Heart Failure: A Progressive Pathology

HEART FAILURE

💬 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. It may be acute or chronic. 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 end-result of various forms of serious heart diseases.

ETIOLOGY

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. The various diseases which may culminate in pump failure by this mechanism are as follows: i) Ischaemic heart disease ⅱ) Myocarditis ⅲ) Cardiomyopathies ⅳ) Metabolic disorders e.g. beriberi ⅴ) Disorders of the rhythm e.g. atrial fibrillation and flutter.
2. INCREASED WORKLOAD ON THE HEART: Increased mechanical load on the heart results in increased myocardial demand resulting in myocardial failure. Increased load on the heart may be in the form of pressure load or volume load. i) Increased pressure load may occur in the following states: a) Systemic and pulmonary arterial hypertension. b) Valvular disease e.g. mitral stenosis, aortic stenosis, pulmonary stenosis. c) Chronic lung diseases. ii) 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: a) Valvular insufficiency b) Severe anaemia c) Thyrotoxicosis d) Arteriovenous shunts e) Hypoxia due to lung diseases.
3. IMPAIRED FILLING OF CARDIAC CHAMBERS Decreased cardiac output and cardiac failure may result from extracardiac causes or defect in filling of the heart: a) Cardiac tamponade e.g. haemopericardium, hydropericardium b) Constrictive pericarditis.

TYPES OF HEART FAILURE

💬Heart failure may be acute or chronic, right-sided or left-sided and forward or backward failure.

ACUTE AND CHRONIC HEART FAILURE 

Depending upon whether the heart failure develops rapidly or slowly, it may be acute or chronic. 

• Acute heart failure Sudden and rapid development of heart failure occurs in the following conditions: i) Larger myocardial infarction ii) Valve rupture iii) Cardiac tamponade iv) Massive pulmonary embolism v) Acute viral myocarditis vi) 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.
• Chronic heart failure More often, heart failure develops slowly as observed in the following states: i) Myocardial ischaemia from atherosclerotic coronary artery disease ii) Multivalvular heart disease iii) Systemic arterial hypertension iv) Chronic lung diseases resulting in hypoxia and pulmonary arterial hypertension v) 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.

LEFT-SIDED AND RIGHT-SIDED HEART FAILURE

Though heart as an organ eventually fails as a whole, but functionally, the left and right heart act as independent units. From clinical point of view, therefore, it is helpful to consider failure of the left and right heart separately. The clinical manifestations of heart failure result from accumulation of excess fluid upstream to the left or right cardiac chamber whichever is initially affected

Schematic evolution of congestive heart failure and its effects.

Left Heart Failure

It is initiated by stress to the left heart. The major causes are as follows:

 

i) Systemic hypertension, most common.

ii) Mitral or aortic valve disease (stenosis)

iii) Ischaemic heart disease

iv) Myocardial diseases e.g. cardiomyopathies, myocarditis.

v) Restrictive pericarditis.

The clinical manifestations of left-sided heart failure result from decreased left ventricular output and hence there is accumulation of fluid upstream in the lungs. Accordingly, the major pathologic changes are as under:

i) Pulmonary congestion and oedema causes dyspnoea and orthopnoea.

ii) Decreased left ventricular output causing hypoperfusion and diminished oxygenation of tissues e.g. in kidneys causing ischaemic acute tubular necrosis, in brain causing hypoxic encephalopathy, and in skeletal muscles causing muscular weakness and fatigue.

HYPERTENSIVE HEART DISEASE 

Hypertensive heart disease or hypertensive cardiomyopathy results from systemic hypertension of prolonged duration and manifesting by left ventricular hypertrophy. Even mild hypertension (blood pressure higher than 140/90 mmHg) of sufficient duration may induce hypertensive heart disease. It is the second most common form of heart disease after IHD. As already pointed out, hypertension predisposes to atherosclerosis. Therefore, most patients of hypertensive heart disease have also advanced coronary atherosclerosis and may develop progressive IHD.

 Amongst the causes of death in hypertensive patients, cardiac decompensation leading to CHF accounts for about one-third of the patients; other causes of death are IHD, cerebrovascular stroke, renal failure following arteriolar nephrosclerosis, dissecting aneurysm of the aorta and sudden cardiac death.

Pathogenesis

  

Pathogenesis of left ventricular hypertrophy (LVH) which is most commonly caused by systemic hypertension is described here.

Stimulus to LVH is pressure overload in systemic hypertension. Both genetic and haemodynamic factors contribute to LVH. The stress of pressure on the ventricular wall causes increased production of myofilaments, myofibrils, other cell organelles and nuclear enlargement. Since the adult myocardial fibres do not divide, the fibres are hypertrophied. However, the sarcomeres may divide to increase the cell width.

LVH can be diagnosed by ECG. Aggressive control of hypertension can regress the left ventricular mass. Abnormalities of diastolic function in hypertension are more common in hypertension and is present in about one-third of patients with normal systolic function.

Right-sided Heart Failure

Right-sided heart failure occurs more often as a consequence of left-sided heart failure. However, some conditions affect the right ventricle primarily, producing right-sided heart failure. These are as follows:

1) As a consequence of left ventricular failure.

ii) Cor pulmonale or pulmonary heart disease in which right heart failure occurs due to intrinsic lung diseases, most common.

iii) Pulmonary or tricuspid valvular disease.

iv) Pulmonary hypertension secondary to pulmonary thromboembolism.

v) Myocardial disease affecting right heart.

vi) 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 (due to caval blood) and portal venous congestion and reduced cardiac output. Accordingly, the pathologic changes are as under:

i) Systemic venous congestion in different tissues and organs e.g. subcutaneous oedema on dependent parts, passive congestion of the liver, spleen, and kidneys, ascites, hydrothorax, congestion of leg veins and neck veins.

ii) Reduced cardiac output resulting in circulatory stagnation causing anoxia, cyanosis and coldness of extremities.