3.2 Heart Failure, Valvular Disease & Cardiac Rhythm Disorders

Heart failure, valvular disease, and arrhythmias are common comorbidities in the clinical exercise setting, and each disrupts the normal cardiovascular response to exercise in a distinct, exam-relevant way.

Heart Failure: Classification and Pathophysiology

Heart failure (HF) is a clinical syndrome in which the heart cannot pump or fill adequately to meet the body's metabolic demands. Current classification, based on left ventricular ejection fraction (LVEF), divides HF into HFrEF (reduced ejection fraction, EF <=40%), HFmrEF (mildly reduced, EF 41-49%), and HFpEF (preserved ejection fraction, EF >=50%). In HFrEF, impaired systolic contractility reduces stroke volume; the heart compensates through neurohormonal activation — the renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system are chronically upregulated, driving fluid retention, vasoconstriction, and progressive ventricular remodeling. Natriuretic peptides (BNP, NT-proBNP) rise as the ventricle stretches and are used both diagnostically and to track decompensation. In HFpEF, the ventricle contracts normally but cannot relax and fill properly (diastolic dysfunction), often related to ventricular stiffness from hypertension, aging, obesity, or diabetes.

Functional limitation is staged using the New York Heart Association (NYHA) classification: Class I (no symptom limitation), Class II (symptoms with ordinary activity), Class III (symptoms with less-than-ordinary activity), and Class IV (symptoms at rest).

Exercise Response Abnormalities in Heart Failure

• Chronotropic incompetence — an inadequate heart-rate rise for a given workload — limits the cardiac-output reserve available during exercise.
• Reduced stroke-volume reserve, from either poor contractility (HFrEF) or poor filling (HFpEF), further compounds the blunted cardiac-output response.
• Delayed heart-rate recovery after exercise reflects autonomic imbalance and is itself a marker of worse prognosis.
• Peripheral factors — skeletal-muscle deconditioning, reduced oxidative capacity, and impaired vasodilatory reserve — also contribute meaningfully to the exertional fatigue and dyspnea that limit HF patients, independent of central cardiac function.

Valvular Heart Disease

Because exertional syncope and angina in aortic stenosis reflect a fixed mechanical limit on cardiac output rather than a trainable physiological deficit, these are true safety red flags that warrant medical clearance and conservative programming, not just RPE-guided caution.

Cardiac Rhythm Disorders

Atrial fibrillation (AFib) is the most common sustained arrhythmia encountered clinically. Chaotic atrial electrical activity produces an irregularly irregular ventricular rhythm and eliminates the atrial kick (the atrial contraction that normally contributes up to 20-30% of ventricular filling), reducing stroke volume — particularly relevant in patients who also have diastolic dysfunction. AFib also increases stroke risk from atrial thrombus formation, so anticoagulation status must be confirmed before exercise, and heart-rate response should be judged by perceived exertion and symptoms rather than a fixed target heart rate, since the rate response to exercise is often unpredictable. Premature ventricular contractions (PVCs) are common and often benign at rest but warrant closer attention if they increase in frequency, become multifocal, or occur in couplets/triplets with exertion. Ventricular tachycardia is a potentially life-threatening rhythm requiring immediate cessation of exercise and emergency activation.

Implanted Devices: Pacemakers and ICDs

Patients with an implantable cardioverter-defibrillator (ICD) have a programmed heart-rate "shock zone" at which the device will deliver anti-tachycardia pacing or a defibrillation shock. Exercise prescription must set a peak training heart-rate ceiling at least 10-20 beats below the programmed detection rate, confirmed with the patient's electrophysiologist or device team, to avoid triggering inappropriate therapy during vigorous exercise. Rate-adaptive pacemakers can help correct chronotropic incompetence but still require awareness of programmed rate limits.

Safety Considerations for the Clinical Exercise Physiologist

Always confirm current EF category, NYHA class, anticoagulation and rate-control status in AFib, and any device programming limits before prescribing intensity. Watch for signs of acute decompensation — new or worsening dyspnea, orthopnea, rapid weight gain, or peripheral edema — which should prompt physician referral rather than continued exercise progression. A brief daily-weight check (a gain of roughly 2-3 lb in a day or 5 lb in a week is a common referral trigger) is a simple, high-value self-monitoring habit to reinforce with heart failure patients between supervised sessions.

Building an Individualized Program Around These Limitations

Because central cardiac-output reserve is fixed or blunted across most of these conditions, exercise programming for HF, valvular disease, and rhythm disorders typically starts conservatively — shorter interval-style bouts with adequate rest, gradual progression guided by symptoms and RPE rather than aggressive heart-rate targets, and close attention to how the patient tolerates the first several sessions before advancing volume or intensity. Peripheral resistance training, performed at moderate loads with attention to symptom response, is a valuable complement to aerobic work in this population, since skeletal-muscle deconditioning is often a larger contributor to exercise intolerance than the central cardiac limitation itself, and improving peripheral oxidative capacity can meaningfully increase functional capacity even when central hemodynamics do not change.