Congestive heart failure pathophysiology

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Congestive Heart Failure Microchapters

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Patient Information

Overview

Historical Perspective

Classification

Pathophysiology

Systolic Dysfunction
Diastolic Dysfunction
HFpEF
HFrEF

Causes

Differentiating Congestive heart failure from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Clinical Assessment

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

Chest X Ray

Cardiac MRI

Echocardiography

Exercise Stress Test

Myocardial Viability Studies

Cardiac Catheterization

Other Imaging Studies

Other Diagnostic Studies

Treatment

Invasive Hemodynamic Monitoring

Medical Therapy:

Summary
Acute Pharmacotherapy
Chronic Pharmacotherapy in HFpEF
Chronic Pharmacotherapy in HFrEF
Diuretics
ACE Inhibitors
Angiotensin receptor blockers
Aldosterone Antagonists
Beta Blockers
Ca Channel Blockers
Nitrates
Hydralazine
Positive Inotropics
Anticoagulants
Angiotensin Receptor-Neprilysin Inhibitor
Antiarrhythmic Drugs
Nutritional Supplements
Hormonal Therapies
Drugs to Avoid
Drug Interactions
Treatment of underlying causes
Associated conditions

Exercise Training

Surgical Therapy:

Biventricular Pacing or Cardiac Resynchronization Therapy (CRT)
Implantation of Intracardiac Defibrillator
Ultrafiltration
Cardiac Surgery
Left Ventricular Assist Devices (LVADs)
Cardiac Transplantation

ACC/AHA Guideline Recommendations

Initial and Serial Evaluation of the HF Patient
Hospitalized Patient
Patients With a Prior MI
Sudden Cardiac Death Prevention
Surgical/Percutaneous/Transcather Interventional Treatments of HF
Patients at high risk for developing heart failure (Stage A)
Patients with cardiac structural abnormalities or remodeling who have not developed heart failure symptoms (Stage B)
Patients with current or prior symptoms of heart failure (Stage C)
Patients with refractory end-stage heart failure (Stage D)
Coordinating Care for Patients With Chronic HF
Quality Metrics/Performance Measures

Implementation of Practice Guidelines

Congestive heart failure end-of-life considerations

Specific Groups:

Special Populations
Patients who have concomitant disorders
Obstructive Sleep Apnea in the Patient with CHF
NSTEMI with Heart Failure and Cardiogenic Shock

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Risk calculators and risk factors for Congestive heart failure pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Saleh El Dassouki, M.D [3], Atif Mohammad, MD

Overview

Heart failure is a complex syndrome whereby there is inadequate output of the heart to meet the metabolic demands of the body. Abnormal function of different anatomic parts of the heart cause heart failure including the pericardium, the myocardium, the endocardium, the heart valves and the great vessels. Symptoms of heart failure are due to a lack of both forward blood flow to the body, and backward flow into the lungs.

Underlying Anatomic Abnormalities

Heart failure may result from an abnormality or dysfunction of any one of the anatomical structures of the heart:

Mechanism by Which Anatomic Structures are Damaged

Systolic versus Diastolic Dysfunction

Heart failure was once thought to be secondary to a depressed left ventricular ejection fraction. However, studies have shown that approximately 50% of patients who are diagnosed with heart failure have a normal ejection fraction (diastolic dysfunction). Patients may be broadly classified as having heart failure with depressed left ventricular ejection fraction (systolic dysfunction) or normal/preserved ejection fraction (diastolic dysfunction). Systolic and diastolic dysfunction commonly occur in conjunction with each other.

Pathophysiology

  • In systolic heart failure, there is reduced contractility of the heart and a reduced left ventricular ejection fraction.
  • In systolic heart failure, there is a failure of blood to move forward (forward failure) and a tendency of blood to move back ward (backward failure).
  • Normally, blood flows from the lungs, into the pulmonary veins, into the left atrium, through the mitral valve, and finally into the left ventricle. When the left ventricle cannot be normally filled during diastole in both diastolic and systolic heart failure, blood will back up into the left atrium and, eventually, into the lungs. The result is a higher than normal pressure of blood within the vessels of the lung. As a result of hydrostatic forces, this high pressure leads to leaking of fluid (i.e. transudate) from the lung's blood vessels into the air-spaces (alveoli) of the lungs. The result is pulmonary edema, a condition characterized by difficulty breathing, inadequate oxygenation of blood, and, if severe and untreated, death.
  • A reduced stroke volume, as a result of a failure of systole, diastole or both. Increased end systolic volume is usually caused by reduced contractility. Decreased end diastolic volume results from impaired ventricular filling – as occurs when the compliance of the ventricle falls (i.e. when the walls stiffen in diastolic dysfunciton).

Compensatory Mechanisms

  • Left ventricular systolic dysfunction is associated with a reduction in stroke volume, the amount of blood the heart ejects with each heart beat.
  • The reduction in stroke volume leads to a reduction in cardiac output which is the stroke volume multiplied by the heart rate.
  • There are two compensatory mechanisms to preserve forward cardiac output (the product of stroke volume and heart rate):
  1. Dilation of the left ventricle to increase the stroke volume and
  2. Increase in heart rate

Pulmonary Edema

End Organ Hypoperfusion

  • The reduction in forward cardiac output leads to hypoperfusion at rest which is suggested by



  • Reduced spare capacity. As the heart works harder to meet normal metabolic demands, the amount cardiac output can increase in times of increased oxygen demand (e.g. exercise) is reduced. This contributes to the exercise intolerance commonly seen in heart failure. This translates to the loss of one's cardiac reserve. The cardiac reserve refers to the ability of the heart to work harder during exercise or strenuous activity. Since the heart has to work harder to meet the normal metabolic demands, it is incapable of meeting the metabolic demands of the body during exercise.
  • Increased heart rate, stimulated by increased sympathetic activity[2] in order to maintain cardiac output. Initially, this helps compensate for heart failure by maintaining blood pressure and perfusion, but places further strain on the myocardium, increasing coronary perfusion requirements, which can lead to worsening of ischemic heart disease. Sympathetic activity may also cause potentially fatal arrhythmias.
  • Hypertrophy (an increase in physical size) of the myocardium, caused by the terminally differentiated heart muscle fibres increasing in size in an attempt to improve contractility. This may contribute to the increased stiffness and decreased ability to relax during diastole.
  • Enlargement of the ventricles, contributing to the enlargement and spherical shape of the failing heart. The increase in ventricular volume also causes a reduction in stroke volume due to mechanical and contractile inefficiency.[3]

The general effect is one of reduced cardiac output and increased strain on the heart. This increases the risk of cardiac arrest (specifically due to ventricular dysrhythmias), and reduces blood supply to the rest of the body. In chronic disease the reduced cardiac output causes a number of changes in the rest of the body, some of which are physiological compensations, some of which are part of the disease process:

  • Arterial blood pressure falls. This destimulates baroreceptors in the carotid sinus and aortic arch which link to the nucleus tractus solitarius. This center in the brain increases sympathetic activity, releasing catecholamines into the blood stream. Binding to alpha-1 receptors results in systemic arterial vasoconstriction. This helps restore blood pressure but also increases the total peripheral resistance, increasing the workload of the heart. Binding to beta-1 receptors in the myocardium increases the heart rate and make contractions more forceful, in an attempt to increase cardiac output. This also, however, increases the amount of work the heart has to perform.
  • Increased sympathetic stimulation also causes the hypothalamus to secrete vasopressin (also known as antidiuretic hormone or ADH), which causes fluid retention at the kidneys. This increases the blood volume and blood pressure.
  • Reduced perfusion (blood flow) to the kidneys stimulates the release of renin – an enzyme which catalyses the production of the potent vasopressor angiotensin. Angiotensin and its metabolites cause further vasocontriction, and stimulate increased secretion of the steroid aldosterone from the adrenal glands. This promotes salt and fluid retention at the kidneys, also increasing the blood volume.
  • The chronically high levels of circulating neuroendocrine hormones such as catecholamines, renin, angiotensin, and aldosterone affects the myocardium directly, causing structural remodelling of the heart over the long term. Many of these remodelling effects seem to be mediated by transforming growth factor beta (TGF-beta), which is a common downstream target of the signal transduction cascade initiated by catecholamines[4] and angiotensin II,[5] and also by epidermal growth factor (EGF), which is a target of the signaling pathway activated by aldosterone[6]
  • Reduced perfusion of skeletal muscle causes atrophy of the muscle fibres. This can result in weakness, increased fatigueability and decreased peak strength - all contributing to exercise intolerance.[7]

The increased peripheral resistance and greater blood volume place further strain on the heart and accelerates the process of damage to the myocardium. Vasoconstriction and fluid retention produce an increased hydrostatic pressure in the capillaries. This shifts the balance of forces in favour of interstitial fluid formation as the increased pressure forces additional fluid out of the blood, into the tissue. This results in edema (fluid build-up) in the tissues. In right-sided heart failure this commonly starts in the ankles where venous pressure is high due to the effects of gravity (although if the patient is bed-ridden, fluid accumulation may begin in the sacral region.) It may also occur in the abdominal cavity, where the fluid build-up is called ascites. In left-sided heart failure edema can occur in the lungs - this is called cardiogenic pulmonary edema. This reduces spare capacity for ventilation, causes stiffening of the lungs and reduces the efficiency of gas exchange by increasing the distance between the air and the blood. The consequences of this are shortness of breath, orthopnea and paroxysmal nocturnal dyspnea.

In severe cardiomyopathy, the effects of decreased cardiac output and poor perfusion become more apparent, and patients will manifest with cold and clammy extremities, cyanosis, claudication, generalized weakness, dizziness, and syncope.

The resultant hypoxia caused by pulmonary edema causes vasoconstriction in the pulmonary circulation, which results in pulmonary hypertension. Since the right ventricle generates far lower pressures than the left ventricle (approximately 20 mmHg versus around 120 mmHg, respectively, in the healthy individual) but nonetheless generates cardiac output exactly equal to the left ventricle, this means that a small increase in pulmonary vascular resistance causes a large increase in amount of work the right ventricle must perform. However, the main mechanism by which left-sided heart failure causes right-sided heart failure is actually not well understood. Some theories invoke mechanisms that are mediated by neurohormonal activation.[8] Mechanical effects may also contribute. As the left ventricle distends, the intraventricular septum bows into the right ventricle, decreasing the capacity of the right ventricle.

Pathology

Microscopic Pathology

Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology




References

  1. Boron and Boulpaep 2005 Medical Physiology Updated Edition p533 ISBN 0-7216-3256-4
  2. Rang HP (2003). Pharmacology. Edinburgh: Churchill Livingstone. p. 127. ISBN 0-443-07145-4.
  3. Template:GPnotebook
  4. Shigeyama J, Yasumura Y, Sakamoto A; et al. (2005). "Increased gene expression of collagen Types I and III is inhibited by beta-receptor blockade in patients with dilated cardiomyopathy". Eur. Heart J. 26 (24): 2698–705. doi:10.1093/eurheartj/ehi492. PMID 16204268. Unknown parameter |month= ignored (help)
  5. Tsutsui H, Matsushima S, Kinugawa S; et al. (2007). "Angiotensin II type 1 receptor blocker attenuates myocardial remodeling and preserves diastolic function in diabetic heart" (– Scholar search). Hypertens. Res. 30 (5): 439–49. doi:10.1291/hypres.30.439. PMID 17587756. Unknown parameter |month= ignored (help)[dead link]
  6. Krug AW, Grossmann C, Schuster C; et al. (2003). "Aldosterone stimulates epidermal growth factor receptor expression". J. Biol. Chem. 278 (44): 43060–6. doi:10.1074/jbc.M308134200. PMID 12939263. Unknown parameter |month= ignored (help)
  7. Template:GPnotebook
  8. Hunter JG, Boon NA, Davidson S, Colledge NR, Walker B (2006). Davidson's principles & practice of medicine. Elsevier/Churchill Livingstone. p. 544. ISBN 0-443-10057-8.

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