A heart arrhythmia is an irregular heartbeat where the heart beats too fast, too slow, or with an erratic rhythm. Some arrhythmias are the direct result of genetic variations passed down through families, stemming from mutations in genes that control the heart’s electrical system. This system relies on ion channels to manage the flow of charged particles like sodium, potassium, and calcium in heart muscle cells. A genetic mutation can alter these channels, disrupting the electrical balance and causing either dangerously slow or fast rhythms.
Common Types of Inherited Arrhythmias
A number of distinct inherited arrhythmias have been identified. Long QT Syndrome (LQTS) is a condition defined by a delay in the heart’s electrical recharging, or repolarization, after each heartbeat. This prolongation, visible as a longer “QT interval” on an electrocardiogram (ECG), can make the heart vulnerable to chaotic and rapid heart rhythms. Mutations in genes responsible for potassium channel function, such as KCNQ1 and KCNH2, account for most LQTS cases.
Brugada Syndrome is characterized by a specific, abnormal pattern on an ECG. This pattern indicates an increased risk of life-threatening ventricular arrhythmias, even in a heart that appears structurally normal. The most commonly implicated gene is SCN5A, which codes for a sodium channel. Faulty sodium channels can alter the electrical potential across the heart muscle, creating the conditions for a dangerous rhythm to develop.
Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a condition where the heart’s rhythm becomes dangerously fast and irregular in response to physical activity or emotional stress. The issue in CPVT lies with how heart cells manage calcium. Mutations in the RYR2 gene, which controls a calcium release channel within heart muscle cells, lead to an inappropriate leakage of calcium when adrenaline is high, triggering abnormal electrical impulses.
Arrhythmogenic Cardiomyopathy (ACM), also known as Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC), is another significant condition. In this disorder, a genetic defect causes heart muscle tissue, primarily in the right ventricle, to be replaced by fatty and fibrous scar tissue. This structural change weakens the heart wall and disrupts the normal pathways of electrical signals. The genetic basis involves mutations in genes for desmosomes, which are proteins that help bind heart muscle cells together.
Signs and Potential Triggers
The signs of a genetic arrhythmia vary, and some people may have no symptoms. When symptoms occur, they relate to a sudden change in heart rhythm that affects blood flow to the brain. Common signs include:
- Fainting (syncope)
- A sensation of a fluttering or racing heart (palpitations)
- Episodes of lightheadedness or dizziness
- Seizures
- Unexplained shortness of breath
Certain events or circumstances can act as triggers, provoking an arrhythmic episode in susceptible individuals. For those with CPVT or some forms of LQTS, an adrenaline increase from strenuous exercise or emotional shock can initiate a dangerous rhythm. For other types of LQTS, a sudden loud noise like an alarm clock can be a trigger.
Fevers are a known trigger for Brugada syndrome, as the change in body temperature can unmask the characteristic ECG abnormalities and provoke an arrhythmia. Certain medications also pose a risk. Drugs that affect ion channels, including some antidepressants, antibiotics, and over-the-counter antihistamines, can further delay the heart’s recharging process in people with LQTS.
The Diagnostic Process
Diagnosing a genetic arrhythmia begins with a review of a person’s medical and family history. A history of unexplained fainting, seizures, or a sudden unexplained death in a young family member can indicate an inherited condition. This information prompts an investigation into an underlying electrical heart disorder that may be present in other relatives.
Following the initial assessment, cardiac tests are used to observe the heart’s electrical activity. The electrocardiogram (ECG) provides a snapshot of the heart’s rhythm and can reveal patterns like the prolonged QT interval of LQTS or the signature of Brugada syndrome. Since an arrhythmia may not occur during a brief ECG, a portable Holter monitor may be used to record the heart’s rhythm continuously for 24 to 48 hours. An exercise stress test is useful for uncovering arrhythmias like CPVT that are induced by exertion.
If clinical findings suggest an inherited arrhythmia, genetic testing can provide a definitive diagnosis. This is done using a blood or saliva sample to screen for mutations in genes known to cause these conditions. A positive genetic test confirms the diagnosis and is also used for screening asymptomatic family members. Identifying carriers allows for preventative strategies to be implemented before a cardiac event occurs.
Management and Treatment Approaches
Once a diagnosis is confirmed, management focuses on preventing life-threatening cardiac events. Treatment strategies include lifestyle changes, medication, and implantable devices.
- Lifestyle Modifications: This involves avoiding known triggers, such as refraining from strenuous sports for those with CPVT or LQTS. It also includes reviewing all medications to avoid those that affect heart rhythm.
- Medications: Beta-blockers are often prescribed to slow the heart rate and blunt the body’s response to adrenaline, making them effective for LQTS and CPVT. Other medications that affect specific ion channels may also be used.
- Implantable Cardioverter-Defibrillator (ICD): For individuals at high risk of sudden cardiac arrest, an ICD may be recommended. This small device is surgically placed in the chest to monitor the heart’s rhythm and deliver an electrical shock to restore a normal beat if a life-threatening arrhythmia is detected.
- Catheter Ablation: In some cases, this minimally invasive procedure may be an option. A thin tube is guided to the heart, where radiofrequency energy is used to destroy the small area of tissue generating abnormal electrical signals, which can reduce the frequency of episodes.