Many arrhythmias have a genetic, or inherited, component, these are called inherited heart conditions (IHC). Genetic testing is used to determine whether or not someone is at risk of a potentially dangerous arrhythmia because of his or her family history.
A genetic test is used to identify genes that can cause an IHC. Within the genes that are associated with IHCs, there are a great number of potential changes that can cause arrhythmias.
Genetic testing, may be either ‘diagnostic’ or ‘predictive’, depending on whether you have already been diagnosed with an IHC or not.
Diagnostic genetic testing is used to determine whether or not there is a genetic cause for an arrhythmia that is know to be inherited in some people.
The aim of diagnostic genetic testing is to identify the genetic cause of an IHC, not to establish a diagnosis.
There are several possible results from diagnostic genetic testing:
- A change in a gene is found. This means a genetic cause of an IHC has been identified.
- The causative gene change is not found. This does not mean the patient does not have the arrhythmia originally diagnosed, just that a genetic cause has not been identified.
- A gene change is found but it is not certain that this is causing the arrhythmia.If your symptoms ‘come and go’ your doctor might suggest a Holter monitor, which is a continuous ECG recoding over approximately 24 hours. Again, electrodes will be placed on your body, and this time they will be taped down. During a Holter Monitor test the wires will be attached to a smaller, portable device that can be strapped to the chest. After the specified time period the monitor can be returned to your doctor to see whether any arrhythmias have been indicated.
If a genetic cause for an arrhythmia is found in a patient, genetic testing can be offered to other members of their family who may be at risk of this same problem.
Predictive testing aims to identify individual risk of developing an inherited condition that is know to run in the patient’s family. There are only two possible results from predictive genetic testing.
- The genetic problem is identified, increasing the risk in that patient of developing a particular arrhythmia
- No potential genetic causes for the arrhythmia are identified, meaning that the patient is at no greater risk of developing this arrhythmia than anyone in the general population.
Genetic testing can only determine whether an individual is at an increased risk of developing an inheritable arrhythmia. It cannot predict the definite development of an arrhythmia, the development of symptoms or their severity.If the cause of your symptoms cannot be determined following an ECG and a Holter Monitor, then your doctor may consider an implantable loop recorder. The ILR can monitor heart rhythms for months at a time, and can remain in place for up to three year. An ILR has to be inserted beneath your skin, just below the collarbone. Arrhythmic episodes are detected for automatic recording. ILRs also allow manual recording in response to symptoms, by pressing a button on a hand held activator, placed over the ILR. This must be done either whilst experiencing symptoms or as near to the event as possible.
The test itself
The genetic test itself uses a blood sample or cheek swab. Genetic scientists will examine the genes in the sample to check for changes that can lead to inherited arrhythmias. Results will be sent back to a genetic counsellor or doctor who will advise the patient of the results and next steps.
Genetic counselling is common before a test to help people understand the implications of a positive result. A counselling appointment will typically last about one hour and will be used educate patients on the arrhythmia being checked, and what that might mean for other family members. It also provides opportunity for discussion on the advantages and disadvantages of genetic testing so that patients can decide if having a genetic test is the right choice.