By the end of this section, you will be able to:
- Define heart failure and hypertrophy.
- Differentiate between the heart failure types: right- vs left-sided heart failure.
- Explain how common causes of heart failure.
- Differentiate between concentric vs eccentric hypertrophy.
What is Heart Failure?
Heart failure is when your heart muscle can not contract strongly enough to eject all of its blood to its destination. As a result, the heart can’t deliver the blood needed for the body to function well AND a redistribution (i.e. backup) of blood due to the poor pumping. As a result, heart failure will have signs and symptoms in both the cardiovascular and non-cardiac systems.
Types of Heart Failure
The type of heart failure depends on the location of the poor pumping. If the right ventricle is too weak in pumping, this is called “right sided heart failure”. If the left ventricle has poor pumping abilities, this is called “left-sided heart failure.
Left sided heart failure can be subdivided into two subtypes:
- systolic failure (a.k.a. heart failure with reduced ejection fraction)
- diastolic failure (a.k.a. heart failure with preserved ejection fraction)
We will discuss these subtypes in more depth in the next chapter
Conditions that Lead to Heart Failure
Heart failure is a result of injury to the heart and/or the heart can’t keep up with what the body needs due to a variety of reasons. Regardless of which type of heart failure, heart failure is commonly caused by:
- Asking the heart to work abnormally hard for too long due to some kind of increased resistance downstream of the ventricle (i.e. ):
- Valvular disease, chronic high blood pressure, severe lung disease
- The heart muscle is directly hurt by:
- Not enough oxygen or nutrients to feed the heart muscle during pumping (eg. decrease blood flow to coronary arteries due to coronary artery disease)
- Increased workload for remaining undamaged heart tissue (e.g. previous myocardial infarction causing loss of viable heart tissue)
- Damage due to infection or inflammation
- Certain medications and illicit drugs
- Heart is not ‘made well’ (i.e. abnormal structure) thus can’t contract and fill efficiently. Examples of abnormal structure are:
- Congenital (i.e. since birth) heart defect of muscles and/or valves,
- Defects in heart’s electrical system causing arrhythmias – resulting in heart beating too fast, slow, or irregular.
Concentric versus Eccentric Hypertrophy
What is Hypertrophy?
Hearts, like any muscle, get bigger and thicker when it has a lot of resistance/workload to frequently push against. It’s like lifting hand weights to increase the size of the bicep. The cells in heart tissue get individually larger – not more numerous. This enlargement of muscle cells – whether it’s cardiac or skeletal muscle – is known as . The muscle cell hypertrophies because it is adding more contractile proteins to enable greater contractile strength. Going back to the bicep example – the larger bicep is because each individual bicep muscle cell undergoes hypertrophy even though it has not changed in muscle cell number.
Thus, the walls of muscle hypertrophy when there is chronically a lot of resistance/workload. That means each cardiomyocyte is undergoing hypertrophy, rather than dividing into more cells (), as cardiomyocytes can’t undergo cell division.
During hypertrophy, cells of the heart wall can:
a) Become bigger in circumference. These plumper cardiomyocytes make the heart wall grow thicker from the outside in, resulting in the heart becoming heavier. The larger in circumference the cells get, the harder it is for oxygen and nutrients to diffuse inside the cell which will eventually cause metabolic problems. This is the basis of concentric hypertrophy
b) Become longer in length and more narrow in circumference. there more narrow cardiomyocytes are ‘stretched out’ because the heart wall is undergoing more tension with over-filling with blood volume. To adapt to this stretching, the heart remodels replacing contracting cardiomyocytes with non-contractile cardiac cells. As a result, the heart wall get thinner with weaker contractile strength. This is the basis of eccentric hypertrophy.
c) Remodel (i.e. change their cellular make up in tissue). When the cardiomyocytes do not get enough oxygen and/or nutrients (e.g. heart attack, extreme hypertrophy) or receive increased inflammatory signals (e.g. inflammation, infection), the cardiomyocytes will die. As a result, the cardiomyocytes are then replaced with connective tissue – principally collagen – which is NOT contractile. As a result, the heart tissue will be less contractile and thus harder to empty the chamber. In addition, the collagen- filled heart wall becomes stiffer thus not as stretchy to fill easily.
Concentric hypertrophy occurs when the left ventricular wall is remodelling due to a chronically increased resistance to push against. The LV wall gets thicker (due to plumper cardiomyocytes) resulting in the space within the ventricle (i.e. lumen) shrinking. This shrinkage of lumen means less volume of blood available to fill during diastole. At first, ejection fraction is preserved despite less diastolic filling, thus giving rise to the alternate terms of “” or “heart failure with preserved ejection fraction”. Because ejection fraction is preserved, the body is getting sufficient supply of blood thus there would be few signs/symptoms.
However, as the wall gets thicker, it becomes stiffer and not as “stretchy” to fill easily. Eventually, there will be a point where the diastolic filling volume will not be enough to maintain sufficient ejection fraction, regardless of how well the LV wall can pump. This is when signs and symptoms will begin to be noticed.
When the heart chambers get overloaded with volume, the cells of the heart wall will compensate by becoming thinner & longer. This overfilling will cause the heart to remodel into a larger lumen with thinner walls and less contractile strength. If this eccentric hypertrophy occurs in the ventricle, this would be or “heart failure with reduced ejection fraction” as the volume to pump is sufficient but the pumping ability is too weak. Unfortunately, as ejection fraction is reduced, there will be even more fluid left in the chamber – thus complicating the already chronic volume overload.
- You can have both concentric and eccentric cardiomyopathy if the heart has to deal with both increased pressure and increased volume.
- Both systolic and diastolic failure have the same end result: the heart can’t pump enough blood out to feed the body.
the pressure/resistance against which the heart must work in order to eject blood for each contraction
tissue is enlarged due to each individual cell becoming larger, often with an increase of cytoplasmic contents such as contractile proteins as in the case with muscle tissue
tissue that is enlarged due to an increased number of new cells
The left ventricle can't fill well during diastole because the ventricular walls can't relax well and/or the ventricular lumen size is reduced
The left ventricle is unable to contract strongly enough during systole. As a result, not enough blood leaves the heart to nourish the rest of the body