Exercise Rehabilitation for Chronic Heart Failure Patients with Cardiac Device Implants

Abstract

In the past decade a significant development in the management and rehabilitation of people with chronic heart failure (CHF) has been the utilization of cardiac devices. The use of biventricular pacemakers, referred to as Cardiac Resynchronization Therapy (CRT) can yield improvements in functional abilities for a select group of CHF patients and the inclusion of implantable cardiac defibrillators (ICDs) may reduce the risk of sudden death. This review provides physical therapists with a basic understanding of how to prescribe exercise for people with CHF who have these device implants.

INTRODUCTION

While the incidence of ischemic heart disease declines, the prevalence of chronic heart failure (CHF) is increasing. The Framingham Heart Study reports that there are over 5,000,000 people with CHF in the United States. These patients have a less than 50% 5-year survival rate following initial diagnosis.¹ Among several important prognosticators that may influence this statistic are exercise capacity and severity of ventricular remodeling. In the past decade several important innovations in the management and rehabilitation of people with CHF have emerged that may improve their survival rate. One significant development is the use of cardiac devices in the treatment of CHF. Biventricular pacemakers and implantable cardiac defibrillators (ICDs) have proven to be effective interventions for some people with CHF.

In approximately 30% of people with CHF, the disease process not only depresses cardiac contractility but also affects the conduction pathways by causing a delay in the onset of right or left ventricular systole.² Cardiac Resynchronization Therapy (CRT) with a biventricular device makes use of atrial-synchronized biventricular pacing to coordinate right and left ventricular contraction, and has been shown to improve the physical abilities of some people with CHF.^{2, 3, 4} Further, many patients treated with CRT also receive an ICD. Patients with a CRT or CRTICD device represent an emerging subpopulation of people with CHF who may be referred for exercise rehabilitation. The purpose of this review is to provide physical therapists with a basic understanding of these devices and how to prescribe exercise and manage rehabilitation for CHF patients with these devices. The paper will begin with a brief overview on the impact of CRT on physical function and exercise capacity. This will be followed by recommendations for aerobic and resistance training. Finally there will be a review on ICDs followed by exercise recommendations.

CARDIAC RESYNCHRONIZATION THERAPY

Biventricular pacing (ie, CRT) aims to restore a synchronized cardiac contraction between the right and left ventricles. Indications for CRT are based on the American College of Cardiology, American Heart Association, and Heart Rhythm Society guidelines that recommend CRT for people with New York Heart Association (NYHA) functional class III or IV CHF who are refractory to pharmacologic therapy and have an interventricular conduction delay (wide QRS complex approximating 120 to 130 ms or greater), an ejection fraction ≤ 35%, and a left ventricular (LV) end-diastolic dimension ≥ 55 mm.^{5, 6} These guidelines reflect the results of several large clinical trials that randomized over 2,500 participants with CHF to CRT versus placebo and demonstrated the benefit of CRT in measurements of functional capacity, exercise tolerance, ventricular remodeling, and reduction in hospitalizations and mortality over a 6-month period.^{2, 7, 8, 9, 10, 11, 12}

Cardiac Resynchronization Therapy has shown to improve NYHA functional class and decrease mortality over one year in some,^{13, 14} but not in all people with CHF.^{15, 16, 17} A meta-analysis of 14 randomized control trials including a total of 4,420 participants demonstrated that 59% managed with CRT improved at least one NYHA functional class; ejection fraction increased by a weighted mean difference of 3.0% (95% confidence interval, 0.9% − 5.1%); 6-minute walk test distance increased by a weighted mean difference of 24 m (95% confidence interval, 13 m − 35 m) and quality of life (QoL) assessed by the Minnesota Living With Heart Failure Questionnaire improved a weighted mean difference of 8.0 points (95% confidence interval, 5.6 − 10.4 points) between baseline and following 6 months of therapy.¹⁸ Notably, the survival benefit associated with CRT appears to be from the 0.64 (95% confidence interval, 0.49 − 0.84) relative risk reduction in progressive heart failure deaths.¹⁸

From the perspective of functional outcomes, CRT has been demonstrated to effectively improve hemodynamics and left ventricular performance,^{3, 4, 19} without an increase in heart rate or myocardial oxygen consumption,^{4, 20} thus contributing to increased exercise tolerance and reduced symptoms in those with severe CHF.^{2, 10, 19, 20, 21, 22, 23} Clinical trials have demonstrated that patients undergoing CRT may experience a number of significant improvements related to physical function (Table 1).

Table 1.

Improvements Associated with Cardiac Resynchronization Therapy in Patients with Chronic Heart Failure

Functional Changes Improved NYHA functional class2, 7, 10, 23, 55, 56 Improved quality of life scores9, 10, 23, 55, 56, 57 Reduced hospitalization2, 9

Exercise Performance Changes Increased 6-minute walk test distance2, 7, 10, 23, 55, 56, 58 Increased treadmill exercise duration2 Increased VO2peak 7, 9, 10, 23, 55, 58 Increased anaerobic threshold55

Cardiac Changes Increased left ventricular ejection fraction2, 23, 56, 59, 60 Decreased left atrial volume11 Decreased left ventricular end-diastolic11, 56, 58, 59, 60 and end-systolic size11, 59, 60 Decreased interventricular mechanical delay56 Reduced mitral regurgitation23, 56, 59 Improved myocardial performance index11, 59 Shortening of QRS interval56

Abbreviations: NYHA, New York Heart Association

It is important to note that approximately 30% of patients undergoing CRT appear to derive no benefit from this therapy. This nonresponder rate is derived from several clinical trials in which 30% to 35% of patients showed either no improvement or worsening symptoms after 6 months of CRT.^{2, 12} Additionally, therapists should be aware that based on clinical trial data there is a 5% risk (95% confidence interval, 4% − 7%) of device or biventricular pacemaker lead malfunction, and a 1.8% risk (95% confidence interval, 1.3% − 2.5%) of infection within the first 6 months of therapy.¹⁸

Since CRT appears to have an immediate and significant impact on physical ability as well as QoL,²⁴ it follows that some patients would be motivated to participate in exercise rehabilitation programs to further enhance their functional ability. However, to date only two small studies have examined the impact of exercise training following CRT.^{25, 26} Conraads et al²⁶ reported that 4 months of endurance training provided a distinct benefit in terms of exercise capacity (as measured by VO_2peak, maximal workload, and circulatory power). In that study, patients who received CRT but no exercise training demonstrated a 16% increase in VO_2peak, whereas combined CRT and exercise training conferred a 40% increase in VO_2peak. Similarly, Belardinelli et al²⁵ reported that 8 weeks of training in addition to CRT enhanced VO_2peak, endothelium-dependent dilation of the brachial artery, and QoL. Thus it appears that exercise training may confer further aerobic benefit for CRT patients; however, this seemingly additional benefit of combined aerobic training and CRT on survival needs to be established in a large sample, randomized control trial.

Aerobic Training

For people treated with CRT, where feasible, a baseline assessment including a graded exercise test with 12-lead ECG, blood pressure, and indirect calorimetry should precede entry into the exercise rehabilitation program.²⁷ The preferred exercise test protocol is the Chronotropic Assessment Exercise Protocol (CAEP), which was designed specifically for the evaluation of rate-responsive pacemakers.²⁸ The CAEP begins at 1.5 metabolic equivalents (METs; where 1 MET = 3.5 ml O₂/kg/min) and consists of two-minute stages with increments of approximately one MET per stage for the first 10 minutes. This protocol allows most patients to complete several stages of exercise and tests the chronotropic response to submaximal exertion that falls within the range of many activities of daily living.²⁹ In addition to collecting accurate resting data, patients should be monitored during a 3 to 5 minute recovery period.^{30, 31} The profile of heart rate (HR) decay has been shown to influence hemodynamics during exercise recovery and patterns of VO₂ during recovery have been shown to accurately reflect central and peripheral limitations.^{31, 32} Ideally, formal reassessment should be repeated at the completion of the exercise program so as to properly monitor progress.³³

Given that CRT recipients are truly a “CHF patient with a pacemaker,” it is suggested that the exercise prescription follow guidelines suggested for people with CHF.^{34, 35} A number of randomized trials have reported benefits for patients with exercise intensities ranging from 40% to 75% VO_2peak to 50% to 80% of the HR reserve.^{36, 37, 38, 39, 40, 41} The training study by Conraads et al²⁶ outlined a training program for CRT patients that incorporated up to 50 minutes of endurance training at a target HR equivalent to 90% of the patient's ventilatory (anaerobic) threshold. The study by Belardinelli et al²⁵ had patients exercise at an intensity approximating 60% of VO_2peak. Because the chronotropic response may be impaired in people with CRT, rating of perceived exertion (RPE) may be the preferred method of monitoring intensity. A Borg RPE scale rating of 11 to 14 on the 20 point scale has been shown to be optimal for CHF patients. If possible, ancillary study data (such as exercise echocardiogram, radionuclide studies, and indirect calorimetry) should be considered when formulating the exercise prescription to ensure that exercise intensity is below that which may result in ischemic wall motion abnormalities,⁴² a drop in ejection fraction, and is below the ventilatory threshold.⁴³

Ideally, those with clinically stable CHF treated with CRT should engage in aerobic activity 3 to 5 times a week for at least 30 minutes to enhance cardiorespiratory fitness.^{25, 26} As many of these patients are elderly, it may be beneficial for them to start with interval training alternating exercise intervals of 3 to 5 minutes with passive recovery intervals of one to 3 minutes. Participants may need to rest frequently during the first few weeks of training, but should be encouraged to slowly lengthen the exercise time and reduce the rest intervals. Daily activity at lower intensities should supplement the exercise program to sustain secondary prevention and mobility benefits.⁴⁴

The therapist should be mindful of possible limiting factors associated with pacing therapy. It is important to remember that (1) if the CRT device is functioning properly, it is always delivering paced beats to the right and left ventricles that are sensed from the left atrium, and (2) the patient's atrial rate may either be intrinsic (ie, their own sinus driven heart rate), or paced. If the patient's atrial rate is paced (or set at a fixed rate), then the physical therapist should be especially mindful of a blunted or delayed heart rate response to exercise. It is important to note that ECG changes (ST-segment depression) associated with myocardial ischemia are often not visible in those who are paced in the ventricle and therefore, careful history taking and observation is essential. Closely monitored clinical observations (ECG abnormalities, quantified reductions or improvements in physiologic responses from baseline assessment, patient perceptions of ability, etc.) should be forwarded to the patient's specialist as an important part of ongoing assessment and care.

Resistance Training

Elderly people with CHF are at particular risk of muscle wasting.⁴⁵ Therefore resistance training may be considered for those treated with CRT. The resistance training should involve small muscle group activity at an intensity equivalent to an RPE of 12–15 on the Borg 6–20 scale; involve 12 to 25 repetitions with short work bouts, and a work to rest ratio of at least 1:2.³⁵ Use of elastic bands (eg, Thera-Band) is also suitable.

It is important to note that upper body strength training may dislodge newly implanted leads, and therefore, resistance training is not recommended for the first several months post-implant. Any activity that could result in a direct impact with the pacemaker should be avoided. Further, people with CRT may have considerable peripheral limitations evident with reductions in muscular endurance and strength as a result of long-term inactivity. Thus, when resistance training is introduced, it should be of only low to moderate intensity and completed twice weekly.

IMPLANTABLE CARDIOVERTER DEFIBRILLATORS

Implantable cardioverter defibrillators are designed to detect and terminate lethal arrhythmias with an electrical shock ranging from approximately 26 to 38 joules.⁴⁶ The ICD is an effective and life-saving therapy for patients with potentially lethal ventricular arrhythmias, and may coexist with a CRT device for managing CHF symptoms in conjunction with optimal pharmacotherapy. The Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure (COMPANION) trial studied the effects of CRT with and without ICD therapy on all cause mortality.⁴⁷ This trial was terminated early on ethical grounds as CRT plus ICD therapy was found to significantly reduce all cause mortality by 40% (from 19% to 11%) versus a 15% reduction in CRT alone.

A small amount of work has been published on exercising patients with ICDs. Friedman and colleagues⁴⁸ reported cases of two patients benefiting physically and psychologically from attendance at an exercise rehabilitation program. One small study by Fitchet et al⁴⁹ prospectively randomized an initial 16 patients to usual care or an individually designed 12-week exercise rehabilitation program found that the training group increased treadmill exercise time by 16% from a baseline mean of 595 seconds to 671 seconds. In that study, patients were trained at intensities approximating 60% to 75% of the age predicted maximum HR with an absolute upper exercise limit 10 beats below the ICD activation threshold. The exercise program included twice weekly supervised 2 hour sessions and patients were also encouraged to participate in community based exercise programs/home based exercise (the volume of this latter training is not detailed and appears to have been unsupervised). Exercises were varied and relatively vigorous including shuttle walking, ball lifting and manipulation, varied stepping exercises, lunges, squats, and arm lifts. Notably, the type, duration, and frequency of exercise, and the recommendation for home based exercise training in the study by Fitchet et al⁴⁹ is not consistent with recommendations for elderly patients with CHF.³⁴ In this exercise training study, no patients experienced an ICD discharge during exercise testing, supervised exercise training, or home training, while two patients received an appropriate ICD shock during the course of the study (one of whom reported to have significantly worsening CHF).⁴⁹ In the same study, nonsustained ventricular tachycardia, not requiring ICD therapy, occurred a total of 18 times in two patients during the course of the exercise program. The authors also reported improved exercising ability and lowered levels of psychological distress posttraining.⁴⁹ One randomized study reported a reduction in the number of ICD discharges in a training group and demonstrated that the presence of nonsustained ventricular tachycardia in the presence of an ICD does not constitute a contraindication for aerobic exercise training.⁵⁰

Exercise prescription for patients with ICDs should be age-, health- and functional capacity-Specific.²⁷ Patients with ICDs should start exercise rehabilitation under supervision with heart rate monitoring. In order to avoid unintended ICD shocks, investigators have employed various heart rate limits of 30 beats,⁵¹ 20 beats,⁵² and 10 beats⁴⁹ below the ICD activation threshold during exercise testing. Both the AHA and the European Association for Cardiovascular Prevention and Rehabilitation recommend that peak target heart rates remain 10 to 20 beats below the ICD activation threshold.^{35, 53} Therefore, it is suggested that a prescribed upper heart rate limit set at 15 (± 5) beats below the ICD activation threshold will provide a sufficient cushion for avoiding unwanted shocks. In addition to this “ICD threshold cushion,” the therapist should ensure target exercise heart rates be kept below the patient's ischemic/angina threshold. Further, pronounced arm and shoulder movement or intense mechanical strain on the ICD could, theoretically, trigger an inappropriate shock.³⁵

The therapist should be aware that within the first 12 months of the ICD implant, up to 5% (95% confidence interval, 4.0% − 6.3%) of combined ICD-CRT devices can malfunction, 1.1% (95% confidence interval, 0.7% − 1.7%) of patients may develop infection at the site of implant (with the most commonly used device generator location being below the left clavicle region), and 7.2% (95% confidence interval, 6.3% − 8.1%) of patients may develop pacemaker/ICD lead problems.¹⁸ Placing a magnet over the ICD generator site will disable the ICD if persistent inappropriate shocks not caused by lethal arrhythmias occur repeatedly. When a shock is delivered, the causes should be assessed and ICD programming, medications, and exercise regime should be reviewed. As with appropriate shock therapy, inappropriate treatments should trigger an examination by the patient's cardiology specialist. It is also important to note that direct contact with an individual during a shock therapy is not harmful to anyone giving aid or reassurance.⁵⁴

SUMMARY

The growing application of device therapy in the treatment of CHF presents a unique challenge for therapists. While CRT may improve the functional abilities of CHF patients, the ability to augment this improvement with exercise programming requires that the therapist understand how to adapt the principles of exercise prescription to this unique patient group. Furthermore, as many patients now receive ICDs along with their CRT pacemakers, the therapist must have an understanding of the devices so as to ensure patient safety during exercise rehabilitation. With the assistance of competent therapists, patients with CRT and ICDs can safely participate in exercise rehabilitation and realize the health benefits associated with exercise training.