What is heart failure?
Heart failure is most simply explained as an inability of the heart to pump enough blood to the body. This may be very mild, leading to little in the way of symptoms, or may be very severe. There are many different causes and reasons for pump failure. To understand this better, it is useful to consider the different components of the heart including the ventricles (main pumping chambers), the atria (smaller chambers), the heart valves, the electrical conduction system in the heart and the blood supply to the heart. It is also important to understand that factors outside of the heart can also worsen the efficiency of the pump.
The ventricles are the main pumping chambers pushing blood to both the body and the lungs. The left ventricle squeezes blood to the body and brain, while the right ventricle pushes blood into the lungs, where it picks up oxygen. When the ventricles squeeze, this is called systole in medical terminology and when they relax in between beats, it is called diastole.
Left ventricular dysfunction
When the left ventricle fails to contract properly, this is called left ventricular systolic dysfunction, which you may see written on medical letters. The ventricle may not be contracting for a number of reasons, including poor blood supply due to coronary disease (narrowings in the arteries supplying blood to the heart), damaged heart muscle from a previous heart attack or a cardiomyopathy (problem with the muscle itself), which can in some patients lead to weakening and dilatation of the ventricle. Some medications can worsen ventricular function and so a review of concurrent medications is necessary.
In some people the left ventricle does not relax properly in diastole (between beats). The muscle may contract well, but in between beats the heart does not fill properly with blood. The heart then contracts, but little blood is expelled with each beat. sometimes impaired relaxation is associated with heart muscle enlargement. Conditions that cause enlarged heart muscle, include high blood pressure and hypertrophic cardiomyopathy which may be genetic, running in families. The heart muscle with high blood pressure has to do significant work to pump out blood and like many muscles progressively enlarges, in response to the exercise. In certain types of cardiomyopathy (problems with the muscle itself) the heart muscle grows in size anyway despite there being no clear trigger. There are a range of less common conditions (infiltrative conditions) which can cause the walls of the heart muscle to enlarge, due to the body depositing abnormal amounts of polysaccharides (type of carbohydrate) or proteins in the muscle itself.
Right ventricular dysfunction
Whilst left ventricular pump failure is common, some patients may have problems with the right ventricle, which pumps blood to the lungs. This can be caused by a similar set of cardiac causes, but may be related to underlying disease in the lungs. Lung disease often leads to lower oxygen levels and constriction of the blood vessels in the lungs. The right ventricle then struggles to pump blood through the lungs and is less efficient at returning blood to the left side of the heart, so that it can be pumped onwards the body.
The atria are the upper chambers of the heart and are important, as they help to squeeze blood into the ventricles (main pumping chambers) in between beats. Conditions that affect the contraction and co-ordination of these upper chambers, can effect the efficiency of the pump. The most common of these is atrial fibrillation (please see section on atrial fibrillation) but there are other possibilities.
The heart valves
In broad terms, problems with any of the heart valves can cause heart failure. There are four valves in the heart including the tricuspid and pulmonary valves on the right side, along with the aortic and mitral valves on the left side. Valves may become thickened and restricted, with poor opening, meaning that that heart chambers struggle to pump blood through them. In other conditions the valves can become incompetent, where they open allowing blood through, but do not close properly allowing blood to pass backwards in between beats. In this setting the heart muscle has to pump far more blood to be effective, as some of the blood it ejects passes back where it came with each beat.
The electrical conduction system
The healthy heart is very synchronised. Problems with the electrical work can cause failure or abnormality of conduction. This results in the heart chambers acting independently, or out of sync, decreasing the efficiency of the pump. Problems with electrical conduction can also cause abnormal contraction, within the ventricles themselves, known as intra-ventricular dysynchrony. An easy analogy is considering an ice cream cone as a pump (the ventricle). It would be best for the cone to contract from the bottom up, squeezing blood out. If the electrical conduction was damaged however and the cone squeezed first at the top, then not all the blood would be expelled efficiently from the bottom.
Blood supply to the heart
If the blood supply to the heart is poor, due to narrowings in the coronary arteries, then this may lead to dysfunction of the pumping chambers, abnormal heart rhythms including atrial fibrillation, problems with the heart valves and failure of the electrical systems in the heart, all of which can lead to heart failure.
Diagnosis, Investigation and Treatment
The diagnosis, investigation and treatment may be very varied and should be focused on the underlying problem. In many patients this will include an ECG (heart tracing) to assess the heart rhythm, an echocardiogram (ultrasound scan) to assess the pump function and valves. There are a range of other scans that may be required in specific individuals, to ensure the blood flow to the heart is normal, or further assess the heart muscle in more detail. Treatments will often include medication but may include procedures to improve the blood supply to the heart, improve electrical conduction (different types of pacemakers) or correct abnormal heart rhythms. Your doctor will be able to advise you further.
Useful educational links
European Society of Cardiology: 2016 ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure
National Institute for Health and Care Excellence: 2010 Chronic heart failure. Management of chronic heart failure in adults in primary and secondary care
National Institute for Health and Care Excellence: 2014 Acute Heart failure: Diagnosis and Management
American College of Cardiology Foundation and American Heart Association: 2013 Guideline for the management of heart failure
ACC/ AHA / HFSA Focused update of the 2013 Guideline for the management of heart failure
British Heart Foundation: An every day guide to living with heart failure