Investigations are performed to gain additional information beyond that which a verbal description and basic physical examination can provide. The primary goal is to try and document the heart rhythm at the time of symptoms so the precise mechanism can be determined. This usually requires a form of electrodardiogram (ECG), which is the electrical recording of the heart rhythm. Different strategies and types of monitoring equipment may be chosen depending on how often the symptoms occur and how long they last for.
It may also be important to perform additional cardiac investigations to see if there is anything wrong with the heart muscle or blood supply that may explain why the arrhythmias are occurring. In some circumstances, blood tests may also be required.
This is the most common form of ECG recording and is taken with the patient lying on a couch and uses stickers on all four limbs as well as 6 across the chest. It produces a 12 second recording with lots of detail. Usually it will only reveal the type of arrhythmia if the person has symtpoms when the ECG is being performed and therefore is helpful for people who have long episodes of arrhythmias that gives them time to visit the doctor or Emergency Department. Sometimes even if the rhythm is normal it may reveal a clue, such as ventricular preexcitation from due to an accessory pathway in Wolff-Parkinson-White Syndrome.
These heart rhythm recorders are attached, worn under the clothing and taken home for a variable length of time. A 24 hour tape will record every heartbeat for the 24 hour period and patients will note in a diary or press a button to indicate symptoms. They are useful for symptoms that occur on a daily basis.
Event recorders can be taken for a longer period and are useful if symptoms occur once a week or less often. Rather than record continuously they will only take an ECG if activated by the patient. Some will also record automatically if they see that the heart rate is very fast or very slow. They can be attached using stickers (taken off for baths and showers and then replaced) or the device can be held against the skin when a recording needs to be made
Sometime it is clear from the description that the arrhythmia symptoms are provoked by exercise, in which case an exercise test may be usful in trying to determine the type of rhythm problem. This test involves walking on a treadmill that very gradually gets steeper and faster, whilst attached to an ECG machine that is recording the heartbeat. The aim is to make the heart and body work hard and cause the arrhythmia to happen in a controlled environment. The test is stopped when the patient becomes too fatigued to continue, the age-dependent maximum heart rate is reached or an abnormality has been recorded.
Sometimes an exercise test is used to see if there is any evidence of coronary artery problems that might result in a lack of blood to the heart.
An echocardiogram (echo for short) is simply an ultrasound scan of the heart. The machine uses soundwaves to create pictures of the beating heart in the same way that it is possible to look at babies in the womb. The echo probe is placed at a number of sites around the front and left side of the chest while the patient is lying on a couch.
It is important to know what the heart looks like and whether there are structural abnormalities such as dilated or weak heart muscle, thickened heart muscle or valve problems as this may indicate that the arrhythmias could be dangerous. It may also influence the choice of medication or other type of treatment and its eventual success
Occasionally it may be appropriate to perform other tests, including blood tests for thyroid function, 24 hour urine collection for adrenaline levels, a cardiac MRI scan or cardiac catheterisation (coronary angiography).