The heart is a beautiful piece of bio-engineering. It has an electrical system that keeps it beating to a regular rhythm. There are valves that keep blood flowing in the right direction and the muscles contract more than once every second without tiring.
Unfortunately, things can go wrong and symptoms may develop. Fortunately, there are tests to assess all the functions of the heart. Investigations include the electrocardiogram (ECG), echocardiogram, treadmill exercise test, cardiac catheterisation and CT coronary angiography.
The Electrocardiogram (ECG)
Chest electrodes can be used to record the electrical signals from the heart. A low signal may be due to heart failure. A signal that takes a long time may mean heart block. The shape of the signal can identify diseases such as coronary disease. Importantly, the ECG tells the heart rate and whether the rhythm is normal or abnormal such as atrial fibrillation.
Treadmill Exercise Test
The ECG is usually recorded at rest but it can also be recorded during exercise on a treadmill. This is useful because some conditions such as angina and arrhythmias are brought on by exercise. The test is often used to test the cardiovascular fitness of commercial drivers and pilots. For instance, the DVLA and CAA use it for licensing purposes.
Cardiac Event Monitor
Sometimes, cardiac symptoms are infrequent and short lasting. This makes it difficult to record an ECG at the time of symptoms but there are a number of options. There are wearable devices which can record ECGs for many days. There are also pocket devices which can be used when symptoms occur. Some devices are small enough to be implanted under the skin for several years. Information from these devices can be transmitted by wireless.
Just as bats use sound to “see”, echocardiography is the use of ultrasound to investigate the structure and function of the heart. This is the same test that is used to see the baby inside a pregnant woman’s womb. It has been described as the Gold Standard test for diagnosing heart failure. Usually, the sound waves are directed towards the heart by placing a probe on the chest wall. This is known as a trans-thoracic echocardiogram.
Sometimes, the images from a transthoracic echocardiogram are not clear because ultrasound waves do not pass well through any lung tissue in the way. An ultrasound probe can be placed down the gullet which is literally just behind the heart. This is known as a trans-oesophageal echocardiogram and the image quality is usually excellent.
In this test, narrow tubes (catheters) are inserted into an artery at the wrist or the top of a leg. The catheters are long enough to reach the heart. Dye is then injected to see the coronary arteries and to assess how well the heart pumps. Nowadays, the test is mainly done from the wrist as it is considered safer.
There are many other investigations. These include a blood test known as BNP (brain natriuretic peptide) which is used to exclude heart failure. A CT coronary angiogram is a non-invasive test to assess the coronary arteries. A cardiac MR scan provides data about the structure and function of the heart as well as about the cardiac muscle. There is some overlap in the information from these tests. Also, each test has different accuracy and some may carry risk. The decision as to which test to use will depend on factors such as patient choice and information required.