3.6 Pathology of CHF
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What is CHF?
- Failure of the heart as a pump
- Not a specific disease, but a complication of other disorders, and due to any condition that places an excess workload on the heart
- Damaged heart muscle contracts weakly or inadequately, and the chambers cannot empty properly
- Leading discharge dx in hospitalized pts over 65 yo
- Very common w/ a poor prognosis, w/ a mortality of more than 50% in less than 5 years
- Underlying or contributing cause of death of an estimated 300,000 individuals annually in the US and for which about 2 million pts are currently being treated
What is the pathophysiology of CHF?
Characterized by diminished CO (forward failure) or damming back of blood in the venous system (backward failure) or both
What are compensatory mechanisms involved in preventing CHF?
- 1. Increased sympathetic stimulation
- 2. Fluid retention
- 3. Cardiac muscle hypertrophy
What does increased sympathetic stimulation due to prevent CHF?
- ↑ both the HR and myocardial contractility by release of Norepinephrine
- In severe CHF, the hearts metabolic needs ↑ sympathetic stimulation, leading to myocardial ischemia and Angina when the coronary blood flow is not adequate to meet the hearts needs
How does the RAS respond in protecting against heart failure and the pitfall of this system to the body?
- Activated which increases Na+ and water retention
- Fluid retained by the kidneys causes a progressive ↑ in the vascular volume w/ an accompanying ↑ in venous return to the heart, leading to ↑ filling and stretching of the myocardium (chamber dilation)
- Increased preload or dilation helps to sustain cardiac performance by enhancing contractility
- Increase in vascular volume ⇉ Edema
What is the mechanism of cardiac hypertrophy in protecting the heart?
- Compensatory response of the myocardium to ↑ mechanical work
- Volume-overloaded ventricles develop hypertrophy accompanied by dilation w/ ↑ ventricular diameters
- Hearts usually range up to about 600 g
What is the difference between heart failure and backward heart failure?
- Forward failure impairs movement of blood into the vessels emerging from the heart
- Backward failure allows blood to accumulate in the vessels or heart chambers located behind the failing ventricles and results in congestion of the pulmonary and venous system circulation
What is the difference between the causes of left heart failure and right heart failure?
- Left - ischemic heart disease, HTN, aortic and mitral valve disease, and non-ischemic myocardial disease (myocarditis)
- Morphologic and clinical effects primarily results from progressive damming of blood w/in the pulmonary circulation and the consequences of diminished peripheral blood flow
- Right - Secondary consequence of left heart failure b/c any ↑ in pressure in the pulmonary circulation incident to left heart failure produces an ↑ burden on the right side; therefore, the causes of right heart failure must include all those that induce left heart failure
- RHF causes congestion of the peripheral organs and extremities
What are the features of the heart and the lungs in left-sided CHF?
- Left ventricle - hypertrophied w/ massive chamber dilation
- Then secondary enlargement of the left atrium
- Enlargement may cause A. Fib. w/ blood stasis and possible thrombus formation w/ the change of emboli
- Lungs - ↑ pressure in the pulmonary veins is transmitted retrograde to the capillaries and arteries, resulting in pulmonary congestion and edema w/ heavy, wet lungs
- Edematous widening of the alveolar septae and accumulation of edematous fluid in the alveolar spaces
What are "Heart Failure Cells" in left sided CHF?
Iron-containing hemoglobin from erythrocytes leak from the congested capillaries into the alveoli, the RBC's are phagocytized by alveolar macrophages and are converted to hemosiderin w/in the edematous fluid
What are the clinical features of left-sided CHF?
Accumulated fluid causes cough, fatigue, limb weakness, and dyspnea (breathlessness) on exertion, along w/ orthopnea which is dyspnea on lying down, relieved by sitting or standing
What are the kidneys like in CHF?
↓ CO causes a reduction in renal perfusion, activating RAS, inducing retention of salt and water, expanding the blood volume, which contributes to the pulmonary edema
What is the brain like in CHF?
Far-advanced CHF, the cerebral hypoxia may give rise to hypoxic encephalopathy w/ stupor, loss of consciousness, restlessness, and possible coma
What is the #1 reason for right-sided CHF?
Left Heart Failure
What is Nut-Meg Liver?
- Liver increased in size and weight, and a cut section displays chronic passive congestion grossly w/ congestion around the central veins histologically
- W/ longstanding CHF, there may be centrilobular necrosis w/ sinusoidal congestion
- Liver can become engorged, and function may be impaired and later liver cells may die
What is the liver pathology in right-sided CHF?
- Elevated pressure in the portal veins and tributaries
- Congestion produces a tense, enlarged spleen (congestive splenomegaly) w/ a weight up to 600 grams
- Pressure in the abdominal veins may lead to the accumulation of fluid w/in the abdomen (ascites)
- Marked congestion leading to a greater fluid retention and peripheral edema
What are the clinical features of right-sided CHF?
- Peripheral Edema - more in lower extremities and in area over the sacrum
- Prominent ankle (pedal) and pretibial edema
- External jugular vein becomes distended, visualized as JVD
- Pleural effusions (>1 liter) may appear and can cause a partial atelectasis
- Congestion of the gut may cause anorexia, pain, and weight loss
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