In simplistic terms, this is an inherited condition which is diagnosed by finding an abnormally muscular heart (ventricular hypertrophy) without an obvious cause to explain the increased muscularity. It is caused by mutations in the genes that encode components of the contractile apparatus of the heart and therefore the heart muscle itself is abnormal and this is why it looks thicker. One thing to understand is that even though it is inherited the physical changes to the muscle walls may appear only later on in life.
It is an important condition to know about for several reasons:
- It is common and can manifest at any age
- It may be asymptomatic and yet can lead to dangerous and life-threatening heart rhythm disturbances and even sudden death in a minority of patients which may be preventable/treatable. It is probably the most common cause of sudden death in patients under the age of 30 and the most common cause of death in athletes.
- It can cause troublesome symptoms and therefore affect quality of life
- Most importantly, it can be passed onto relatives and children and therefore mandates family screening.
The prevalence is probably somewhere between 1 in 500 to 1 in 200 people. Much of the diagnosis is based on visualising the abnormally thickened heart muscle without finding another cause for it. Whereas we previously used Echo, we are now beginning to use MRI scanning (which allows better visualisation of the walls of the heart) and this is beginning to pick up even more cases of this condition hence the increased prevalence.
In the vast majority of patients, the increased muscle thickness is more prevalent in one part of the heart (esp the septum) and this is called assymmetrical hypertrophy which is very suggestive of the diagnosis because with other causes of hypertrophy such as hypertension, you would expect concentric hypertrophy. It is also worth noting that in some patients the thickening of the heart muscle can actually obstruct the blood flow out of the heart. This is called hypertrophic obstructive cardiomyopathy (HOCM).
What are the symptoms:
Many patients have no symptoms whatsoever and the only way they come to attention is because they were having an ECG or an Echo for some other reason or an astute doctor heard a heart murmur.
Those who do complain of symptoms often complain of breathlessness, fatigue, exercise intolerance, chest pains, palpitations, dizziness and blackouts (esp during or immediately after exertion)
Why do the symptoms happen:
There are a number of reasons. In patients with obstructive cardiomyopathy, the inability to get the blood our quickly enough especially during exertion can cause symptoms of a lack of blood everywhere and therefore less blood to the brain would cause dizziness and less blood to the rest of the body would cause fatigue and less blood to the heart arteries may cause chest pains. Sometimes the altered dynamics of blood trying to get through the obstruction can suck an adjacent mitral valve towards the jet which causes leaking of the mitral valve and can worsen the obstruction.
When there is a lot of muscle, it can outstrip its own blood supply and therefore at times of stress, the blood may not be able to supply all the heart muscle which can make small parts suffocate and cause the heart muscle to progressively weaken. In addition the suffocating muscle may become electrically irritable and thereby propagate heart rhythm abnormalities
As the muscle itself is abnormal, it can become irritable and cause heart rhythm disturbances at any time
Finally as the muscle is abnormally thickened, it is stiff and therefore does not relax as well as it should and this results in it not filling with as much blood and therefore pumps out less blood than is expected of it and as the heart rate increases, time allowed for relaxation gets even less and therefore the whole situation gets worse.
What tests do you need?
ECG: The ECG is often abnormal in some way. In fact less than 10% of patients with HCM have a normal ECG. As HCM is characterised by increased muscle thickness, the ECG may show very big complexes reflecting the increased muscle and there may also be abnormalities of the P waves, and T waves. An abnormal ECG should always prompt an echocardiogram.
Echo: The echocardiogram is the gold standard test in common practice. Usual wall thickness is in the order of 10mm. The finding of unexplained wall thickness of > 15mm is usually highly suggestive of the diagnosis. In a first degree relative of an affected person, a wall thickness of 13mm may also be highly suggestive. In addition, most of the time the abnormal thickness is located in one part of the heart compared to the others. Common areas to look for the abnormal thickness are in the septum, or even at the apex of the heart. This is why what we refer to as asymmetrical hypertrophy. The echo can also look for evidence of outflow obstruction and whether the mitral valve is affected by being pulled into the outflow by the acceelrated flow.
MRI: This is not necessary if the diagnosis is confirmed on a good quality echo. However many times the echo images may be substandard in which case an MRI will offer a much better image of the heart. In addition, MRI is very useful to look for scar (otherwise known as fibrosis) and there is some evidence that patients with a lot of fibrosis have a greater risk of heart rhythm abnormalities and death
A lot of additional testing is less about making the diagnosis but actually trying in some way to work out the patients’ risk for the future. These tests include:
- Heart rhythm monitoring – Patients may have asymptomatic heart rhythm disturbances especially runs of ventricular tachycardia which therefore points to a higher risk patient. Patients also have a higher incidence of atrial fibrillation and this is a particular high risk population for stroke and therefore regardless of the CHADS2VASC score, patients should be started on long term anticoagulation if found to have AF
- Exercise testing – It is useful to study how the heart copes with stress. In particular, we look for whether there is a drop in blood pressure on exercise. This indicates that the heart is not able to get blood enough to meet the body’s demands and points to a person who is at a higher risk.
As HCM is an inherited condition, it is important for all 1st degree relatives to be screened when this condition is diagnosed in a family member. Screening involves having an ECG and echocardiogram. Even if the tests are normal, the manifestations may develop (and most commonly in adolescence) so it is worth doing these tests annually in children from 12year to 18 years and 5 yearly thereafter.
I think it is also worth patients and their family members seeing a geneticist as some (but not all) gene abnormalities have been identified and if the affected member has a certain abnormality then we can look for the same abnormalities in the relatives and work out if they carry the abnormal gene. It is worth knowing that even though you may have the same gene it does not mean that the disease process will follow the same pattern and therefore all the other risk stratification has to be carried out and affected patients have to be assessed on an individual by individual basis.
I hope you found this blog useful. The management of HCM is a very complex subject and will need another blog which I promise to do very soon. Once again I hope you found this useful and would be so grateful if you would consider sharing with anyone you feel may benefit.