What is cardiac fatigue, particularly in older adults with a history of cardiovascular disease, such as heart failure or coronary artery disease (CAD)?

Cardiac Fatigue: Definition and Clinical Significance

Cardiac fatigue refers to the symptom of tiredness and reduced physical capacity that occurs as a cardinal manifestation of heart failure, resulting from impaired cardiac output, skeletal muscle deconditioning, and neurohormonal dysfunction—not from direct "fatigue" of the heart muscle itself. 1

Core Definition and Pathophysiology

Cardiac fatigue is one of the two cardinal manifestations of heart failure syndrome, alongside dyspnea, and represents a complex symptom with multiple underlying mechanisms 1:

• Fatigue limits exercise tolerance and impairs functional capacity, though it may not always dominate the clinical picture simultaneously with fluid retention 1
• The symptom is frequently reported but non-specific, with multiple potential causes beyond cardiac dysfunction 1
• Physical fatigue relates to loss of skeletal muscle efficacy due to cardiac output mismatch during exercise, muscle and microcirculatory deconditioning, neuroendocrine dysfunction, and associated metabolic disorders 2

Key Mechanisms in Older Adults with Cardiovascular Disease

Peripheral Adaptation Abnormalities

• Impaired peripheral perfusion during exercise represents a primary mechanism, as cardiac output fails to meet metabolic demands 3
• Reduced oxidative capacity of skeletal muscle develops from chronic underperfusion and deconditioning 3
• Loss of skeletal muscle mass and strength occurs as a late manifestation of heart failure 1
• Signals from skeletal muscle are interpreted by the brain as fatigue, explaining why treatment response may be slow until skeletal muscle quality is restored 1

Cardiovascular-Specific Factors

• Variation in mitral regurgitation or transitory dysrhythmias commonly exacerbate the fatigue experience 1
• New York Heart Association (NYHA) functional class correlates with fatigue severity, though the relationship between ejection fraction and symptoms is poorly understood 1, 4
• Hemoglobin level and history of stroke are biological factors associated with increased fatigue 4

Clinical Presentation in Older Adults

Characteristic Features

• Approximately 40% of patients with stable coronary artery disease report fatigue more than 3 days per week lasting more than half the day 5
• Women report higher fatigue intensity and more interference from fatigue compared to men (p = .003 and p = .007 respectively) 5
• Older adults may present with fatigue as an isolated anginal equivalent symptom, particularly those without typical chest pain 1

Psychological Dimensions

• Depressive symptoms are the sole predictor of both fatigue intensity and interference in regression analyses of patients with stable coronary heart disease 5
• Mental fatigue corresponds to predominantly depressive mood disorders, representing a distinct entity from physical fatigue with different pathophysiological mechanisms 2
• Depression is a key psychological factor associated with fatigue across heart failure populations 4

Diagnostic Approach

Critical Distinctions

• The apparent discordance between ejection fraction severity and functional impairment is not well understood—patients with very low ejection fraction may be asymptomatic while those with preserved function may have severe disability 1
• Patients may discount fatigue as they adapt to symptoms, meaning standardized measures alone may provide an incomplete picture of fatigue burden 5
• Fatigue must be distinguished from dyspnea, though both symptoms often coexist and share overlapping mechanisms 1

Assessment Components

• Functional testing should investigate both physical dimensions (exercise capacity) and mental dimensions (mood disorders) to analyze their respective roles 2
• NYHA functional classification stratifies patients by symptom severity from Class I (no limitation) to Class IV (symptoms at rest) 1, 6
• Qualitative interviews may reveal higher interference from fatigue than captured by standardized questionnaires alone 5

Clinical Implications

Prognostic Significance

• Fatigue is responsible for deterioration of quality of life and prognosis in cardiovascular disease 2
• Studies show conflicting evidence related to the prognostic implications of fatigue, indicating need for further research 4
• The symptom may indicate worsening heart failure condition, requiring patient education about monitoring 7

Management Considerations

• Exercise training can partially reverse peripheral alterations, improve exercise capacity, and alleviate fatigue 3
• Rehabilitation has an essential role due to its global approach addressing both physical and psychological dimensions 2
• Social factors including relationship strain, loneliness, and isolation relate to fatigue and should be addressed 4
• Few nonpharmacologic interventions have been tested but show some promise for alleviating fatigue in heart failure 4

Common Pitfalls

• Do not assume fatigue correlates directly with ejection fraction—the relationship is complex and poorly understood 1
• Do not overlook depressive symptoms—they are the strongest predictor of fatigue burden in stable coronary disease 5
• Do not rely solely on patient self-report—patients may minimize fatigue as they adapt to chronic symptoms 5
• Do not ignore the skeletal muscle component—restoration of muscle quality is necessary for symptom improvement 1