This was a prospective randomized study performed in the period from April 2017 to April 2018. Informed consents were provided by all participants and institutional ethics committee approval was obtained.
The study was conducted on 60 adult ischemic heart disease patients who had recovered from an anterior wall STEMI managed by primary PCI and for whom complete coronary revascularization was performed using coronary angioplasty in the 6 months prior to enrollment. At the time of enrollment, all patients were free of angina or angina-equivalent symptoms and on guideline-directed medical therapy for ischemic heart disease titrated up to the maximal tolerated doses. The study protocol did not allow the type or dosage of lipid-lowering medications, beta-blockers, or other heart rate control medications to be changed for the whole duration of the study. If a change in dosage or type of the previous medications was deemed medically necessary, the patient would be excluded from the study.
All patients were enrolled in the outpatient phase 2 cardiac rehabilitation program provided at our institution. We randomized the patients using 1:1 allocation into two equal groups (30 each). One group joined the standard 12-week program provided at our institution with twice weekly sessions (low contact frequency). The other team joined a 6-week program with four weekly sessions (high contact frequency). The total number of sessions for all patients was the same (n = 24).
Patients were excluded from the study if they had any of the following: angina or angina-equivalent symptoms; non-revascularized significant coronary stenosis; recent (less than 1 month) acute coronary syndrome or MI; left ventricular ejection fraction (LVEF) less than 35%; New York Heart Association functional class III or IV [14]; recent (less than 1 month) acute myocarditis, pericarditis, or endocarditis; more than mild valvular stenosis or regurgitation; hypertrophic cardiomyopathy; current arrhythmias; history of pacemaker or intracardiac electric device implantation; moderate or severe pulmonary hypertension; chronic obstructive airway disease; chronic renal failure; any acute illness; history of transient ischemic attacks or cerebrovascular stroke; physical disabilities that would interfere with treadmill exercise training; previous participation in a cardiac rehabilitation program; changing the type or dosage of lipid-lowering medications, beta-blockers, or other heart rate control medications at any point during the study; or cognitive impairment.
Patient interviews and assessments
Patient interviews involved through history taking and clinical examination. Baseline patient demographics and risk factors for coronary artery disease were acquired. It was confirmed that patients were on guideline-directed medical therapy including a beta-blocker; an angiotensin-converting enzyme inhibitor or an angiotensin II receptor blocker; aspirin; and a lipid-lowering medication with titratable medications at maximal tolerated doses.
A venous blood sample was obtained after a 12-h fasting period to assess each participant’s lipid profile: total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) levels. The first three were measured using enzymatic methods, while LDL-C was defined using the Friedewald formula: LDL-C = [total cholesterol] − [HDL-C] − (1/5 triglycerides) [15].
Trans-thoracic echocardiography was performed using a Vivid 7 machine (GE Vingmed, Horten, Norway) using an M4S matrix-array probe with a frequency range of 1.7–3.4 MHz with the patient in the left lateral decubitus position. Echocardiography was performed by an individual accredited by the European Association of Cardiovascular Imaging. LVEF was calculated using the bi-plane Simpson’s method of discs from the apical 4- and 2-chamber views [16].
Cardiac rehabilitation program
Patients were enrolled into one of two 24-sessions cardiac rehabilitation programs. Both programs were managed by a team of cardiologists, nutritionists, physiotherapists, trained nurses, and psychiatrists.
The 12-week (low contact frequency) program
This is the standard program offered at our institution which involves twice weekly supervised exercise training sessions over a 12-week period.
Each session had 5–10 min of warm up, at least 20 min of aerobic treadmill training, and 5–10 min of cool down. Sessions would last up to 40 min towards the end of the program.
Patients’ exercise intensity was gradually increased from 50 to 80% of the heart rate reserve.
The 6-week (high contact frequency) program
This program involved four times weekly supervised exercise training sessions over a 6-week period.
Each session had 5–10 min of warmup, at least 20 min of aerobic treadmill exercise training, and 5–10 min of cool down. Sessions lasted up to 40 min towards the end of the program.
Patients’ exercise intensity gradually increased from 50 to 80% of heart rate reserve according to each patient’s ability.
Cardiac rehabilitation session design
Both programs included group teaching sessions about coronary artery disease and risk factor modification, in addition to, nutritional counseling, and smoking cessation advice. Group and individual psychiatric counseling were provided to patients.
Symptom-limited treadmill exercise training was carried out at baseline for all patients following the modified Bruce protocol to estimate each patient’s peak heart rate.
Target heart rate was then estimated by the Karvonen formula [17] with an exercise intensity of 50–80% of the heart rate reserve.
The Karvonen method for training heart rate estimation is as follows: target heart rate = resting heart rate + (training percentage required × heart rate reserve).
Heart rate reserve is calculated as follows: peak heart rate − resting heart rate.
During the sessions, patients were monitored using telemetry and were directly supervised by a nurse. An on-site physician supervised three patients in the cardiac rehabilitation unit at a time.
Exercise parameters assessed
The following exercise parameters were recorded for each patient:
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Metabolic equivalent of tasks (METs): these were automatically calculated by the treadmill software where one MET is defined as the amount of oxygen consumed while sitting at rest. One MET equals 3.5 ml of oxygen per kilogram of body weight per minute [18].
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Total exercise time: defined as the total duration of the symptom-limited exercise test.
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Resting heart rate: defined as the patient’s baseline heart rate before starting the symptom-limited exercise test.
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Peak heart rate: defined as the maximum heart rate achieved in the symptom-limited exercise test.
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Heart rate recovery at 1 min: heart rate recovery is defined as the rate at which heart rate declines in the minutes following cessation of physical exercise. We calculated it by subtracting each patient’s heart rate after 1 min of recovery from their peak heart rate [19].
Patient follow-up assessments
At the end of each of the 6- and 12-week programs, lipid profile, LVEF, and exercise parameters were re-assessed using the same methods described before.
Statistical analysis
Data were collected, revised, coded, and inputted into the IBM statistical package for social science (SPSS) version 24. Data were tested for passing normality. The study power was more than 80. Categorical data were presented as number and percentages; continuous data were presented as mean and standard deviations. Categorical data were compared by using Fisher’s exact test. Continuous data were compared using student’s paired t test. Significance level (p value) was set at less than 0.05.
