2.3 Heart Failure (HFrEF/HFpEF), Cardiomyopathies & Valvular Heart Disease

2.3 Heart Failure (HFrEF/HFpEF), Cardiomyopathies & Valvular Heart Disease

Heart failure, primary cardiomyopathies, and valvular heart diseases represent complex clinical populations in cardiac rehabilitation. Formulating safe, effective exercise prescriptions requires understanding ventricular remodeling, the neurohormonal drivers of decompensation, the pharmacological foundations of Guideline-Directed Medical Therapy (GDMT), and the hemodynamic constraints of valvular stenosis and regurgitation.

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Heart Failure Phenotypes: Systolic vs. Diastolic Mechanics

Heart failure (HF) is a clinical syndrome characterized by cardinal symptoms (dyspnea, fatigue, peripheral edema) resulting from structural or functional abnormalities that impair ventricular filling or blood ejection:

1. Heart Failure with Reduced Ejection Fraction (HFrEF)

• Diagnostic Criterion: Left Ventricular Ejection Fraction (LVEF) $\le 40%$.
• Pathophysiological Mechanism: Primary systolic pump failure. Myocardial injury (e.g., extensive myocardial infarction, genetic mutations, viral myocarditis, or chronic volume overload) causes progressive cardiomyocyte loss. Surviving cardiomyocytes elongate, producing eccentric ventricular remodeling, chamber dilation, spherical geometric distortion, and elevated end-diastolic wall tension.
• Neurohormonal Activation: Falling forward stroke volume triggers chronic hyperactivation of the Sympathetic Nervous System (SNS) and the Renin-Angiotensin-Aldosterone System (RAAS), accompanied by excessive vasopressin release. While initially compensatory, sustained neurohormonal drive promotes systemic vasoconstriction, renal sodium and water retention, cardiomyocyte apoptosis, and progressive interstitial fibrosis, accelerating a downward spiral of cardiac decompensation.

2. Heart Failure with Mildly Reduced Ejection Fraction (HFmrEF)

• Diagnostic Criterion: LVEF $41%\text{ to }49%$.
• Clinical Nuance: An intermediate phenotype exhibiting characteristics of both systolic and diastolic impairment. Large clinical trials confirm that patients with HFmrEF achieve significant reductions in mortality and hospitalizations from guideline therapies established for HFrEF.

3. Heart Failure with Preserved Ejection Fraction (HFpEF)

• Diagnostic Criterion: LVEF $\ge 50%$ with objective evidence of spontaneous or provokable elevated LV filling pressures (e.g., elevated BNP/NT-proBNP, $E/e' \text{ ratio} >14$, left atrial volume index $>34\text{ mL/m}^2$, or pulmonary capillary wedge pressure $>15\text{ mmHg}$ at rest or $>25\text{ mmHg}$ during exercise).
• Pathophysiological Mechanism: Primary diastolic dysfunction. Ventricular systolic ejection is preserved, but the left ventricle exhibits impaired active relaxation during early diastole (impaired lusitropy) and increased passive myocardial stiffness during late diastole. This leads to concentric left ventricular remodeling or hypertrophy.
• Etiological Drivers: Strongly associated with aging, chronic arterial hypertension, obesity, diabetes mellitus, and sedentary lifestyles. Comorbidities induce systemic, low-grade microvascular endothelial inflammation, impairing nitric oxide/cyclic GMP/protein kinase G signaling in cardiomyocytes, promoting hypophosphorylation of the structural protein titin and extensive interstitial collagen cross-linking.

4. Heart Failure with Improved Ejection Fraction (HFimpEF)

• Definition: Patients with baseline LVEF $\le 40%$ who demonstrate an absolute increase of $\ge 10$ points, achieving a repeat measurement of $>40%$.
• Crucial Clinical Rule: Under the landmark TRED-HF trial, discontinuing guideline-directed medications in patients with "recovered" or improved ejection fraction precipitates relapse of systolic dysfunction and heart failure hospitalization in over 40% of patients within 6 months. GDMT must be continued indefinitely, even when LVEF normalizes.

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Longitudinal Staging vs. Functional Classification: ACC/AHA vs. NYHA

Clinical evaluation of heart failure integrates two complementary classification systems:

[ACC/AHA Stages: Irreversible Structural Progression]
  Stage A (At Risk) --> Stage B (Pre-HF) --> Stage C (Symptomatic HF) --> Stage D (Advanced HF)
                                                     |
                                       [NYHA Classes: Dynamic Exertional Severity]
                                       Class I   (No limitation)
                                       Class II  (Slight limitation; ordinary activity)
                                       Class III (Marked limitation; minimal activity)
                                       Class IV  (Symptoms at rest)

ACC/AHA Stages of Heart Failure

ACC/AHA stages describe the biological, structural progression of disease along an irreversible continuum (patients move forward, never backward):

• Stage A (At Risk for HF): Patients without structural heart disease, symptoms, or biomarker elevation, but with predisposing risk factors (hypertension, diabetes, ASCVD, obesity, metabolic syndrome, cardiotoxin exposure).
• Stage B (Pre-Heart Failure): Objective structural heart disease (e.g., LV hypertrophy, chamber enlargement, prior MI, asymptomatic valvular disease) or elevated biomarkers (BNP/NT-proBNP or cardiac troponin), without current or prior symptoms or signs of HF.
• Stage C (Symptomatic Heart Failure): Structural heart disease WITH current or previous symptoms of heart failure. All patients entering cardiac rehabilitation for HFrEF or HFpEF are in Stage C or D.
• Stage D (Advanced Heart Failure): Severe, refractory heart failure symptoms that interfere with daily activities and cause recurrent hospitalizations despite optimized GDMT; requiring advanced interventions (intravenous inotropes, Left Ventricular Assist Device [LVAD], cardiac transplantation, or palliative care).

New York Heart Association (NYHA) Functional Classes

NYHA classes quantify functional capacity and symptom burden. Unlike ACC/AHA stages, NYHA class is dynamic and fluctuates upward or downward with medical treatment, diuresis, and exercise training:

• Class I: No limitation of physical activity. Ordinary physical activity does not cause undue fatigue, palpitation, or dyspnea.
• Class II: Slight limitation of physical activity. Comfortable at rest. Ordinary physical activity (e.g., climbing two flights of stairs, carrying groceries) results in fatigue, palpitations, or dyspnea.
• Class III: Marked limitation of physical activity. Comfortable at rest. Less than ordinary activity (e.g., walking across a flat room, showering, dressing) produces fatigue, palpitations, or dyspnea.
• Class IV: Inability to carry on any physical activity without discomfort. Symptoms of heart failure are present even at rest. Any physical exertion increases discomfort.

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Guideline-Directed Medical Therapy (GDMT): The Four Pillars of HFrEF

Modern management of HFrEF is built upon four foundational drug classes ("The Four Pillars") that act synergistically to block maladaptive neurohormonal pathways, reverse adverse ventricular remodeling, decrease hospitalizations, and reduce mortality by over 60% when co-administered:

1. Angiotensin Receptor-Neprilysin Inhibitor (ARNI): Sacubitril/Valsartan is the preferred first-line agent, superior to traditional ACE inhibitors or ARBs. Sacubitril inhibits neprilysin, preventing the enzymatic degradation of endogenous natriuretic peptides (ANP, BNP) and bradykinin (promoting natriuresis, diuresis, and vasodilation), while valsartan blocks the angiotensin II type 1 ($AT_1$) receptor. Critical Clinical Rule: Transitioning from an ACE inhibitor to an ARNI requires a mandatory 36-hour washout period to eliminate the risk of life-threatening angioedema. ACE inhibitors (lisinopril, enalapril) or ARBs (losartan, valsartan) remain acceptable alternatives if an ARNI is financially inaccessible or contraindicated.
2. Evidence-Based Beta-Blockers: Only three specific beta-blockers are proven to reduce mortality in HFrEF: Carvedilol (non-selective $\beta_1/\beta_2$ with $\alpha_1$ vasodilating blockade), Metoprolol Succinate (extended-release $\beta_1$-selective; short-acting metoprolol tartrate is NOT approved for mortality reduction), and Bisoprolol ($\beta_1$-selective). Beta-blockers protect cardiomyocytes from toxic chronic catecholamine overdrive, down-regulate arrhythmogenic triggers, and promote reverse mechanical remodeling. Exercise Consideration: Beta-blockers blunt heart rate responses during exercise. In cardiac rehabilitation, exercise intensity must be guided by Rating of Perceived Exertion (RPE 11–14 on the 6–20 Borg scale) rather than raw age-predicted heart rate formulas.
3. Mineralocorticoid Receptor Antagonists (MRA): Spironolactone or Eplerenone. Competitive aldosterone antagonists that block mineralocorticoid receptors in the kidney and myocardium, blunting aldosterone-induced interstitial collagen synthesis, cardiac fibrosis, and potassium wasting. Safety Monitoring: Serum potassium and renal function must be tracked rigorously; MRAs are held or avoided if serum potassium exceeds $5.0\text{ mEq/L}$ or estimated glomerular filtration rate (eGFR) falls below $30\text{ mL/min/1.73 m}^2$.
4. Sodium-Glucose Cotransporter-2 (SGLT2) Inhibitors: Dapagliflozin or Empagliflozin. Originally developed for type 2 diabetes, large randomized trials (DAPA-HF, EMPEROR-Reduced, DELIVER, EMPEROR-Preserved) demonstrate that SGLT2 inhibitors significantly reduce cardiovascular death and HF hospitalizations in both diabetic and non-diabetic patients across the entire spectrum of LVEF. Mechanisms include osmotic diuresis and natriuresis, decreased preload and afterload, improved myocardial cellular energetics, inhibition of the cardiac sodium-hydrogen exchanger (NHE), and reduction in serum uric acid.

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Cardiomyopathies: Phenotypes & Exercise Safety Implications

Cardiomyopathies are primary diseases of the myocardium categorized by structural and functional presentation:

• Dilated Cardiomyopathy (DCM): Characterized by biventricular or isolated left ventricular dilation with global systolic impairment ($LVEF <40%$) in the absence of severe coronary artery disease or pressure overload. Etiologies include genetic mutations (e.g., titin [TTN] mutations in ~25% of familial cases), post-viral myocarditis (Coxsackie B, parvovirus B19), toxic exposures (chronic heavy alcohol consumption, anthracycline chemotherapy such as doxorubicin), and peripartum cardiomyopathy. Responds favorably to GDMT and individualized, moderate-intensity aerobic rehabilitation.
• Hypertrophic Cardiomyopathy (HCM / HOCM): Characterized by unexplained, marked left ventricular hypertrophy (wall thickness $\ge 15\text{ mm}$, or $\ge 13\text{ mm}$ in first-degree relatives), typically affecting the interventricular septum asymmetrically. Transmitted as an autosomal dominant trait affecting sarcomeric proteins (most commonly MYH7 and MYBPC3). In roughly 70% of patients, dynamic Left Ventricular Outflow Tract (LVOT) obstruction develops due to Systolic Anterior Motion (SAM) of the mitral valve: during rapid systolic ejection, the high-velocity flow through a narrowed outflow tract creates a hydrodynamic pressure drop (Venturi effect) that drags the anterior mitral leaflet toward the hypertrophied septum, obstructing forward aortic flow.
  • Factors Exacerbating LVOT Obstruction: Decreased ventricular preload (dehydration, prolonged standing, Valsalva maneuvers), increased inotropy (strenuous exertion, catecholamines), or decreased afterload (vasodilators). Dynamic LVOT gradients cause exertional presyncope, syncope, and ventricular arrhythmias.
  • Exercise Safety Directive: HCM is the leading cause of sudden cardiac death (SCD) in young athletes. Vigorous competitive sports, burst high-intensity training, and heavy isometric straining are strictly contraindicated. In cardiac rehabilitation, patients with non-obstructive or medically controlled HCM can participate in low-to-moderate steady-state aerobic conditioning with continuous telemetry, avoiding dehydration, hot environments, and sudden postural changes.
• Restrictive Cardiomyopathy (RCM): Characterized by rigid, non-compliant ventricular walls that severely restrict diastolic filling while maintaining normal or near-normal systolic chamber dimensions and ejection fraction. Causes biatrial enlargement. Primary etiologies include cardiac amyloidosis (deposition of misfolded immunoglobulin light-chain [AL] or transthyretin [ATTR] amyloid fibrils; treated with the stabilizer tafamidis), cardiac sarcoidosis (non-caseating granulomas causing conduction blocks), and hemochromatosis. Cardiac output is fixed and rate-dependent; strenuous exertion precipitates marked dyspnea and syncope.

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Valvular Heart Disease: Hemodynamic Lesions, Murmurs & Safety

Clinical Focus: The Aortic Stenosis Triad & Severe Criteria

Severe Aortic Stenosis is defined by: Aortic Valve Area (AVA) $\le 1.0\text{ cm}^2$ (or AVA index $\le 0.6\text{ cm}^2/\text{m}^2$), mean transvalvular gradient $\ge 40\text{ mmHg}$, or peak aortic jet velocity $\ge 4.0\text{ m/s}$.

• When severe AS becomes symptomatic, the classic triad marks a dire clinical trajectory:
  1. Angina: 5-year average survival without intervention.
  2. Syncope (exertional): 3-year average survival without intervention.
  3. Dyspnea / Heart Failure: 2-year average survival without intervention.
• Cardiac Rehab Rule: Symptomatic severe aortic stenosis is an absolute contraindication to all exercise testing and cardiac rehabilitation training due to fixed cardiac output, inability to augment cerebral perfusion during exercise vasodilation, and the high hazard of fatal ventricular fibrillation.

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Advanced Valvular Interventions: Surgical vs. Transcatheter

When valvular lesions reach critical severity, interventional correction is indicated:

1. Surgical Valve Replacement (SAVR/SMVR):
   • Mechanical Valves: Bileaflet pyrolytic carbon designs offer indefinite mechanical durability (>20–30 years), making them standard in younger patients ($<50\text{--}65\text{ years}$). However, their thrombogenic surfaces mandate lifelong anticoagulation with Warfarin (Coumadin). Target International Normalized Ratio (INR) is 2.0–3.0 for aortic mechanical prostheses and 2.5–3.5 for mitral mechanical prostheses (or aortic prostheses with risk factors). Direct Oral Anticoagulants (DOACs like apixaban) are strictly contraindicated with mechanical valves.
   • Bioprosthetic (Tissue) Valves: Bovine pericardial or porcine aortic valves exhibit low thrombogenicity and do not require lifelong anticoagulation. However, they undergo structural valve deterioration with a durability of 10 to 15 years.
2. Transcatheter Aortic Valve Replacement (TAVR): An expandable bioprosthetic valve crimped onto a catheter is deployed within the calcified native aortic valve, predominantly via a percutaneous transfemoral arterial approach. Indicated across the entire surgical risk spectrum (from prohibitive to low risk). Eliminates median sternotomy, allowing immediate mobilization without sternal precautions, enabling early Phase II CR enrollment.
3. Transcatheter Edge-to-Edge Repair (TEER / MitraClip): A percutaneous transseptal catheter delivers a mechanical clip that grasps the free edges of the anterior and posterior mitral leaflets, creating a double-orifice mitral valve. Indicated for severe, symptomatic secondary (functional) mitral regurgitation in patients with HFrEF on optimal GDMT who remain symptomatic (supported by the landmark COAPT trial, showing substantial mortality and HF hospitalization reductions).

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Clinical Application: Exercise Prescription in a Patient on HFrEF GDMT

A 68-year-old male with ischemic cardiomyopathy (LVEF 28%, NYHA Class II, ACC/AHA Stage C) enrolls in Phase II cardiac rehabilitation. His medications include Sacubitril/Valsartan 49/51 mg BID, Carvedilol 25 mg BID, Spironolactone 25 mg daily, and Empagliflozin 10 mg daily:

1. Hemodynamic Evaluation: Baseline resting blood pressure is 106/68 mmHg, heart rate is 58 bpm, and weight is stable. His LVEF $\le 35%$ qualifies him for CMS Phase II CR coverage under standard medical guidelines.
2. Exercise Intensity Titration: Because high-dose carvedilol suppresses chronotropic acceleration, target heart rate formulas (such as percentage of age-predicted maximum HR) are physiologically invalid. The clinician prescribes aerobic exercise using Rating of Perceived Exertion (Borg 6–20 scale) targeting an RPE of 11 to 14 ("light" to "somewhat hard"), accompanied by pre- and post-session weight checks to detect occult fluid retention.