Broadly speaking there are 3 things that can go wrong with the heart.
- The heart is a pump and that pump may be faulty either due to congenital problem or an acquired problem. If the pump is in any way defective then not as much blood comes out of the heart and the body and all our vital organs will get less blood than they should and this could lead to harm. So cardiomyopathies, valve problems, myocarditis and previous heart attacks all cause a problem with the pumping function of the heart.
- The pump needs a blood supply and even though the pump itself may be strong, there may be a developing problem with the blood vessels (the coronary vessels) which may block the blood vessel and therefore damage the heart. This is how heart attacks happen and therefore a comprehensive evaluation of the heart should always include some assessment of the heart arteries even if the heart as a pump looks strong
- Finally the heart is also an electrically driven organ and therefore a malfunction of the electrics could lead to the heart malfunctioning as a pump even if it were strong and this could cause a problem.
So virtually all the tests that we do on the heart are driven by the need to know more about the pumping ability of the heart, the heart arteries and the electrics of the heart.
So today i wanted to talk to you about what each heart test tells us about these different aspects of heart disease
Tests that tell you about the heart as a pump
The most commonly used test to assess the heart as a pump is an echocardiogram. This is an ultrasound (a bit like the type that we use on pregnant women to look at the baby). An ultrasound will allow you to visualise the heart, measure the sizes of the chambers, assess the heart valves and work out how well the heart functions as a pump. If the heart has been left damaged, then that part of. the heart will be seen not to move like undamaged parts and this can therefore reliably tell us about persisting heart damage. This is important for 2 reasons:
It tells us that the patient’s symptoms are not due to underlying heart disease and b) the heart will cope with stress much better than if it is damaged.
An echo is easy to do, risk free and easily accessible. It is also unique because it works using the Doppler effect, you can get not only an anatomical evaluation of the heart but also physiological assessment. Nevertheless it does have some limitations:
It tells us about the present and the past but does not generally tell us about the future.
It is operator dependant and requires specialised machinery
The images you get may vary from patient to patient.
You don’t see the heart in 3 dimensions and because of the heart moves in many different ways, you are only getting a limited assessment of the heart and you don’t get as good a sense of tissue composition
A more advanced way of studying the heart as a pump is through cardiac MRI. Cardiac MRI offers some great advantages:
- You get much better spatial resolution and therefore get much clearer images
- You have no imaging constraints
- MRI can tell you about tissue composition
There are however problems with cardiac MRI as well. It is a super specialised discipline. It requires very expensive machinery. It is inherently uncomfortable for the patient as you have to lie in a tight tunnel for up to an hour. Some patients with pacemakers and metal prosthesis can’t be exposed to such strong magnetic fields. Overall though a normal cardiac MRI is even more reassuring than a normal echocardiogram.
Are there any other easier tests that can tell you about the heart as a pump?
A simple standard 12 lead ECG can be helpful. The ECG is basically telling you about the journey of the electrical signals as they travel through the heart and therefore if there is a problem with the heart as a pump such as previous damage then the ECG pattern that you see may change from what a normal pattern should look like. It has to be a 12 lead ECG because you want to look at the heart from different angles otherwise you are getting a very skewed view from a single lead or 3 lead eCG. A normal ECG is generally reassuring but does not give you anywhere near the information that uou would get from an ECHO or MRI scan.
A blood test called BNP.
When the heart is not functioning optimally, it struggles to get the blood out with as much vigour and therefore the pressure within the heart increases. As the pressure increases the chambers of the heart stretch and release a biochemical called BNP. This biochemical serves to open up blood vessels and thereby reduce the pressure on the heart. BNP can be measured and if the BNP is exceptionally high then it is likely that the heart is not working as well as a pump as it should. The advantage of BNP is that it is just a simple blood test. The disadvantage is that the BNP can sometimes be high for other reasons and therefore you can have false positive BNP readings. A normal BNP however is generally reassuring.
So those are the tests that look at the structure of the heart
Now let’s talk about the second thing that can go wrong with the heart and that is narrowing of blood vessels. Generally the ECG or ECHO does not tell you about the blood vessels until when the blood vessels are so critically narrowed that the heart muscle is actually suffocating. If you have narrowing in blood vessels which only stop blood from getting through at times of stress or exercise then an ECG or an ECHO at rest may be completely normal despite there being a problem.
So we need different tests when we are evaluating the heart arteries.
These can broadly be divided into anatomical tests and functional tests. These actually offer complimentary information.
These look for coronary disease
The gold standard test is an invasive angiogram where a catheter is inserted into an artery, pushed all the way up, and dye is injected into the coronary arteries and this way the lumen of these arteries is delineated and any narrowings can easily be identified. The advantage of an angiogram is that if a narrowing is detected, it can be fixed with a stent at the same sitting as you are already inside the body.bAn invasive angiogram is very much the gold standard but it is an invasive test and carries some risk of damage to the blood vessels or the heart and also exposure to radiation and therefore is best reserved for high risk patients.
Another anatomical test that is now increasingly being utilised is CT angiography. This is a non-invasive test where a dye is injected into the back of the hand, the heart is slowed down to prevent too much movement and pictures of the heart and its blood vessels are taken with a CAT scanner. This is an exceptionally good test because it tells us not only about the present but also about the future. Patients with a completely normal CT scan are very unlikely to have a heart attack within the next 3-5 years. The problem with CT scanning is if you see something. Many times plaque within the heart arteries may have some calcium in it and calcium is extremely reflective and therefore may obscure what is behind it meaning that you may not accurately be able to work out how tight the vessel is because of this reflection of the rays by calcium and therefore not uncommonly many patients then end up having to an angiogram.
Functional tests – these tests are not directly looking at the coronary arteries but instead look at the heart muscle itself and tell us whether heart muscle gets all the blood it needs when it needs it. These are therefore not looking for coronary disease but instead ischemia heart disease. These don’t tell you if you have any narrowings but do tell you if you have narrowing that is so significant that it is actually preventing blood from getting through to the heart muscle. If there is a demand supply mismatch then it is most likely to show up during stress and therefore all these tests usually are done by inducing stress in the patient either via exercise or medications.
Common functional tests that we use are:
ECG stress tests – here a patient is attached to an ECG and stressed and we look on the ECG to see if there are any changes that develop as the patient’s heart is stressed. An ECG stress test is easily available but as you are only relying on the ECG, you do not get as much information as you could by actually visualising the heart such as with an ECHO. In addition, often especially in women you can get false positive results and therefore they are not recommended in women
STress echo – here an echo is done at rest and then the patient is stressed and when the heart is working really hard, the echo is repeated. Then we compare the two pictures. If the heart muscle looks like it is working pumping harder at stress compared to rest then we can conclude that there can’t be a significant narrowing in the blood vessels. If there is a significant narrowing then that part of the heart will not get as much blood during stress and therefore should not be able to pump harder and that can easily be seen on the images.
Similarly another way is stress perfusion scans. Here the patient is given some dye. The dye goes where blood goes and the heart lights up in dye. We then exercise the patient, give the dye again and take another image. If we see that the heart is covered in dye at rest and similarly on exercise then we can conclude that there is no restriction to blood. If on the other hand we see that at stress there is an area that does not light up with dye then that suggests a heart artery narrowing.
Remember functional tests tell you about ischemia and anatomical tests tell you about coronary disease. It is still possible to have ischemia without coronary disease. If a patient is very anaemic and has very little blood then the heart may still suffocate i.e. become ischemic even in the absence of coronary disease.
Finally there may be electrical problems with the heart and unfortunately these are usually only diagnosed when they are actually happening. It is impossible to predict these. What I mean is that just because I have a normally pumping heart and normal blood vessels, I am still not immune to developing a heart rhythm problem. The reassuring thing however is that if I do have a normally pumping heart and normal blood vessels then it is unlikely that most heart rhythm disturbances will be dangerous because my heart should be able to cope even if the heart rate goes up to 200/min.
In terms of diagnosing heart rhythm abnormalities, we can only accurately diagnose a problem if you catch it happening on ECG. Usually even a single lead ECG is enough because the rhythm is the rhythm. So when a patient has palpitations, the only way to catch the palpitations is to provide the patient with a heart monitor for as long as a duration as possible in order to maximise the chances of catching it. If the patient has noticed a particular trigger such as stress then you can try and provoke the symptoms whilst the patient is wearing the monitor.
There are different types of monitors available and it is only worth getting the one that is of long enough duration to catch the symptoms.
Most places use a 24 hour Holter which tends to be a waste of time as it is uncommon for patients to get their symptoms reliably within a mere 24 hour period.
More recently it is possible to acquire wearable heart patches that can record continuously for 1 week, 2 weeks and even 4 weeks.
The most reliable way however is a REVEAL device which is a tiny device that can be implanted under the skin that is constantly on the patient with a battery of up to 2 years and this will catch any rhythm disturbances during that period.
This brings us to the end of this talk. I hope you found it useful. I would love to hear your thoughts. Thank you so much for listening.
Keywords: Cardiac MRI; ECHO; tests for the heart; ECG; BNP; Holter monitoring; Dr sanjay Gupta; York; Yorkcardiology; tests for the heart