Pathophysiology
I-3. Heart failure: causes and symptoms
心不全の原因と症状
What is Heart Failure?
- A clinical syndrome of progressive weakening of the heart’s pump function, causing changes at systemic, organ, and cellular levels.
- Ultimately leads to death via progressive loss of myocardial cells and arrhythmias.
- Prevalence is rising with the aging population.
Classification
- Acute vs chronic — by speed of onset (acute, e.g. myocardial infarction).
- Forward vs backward:
- Forward failure — cannot pump forward → ↓systemic perfusion (cyanosis).
- Backward failure — cannot clear venous blood → congestion in lungs and/or systemic veins.
- Systolic vs diastolic (Ejection fraction, EF = SV/EDV; healthy 55–75%):
- Diastolic dysfunction — EF 35–50% (HFpEF, preserved EF).
- Systolic dysfunction — EF <35% (HFrEF, reduced EF).
- Left vs right sided.
- Congestive HF — failure to clear blood from behind → congestion.
Symptoms by location
- Left-sided, backward → LA + pulmonary congestion → pulmonary edema: rales, dyspnea, orthopnea, paroxysmal nocturnal dyspnea.
- Left-sided, forward → weakness/fatigue (↓O₂ supply), nycturia (at rest at night, blood redistributes to kidneys → ↑urine).
- Right-sided, backward (from ↑pulmonary pressure) → edema, hydrothorax, congestive hepatomegaly (nutmeg liver), distended neck veins, cyanosis, S3 gallop.
Provoking & Exacerbating Factors
- Underlying (true) causes: ischemic heart disease, hypertension (↑afterload → ↑O₂ demand), diabetes (coronary vascular damage), cardiomyopathies, valvular heart disease.
- Precipitating/decompensating factors (don’t cause HF but worsen it):
- Increased workload: volume overload (renal failure, high Na⁺), pressure overload (high BP, PE), ↑metabolic need (fever, infection, hyperthyroidism).
- Same workload, weaker heart: ischemia (↓ATP), arrhythmia, endo-/myocarditis, drug effects.
Diagnosis
- History + symptoms + physical exam.
- ECG (non-specific; a fully normal ECG can exclude HF) + chest X-ray.
- Biomarkers: BNP, NT-proBNP, ST2, hs-TnT — the worse the HF, the higher NT-proBNP.
- Echocardiography (measures EF).
Pressure–Volume Loop Changes
- CO = HR × SV. Heart determinants: inotropy (contractility), lusitropy (relaxation/filling). Circulation: preload, afterload.
- Isolated ↑HR doesn’t raise CO much — shorter diastole → less filling → weaker contraction (Frank-Starling).
- PV-loop area = mechanical work (larger area = higher workload).
- ↓Inotropy (systolic dysfunction): flatter end-systolic PV slope → smaller loop area = low workload.
- ↓Lusitropy (diastolic dysfunction): less filling at the same end-diastolic pressure → smaller area = low workload.
- Ischemia can cause both together: ↓O₂ → poor contraction (systolic) + stiffer muscle → poor filling (diastolic).
一問一答
▶What is heart failure?
A clinical syndrome of progressive weakening of the heart's pump function causing systemic, organ, and cellular changes, ultimately leading to death via myocardial cell loss and arrhythmias.
▶How is heart failure classified?
Acute vs chronic, forward vs backward, systolic vs diastolic, left vs right sided, and congestive (failure to clear blood → congestion).
▶What is the difference between forward and backward heart failure?
Forward failure: cannot pump blood forward → ↓systemic perfusion (cyanosis). Backward failure: cannot clear venous blood → congestion in lungs and/or systemic veins.
▶How are HFrEF and HFpEF defined by ejection fraction?
Healthy EF is 55–75%. Diastolic dysfunction = EF 35–50% (HFpEF, preserved); systolic dysfunction = EF <35% (HFrEF, reduced).
▶What are the symptoms of left-sided backward heart failure?
Left atrial + pulmonary congestion → pulmonary edema: rales, dyspnea, orthopnea, and paroxysmal nocturnal dyspnea.
▶What are the symptoms of left-sided forward heart failure?
Weakness/fatigue (↓O₂ supply) and nycturia (at rest at night, blood redistributes to the kidneys → ↑urine).
▶What are the main underlying (true) causes of heart failure?
Ischemic heart disease, hypertension (↑afterload → ↑O₂ demand), diabetes (coronary vascular damage), cardiomyopathies, and valvular heart disease.
▶What are the symptoms of right-sided backward heart failure?
Peripheral edema, hydrothorax, congestive hepatomegaly (nutmeg liver), distended neck veins, cyanosis, and an S3 gallop.
▶What is the difference between causes and precipitating factors of heart failure?
True causes produce HF (e.g., ischemia, hypertension), whereas precipitating/decompensating factors don't cause HF but worsen it (e.g., volume/pressure overload, fever, arrhythmia).
▶Which factors increase cardiac workload and can decompensate heart failure?
Volume overload (renal failure, high Na⁺), pressure overload (high BP, pulmonary embolism), and increased metabolic need (fever, infection, hyperthyroidism).
▶What biomarkers are used in diagnosing heart failure?
BNP, NT-proBNP, ST2, and hs-TnT; the worse the heart failure, the higher the NT-proBNP.
▶What is the gold-standard test for measuring ejection fraction in heart failure?
Echocardiography.
▶Why doesn't an isolated increase in heart rate raise cardiac output much?
Faster rate shortens diastole → less filling → weaker contraction (Frank-Starling), so CO does not rise proportionally.
▶What does the area of the pressure-volume loop represent, and how does it change in systolic dysfunction?
PV-loop area = mechanical work. In systolic dysfunction (↓inotropy), the end-systolic PV slope flattens → smaller loop area (lower work output).
▶How does the pressure-volume loop change in diastolic dysfunction?
↓Lusitropy means less filling at the same end-diastolic pressure → smaller loop area.
▶Why can ischemia cause both systolic and diastolic dysfunction?
↓O₂ impairs contraction (systolic) and makes the muscle stiffer, impairing filling (diastolic).
▶What determines cardiac output and its cardiac/circulatory components?
CO = HR × SV. Cardiac determinants: inotropy (contractility) and lusitropy (relaxation/filling). Circulatory determinants: preload and afterload.
▶What is the value of ECG in diagnosing heart failure?
It is non-specific, but a fully normal ECG can essentially exclude heart failure.
▶Why does congestive hepatomegaly occur in right heart failure, and what is its appearance?
Backward congestion of systemic veins backs blood up into the liver, producing a "nutmeg liver" appearance.
▶What commonly causes right-sided heart failure?
Increased pulmonary pressure (often from left-sided failure), which raises the right ventricle's workload.