CGAP - Understanding genetic arrhythmias
What is an Arrhythmia and Why Does It Matter?
An arrhythmia is an abnormal heart rhythm recognized as a change in the speed or pattern of the heartbeat. In a healthy heart, the rhythm of the heart is stable because all of the different parts of the heart's electrical system interact in the correct sequence to keep the heart running smoothly. A normal heartbeat is called "normal sinus rhythm," and at rest the heart normally beats with a regular rhythm of 60 to 100 beats per minute. When disease or injury alters the normal sinus rhythm we say that the heart has developed an arrhythmia. Arrhythmias matter because some arrhythmias can be life-threatening if left untreated.
The heart itself is made up of four chambers. The upper chambers, called atriums, receive and collect blood. The lower chambers, called ventricles, pump blood to the rest of the body. Working together, the chambers ensure that the body receives the volume of blood it needs to function properly.
Sometimes, however, the chambers don't work smoothly together. For example, the heart can beat too slowly resulting in too little blood pumped out to the rest of the body; slow heart rates are called bradycardias. Or the heart can beat so rapidly that it does not completely fill with blood, resulting in less blood pumped to the body than the body needs. Fast heart rates are called tachycardias. Sometimes the heartbeat is very irregular, with no consistent pattern. This condition is called fibrillation.
What Causes an Arrhythmia?
Some arrhythmias are caused by structural damage to the heart as a result of prior heart attacks. Some arrhythmias are caused by genetic factors, and in these cases we refer to the condition as a genetically-linked arrhythmia. Genetic arrhythmias are thought to be the result of either an inherited characteristic or a spontaneous genetic mutation. Genetic arrhythmias are the types of arrhythmias studied by the Comprehensive Genetic Arrhythmia Program (CGAP).
What are the Different Types of Abnormal Heart Rhythms?
There are several types of abnormal heart rhythms. Some abnormal rhythms occur in the upper chambers (atria) while others occur in the lower chambers (ventricles). Listed below are some of the more common arrhythmias. To learn more about these conditions, click here and read the descriptions under the Conditions we treat section:
- Atrial Fibrillation
- Atrial Flutter
- Atrial Tachycardia
- Complete Heart Block
- Supraventricular Tachycardia
- Ventricular Fibrillation
- Ventricular Tachycardia
- Wolff-Parkinson-White Syndrome
Diagnosing Genetic Arrhythmias
If your doctor suspects you may have an inherited arrhythmia, he or she will order one or more of the following diagnostic tests. The purpose of these tests is to find out what the right diagnosis is for you and to help determine whether your symptoms are genetic in nature.
If your symptoms are determined to be genetic, and you have already had clinical genetic testing that shows no known mutations, you may be qualified to enroll in our program. Our program team will review your request and make a determination based on your test results and their overall evaluation of your medical condition.
Tests that are used to help establish diagnosis of a genetically-linked arrhythmia fall into three broad categories and include:
1. Genetic Testing/Research Genetic Analysis
Genetic tests can be used to help determine the right diagnosis and the best treatment for an individual, as well as helping to determine which family members inherited the condition. It can also relieve a lot of worrying by determining which family members did not inherit the condition.
Currently, genetic testing cannot find the cause of hereditary arrhythmias in 25-75% of cases. This may be because the condition is caused by a mutation in a gene that researchers have not found yet.
When regular genetic testing cannot find the genetic cause, individuals and families can take part in research genetic analysis that aims to find new genes. This sort of research is one of the main goals of CGAP.
2. Non-Invasive Tests
Electrocardiogram - The electrocardiogram (ECG or EKG) records the heart's electrical activity. Small patches called electrodes are placed on your chest, arms and legs, and are connected by wire to the ECG machine. Your heart's electrical impulses are translated into a wavy line on a strip of moving paper, enabling doctors to determine the pattern of electrical current flow in the heart and to diagnose arrhythmias and heart damage.
Holter Monitor - A Holter Monitor is a small, portable, ECG machine that you are hooked up to and wear for 24 hours. It enables continuous recording of your ECG as you go about your daily activities. You will be asked to keep a diary log of your activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting ECG that only records for a few seconds.
Exercise Stress Test - The Exercise Stress (Treadmill) Test enables physicians to record your heart's electrical activity during exertion. This is important for arrhythmias that may be generated only during exertion.
Event Recorder - An Event Recorder (Loop Recorder) is a small portable transtelephonic monitor that may be worn for several weeks. This type of recorder is good for patients who don't experience symptoms very often. The monitor "loops" a two minute recording into its memory that is continually overwritten. When you experience symptoms, you press a "Record" button on the monitor which stores a correlating strip of ECG material. The recordings are telephoned to a 24-hour monitoring station and faxed directly to the requesting physician.
Cardiac Magnetic Resonance Imaging (MRI) - Cardiac MRIs may be used to assess the tissue composition of the cardiac chambers and allows for detection of scars or fatty deposits in the heart.
Tilt-Table Test - Tilt Table testing is used to diagnose fainting or black-out spells (vasovagal syncope) by trying to reproduce the black-out episodes. You are tilted upright to about 60 degrees on a special table for a period of time with continuous recording of your ECG and blood pressure.
3. Invasive Tests
The Electrophysiology (EP) Study -The EP Study involves placement of an electrode catheter into the heart, and is a technique frequently used to help diagnose arrhythmias, and to evaluate how effective previous attempts at treatment have been. Serious arrhythmias can be treated during an EP Study through the use of catheter ablation.
Treating Genetic Arrhythmias
There are several treatment options available depending on the type and severity of your arrhythmia and the results of your clinical genetic testing. Your program team and your doctor will decide which treatment is right for you.
Medications - Certain anti-arrhythmic drugs change the electrical signals in the heart and help prevent abnormal sites from starting irregular or rapid heart rhythms.
Implantable Device (Pacemaker) - All pacemakers work on "demand" and are used to treat slow heart rhythms. They are small devices that are implanted beneath the skin below the collar bone and connected to a pace wire(s) positioned inside the heart through a vein; this delivers a small electrical impulse to stimulate the heartbeat when it is going too slow.
Catheter Ablation - A technique pioneered at UCSF, radiofrequency catheter ablation destroys or disrupts parts of the electrical pathways causing the arrhythmias, providing relief for patients who may not have responded well to medications, or who would rather not or can't take medications.
Implantable Cardioverter Defibrillator - An implantable cardioverter defibrillator is a device for people who are prone to life-threatening rapid heart rhythms. It is slightly larger than a pacemaker and usually is implanted beneath the skin below the collar bone. It is connected to a defibrillation/pace wire(s) positioned inside the heart through a vein. It has the capability of delivering an electric shock to the heart when it determines the heart rate is too fast. It also is capable of pacing or stimulating the heart when it is going too slow.
Clinical Genetic Counseling - Being diagnosed with a genetic arrhythmia can bring up difficult emotions, including fears about sudden cardiac death, confusion about a new diagnosis, and worries about passing the condition on to other family members. Genetic counselors are specially trained to help individuals and their families navigate these adjustments and to learn how to apply this knowledge to their future life choices. Genetic counselors will also help you sort out who else in your family could have an inherited arrhythmia.