*6.1. Acute Coronary Syndromes*

Acute coronary syndromes (ACSs) represent a spectrum of clinical presentations, including acute ST-segment elevation myocardial infarction (STEMI), acute non-ST-segment elevation myocardial infarction (NSTEMI), and unstable angina (UA) and are typically associated with the rupture of an atherosclerotic plaque and partial or complete occlusive thrombosis [1]. Exercise-based cardiac rehabilitation has been evaluated comprehensively in patients referred after acute MI. A meta-analysis of 36 randomized control trials, including 6111 patients after myocardial infarction, demonstrated that cardiac rehabilitation was clearly associated with a 36% reduction in cardiac deaths, a 26% reduction in total mortality, and a 47% reduction in reinfarction rate [2]. The recent meta-analyses conducted by Anderson and Ji have supported these findings [3,4]. Potential mechanisms responsible for mortality reduction entail an reduced sympathetic, then enhanced parasympathetic tone or ischemia-induced preconditioning [5]. Cardiac rehabilitation following acute coronary syndromes has received a class I indication (i.e., mandatory) in the international guidelines. It is typically delivered in the form of an outpatient program, whereas a residential cardiac rehabilitation program is recommended for:


A phase II program following acute coronary syndrome should incorporate patient assessment, including the evaluation of the arterial puncture site; functional capacity and angina threshold assessment based on a symptom-limited exercise test; exercise training; dietary counseling; body mass control; lipid management; blood pressure management; smoking cessation; and psychosocial support. The scope of early mobilization was described earlier in this book. Phase II should begin as soon as possible after an acute event. Patients diagnosed with myocardial infarction or unstable angina who have undergone percutaneous coronary intervention should optimally commence a cardiac rehabilitation program within the first 14 days after

hospital discharge, and this period can be prolonged in the case of patients with multiple risk factors, with a complicated course of disease, or who are at high risk [6].

Phase II with medically supervised exercise training typically includes 2–3 sessions per week for outpatients and 5–6 sessions per week for residential and hybrid cardiac rehabilitation patients. Each session usually lasts 30–60 min. General rules of exercise training following the FITT-VP formula have been described elsewhere [7]. Moderate-intensity aerobic exercise (45–59% of peak oxygen consumption, 55–69% of peak heart rate, 40–59% of heart rate reserve, 4–6 METs, or 12/20–14/20 on the Borg scale) is initially recommended for low-risk patients. Intermediateand high-risk patients should begin exercise at an intensity of 40% of heart rate reserve [7,8]. High- and maximal-intensity interval training for patients following acute coronary syndromes has recently been an object of research. After 2 weeks of moderate-intensity training (as an adaptation phase), patients exercised at 95–100% of their heart rate reserve (maximal-intensity training) or at 85% of their heart rate reserve (high-intensity training) 3 days per week for 4 weeks. The primary outcome was maximal oxygen uptake. The secondary outcomes were major cardiovascular complications. After six weeks of aerobic interval training, maximal oxygen uptake increased significantly in both groups, with a greater increase seen in maximal-intensity effort. Furthermore, no major cardiovascular or musculoskeletal complications were noted [9].

### *6.2. Chronic Coronary Syndromes*

Chronic coronary syndromes are defined as occurring in patients with stable angina, patients who are symptomatic >1 year after initial diagnosis or revascularization, and patients with angina and suspected vasospastic or microvascular disease [7]. The most frequently observed clinical picture of stable coronary artery disease is the occurrence of recurrent, transient episodes of chest pain at a certain level of exertion that can be relieved with rest or nitroglycerin. Thus, stable angina reflects a mismatch between demand and supply [10]. The beneficial effect of regular physical exercise as part of a multifactorial intervention in terms of improving symptom-free exercise tolerance and myocardial perfusion in patients with stable coronary artery disease and the deceleration of the disease progression over time have been documented [11,12]. One of the most influential accounts came from a study by Humbrecht. A randomized study was designed with the aim of comparing the effects of exercise training versus standard percutaneous coronary intervention with stenting on clinical symptoms, angina-free exercise capacity, myocardial perfusion, cost-effectiveness, and the frequency of a combined clinical end point (death of cardiac cause, stroke, coronary artery bypass graft surgery, angioplasty, acute myocardial infarction, and worsening angina with objective evidence resulting in hospitalization). A total of 101 male patients aged ≤70 years

were enrolled following routine coronary angiography and randomized to 12 months of exercise training—i.e., 20 min of bicycle ergometry per day—or to percutaneous coronary intervention. Compared with the coronary intervention group, 12 months of regular physical exercise in patients with stable coronary artery disease resulted in a superior event-free survival (with 70% in the PCI group and 88% in the training group). The exercise intervention was associated with a higher exercise capacity and maximal oxygen uptake after 12 months than in the PCI group (the maximal exercise tolerance increased significantly by 20%, while maximal oxygen uptake increased by 16%). It is noteworthy that no adverse events were recorded during the training sessions in any patient [13].

Exercise-based cardiac rehabilitation is recommended by the American College of Cardiology/American Heart Association and the European Society of Cardiology for patients diagnosed with chronic coronary syndromes to help them manage risk factors and to reduce recurrence of the disease; however, the referral and program participation rates remain suboptimal compared with those seen in patients after acute coronary syndromes. This relates particularly to patients with multiple risk factors, women, and the elderly [14,15]. The progress of early mobilization and exercise training for patients with stable angina depends on the clinical situation the coronary intervention has been performed for, the patient's clinical status after the procedure, their revascularization level, and the presence of complications related to the puncture site (i.e., bleeding, hematoma, fistula, infection). A moderate- or moderate-to-high-intensity exercise regimen is typically utilized [6,16]. Supervised exercise training principles were described earlier in this book in a dedicated chapter.

### *6.3. Coronary Artery Bypass Graft Surgery*

All patients undergoing coronary artery bypass graft surgery should be referred to a cardiac rehabilitation program due to its beneficial effects, as confirmed in numerous studies [17,18]. In an observational trial of 846 patients after coronary artery bypass graft surgery (CABG), 69% of whom participated in a cardiac rehabilitation program, after a mean follow-up of 9 years, a 46% relative risk reduction and a 12% absolute risk reduction in all-cause mortality were reported. These findings were independent of age, sex, prior myocardial infarction, or the presence of diabetes [19]. In another study including 3975 patients after CABG, an all-cause mortality reduction of 20% with in-patient cardiac rehabilitation and 40% with supervised exercise training were observed [20]. The principles of in-patient prehabilitation followed by post-operative early mobilization and combined aerobic, resistance, and inspiratory muscle training have been extensively studied [21]. The details of phase I cardiac rehabilitation were depicted earlier in this book. Phase II of cardiac rehabilitation should optimally begin four weeks after coronary artery bypass graft surgery and may commence earlier in a center experienced with

patients who have undergone cardiac surgery. The duration of the exercise training program should be individualized, depending on the patient's profile (i.e., age, fitness level, risk factors, adherence), but at minimum, it should include at least 24 sessions [22]. Patients undergoing coronary artery bypass graft surgery are typically older, present with comorbidities, and have a lower functional capacity level. Prior to commencing exercise training, a functional capacity assessment should be performed in the form of a six-minute walk test, symptom-limited exercise test (optimally four weeks after surgery), or submaximal exercise test (with a target of 70% of maximal heart rate). The maximal exercise test should not be executed within the four weeks following CABG. The exercise training program following CABG results in numerous cardiovascular and peripheral adaptations, including improved blood flow in exercising muscles, enhanced oxidative capacity of the working skeletal muscles, and the correction of endothelial dysfunction in the skeletal muscle vasculature. The supervised exercise training prescription should be based on clinical conditions, exercise capacity, left ventricular performance, and the type of surgery performed [6]. Thus, the postoperative rehabilitation principles are determined by many factors. The authors recommend enrolling patients after CABG into corresponding aerobic ABCD training models, as described earlier, in relation to their clinical outlook, their echocardiographic left ventricular performance, the presence of arrhythmia or ischemia, their functional capacity level, the presence of surgery-related complications, and their comorbidities (Table 43). As described earlier in a chapter concerning risk stratification, all characteristics listed must be present for patients to remain low-risk, whereas even one of characteristics listed places patients as moderate- or high-risk. The principles of strength training following cardiac surgery, including adequate timing and the acceptable load, can be found earlier in this work in the chapter dedicated to resistance training.


**Table 43.** Rehabilitation models for patients after cardiac surgery.

Abbreviations: CABG—coronary artery bypass grafting; ECG—electrocardiogram; GFR—glomerular filtration rate; LVEF—left ventricular ejection fraction; METS—multiples of resting metabolic equivalent; 6 MWT—six-minute walk test; NYHA—New York Heart Association. Source: Adapted from [23].

### *6.4. Valve Surgery*

### 6.4.1. Rationale

The epidemiology of valve disease has changed, and degenerative valve disease dominates nowadays in operating theaters, indicating the ageing surgical population and the challenges of the rehabilitation process [24]. Benefits of the cardiac rehabilitation program after valve surgery in terms of short-term physical capacity improvement and an earlier return to work have been documented, with a beneficial effect on peak oxygen uptake seen at 4 months—i.e., 24.8 mL/kg/min, compared with 22.5 mL/kg/min for a usual care group [25]. Therefore, a cardiac rehabilitation program should be offered to all patients after valve surgery, including those who have undergone percutaneous interventions, i.e., following percutaneous valve replacement, repair, the implantation of clips, etc. [7]. A multidisciplinary team should be involved in the cardiac rehabilitation program after valve surgery, particularly for patients with a postoperative course complicated by heart failure [26]. Valve surgery is typically performed during the symptomatic period, typically at the advanced stage of heart failure; thus, the improvement in the functional capacity and the left ventricular systolic function is extended over time [6]. Exercise tolerance after mitral valve replacement is much lower than that after aortic valve replacement, particularly in the presence of residual pulmonary hypertension [26]. Transcatheter aortic valve implantation (TAVI) has recently been implemented as the procedure of choice for elderly patients with severe aortic stenosis and a high perioperative mortality risk for surgical aortic valve replacement. Moreover, TAVI seems to also be non-inferior to surgical valve replacement in patients at intermediate surgical risk [27,28]. Existing data on transcatheter aortic valve replacement and exercise-based cardiac rehabilitation programs are limited (mainly due to the low enrollment, compared with surgical replacement, and a lack of consistency). In an observational trial evaluating the effects of eight weeks of combined endurance and resistance training in a group of elderly TAVI patients, compared to those given usual care without structured exercise, significant improvements in exercise capacity, muscular strength, and quality of life in the exercise group were observed. In addition, the exercise training did not affect negatively prosthetic valve function, whereas, in a recent trial, exercise training resulted in preserved long-term improvements, compared to usual care, in oxygen uptake at the anaerobic threshold but not in peak oxygen uptake, muscular strength, or quality of life [29,30].

### 6.4.2. Exercise Prescription

The general rules of the cardiac rehabilitation program implemented after valve surgery are analogous to those described for post-CABG. The individual rehabilitation plan is based on [6,31]:


Phase I of cardiac rehabilitation taking place in the intensive care unit and in cardiac surgery departments is typically prolonged compared with post-CABG. Phase II is recommended to be implemented within a few weeks after surgery and should optimally last for 8–12 weeks. For patients with heart failure complications in their postoperative course, a residential program should be offered, if available. Patients who have undergone an uncomplicated replacement of their aortic and mitral valves can begin phase II after two and three weeks, respectively [32].

The initial assessment before commencing exercise training should involve echocardiographic assessment—i.e., assessment of the transvalvular pressure gradient, grade of valvular insufficiency, and presence of pericardial effusion [7]. Typically, the low to moderate aerobic training intensities are utilized initially. The Borg scale is a useful adjunct in the case of patients with atrial fibrillation. The anticoagulation regimen is of special importance after the implantation of mechanical valves, and patients should be educated about adequate anticoagulation rules.

## *6.5. Heart Failure*

## 6.5.1. Rationale

The low exercise tolerance observed in patients with heart failure is a consequence of their diminished exertional response of cardiac output, impaired vasodilation, and increased systemic vascular resistance [33,34]. Based on physical capacity levels, patients diagnosed with heart failure can be classified into three groups [35]:


All patients diagnosed with heart failure at NYHA class I-III, irrespective of their left ventricular ejection fraction value, should be referred to a cardiac rehabilitation program [36,37]. Improvements in exercise capacity, symptoms, and quality of life and reductions in the hospital re-admission rate after participation in a cardiac rehabilitation program in patients with heart failure have been documented [38,39]. The quantitative beneficial effects of cardiac rehabilitation have been depicted and include [40,41]:


### 6.5.2. In-Patient Phase

In-patient rehabilitation should begin as soon as possible after hospital admission [40]. Once a patient's clinical stability is attained, gradual mobilization (calisthenics exercises with simple movements, without weights or equipment) should commence to increase body strength and flexibility. The resistance training of small muscle groups should be also implemented, with the initial intensity kept below 30% of the one repetition maximum. Inspiratory muscle training is essential [42]. The plan suggested depends on patients' hemodynamical status and the stage of the disease (as presented in Table 44).


**Table 44.** In-hospital early mobilization model for patients with heart failure.


**Table 44.** *Cont*.

### 6.5.3. Phase II Initial Assessment

There is no consensus regarding the optimal timing for the initiation of exercise training, with the typical practice for most cardiac rehabilitation centers being beginning at least one month after a decompensation episode [43]. Knowledge of the underlying cause of heart failure, recent pharmacotherapy, and the current functional capacity level before commencing an exercise program is essential. Detailed physical examination should assess signs of pulmonary congestion or peripheral edema. The initial exercise intensity should preferably be based on cardiopulmonary testing (the gold standard for patients with heart failure), utilizing the Naughton or modified Bruce protocol on a treadmill or an incremental or ramp protocol on a bicycle ergometer with a load increase of 5–10 W/min [7]. The exercise intensity should be set with relation to the ventilatory threshold, as was extensively discussed in the exercise intensity chapter of this book. If CPET is unavailable, intensities of 40%–70% of heart rate reserve and Borg scale values of 10–14 are recommended.

Contraindications to the commencement of exercise training for individuals with heart failure include [32,35]:

Absolute contraindications:


uncontrolled blood pressure (SBB above 180 mmHg, DBP above 120 mmHg), hypotension, resting angina, new resting ischemic ECG changes, new onset of unstable hemodynamically atrial fibrillation, an advanced atrioventricular block without a pacemaker, and acute heart failure;


Relative contraindications:


Training should be stopped with a subsequent intensity modification in the case of excessive fatigue, a significant increase in systolic blood pressure with symptoms of exercise intolerance, a blood pressure drop with exercise, the presence of exercise-induced supraventricular or ventricular arrhythmias, a significant reduction in oxygen saturation, or after ICD intervention.

6.5.4. Exercise Prescription

The principles of exercise were described in detail in this book in a chapter dedicated to exercise prescription for high-risk patients. The initial duration and frequency of aerobic training should be based on the functional capacity level [35]:

<3 METs (<0.5 watt/kg): 5–10 min exercise in a few sessions per day; 3–5 METs (0.5–1.2 watt/kg): 15 min sessions 1–2 times a day; >5 METs (>1.2 watt/kg): 20–30 min once a day.

For patients with very low functional capacity, frequent short bouts of low-intensity exercise are suggested initially ("start low and go slow"). Regular body weight monitoring is important so as not to ignore fluid retention. Moderate-intensity continuous endurance training is recommended as a baseline protocol. If interval training is prescribed, low-intensity bicycle ergometer training with 30 sec hard segments at 50% of workload and 1 min recovery segments below 20 watts is utilized [7].

With training progression, the primary goal in an interval regimen is to increase the duration up to 30 min and change the work-to-recovery ratio of 1:2 to 1:1 (by increasing the duration of active segments and/or shortening the recovery time). In continuous exercise, after attaining the duration of the conditioning phase of 40–60 min, exercise intensity should be increased subsequently. Selected patients can progress on to HIIT [44].

Resistance training usually includes a work-to-rest ratio of 1:2—i.e., 30–60 s of exercise with a subsequent 1–2 min rest. Resistance training progression should be phasic [7,35]:


Full training progression requires at least 3–4 weeks.

Inspiratory muscles training is essential, particularly during the in-patient phase. Typically, 30% of the maximum inspiratory mouth pressure is recommended initially, being increased every 7–10 days, with a target of 60%. Such training lasts for 20 min daily, 3–5 days a week, for 8 weeks [42].

The European Association of Cardiovascular Prevention and Rehabilitation summary of exercise training for patients with heart failure is presented in Table 45 [35].


**Table 45.** EACPR exercise training prescription for patients with heart failure.

Abbreviations: EACPR—European Association of Cardiovascular Prevention and Rehabilitation; VO2—oxygen uptake; 6 MWT—six-minute walk test. Source: Reprinted from [35].

### *6.6. Implantable Cardiac Electrical Devices*

### 6.6.1. General Remarks

A growing number of patients referred to cardiac rehabilitation have implanted cardiac electrical devices—i.e., a permanent pacemaker (PPM), cardiac resynchronization therapy (CRT), or an implantable cardioverter-defibrillator (ICD). Patients with PPM, CRT, or ICD are considered eligible for cardiac rehabilitation programs [45,46]. Exercise training in this group of patients can be implemented safely, and evidence shows that cardiac rehabilitation can almost double physical capacity after CRT implantation [47,48]. The exercise training of patients with implanted cardiac electrical devices requires special attention from cardiac rehabilitation staff, as apart from the supervision of the exercise training, adequate knowledge about the proper functioning of the devices is essential [49]. During phase I of cardiac rehabilitation, attention is required to prevent extensive movements on the side of the implant to avoid strain and lead fracture. Upper-body-strength-targeted exercise may cause the dislodgement of implanted lead; thus, resistance training is not recommended for 4–6 weeks after device implantation [7]. Upon admission to phase II, an initial assessment should

involve evaluation of the indication for the implantation; assessment of the presence of underlying heart disease, including events that have occurred; wound inspection; and the determination of the device position. Device interrogation is essential, particularly of the firing mode for ICD or CRT with a defibrillator (CRT-D). As heart rate during exercise should not exceed the ICD therapy threshold, the upper limit of the training heart rate should be set between 10 and 20 beats/min below the detection threshold [50]. Other important device parameters include sensing, pacing threshold, pacing percentage, and arrhythmia record. Functional capacity assessment should be performed as a symptom-limited test, preferably a cardiopulmonary exercise test, in order to provide additional information about chronotropic response to exercise, exercise-induced arrhythmias, and maximum tracking rate [51]. Exercise prescription for cardiac electrical devices recipients may follow the rules for heart failure patients, considering the upper limits of the device, and should incorporate the continuous endurance or interval model, last for 30–60 min, and be performed 3–5 days a week. Resistance training can begin after 6 weeks and include 2–3 sets of 10–12 repetitions per set at 40–70% of one repetition maximum and a rate of perceived exertion of 12–15, with attention paid to shoulder movements on the side of the implant.

### 6.6.2. Special Considerations

## Permanent Cardiac Pacemaker

Before the start of phase II, stimulation parameters should be analyzed. Patients should notify cardiac rehabilitation staff about any symptoms that may be related to incorrect stimulation (such as palpitations, syncope, or dizziness).

## Cardioverter-Defibrillator

An initial assessment should include the patient's history of ICD shocks and the relation of dysrhythmias and ICD shocks to exertion. Continuous ECG monitoring is mandatory during exercise sessions involving ICD recipients, and the upper limit of the training heart rate should be set 10–20 bpm below the fire rate. Exercise training is contraindicated in the presence of uncontrolled ventricular arrhythmias. If ICD intervention occurs during exercise training, the session must be stopped, and ICD control and the consultation of an electro-cardiologist are mandatory. Exercise sessions should be resumed rapidly after a change in pharmacotherapy and/or the reprogramming of the device to avoid ICD discharge becoming a psychological barrier to physical activity [52].

### Cardiac Resynchronization Therapy

Exercise training should follow the rules of training for individuals with heart failure (in the case of CRT device with defibrillation function—i.e., CRT-D—the

additional rules for ICD recipients apply). The cardiac rehabilitation team should know the type of device inserted (CRT or CRT-D) and the upper tracking limit value (stimulation with conduction 1:1). Some important points should be taken into accounts during exercise in CRT recipients—e.g., that exercise can induce sinus tachycardia above the upper tracking limit, leading to the inadequate tracking of the sinus rhythm, or that changes in atrio-ventricular conduction can cause a loss of resynchronization [53].
