The heart is a beautiful piece of bioengineering. It has an electrical system to make it contract in a regular rhythm. Different parts of the heart operate at contrasting pressures and there are valves to make sure blood flows in the right direction. The muscle of the heart contracts more than once every second without tiring.
Unfortunately, things can go wrong and there are investigations which can study any of these different aspects. The most commonly used investigations are probably the electrocardiogram (ECG), echocardiogram, treadmill exercise testing, cardiac catheterisation and CT coronary angiography.
The Electrocardiogram (ECG)
Electrodes can be placed on the chest to record the electrical signals from the heart. The signal size gives an indication of the amount of cardiac muscle and how well it is contracting. Signal duration can tell us about abnormal electrical resistance. The pattern of the signals indicate whether there is disease such as a lack of blood flow to the heart. The regularity and frequency of the signals indicate whether the cardiac rhythm is normal or abnormal as in atrial fibrillaion.
Treadmill Exercise Test
The ECG is usually recorded when at rest. However, it can also be recorded during exercise on a treadmill. In this way, it can give information about the heart rate response and physical fitness. It is most commonly used to diagnose coronary disease. There are more accurate tests for diagnosing coronary disease but it is still an important test and frequently used by regulatory authorities such as the DVLA and CAA.
When symptoms are infrequent, ECGs can be recorded using wearable or pocket devices. Some ECG devices are small enough to be implanted under the skin for several years. In some cases, information can be transmitted wirelessly to the medical team.
Although very useful, the amount of recorded data may be overwhelming and require a lot of analysis time.
This is the use of ultrasound to investigate the structure and function of the heart. It is the same test that is used to see the baby inside a pregnant woman's womb. The test has been described as the Gold Standard 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 transthoracic 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.
In this case, the probe can be placed down the gullet which is literally just behind the heart. This is known as a transoesophageal echocardiogram and the image definition is usually excellent.
This involves passing narrow diameter tubes (catheters) to the heart. Dye can then be injected into the chambers and coronary arteries. Pressure can also be measured. Interventions such as coronary stenting and bypass surgery can then be carried out.
Previously, the pulse of the femoral artery at the top of a leg was found and the catheter introduced there. Now, the radial artery at the wrist can be used and this approach is becoming increasingly common as it is generally safer.
There are many other investigations. A blood test known as BNP (brain natriuertic peptide) can be used to exclude heart failure. A CT coronary angiogram can be used to exclude coronary disease. A cardiac MR scan is invaluable for examining the muscle of the heart.
There is some overlap in the indications for these tests. 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.