questionnaire about the safety and nature of exercise testing conducted less than or equal to 4 weeks after acute myocardial infarction (AMI). Of 570 institutions, 193 reported that they routinely performed testing early after AMI and data were provided on 151,949 tests. A majority (111 or 58%) used a low-level testing protocol, 50 (26%) used symptom-limited testing and 32 (16%) used both types. Testing was routinely conducted less than or equal to 14 days after AMI by 147 (76%) respondents, whereas 46 (24%) tested 15 to 28 days after AMI. Thirty-three (17%) respondents used a standardized research protocol and 160 (83%) did not. There were 41 (0.03%) fatal, 141 (0.09%) major nonfatal and 2,124 (1.4%) other cardiac complications reported during testing. No difference in incidence of major complications was observed at centers using a clinical versus research protocol. Compared with clinic-based testing, hospital-based testing had an increased risk for all major (2.1) and nonfatal major complications (2.1). Although a symptom-limited protocol increased the overall risk for major cardiac complications by 1.9 times compared with a low-level protocol, the incidence of fatal complications during symptom-limited testing (0.03%) was quite low and this greater risk is of dubious clinical importance.

Rehabilitation of the patient with coronary heart disease. New information for improved care

The benefits of early ambulation and predischarge exercise testing for stable patients after acute myocardial infarction have been well documented. Early exercise testing can help stratify patients into risk categories; these can guide recommendations for further diagnostic testing for medical or surgical interventions, as well as suggest appropriate activity levels after hospital discharge. The scope of cardiac patients currently considered eligible for exercise rehabilitation is far greater than in the past. Exercise training can improve functional capacity, predominantly mediated by peripheral adaptations; guidelines must be developed for the exercise training and surveillance of severely ill and elderly coronary patients. Education in coronary risk reduction and counseling to limit psychosocial complications of coronary disease and encourage return to work when appropriate can improve the coronary patient's functional status and clinical outcome. Further research is needed to determine the rehabilitative needs of more severely impaired, medically complex patient subgroups and the most cost-effective means of delivering rehabilitative services.

Which exercise test variables are of prognostic importance post-myocardial infarction?

The prognostic value of parameters noted on pre-discharge exercise testing was assessed in 300 survivors of acute myocardial infarction. Exercise testing was performed at a mean of 9 days post-infarction. Each patient's data were studied for the presence of ST-segment depression or elevation greater than or equal to 0.1 mV in any of the 12 leads recorded, angina pectoris, exertional hypotension and duration of exercise. The patients were followed for a mean of 12 months and the incidence of death, reinfarction, angina pectoris, heart failure and coronary revascularization procedures was noted. All variables studied, other than the presence of exercise-induced ST-segment elevation, were significantly associated with the occurrence of subsequent cardiac events (P less than 0.001). Exercise-induced ST-segment depression identified 80% of patients who developed complications and was significantly more sensitive than any of the other variables as a prognostic marker (P less than 0.05). The finding of angina pectoris, an abnormal blood pressure response or a limited exercise tolerance in association with exercise-induced ST-segment depression heightened the prognostic implications of this variable.

A randomized controlled trial of hospital discharge three days after myocardial infarction in the era of reperfusion

To evaluate the feasibility and cost savings of hospital discharge three days after acute myocardial infarction, we screened 507 consecutive patients prospectively for clinical complications and exercise-test performance. Of 179 patients whose condition was classified as uncomplicated (no angina, heart failure, or arrhythmia 72 hours after admission), 126 underwent early exercise testing and 90 had no provocable myocardial ischemia. Eighty of these patients were randomly assigned to early (day 3) or conventional (days 7 to 10) hospital discharge. Seventy-six of them had received coronary reperfusion therapy (thrombolysis, angioplasty, or both). At six months of follow-up, there were no deaths or new ventricular aneurysms, and the early-discharge and conventional-discharge groups had similar numbers of hospital readmissions (6 and 10), reinfarctions (none and 5), and patients with angina (3 and 8). In the early-discharge group, 25 of 29 previously employed patients returned to work 40.7 +/- 21.9 days (mean +/- SD) after admission, as compared with 25 of 27 patients in the conventional-discharge group, who returned to work after a mean of 56.9 +/- 30.3 days (P = 0.054). The mean cumulative hospital and professional charges were $12,546 +/- 3,034 in the early-discharge group, as compared with $17,868 +/- 3,688 in the conventional-discharge group (P less than 0.0001). In carefully selected patients with uncomplicated myocardial infarction, hospital discharge after three days is feasible and leads to a substantial reduction in hospital charges. Before this strategy can be widely recommended, however, its safety must be confirmed in larger prospective clinical trials.

Exercise capacity prior to myocardial infarction relates inversely to enzyme activity during infarction

Epidemiological studies suggest that myocardial infarction occurs less commonly in physically fit individuals, indicating an inverse relationship between fitness and coronary arterial disease. In this study, the exercise capacity measured prior to infarction, was related to enzyme activity during subsequent infarction. Out of 512 consecutive male patients with acute infarction 35 were found who had previously performed an eligible exercise test. The exercise capacity was inversely related to enzymic activity during the infarction.

Exercise testing three days after onset of acute myocardial infarction

To determine the feasibility and predictive value of early exercise testing 72 hours after acute myocardial infarction, 109 consecutive patients who received reperfusion therapy were prospectively evaluated. In the group studied, in 87 (80%) the course was uncomplicated 3 days after admission, as defined by a lack of congestive heart failure, arrhythmias and angina, and 53 patients (49%) performed heart rate-limited (140 beats/min) treadmill exercise. These patients exercised for 7.9 +/- 3.4 minutes, achieving a heart rate of 129 +/- 11 beats/min and a systolic blood pressure of 151 +/- 27 mm Hg. The exercise test was not accompanied by any protracted ischemia, infarction or significant arrhythmias. Accompanying tomographic thallium-201 scintigraphy demonstrated a reversible perfusion defect in 14 patients (26%), no evidence for ischemia in 36 patients (69%) and an equivocal result in 3 patients (6%). Of the 14 patients with a positive exercise-thallium test result, 4 had an adverse clinical outcome of either reinfarction, postinfarction angina or ventricular tachycardia during hospital days 4 to 10; an adverse in-hospital outcome was not seen in the 40 patients with a negative exercise-thallium test result (p = 0.009). Thus, early exercise testing after acute myocardial infarction is safe in selected patients with an uncomplicated course and the test is predictive of in-hospital clinical outcomes.