What is Reentrant Arrhythmias?
Tachyarrhythmias, a type of heart disorder where the heart beats too quickly, can occur in one of three ways: reentry, enhanced automaticity, or triggered activity. Reentry is the most frequent cause of arrhythmia and is responsible for the majority of both supraventricular (occurring above the ventricles) and ventricular (occurring in the ventricles) tachycardias, kinds of rapid heart rhythms. Reentrant arrhythmias happen when an electrical signal in the heart doesn’t end as it should, but instead continues to excite recovered heart tissues, creating a circuit around an obstacle which can be physiological (naturally occurring in the body) or anatomic (related to bodily structure).
There are several types of reentrant arrhythmias. These include atrial fibrillation, atrial flutter, atrioventricular nodal reentrant tachycardia, atrioventricular reciprocating tachycardia, other pathway-related tachycardia, and ventricular tachycardia. In atrial fibrillation, multiple reentry circuits are found in the left atrium and pulmonary veins, while a large reentry circuit is characterizing atrial flutter in the right atrium. It’s important to know that atrioventricular nodal reentry tachycardia is the most common reentrant supraventricular tachycardia and uses the atrioventricular (AV) node as its reentry circuit. Ventricular tachycardia, where the reentry circuit is complex and formed by a scar in the myocardium (heart muscle), can also involve branch bundles as a part of the reentry circuit.
The symptoms and outcomes of different reentry arrhythmias can vary broadly. For instance, atrioventricular nodal reentrant tachycardia is the most harmless reentrant arrhythmia, while ventricular tachycardia related to a scar can be life-threatening. Atrial fibrillation and atrial flutter can lead to blood clot complications whereas, pathway-related tachycardia may put a person at risk of sudden cardiac death. Recent technological advancements have helped improve our understanding of reentrant arrhythmias, and ablation, a procedure that destroys tiny areas in the heart that are triggering an abnormal heart rhythm, has emerged as a successful treatment choice. To develop a patient management plan, it is necessary to understand the root causes and basic mechanisms of reentrant arrhythmias.
What Causes Reentrant Arrhythmias?
Reentry arrhythmias, or abnormal heart rhythms, can appear in many ways, depending on the specific type of abnormal rhythm present. If the problem starts in the atrioventricular (AV) node, a small mass of tissue that’s part of the heart’s electrical system, the abnormal rhythm happens because of a structural issue in the AV node itself. The AV node has two pathways: a slow one and a fast one. When working well, re-excitation (the restarting of the electrical activity) of the node doesn’t happen.
Atrioventricular reciprocating tachycardia and other tachycardias (fast heart rates) occur because of congenital connections (those present from birth) between the upper and lower chambers of the heart or connections between different parts of the heart’s electrical system. Tachycardias are more common in the presence of congenital heart conditions, like Ebstein anomaly and the transposition of the great arteries. Genetic causes for non-AV nodal circuits are often seen in young patients with reentrant arrhythmias. Certain conditions that affect how the body stores glycogen or mutations in specific proteins have been linked to the creation of these circuits.
Atrial fibrillation, an irregular and often rapid heart rate, is the most common type of sustained abnormal heart rhythm. Many factors can cause or trigger atrial fibrillation. Heart-related causes include mitral valve diseases, heart failure, ischemia (a reduced blood supply), intracardiac shunts, and high blood pressure. Advanced age is a leading cause of atrial fibrillation in people with otherwise normal hearts. Electrical changes in the left atrium, a chamber in your heart, can sustain atrial fibrillation. A number of genetic mutations can cause fibrosis (the formation of excess fibrous tissue) in the atria and lead to atrial fibrillation.
Reentry ventricular arrhythmias, abnormal rhythms that start in the ventricles (the two lower chambers of the heart), are usually caused by structural heart diseases and scar tissue in the heart muscle. Ischemic cardiomyopathy, a condition where a lack of blood to the heart causes heart muscle to become enlarged and weakened, is the main cause of reentrant ventricular tachycardia. It’s followed by non-ischemic, dilated cardiomyopathy, a type of heart disease that affects the heart muscle. A rare type of abnormal rhythm, bundle branch reentrant ventricular tachycardia, is characterized by a reentry circuit involving both bundle branches. This type of abnormal rhythm is usually seen in patients with cardiomyopathies (disease of the heart muscle) and structural heart diseases that have significant disease in the conduction system. However, patients with structurally normal hearts have been described in medical literature.
Risk Factors and Frequency for Reentrant Arrhythmias
Heart rhythm disturbances, or arrhythmias, that start with early activation are not rare. They’re seen in about 1 to 3 of every 1,000 people in the United States. Interestingly, most people found to have such an early activation on routine heart recordings (electrocardiograms) don’t have any other heart diseases.
Wolff-Parkinson-White (WPW) syndrome is one such condition and it happens in 15 out of every 10,000 patients. WPW is more common among men. The place where the extra, “shortcut” pathway in the heart (the cause of the problem in WPW) is most often found is the left free wall.
- About 53% of the time, the pathway is in the left free wall.
- In 36% of cases, it’s in the posteroseptal wall.
- 8% of the time, it’s in the right free wall.
- Rarely (3%), it’s in the anteroseptal wall.
AVNRT is a condition where the heart suddenly races, and it’s the most common kind of paroxysmal supraventricular tachycardia, another type of abnormal heart rhythm. It’s estimated that nearly 89,000 people are newly diagnosed with this sort of rapid heartbeat every year, and about half a million live with it in the United States. Women are more often affected than men.
Atrial fibrillation is a type of irregular heartbeat that has been growing exponentially in prevalence over the past five decades, mainly due to an aging population. Today, around six million people in the United States have atrial fibrillation, and that number is expected to balloon to 16 million by 2050. By the same year, more than 70 million Asians are expected to have atrificial fibrillation. Another irregular rhythm, atrial flutter, is less common and usually shows up alongside other heart problems. It occurs in about 200,000 new cases each year in the United States.
Sustained ventricular tachycardia, a rapid heart rate starting in the heart’s lower chambers, is often triggered by scar tissue in the heart and is the most common kind of reentrant ventricular tachycardia. This condition is a leading cause of sudden cardiac death, and about 70 in every 100,000 people in the general population experience sudden cardiac death each year in the United States.
Signs and Symptoms of Reentrant Arrhythmias
Supraventricular reentrant arrhythmias are heart conditions that can present themselves in varying ways; however, some common symptoms include heart palpitations, shortness of breath, or chest pain. Some patients may not show any symptoms until a serious complication develops like atrial fibrillation. Often, the diagnosis is made through an ECG or a rhythm strip for a separate medical issue. Patients with this condition may also experience nervousness, anxiety, neck pounding, lightheadedness, and fainting. While fainting is rare, it’s important not to overlook it, especially in patients with a condition known as Wolf-Parkinson-White (WPW) syndrome.
Ventricular reentrant arrhythmias, on the other hand, can pose a severe risk to life. These patients may also experience heart palpitations, chest pain, and shortness of breath, but they could also faint or go into cardiac arrest. Patients with ventricular tachycardia (a type of reentrant arrhythmia) tend to be older and commonly experience shortness of breath, chest pain, and dizziness more than heart palpitations.
Learning the patient’s past medical and surgical history is key when suspecting reentrant arrhythmia. Some heart surgeries or medications can trigger these arrhythmias, so having full knowledge about these factors can help with diagnosis and treatment. It’s essential to check for anything that might cause other similar conditions in symptomatic patients. Sometimes, patients with reentrant supraventricular arrhythmia show no signs of the disease in a physical examination. Those with reentrant ventricular arrhythmia, however, might display signs of underlying heart disease or heart failure.
Testing for Reentrant Arrhythmias
If your doctor suspects you might have a condition called reentrant supraventricular tachycardia, a type of fast heart rhythm, they’ll likely start the diagnosis process in an emergency department. To confirm the diagnosis, they will primarily rely on an electrocardiogram (ECG). An ECG is a test that checks for problems with the heart’s electrical activity.
The ECG during a rapid heartbeat episode is often compared with an ECG taken when the heart is beating at a normal rhythm. The shapes and patterns of the electrical waves in the ECG can provide valuable clues about where the rapid heartbeats are originating and help determine the likely cause of this irregular heart rhythm. In some cases, if the fast-beating episode isn’t currently happening, the regular ECG can still hint towards some possible causes. For example, certain irregularities, like a delta wave seen in WPW Syndrome, indicate that your heart’s extra electrical pathway might likely be the cause of the rapid heartbeats.
Sometimes, they might also suggest a continuous ECG monitoring test if your resting ECG shows no irregularities or the heart condition isn’t obvious. The current guidelines often recommend an echocardiogram, a type of ultrasound of your heart, to check its structure and functioning. In some cases, they might also want to conduct certain tests to evaluate your thyroid function and other targeted investigations.
In cases where a ventricular tachycardia, a rapid heart rate caused by irregular electrical signals in the lower chambers of the heart, is suspected, the diagnosis is also usually made through a 12-lead ECG. If you have symptoms occurring specifically during physical activity, a type of ECG test called an exercise ECG might be done to catch any exercise-induced rapid heartbeats. For people with symptoms but no documented irregular rhythms yet, an ambulatory ECG, which monitors your heart rhythm during your regular activities, might be recommended. In cases where symptoms are infrequent, a device called an implantable cardiac monitor, used to record heart rhythms over a long period of time, maybe helpful.
All patients suspected of having rapid heartbeats should preferably have an echocardiogram to evaluate their heart structure and functioning. In some cases, your doctor might recommend a cardiac magnetic resonance imaging, a type of heart scan that uses magnetic fields and radio waves to create detailed images of your heart. This imaging test can also provide valuable information about your prognosis with reentrant ventricular tachycardia, meaning how the disease might progress and what could be the likely outcome. An invasive electrophysiology study, another type of heart test, is no longer typically recommended for the diagnosis; however, it can still be useful in determining the risk level for patients who do not meet the criteria for a preventive heart device implantation.
Treatment Options for Reentrant Arrhythmias
Having a reentrant arrhythmia, which is a type of abnormal heart rhythm, requires different courses of treatment depending on the patient’s condition. The first step is assessing the patient’s stable condition—meaning how well their blood is circulating and how stable the heartbeat is.
For patients in a more critical condition, a life-saving procedure known as electrical cardioversion is the go-to treatment. This procedure uses electric shocks to restore a normal heart rhythm. If the arrhythmia occurs along with cardiac arrest, immediate advanced cardiac life support measures need to be initiated.
For those in stable condition, there are different steps involved in managing reentrant supraventricular tachycardia (SVTs), an excessively fast heart rhythm. First, the patient is encouraged to do vagal maneuvers or exercises that can help normalize the heart rate. The Valsalva maneuver, for instance, involves forcefully exhaling against a closed airway. There’s also the carotid artery massage involving gentle pressure applied to the carotid sinus situated near the throat.
However, if these maneuvers don’t work, medicines are used. Adenosine, delivered through an IV, is often the first choice for acute treatment. If that doesn’t work, medicines known as non-dihydropyridine calcium channel-blocking drugs and beta blockers can be used.
Anti-arrhythmia medications can be beneficial for some patients. However, caution should be exercised with patients with a condition known as Wolff-Parkinson-White syndrome, as certain types of medication can block the natural pathways in the heart, potentially leading to ventricular fibrillation (irregular heartbeats) and possible cardiac arrest.
After stabilizing the immediate condition, all patients need to be referred to a specialist known as an electrophysiologist for further treatment. This might include a procedure called catheter ablation which intentionally scars small areas in the heart that may be responsible for the abnormal rhythm. The success rate for this procedure is quite high, and complications are rare.
For patients with a different type of reentrant arrhythmia, called ventricular arrhythmia, which affects the lower chambers of the heart, medicines such as procainamide, amiodarone, or sotalol may be given through an IV. However, if the patient’s condition is critical or unstable, electrical cardioversion is again the preferred treatment. In case of frequent recurrence, beta-blockers and long-term antiarrhythmic drugs are considered.
A device called an implantable cardioverter-defibrillator (ICD), which helps to regulate abnormal heart rhythms, may also be thoughtfully recommended for some patients. If the criteria is met, an ICD should be implanted as soon as possible.
The ultimate goal in all cases of reentrant arrhythmia is to stabilize the patient, restore a normal heart rhythm, reduce the risk of future episodes, and improve quality of life.
What else can Reentrant Arrhythmias be?
When looking at reentrant arrhythmias, or irregular heart rhythms, doctors have to consider other similar conditions, particularly other fast heart rhythms. This is because most reentrant circuits, which cause these types of heart rhythms, are located above the heart’s lower chambers. As a result, other fast heart rhythms that originate in the upper chambers can be mistaken for reentrant arrhythmias. Your doctor will likely use a 12-lead EKG, a test that checks the electrical activity of your heart, during the fast heart rhythm and when the heart rhythm is normal to differentiate these conditions from each other.
Conditions that might be considered include:
- Sinus tachycardia
- Atrial tachycardia
- Ectopic junctional tachycardia
- Torsades de pointes
- Accelerated atrioventricular rhythm
- Idiopathic ventricular tachycardia
What to expect with Reentrant Arrhythmias
The outlook for reentrant arrhythmias, a type of irregular heart rhythm, depends on where in the heart it originates. Conditions like atrial fibrillation and atrial flutter carry an ongoing risk of developing a blood clot that can cause stroke, even without other heart abnormalities. Depending on the individual, the annual risk of stroke can vary broady. Low-risk patients have a less than one percent risk of stroke each year, while those in high-risk groups can face a 7 to 10% risk if they don’t receive the right blood-thinning medication.
There’s a different outlook for those with atrioventricular nodal reentrant tachycardia. In this conditon the prognosis is excellent, with over 95% of people being free of arrhythmias after a successful procedure called ablation. This procedure modifies the slow atrioventricular nodal pathway, which is involved in conducting electrical signals in the heart.
Wolf-Parkinson-White syndrome also has a lifetime risk of sudden cardiac death of less than one percent if left untreated. However, a procedure called radiofrequency ablation can eliminate this risk, and it’s usually highly effective with low recurrence rates.
Unfortunately, reentrant ventricular arrhythmias, which are usually found in patients with cardiomyopathy (heart muscle disease), don’t have a good prognosis. These arrhythmias in patients with cardiomyopathy can lead to worsened heart failure, repeated hospital stays, reduced quality of life due to hospital admissions, and repeated shocks from an implanted defibrillator. It may even result in sudden cardiac death. While procedures like ablation of ventricular tachycardia (a type of fast heart rhythm) can reduce the recurrence of such arrhythmias and the need for defibrillator shocks, it doesn’t improve the overall survival rates for these patients.
Possible Complications When Diagnosed with Reentrant Arrhythmias
Complications from reentrant arrhythmias, or heart rhythm problems, can change depending on where they originate in the heart. As with any unstable heart rate, these conditions can lead to changes in the heart’s structure, impaired blood circulation and potentially even heart failure.
In certain cases like Wolff-Parkinson-White syndrome, the patient may have a fast heart rate due to an extra electrical pathway in the heart. This could result in a type of arrhythmia called fibrillation, which can cause the heart’s chambers to beat rapidly and out of sync, and sometimes even result in sudden cardiac death.
Though the atrioventricular nodal reentrant tachycardia condition, frequent episodes of fast heartbeats, is generally harmless, it can cause fainting, chest pain, and heart failure, especially in the elderly.
Conditions like atrial fibrillation (irregular heartbeats) and atrial flutter (rapid heartbeats) come with the risks of blood clots, complications from blood thinners, and heart failure. Heart rhythm problems affecting the lower chambers of the heart can lead to worsened heart failure, repeated hospital stays, and recurrent shocks from an implanted defibrillator. In turn, these can negatively influence the patient’s quality of life and survival rate.
Heart ablation, a treatment for arrhythmias, may also lead to complications. These may include bleeding where the tools were inserted, injury to heart valves, blood vessels, and heart chambers leading to fluid collection around the heart, and, in extreme cases, heart tamponade, an emergency condition where the fluid prevents the heart from filling properly. Another rare but serious complication could be the inadvertent creation of another arrhythmia, which may destabilize the patient. The treatment for AVNRT and AVRT could result in a block in the communication between the upper and lower chambers of the heart, which may necessitate the use of a pacemaker.
Preventing Reentrant Arrhythmias
Patients should understand that reentrant arrhythmias, or abnormal heart rhythms, are caused by an issue with the heart’s electrical system, which is responsible for regulating the heart’s beat. This condition happens when a sort of loop is formed within this system, prompting it to constantly restart itself. Common signs of this condition can include feelings of anxiety, dizziness, a rapid heart rate, and brief loss of consciousness.
Patients are encouraged to keep an eye out for concerning symptoms such as prolonged periods of headaches, a rapid heartbeat, and a feeling of near-fainting, known as presyncope. Seeking medical help promptly is advised, particularly for those who faced a previous heart attack, have been treated with a procedure called ‘ablation’ to correct heart rhythms, or those who frequently experience these symptoms.
