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Exercise and the heart: safety of medically supervised outpatient cardiac rehabilitation exercise therapy. A 16-Year follow-up

Barry A. Franklin, PhD

Cardiac Rehabilitation and Exercise Laboratories
Beaumont Rehabilitation and Health Center
Birmingham, Michigan, USA

The safety of physical training for coronary patients is largely based on two major surveys of cardiovascular events during outpatient exercise therapy. The initial survey involved 30 cardiac rehabilitation programs in the United States and Canada during a period from 1960 to 1977; 1 nonfatal and 1 fatal event occurred every 34,673 and 116,402 participant-hours, respectively.1 A larger survey of 142 US cardiac rehabilitation programs (1980 to 1984) reported 29 cardiovascular complications (21 cardiac arrests and 8 myocardial infarctions [MI]), including three fatal events, in the course of 2,351,916 hours of outpatient exercise training2. However, these complication rates, derived from an aggregate retrospective analysis of information from multiple centers elicited by questionnaire, are not necessarily generalizable to contemporary cardiac patients who receive more aggressive therapies and are generally older with more coexisting illnesses. The data from both surveys antedate the current use of risk stratification procedures, revascularization, and newer pharmacotherapies for coronary patients. No morbidity or mortality data were reported by gender, patient age, risk status, or time of event, nor was definitive information available regarding the effects of levels of medical supervision and electrocardiographic monitoring. To examine the safety of medically supervised outpatient cardiac rehabilitation therapy (phases 2 and 3) in a single center over a 16-year period (1982 through February 13, 1998), a retrospective review of actual patient exercise hours and major cardiovascular complications was carried out. The complications were defined as cardiac arrest or acute MI, with specific reference to patient characteristics, risk stratification criteria, and morning vs afternoon events.



The subjects in this study included 3,335 patients who were referred for exercise-based cardiac rehabilitation (phases 2 and 3) during a 16-year period between 1982 and February 13, 1998. Average age was 61.6 + 11.3 years; men made up approximately 70% of the population. Overall, referrals included MI, coronary bypass, and angioplasty patients, as well as patients with or without residual ischemia, compensated heart failure, cardiomyopathy, and threatening ventricular arrhythmias; patients with nonischemic heart disease; patients who had undergone pacemaker or cardioverter-defibrillator implantation, heart valve repair or replacement, and cardiac transplantation; elderly patients and medically complex patients taking multiple cardiac and other medications. Retrospective risk stratification was performed with the American Association of Cardiovascular and Pulmonary Rehabilitation criteria.3

Exercise Program
The William Beaumont Hospital Cardiac Rehabilitation Center, Birmingham, MI, is a large facility located in a renovated junior high school approximately 2 miles from the hospital. Between 1982 and February 13, 1998, the medically supervised exercise programs included phases 2 and 3 outpatient cardiac rehabilitation. The 4 to 5 morning and 2 afternoon phase 3 exercise classes were expanded in 1996 from 3 to 6 days per week giving participants two scheduling options: Monday, Wednesday, Friday or Tuesday, Thursday, Saturday. Ancillary program services include nutrition counseling, a psychosocial support group, a lipid clinic, and a smoking cessation program.

Patients are referred to the cardiac rehabilitation program by their attending physician typically 1 to 6 weeks after discharge from the hospital for MI, an acute coronary syndrome, or revascularization surgery. Entry exercise stress tests (low-level or symptom-limited) are generally required but may be waived (per physician request) for selected phase 2 candidates. The phase 2 cardiac rehabilitation program consists of 50-min aerobic exercise sessions using interval or circuit training performed 3 times per week for 4, 6, and 8 weeks for low, moderate, and high-risk patients, respectively, and includes continuous ECG telemetry monitoring and blood pressure measurements at rest and during exercise. Phase 3 has a similar exercise format but with instantaneous ECG4 and blood pressure monitoring (once a week). Patients are encouraged to enter the phase 3 program after phase 2 where they have access to a variety of arm and leg ergometers, treadmills, automated stepping simulators, cross-country skiing devices, and progressive resistance equipment. A swimming pool program serves as an added option. Compliance with the phase 2 and 3 programs averaged 83 and 66%, respectively.

Exercise Prescription
In each program, prescription heart rate and metabolic equivalent (MET [1 MET=3.5 mL O2/kg/min]) ranges are set at 50 to 80% of the peak achieved during exercise stress testing using the heart rate reserve5 method, or the heart rate of 10 beats per minute or more below the ischemic ECG (> 0.1 mV), or the anginal threshold.6 The rating of perceived exertion (on a scale of 6 to 20) is also used as an adjunct to heart rate as an intensity guide for exercise training.7 Exercise rated as 11 (fairly light) to 13 (somewhat hard) generally corresponds to the upper limit of prescribed training heart rates during the early stages of outpatient cardiac rehabilitation (phase 2); later, for higher levels of training (phase 3), ratings of 12 to 14 are appropriate. For phase 2 participants who have not yet undergone exercise testing, the target heart rate for training is prescribed at 20 to 30 beats per minute above standing resting heart rate. In phase 3, exercise stress tests are recommended annually to update the exercise prescription.

Supervisory gym staff included registered nurses, exercise physiologists/specialists, and exercise technicians trained in basic or advanced life support or both. Most were certified by the American College of Sports Medicine as an exercise specialist or program director or both.6 Crash carts with defibrillator, oxygen, and suction were available in the gym. Emergency response in-service training for staff is performed quarterly. Supervisory staff-to-patient ratios are approximately 1:4 and 1:15 in phases 2 and 3, respectively. These ratios are further complemented by student interns in training. Supervising physicians are immediately available for selected classes. A dedicated "red phone" connects the facility to the nearby emergency medical system.



Between 1982 and February 13, 1998, 292,254 patient exercise hours (45,679 phase 2; 246,575 phase 3) were recorded. Overall, 5 major cardiovascular complications (3 nonfatal MIs and 2 cardiac arrests) occurred. These involved 4 men and 1 woman (-X + SD age=58.0 ± 18.3 years) with a history of previous MI, bypass surgery, angioplasty, or combinations thereof (Table l). Estimated fitness levels ranged from 8 to 15 METs.8 Both patients who experienced cardiac arrest were successfully resuscitated; however, one (patient 3) died during the related hospitalization. Three of the five cardiovascular complications were during morning hours. All 5 complications occurred in phase 3 (total duration in the cardiac rehabilitation program ranged from 3 to 160 months). Accordingly, overall rates of major cardiovascular complications per patient exercise hours were 1 per 49,315 for phase 3 and 1 per 58,451 for phases 2 and 3 combined.

Using the American Association of Cardiovascular and Pulmonary Rehabilitation criteria for risk stratification 3 three patients (patients 1, 3, 5) were classified as high risk because of a reduced ejection fraction < 30%); (patient 5) had a history of malignant ventricular arrhythmias and an implantable cardioverter defibrillator, whereas (patients 2 and 4) were classified as moderate risk because of reversible perfusion defects, ischemic ST segment depression, or both. One of the two cardiac arrests occurred in a chronic intensity violator.

Table 1

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Pathophysiologic evidence suggests that vigorous physical exertion may evoke transient oxygen deficiency at the subendocardial level that is exacerbated by venous pooling in recovery (Fig l). Symptomatic or silent myocardial ischemia9 can alter depolarization, repolarization, and conduction velocity, triggering threatening ventricular arrhythmias which may degenerate into ventricular tachycardia or fibrillation. The risk of cardiac arrest during strenuous exercise, compared with that at other times, may be more than 100-fold greater during or soon after exertion.10 Other studies have shown that the risk of acute MI after strenuous exercise was two to six times greater than the risk during periods of lighter activity or rest.11,12

This study examined the incidence of cardiovascular complications of medically supervised cardiac rehabilitation exercise in a single center. Over a 16-year period, five major cardiovascular complications (2 cardiac arrests and 3 nonfatal MIs) resulted in a frequency of 1 major complication per 58,451 patient exercise hours, a figure that is lower than the rate of 1 per 26,715 reported by Haskelll in 1978 and slightly higher than the 1 per 81,101 patient exercise hours reported by Van Camp and Peterson2 in 1986. Recently, Vongvanich et al13 reported 4 major complications (3 cardiac arrests and 1 nonfatal MI) during 268,503 outpatient exercise hours, corresponding to 1 cardiovascular event per 67,126 patient exercise hours.

A comparative summary of reports regarding the incidence of serious cardiovascular complications in medically supervised cardiac rehabilitation programs since the mid-1980s is shown in Table 2.2,13,14 0ur results demonstrated a slightly lower rate of cardiac arrest (1 per 146,127 patient exercise hours) but a higher rate of acute MI (1 per 97,41.8 patient exercise hours). In one recent series, all three patients with cardiac arrest were successfully resuscitated by supervisory gym staff. 13 Similarly, both of the cardiac arrests noted in this study were successfully treated by nursing staff assisted by exercise physiologists-technologists and emergency medical service backup without direct gymnasium supervision by a physician (ie, in the exercise room). Further analysis of the most recent cardiac rehabilitation program survey revealed that 18 of 21 cardiac arrest patients (86%) were successfully resuscitated.2


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Fig.1: Physiologic alteration accompanying acute exercise and recovery and their possible sequelae. HR=heart rate: SBP=systolic blood pressure; MVO2 =myocardial oxygen uptake; CHD- coronary heart disease

Table 2

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All of the complications in this study occurred in moderate-to-high-risk patients, suggesting that contemporary risk stratification criteria can identify those at increased risk for exercise-related cardiovascular complications. Moreover, in a subsequent analysis of the previously referenced program survey, 16 of 20 cardiac arrest patients (80%) were categorized as high-risk coronary patients by standard risk stratification procedures.15 Ten of the 16 (63%) had multiple indicators of poor prognosis. In the present study, 4 of the 5 patients with complications had had recent treadmill evaluations with estimated fitness levels ranging from 8 to 15 METS. These findings, in agreement with previous reports,16 indicate that a deterioration in clinical status can occur despite regular exercise training and serial improvements in aerobic fitness. Although none of the complications in this study occurred during phase 2, it is difficult to attribute this to ECG monitoring per se, since these patients were more intensely supervised, had a lower exercise intensity, and accrued a smaller number of exercise hours. The present results also support previous studies in that cardiovascular complications appear to be unrelated to the duration in the program or time from the acute cardiac event.1,17-19 In this study, the duration of program participation for the 5 untoward events ranged from 3 to 160 months.

The safety of high-intensity exercise training regimens has been challenged in retrospective reports of coronary patients who developed cardiac arrest or ventricular fibrillation during or shortly after medically supervised rehabilitation exercise.17,19,20 Hossack and Hartwig 19 identified patients at increased risk of untoward events as those having a markedly ischemic exercise ECG, an above-average functional capacity, or a record of poor compliance to the prescribed training heart rate range. Similarly, Hambrecht et a121 reported a patient who experienced cardiac arrest after exceeding bis training heart rate by > 30% during group exercise, as documented by Holter monitoring. One of the two cardiac arrests in this study occurred in a chronic exercise intensity violator.

It has been suggested that a variety of pathophysiologic mechanisms for acute cardiac events are more likely to be operative during the early morning hours .22 These mechanisms include potential triggers of coronary artery plaque rupture and thrombosis such as circadian surges in heart rate, blood pressure, catecholamines, and hydrocortisone (cortisol); platelet aggregation; coronary vascular tone; plasma viscosi ; and fibrinolytic activity associated with awakening and assuming an upright posture. Superimposed physical stresses can accentuate these responses and thus heighten the risk of cardiovascular events .23 The rehabilitation program in this study offered 4 to 5 morning and 2 afternoon phase 3 classes and had 3 morning and 2 afternoon complications over a 16-year period. Similarly, an observational report of outpatient exercise rehabilitation that compared morning-hours exercise with afternoon-hours exercise reported an overall cardiac complication rate (syncope, arrhythmia, MI, or sudden death) of 3.0 per 100,000 patient-hours for morning patients and 2.4 per 100,000 patient-hours for afternoon patients, an insignificant difference .24

In summary, these results demonstrate a low frequency of major cardiovascular complications in a single center exercise-based cardiac rehabilitation program over a 16-year period ending in February 13, 1998. Direct physician presence during the sessions does not appear necessary for safety. Contemporary risk stratification criteria appear to identify patients at risk for exercise-related cardiovascular complications.



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Co-Authors: Kimberly Bonzheim, MSA; Seymour Gordon, MD; and Gerald C. Timmis, MD

Chest 1998,114:902-906, with permission.