Mount Elizabeth Novena Specialist Centre
38 Irrawaddy Road, #06-51/52; Singapore 329563
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Understanding Heart Failure Part 1
Heart Function
updated 26 July 2020
You (or someone you know) may have been told that you have "heart failure". The words are scary but it really is a medical definition which does not have a plain English equivalent. It can be serious but can be managed if you understand how it works.
It is one of the most common cause of admission to our hospitals but once our patients understands how it works, they can dramatically reduce the chance that they will need to be admitted to hospital.
You will need to monitor your weight and blood pressure and at the same time limit the amount of salt (and hence water) that you take in daily. Some medications have to be taken daily while some like the "water tablet" i.e. Frusemide or Bumetamide may need adjustment every few days.
How do we know if the heart is pumping properly
Systolic Function
Most people imagine that the heart is a pump. A measure of how good a pump is would probably be how much water (volume) it can pump and to what height (pressure). So a good pump for a fish tank would be one that pumps a small volume of water at a low pressure while a fireman may want a pump that pumps a large volume of water at a high pressure. A pump from a fire-engine would be useful for the fireman and bad for the fish. So a measure of how the heart is pumping would be to measure the pressure (our blood pressure) and volume (the stroke volume or how many c.c. of blood is ejected with each heart beat). This is essentially what we call the "Systolic Function".
A common way doctors quantify Systolic Function would be to measure the % of blood ejected with each heart beat and this is commonly called "Ejection Fraction" or "EF". A normal EF would be about 55% - 65%. This became a popular method as it was relatively easy to measure with an Echocardiography machine, once these machines became smaller, cheaper and faster in the 1980's with the advent of mass produced microprocessors like the Intel 8088 and Motorola 68000 chips.
We know that Ejection Fraction / EF is not a perfect way to measure systolic function, as it does not take into account the pressure of the blood and resistance of the arteries it is pumping the blood into. There are of course many other ways we use to measure Systolic Function but EF has become a convenient measure of heart function that is easily communicated to fellow doctors and patients.
Figure 1 shows a heart with a normal EF of ~ 55% and Figure 2 shows a heart with an EF of ~ 10%.
Figure 1
Figure 2
Diastolic Function
While it is important to know how much blood is being pumped out aka Systolic Function. The volume of blood and pressure at which the blood enters the heart is equally important. This is called the Diastolic Function.
It is actually very difficult to measure Diastolic Function as we cannot measure (easily) the pressure of the blood entering the heart. To do that, we would need to insert and park a pressure transducer inside the heart chamber (the left ventricle). The wire with the pressure transducer would need to come in from a vein in the arm or leg and enter the right heart, cross the atrial septum into the left atrium and pass the mitral valve into the left ventricle. Instead of using the vein; the only other method would require a wire from an artery in the wrist or groin which crosses the aortic valve (backwards) into the left ventricle.
The pressure of the blood entering the heart from the lungs cannot be too high as the lungs cannot tolerate high pressures. High pressures in the lung will lead to water leaking out into the air sacs causing Pulmonary Oedema or "water in the lungs". But if the heart is either very stiff or has enlarged or both, then the filling pressure of the heart will increase. During the period when the heart is receiving blood (called diastole), there is direct communication between the left ventricle, left atrium and the arteries of the lung. So elevated filling pressures in the heart is "transmitted" to the lungs and this leads to water in the lung and / or swelling of the feet or arms as well.
Figure 3 shows a Chest X-Ray of a patient with water in the lungs, there is a dialysis catheter inserted. The EF (Figure 4) is ~ 65% and the clues that the filling pressure may be elevated are the big left atrium and thickened heart muscles of the left ventricle making it very stiff.
Figure 3
Figure 3
Figure 4
Left Atrium
Left Ventricle
Heart Failure Reduced EF (HFPEF) and Heart Failure Preserved EF (HFREF)
Since the 1980's Heart Failure has been defined using poor EF and most research was carried out in these type of heart failure patients, But in patients with Heart Failure and normal EF, it was hard for a doctor to be sure that his / her patient with swollen legs or water in the lungs had heart failure as there are many other causes of swollen legs and water in the lung. The doctor can, by trial and error try the patient on medication that forces the kidney to pass out water or bring the patient to an invasive laboratory in a hospital to insert a catheter into the heart via the leg veins to measure the internal pressures of the heart.
Thankfully there are now several ways a doctor can diagnose and monitor a patient with heart failure in the clinic.
1. NT-Pro BNP
2. Echocardiogram (as mentioned above)
NT-Pro BNP (N-terminal Pro-Brain Naturetic Peptide).
This is a protein that was first discovered by Japanese scientist, Sudoh et al in 1988 in porcine brains hence the name BNP or Brain Naturetic Peptide. Recently we have shown that NT-Pro BNP is useful marker of heart failure in both New Zealand (European ethnicity) and Singaporean (Asian ethnicity) patients.
BNP's role in treatment
The latest and most promising medical therapy for heart failure involves a drug which stops BNP from breaking down, and we were fortunate to be involved in the PARADIGM-HF study with this "first in class" drug called Sacubitril/Valsartan (marketed as Entresto) which helps to increase the body's levels of BNP and has been shown to improve a patient's ability to work further as well as live longer. This was the first drug therapy which showed improved mortality since 1999 (RALES NEJM 1999).