Heart Failure : Overview, Etiology, Pathogenesis, Types, & Treatment
Definition
- Heart failure is defined as the pathophysiologic state in which impaired cardiac function is unable to maintain an adequate circulation for the metabolic needs of the tissues of the body.
- The term Congestive heart failure (CHF) is used for the chronic form of heart failure in which the patient has evidence of congestion of peripheral circulation and of lungs.
- CHF is the common end point for many forms of cardiac disease and typically is a progressive condition that carries an extremely poor prognosis.
- Most cases of HF are due to systolic dysfunction—inadequate myocardial contractile function, characteristically a consequence of ischemic heart disease or hypertension.
- In order to maintain normal cardiac output, several compensatory mechanisms play a role as under:
– Cardiac hypertrophy
– Cardiac dilatation
– Tachycardia
Etiology
Heart failure may be caused by one of the following factors, either singly or in combination:
1. Intrinsic pump failure : The most common and most important cause of heart failure is weakening of the ventricular muscle due to disease so that the heart fails to act as an efficient pump e.g.
- Ischaemic heart disease
- Myocarditis
- Cardiomyopathies
- Metabolic disorders e.g. Beriberi
- Disorders of the rhythm e.g. atrial fibrillation and flutter
2. Increased work load on the heart : Increased load on the heart may be in the form of pressure load or volume load.
Increased pressure load may occur in the following states:
- Systemic and pulmonary arterial hypertension.
- Valvular disease e.g. mitral stenosis, aortic stenosis, pulmonary stenosis.
- Chronic lung diseases.
Increased volume load occurs when a ventricle is required to eject more than normal volume of the blood resulting in cardiac failure. This is seen in the following conditions:
- Valvular insufficiency
- Severe anaemia
- Thyrotoxicosis
- Arteriovenous shunts
- Hypoxia due to lung diseases.
3. Impaired filling of cardiac chambers : Decreased cardiac output and cardiac failure may result from extra-cardiac causes or defect in filling of the heart:
- Cardiac tamponade e.g. haemopericardium, hydropericardium
- Constrictive pericarditis.
Types
Depending upon whether the HF develops rapidly or slowly:
1. Acute HF : Sudden and rapid development of heart failure occurs in the following conditions:
- Larger myocardial infarction
- Valve rupture
- Cardiac tamponade
- Massive pulmonary embolism
- Acute viral myocarditis
- Acute bacterial toxaemia.
In acute heart failure, there is sudden reduction in cardiac output resulting in systemic hypotension but oedema does not occur. Instead, a state of cardiogenic shock and cerebral hypoxia develops.
2. Chronic HF : More often, heart failure develops slowly as observed in the following states:
- Myocardial ischaemia from atherosclerotic coronary artery disease
- Multivalvular heart disease
- Systemic arterial hypertension
- Chronic lung diseases resulting in hypoxia and pulmonary arterial hypertension
- Progression of acute into chronic failure.
In chronic heart failure, compensatory mechanisms like tachycardia, cardiac dilatation and cardiac hypertrophy try to make adjustments so as to maintain adequate cardiac output. This often results in well-maintained arterial pressure and there is accumulation of oedema.
Depending upon part:
HF can affect predominantly left or right side of the heart or may involve both sides.
1. Left-sided HF
- Most common
- The major causes are systemic hypertension, mitral or aortic valve disease (stenosis), ischaemic heart disease, restrictive pericarditis, myocardial diseases e.g. cardiomyopathies, myocarditis.
- The major clinical menifestations are Dyspnoea, Cardiomegaly, Tachycardia, A 3rd heart sound S3, Fine rales at lung bases
2. Right-sided HF
- Right heart failure usually is the consequence of left-sided heart failure, since any pressure increase in the pulmonary circulation inevitably produces an increased burden on the right side of the heart.
- However, some conditions affect the right ventricle primarily, producing right-sided heart failure. These are consequence of left ventricular failure, cor pulmonale, pulmonary or tricuspid valvular disease, pulmonary hypertension secondary to pulmonary thromboembolism, myocardial disease affecting right heart, congenital heart disease with left-to-right shunt.
- Whatever be the underlying cause, the clinical manifestations of right-sided heart failure are upstream of the right heart such as -systemic and portal venous congestion, including hepatic and splenic enlargement, peripheral edema, pleural effusion, & ascites, reduced cardiac output.
- The major morphologic and clinical effects of pure right-sided heart failure differ from those of left-sided heart failure in that engorgement of the systemic and portal venous systems typically is pronounced and pulmonary congestion is minimal.
- Of note, in most cases of chronic cardiac decompensation, patients present with biventricular CHF, encompassing the clinical syndromes of both right-sided and left-sided heart failure.
Treatment
Heart failure can be managed as follows:
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