Resynchronizing the heart in heart failure
Channel: York Cardiology
Date: 22/05/2022

Today’s video is on the subject of heart failure and in particular on special type of pacemaker which can make a significant improvement to the quality of life and length of life in patients with heart failure.

What is heart failure.

The heart is a pump and if the heart is in some way damaged - be that by a heart attack or a virus or harmful drugs then the heart is unable to pump out enough blood to meet the body’s requirements especially when the body is asking for more blood such as during exercise. This inadequacy of the heart is often manifested with symptoms of breathlessness, fatigue and exercise intolerance and this is termed heart failure. Virtually all forms of heart disease, if progressive and if left unchecked will eventually end up with the heart weakening and thereby developing heart failure

People with heart failure in general will not live as long as they would have if they had a strong heart and in general they do not feel as good as they would if they had a strong heart and therefore heart failure will negatively impact on both length of life and quality of life. 

It is also important to understand that heart failure if left untreated is a progressive condition and i will try and explain how this happens.

When the heart pumps less blood out, our kidneys receive less blood than they expect and they therefore act almost in the same way as when one is dehydrated. They start retaining more salt and water in order to boost the circulatory volume. However the problem is not that we are lacking volume, it is just that the volume is not getting to the kidneys and therefore by increasing the volume, the kidneys still dont get the blood they expect and therefore they continue to increase retention of salt and water and slowly and gradually the amount of volume in the vascular system and the amount of blood enetering the heart progressively increases and the heart which has to contain all this blood starts stretching and in doing so, it becomes flabbier and weaker. 

The aims therefore in the management of heart failure are to try and firstly improve the patients quality of life by relieving symptoms but also try and prolong their life by giving them those medications that reduce the progression of heart failure. We now do have some really good medications that help do both and these include:

ACE Inhibitors/Entresto
Beta Blockers
MRAs - Mineraloreceptor antagonists
SGLT2 inhibitors

And ideally anyone with heart failure should be on all these medications unless they are intolerant or in some way the medications are contraindicated.
Nevertheless despite all the medications, a substantial proportion of heart failure patients remain significantly symptomatic and this is where cardiac resynchronication therapy has proved to be a game changer.

What we have realised is that as the heart gets weaker, it also gets bigger and flabbier and therefore electrical impulses take longer to get to some parts of the heart (usually the free wall of the left ventricle) compared to others. This means that some walls of the heart end up contracting earlier than others and this is referred to as cardiac desynchrony.

The way to think of cardiac dysnchrony is to think of a sac of potatoes. If you want to empty a sac of potatoes most efficiently, you would want to hold the bottom of the sac at both ends and then tip it over. If you only held one corner then some potato would fall to the other side rather than fall out of the sac. This is very similar to what happens with blood when it comes out of the heart. The heart will function more effectively if all the walls contract in synchrony and the greater the cardiac dysynchrony the more inefficient the heart is.

How do we know if there is cardiac dysynchrony?

The easiest way is to look at the ECG. On the ECG, we have the QRS complex and the duration of the QRS complex guides us on how long it has taken for the electrical impulses to go around the ventricles. The longer the QRS duration, the more the dysynchrony esp if there is a pattern called Left bundle branch block. The usual duration of the QRS is less than 120ms and if the QRS is more than 120ms then there is some dysynchrony and if it is more than 150ms then there is a lot of dysynchrony. In advanced heart failure, we also know that the longer the QRS, the poorer the prognosis and therefore scientists became very interested in exploring ways to reduce this dysynchrony. This led to the development of a special type of pacemaker called a BiV pacemker which involved putting a lead in the right ventricle and one in a vessel called the coronary sinus which overlies the left ventricle. This then allows a pacemaker to deliver electrical impulses to the ventricles in synchrony and hence allow for a more effective contraction of the heart.