Heart failure is a condition when the heart can’t pump strongly enough to supply the body with oxygenated blood. There are many causes of heart failure which can be loosely organized as too much resistance/workload, direct damage to heart tissue, or abnormal heart structure.
Heart failure can be identified based on the site of the problematic pumping: left- vs right-sided heart failure. To compensate for the cause of the heart failure, the heart remodels and hypertrophies. The manner of hypertrophy (concentric vs eccentric) allows the heart to contract better but this is not sustainable. Histologically, remodeling is evident (ie cardiomyocytes get too plump to be nourished; contracting tissue gets replaced with stiffer and/or non contractile collagen tissue) and provide clues to the poor pumping. Thus, based on the manner of hypertrophy, left sided heart failure can be further subdivided into diastolic (or preserved ejection fraction) or systolic (or reduced ejection fraction) heart failure.
Left sided heart failure involves weak pumping of the left ventricle. This results in poor blood delivery to all parts of the body manifesting overall body weakness and fatigue. The blood that can’t be ejected out of the left ventricle, due to the poor pumping, will back up into the lung vasculature thus causing pulmonary consequences such as pulmonary edema. Due to the nature of excess fluid in alveoli, pulmonary edema may cause problems with oxygenation of blood and infection (pneumonia).
Right sided heart failure involves weak pumping of the right ventricle. Histologically, the right heart remodels to address both increased resistance and fluid overload, most often due to a pulmonary problem such as pulmonary hypertension. This remodeling is known as cor pulmonale. Insufficient pumping of the right ventricle results in poor blood delivery to the left heart: thus symptoms of right-sided overlap with those of left-sided. The blood that can’t get into the lungs cause a back up of blood into the right atrium and then into the superior & inferior vena cavae. This manifests as engorgement of the veins which are tributaries to the vena cavae: for SVC that would be engorged neck & subclavian veins. For IVC, that would be engorged abdominal veins manifesting in impaired venous drainage of both internal organs (e.g. liver) and external structures (e.g. legs & feet). Often – but not always – right sided heart failure develops from a pulmonary cause (i.e. high resistance) to its weak pumping. Thus, pulmonary symptoms might also be present. Right-sided heart failure can develop due to the pulmonary congestion seen in left-sided, but it not always the case.
Diagnosis of heart failure is done through a multidisciplinary team of allied health professionals. Cardiac ultrasound (echocardiogram) shows real-time anatomy and function of the heart. Cardiac ultrasound allows for measurements of heart structures (e.g. aortic valve opening) and determine pumping abilities (i.e. ejection fraction, wall kinetics) and extent of remodelling (e.g. wall thickness). Medical radiography technologists take X-rays of the chest thus allowing for a visualization of both heart size and lung structure. X-rays are good at determining the extent of pulmonary vessel engorgement and alveolar fluid as they create a radio-opacity (i.e. white/gray on X-ray) in a normally radio-luscent (i.e. black on X-ray) lung.
Pulmonary edema often can cause infection and pneumonia. Again, X-rays are useful in diagnosing pneumonia. However, medical laboratory technologists (microbiologists) can determine the pathogen causing the pneumonia and the antimicrobial agent which can be used to treat the infection (e.g. antibiotic)
- Heart failure is poor pumping – the site of the problem determining if it is left- vs right-sided heart failure.
- In response to the cause of heart failure, the heart will remodel (hypertrophy) to try to preserve pumping abilities. However, this is unsustainable. Eventually, there will be insufficient blood going to the body AND signs of blood backing up into structures upstream- thus causing further complications.
- Left sided heart failure will have signs of poor oxygenation to the whole body and lung symptoms such as pulmonary edema.
- Right sided heart failure will have signs of poor oxygenation to the whole body AND back up of blood in the tributaries of the vena cavae.
- Cardiac ultrasound gives a real time assessment of heart structure and function.
- Chest Xray gives a visualization of the size of the heart and the degree of fluid in lungs.
- Microbiologist can identify the pathogen that is causing pneumonia and suggest an antimicrobial as a treatment.
Author: Dr. Jennifer Kong (BCIT & UBC)
Gross anatomy video: Helen Dyck (UBC)
Histopathology video: Dr. Jonathan Bush (UBC, BC Childrens Hospital)
Cardiac Sonographer: Heather Bourke (Diagnostic Sonography, BCIT)
Videoproducer: Ian Whittlesey (BCIT)