Introduction to Heart Failure

1. Definition of Heart Failure

Heart failure (HF) is a clinical syndrome characterized by the heart’s inability to pump blood adequately to meet the body’s metabolic demands or to do so only at elevated filling pressures. It results from structural or functional impairment of ventricular filling or ejection of blood, leading to symptoms such as breathlessness, fatigue, exercise intolerance, and fluid retention (edema, ascites, pulmonary congestion).

Contrary to common perception, heart failure is not a single disease but rather a complex syndrome with multiple causes and heterogeneous presentations. It is the final common pathway of many cardiovascular disorders, including ischemic heart disease, hypertension, valvular disease, and cardiomyopathies.

Modern definitions from the European Society of Cardiology (ESC) and American College of Cardiology/American Heart Association (ACC/AHA) emphasize three components:

Symptoms: Dyspnea, fatigue, orthopnea, paroxysmal nocturnal dyspnea.
Signs: Elevated jugular venous pressure (JVP), pulmonary rales, peripheral edema.
Objective evidence: Structural/functional cardiac abnormality (reduced ejection fraction, diastolic dysfunction, elevated natriuretic peptides).

2. Epidemiology and Global Burden

Prevalence

Globally, 64 million people are estimated to be living with heart failure (according to the 2021 Global Burden of Disease Study).
In developed countries, prevalence is around 1–2% of adults, rising to ≥10% in individuals over 70 years old.
In low- and middle-income countries (LMICs), prevalence is increasing due to aging populations, rising rates of hypertension, diabetes, and obesity.

Incidence

Each year, ~1–2% of adults in high-income countries develop HF, with higher rates in older adults.
The incidence is declining slightly in high-income nations due to better management of acute myocardial infarction and hypertension, but survival after diagnosis is still poor.

Mortality and Prognosis

Despite advances, HF carries a grim prognosis.
Five-year survival rate after diagnosis is ~50%, worse than many cancers.
Hospitalization for acute decompensated HF is associated with 20–30% one-year mortality.

Economic Burden

HF is among the most costly chronic diseases.
In the US alone, annual costs exceed $30 billion, with a significant portion due to hospital admissions.
LMICs face a dual challenge: rising prevalence and limited healthcare resources.

Regional Variations

High-income countries: Ischemic heart disease is the leading cause of HF.
Africa & parts of Asia: Hypertension, rheumatic heart disease, and untreated cardiomyopathies remain significant contributors.
South Asia & Middle East: Younger age at diagnosis compared to Western populations.

3. Classification of Heart Failure

Based on Ejection Fraction (EF)

Modern guidelines classify HF according to left ventricular ejection fraction (LVEF), as measured by echocardiography:

Heart Failure with Reduced Ejection Fraction (HFrEF)
- LVEF ≤40%
- Often due to ischemic heart disease, dilated cardiomyopathy, or long-standing hypertension.
- Pathophysiology: impaired systolic function → reduced stroke volume.
- Strong evidence base for treatment (ACE inhibitors, beta-blockers, ARNI, SGLT2 inhibitors, MRAs).
Heart Failure with Preserved Ejection Fraction (HFpEF)
- LVEF ≥50%
- Common in elderly, hypertensive, diabetic, and obese patients.
- Pathophysiology: abnormal relaxation and increased stiffness → impaired ventricular filling despite normal EF.
- Treatment: Symptom relief (diuretics), comorbidity management. Evidence-based therapies are limited, though SGLT2 inhibitors are promising.
Heart Failure with Mildly Reduced Ejection Fraction (HFmrEF)
- LVEF 41–49%
- Intermediate group with characteristics of both HFrEF and HFpEF.
- Response to HFrEF therapies (ARNI, SGLT2i) suggests overlap with reduced EF physiology.

Other Classifications

By Clinical Course

Acute Heart Failure: Rapid onset of symptoms (e.g., pulmonary edema, cardiogenic shock).
Chronic Heart Failure: Long-standing, stable or progressively worsening symptoms.

By Side of Heart Involvement

Left-sided HF: Pulmonary congestion, dyspnea, orthopnea.
Right-sided HF: Peripheral edema, ascites, hepatomegaly, elevated JVP.
Biventricular HF: Features of both.

By Functional Status

New York Heart Association (NYHA) classification:
- Class I: No limitation of physical activity.
- Class II: Slight limitation; comfortable at rest but symptoms with ordinary activity.
- Class III: Marked limitation; comfortable at rest but symptoms with less-than-ordinary activity.
- Class IV: Symptoms at rest, unable to carry out any physical activity.

4. Clinical Importance of Heart Failure

1. Major Cause of Morbidity and Mortality

HF is a leading cause of hospitalization among adults over 65 years. Recurrent hospitalizations contribute to poor quality of life, healthcare costs, and increased mortality.

2. Progressive Nature

HF is a progressive syndrome, often worsening over time despite optimal therapy. Once diagnosed, it frequently leads to repeated admissions and declining functional status.

3. Quality of Life Impact

Patients experience reduced exercise tolerance, frequent fatigue, fluid retention, and psychological stress. Depression and anxiety are common comorbidities.

4. Comorbidity Burden

HF often coexists with:

Diabetes mellitus
Chronic kidney disease
COPD
Anemia and iron deficiency
Atrial fibrillation

These comorbidities complicate management and worsen prognosis.

5. Clinical Challenges

Diagnostic challenge: Symptoms can mimic other diseases (e.g., COPD, obesity).
Therapeutic gap: While HFrEF has strong evidence-based treatments, HFpEF has fewer proven therapies.
Resource constraints: Limited access to advanced therapies in LMICs worsens outcomes.

6. Public Health Significance

Rising prevalence due to aging populations and survival after acute MI.
Represents a global health crisis, especially in developing nations with limited infrastructure.
Preventive strategies (controlling hypertension, diabetes, and obesity) are essential.