Heart failure is a pathophysiological state of the heart when cardiac performance is too low to maintain the cardiac output to meet the demands of the metabolizing tissues.
PATHOPHYSIOLOGY OF HEART FAILURE
Cardiac failure can occur in the following three situations:
1. Increase in preload. According to the Starling law of heart, an increase in preload (end-diastolic volume) augments cardiac function, but when there is too much increase in preload then leads to ventricular dilatation and heart failure.
2. Increase in afterload (resistance), e.g. in hypertension there is resistance to outflow of blood from the heart which causes overstretching leading to ventricular dilatation and heart failure.
3. Reduction in myocardial contractility, i.e. decrease in pumping ability of the heart decreases the cardiac output. The interaction of these three variables leads to the development of cardiac failure.
TYPES AND CAUSES OF HEART FAILURE
Heart failures can be classified by various ways:
I. Depending on the involvement of side of heart
1. Left heart failure. Anatomically, left heart comprises left atrium, left ventricle, aortic valve and mitral valve. The left heart failure, therefore, refers to the reduction in left ventricular output leading to elevation of left ventricular volume and pressure and its transmission to left atrium and pulmonary veins. The conditions causing left heart failure are:
(i) Left ventricular outflow obstruction due to:
Systemic hypertension
Aortic valve stenosis
Coarctation of aorta
ii) Left ventricular inflow obstruction due to mitral stenosis
(iii) Reduced ventricular contractility due to:
Cardiomyopathy particularly involving left ventricle and Anterior wall myocardial infarction.
2. Right heart failure. Like left heart, anatomically right heart includes right atrium, right ventricle and tricuspid and pulmonary valves. Right heart failure is a condition in which there is reduction in the right ventricular output leading to rise in the right ventricular and right atrial pressure, which further causes rise in jugular venous pressure, oedema, congestive hepatomegaly and congestion of viscera except lungs.
3. Biventricular (congestive) heart failure. In this condition, there is simultaneous involvement of right and left heart due to disease of myocardium, or left ventricular failure after sometimes involves the right heart also.
II. Depending on inadequate cardiac output
1. Forward heart failure results due to inadequate cardiac output
2. Backward heart failure is the one in which decreased cardiac output results in elevation of the end-diastolic volume and thus increases the ventricular pressure. The elevation of left and right ventricular pressure results in pulmonary and systemic congestion, respectively.
III. Systolic and diastolic heart failure
1. Systolic heart failure occurs due to poor myocardial contractility (systolic dysfunction).
2. Diastolic heart failure results due to poor ventricular filling because of defective relaxation. Both systolic and diastolic heart failures coexist particularly in myocardial infarction.
IV. High output and low output failure
1. High output failure is a state in which cardiac output remains high, i.e. at the upper limit of normal cardiac output (3.5 L/m2/min) even though cardiac functions are depressed. Various conditions which result in high output failure are:
Fever,
Thyrotoxicosis,
Anaemia, and
Beriberi.
2. Low output failure. In this state, cardiac output remains at its lowest limit (2.5 L/m2/min) at rest and in stressful conditions becomes further depressed, as in the case of heart failure secondary to ischaemic heart disease, hypertension, valvular and pericardial diseases.
CLINICAL FEATURES OF HEART FAILURE
Clinical features depend on the underlying disease and type of heart failure and these are as under:
1. Features due to low cardiac output are:
Fatigue,
Hypotension,
Poor tolerance to stress and
Oliguria.
2. Features due to the left heart failure are:
Cardiomegaly,
Cardiac arrhythmia,
Dyspnoea and orthopnoea.
3. Features due to the right heart failure are:
Rise in jugular venous pressure,
Hepatomegaly,
Peripheral oedema, ascites and hydrothorax.
4. Features of chronic heart failure:
Raised jugular venous pressure,
Oedema and
Congestive hepatomegaly.
DIAGNOSIS OF HEART FAILURE
Diagnosis of heart failure is mainly based on its clinical features and following investigations which are performed to establish the nature, severity and complications which have occurred.
1. Electrocardiography (ECG) findings may reveal arrhythmia, ventricular hypertrophy and myocardial infarction.
2. Radiography of chest may show enlargement of heart, congestion of lungs and certain valvular defects.
3. Biochemical tests include estimation of blood urea and electrolytes for renal failure, hypokalaemia and hyponatraemia.
TREATMENT OF HEART FAILURE
The basic principles of treatment of heart failure are aimed at to:
Remove the precipitating factors,
Correct the underlying cause,
Control the congestive heart failure state and
Prevent complications.
In general, following measures are employed as a treatment of cardiac failure:
A. To reduce cardiac workload
For this, complete bed rest is advised or patient is hospitalized for 1–2 weeks,
Small and light meals are recommended and
Drugs (like sedatives and antianxiety) are prescribed.
B. To improve myocardial contractility. Drugs like cardiac
glycosides (digitalis) and sympathomimetic amines are prescribed.
C. To control fluid retention. Dietary salt intake is restricted and diuretics are given.
D. To reduce afterload, use of vasodilator drugs, especially
angiotensin-converting enzyme inhibitors (captopril and enalapril) is recommended.