Heart Failure Flashcards
Heart Failure
Heart failure is a condition in which the heart cannot meet the functional needs of the body.
It may be of sudden onset (acute) or chronic.
It elicits a number of hemodynamic, neural, hormonal, and renal responses, and it is clinically assessed as compensated or decompensated.
In broad terms, the diseases causing heart failure can be classified into two main groups:
- Cardiac diseases: This group includes all primary and secondary heart diseases, such as coronary heart disease, endocarditis, cardiomyopathies.
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Extracardiac causes of heart failure: The main extracardiac causes of heart failure can be classified further as:
- Pressure overload (e.g., hypertension)
- Volume overload (e.g., hypervolemia due to water and sodium retention)
- Increased demand (e.g., increased metabolism in hyperthyroidism)
When cardiac function is impaired or the workload increases, the following compensatory mechanisms attempt to maintain arterial pressure and organ perfusion:
- Frank-Starling mechanism: Increased filling pressures dilate the heart and thereby increase functional cross-bridges in the sarcomeres, enhancing contractility.
- Myocardial hypertrophy with increased expression of contractile apparatus.
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Activation of neurohumoral systems.
- Autonomic nervous system adrenergic stimulation, increasing heart rate, contractility, and vascular resistance.
- Modulating blood volume and pressures by activation of the renin-angiotensin-aldosterone axis and release of atrial natriuretic peptide
What are the most common cardiac causes of heart failure?
- Most frequently heart failure occurs due to progressive deterioration of myocardial contractile function (systolic dysfunction); causes include ischemia, pressure or volume overload due to valvular disease, or primary myocardial failure.
- Occasionally CHF results from the inability of the heart chamber to relax and fill during diastole (diastolic dysfunction); causes include hypertrophy (most common), fibrosis, amyloid deposition, or constrictive pericarditis. This occurs more commonly over age 65 and more so in women than men.
The heart responds to pressure or volume overload by?
- Because adult myocytes cannot classically proliferate, the heart responds to pressure or volume overload by increasing myocyte size (myocyte hypertrophy);
- Similar hypertrophy is stimulated by chronic trophic signals (e.g., β-adrenergic signaling).
- The result is a larger and heavier heart.
What happens in pressure-overload hypertrophy (e.g., due to hypertension or aortic stenosis)?
New sarcomeres are assembled in parallel to the long axes of cells, expanding the cross-sectional area of myocytes in ventricles and causing a concentric increase in wall thickness.
What happens in volume overload hypertrophy (e.g., due to valvular insufficiency)?
New sarcomeres are assembled in series, causing ventricular dilation.
Best measure of hypertrophy in dilated hearts?
Heart weight.
Heart failure with volume or pressure overload may eventually result from a combination of:
- Aberrant myocyte metabolism.
- Alterations in intracellular calcium flux.
- Apoptosis.
- Genetic reprogramming.
- Increased heart mass is also an independent risk factor for sudden (presumably arrhythmic) cardiac death.
Left-Sided Heart Failure
Major causes:
- Ischemic heart disease (IHD)
- Hypertension
- Aortic and mitral valve disease.
- Intrinsic myocardial disease.
- Left-sided failure can be due to either systolic failure (inadequate contractile function) or diastolic dysfunction leading to poor filling.
Manifestations:
- Pulmonary congestion and edema due to regurgitant flow or impaired pulmonary outflow.
- Left atrial dilation with atrial fibrillation.
- Hypoxic encephalopathy due to reduced central nervous system perfusion.
- Reduced renal perfusion:
- Salt and water retention
- Ischemic acute kidney injury (AKI)
- Impaired waste excretion, causing prerenal azotemia
Right-Sided Heart Failure
Right-sided heart failure is most commonly caused by left-sided failure; thus in most cases patients present with biventricular CHF.
Isolated right-sided heart failure is caused by tricuspid or pulmonic valvular disease or by intrinsic pulmonary or pulmonary vasculature disease, causing functional right ventricular outflow obstruction (cor pulmonale).
Right-sided failure is manifested by the following:
- Right atrial and ventricular dilation and hypertrophy.
- Edema, typically in dependent peripheral locations (e.g., feet, ankles, sacrum) with serous ef usions in pericardial, pleural, or peritoneal spaces.
- Hepatomegaly with centrilobular congestion and atrophy, producing a nutmeg appearance (chronic passive congestion). With severe hypoxia, there is centrilobular necrosis, and elevated right-sided pressures cause central hemorrhage. Subsequent central fibrosis creates cardiac sclerosis.
- Congestive splenomegaly with sinusoidal dilation, focal hemorrhages, hemosiderin deposits, and fibrosis.
- Renal congestion, hypoxic injury, and AKI (more marked in right versus left-sided CHF).
Therapies for CHF
Therapies for CHF are primarily pharmacologic; they include diuretics to relieve fluid overload, angiotensin-converting enzyme inhibitors to block the renin-angiotensin-aldosterone axis, and β-1 blockers to lower adrenergic tone. Newer approaches include mechanical assist devices and resynchronization of electrical impulses to maximize cardiac efficiency.
What is the difference between forward and backward heart failure?
- Forward failure includes signs and symptoms of ischemia due to reduced systolic output.
- Backward failure includes signs of congestion due to inadequate emptying of the heart chambers.
In most clinical conditions, there are signs of both forward and backward failure.
What is high-output heart failure?
This subset of heart failure is characterized by a high cardiac output (high systolic ejection fraction) caused by increased demand. It is typically encountered in conditions such as anemia, thyrotoxicosis, beriberi, and pregnancy. Prolonged ventricular overload leads ultimately to overexhaustion of the heart and heart failure.
