What is Reentry Arrhythmia?
Reentry refers to a situation where the heart displays an abnormal recurrent rhythm. Here, the signal that sparks the heart’s beats, also known as an action potential, travels in a constant loop. This condition differs from others where the abnormal rhythm is due to problems in signal generation like automaticity and triggered activity. The concept of reentry has been understood for over a century, traced back to the work of Mines and Garrey.
Heart rhythms that result from reentry include fast-paced abnormal rhythms such as atrial flutter, atrioventricular nodal reentry, atrioventricular reentry seen in conditions like Wolff-Parkinson-White syndrome, and ventricular reentry like bundle branch reentry. The significance of reentry in causing abnormal rhythms and its potential as a target for treatment in cases of atrial fibrillation is currently being researched.
The primary role of the heart is to keep blood flowing throughout the body. For this to happen, the heart cells called myocardiocytes contract in a methodical and rhythmical way. This process is facilitated by a mechanism called electro-mechanic coupling (EMC) which transforms electrical signals into contractions. The action potential sequence starts from an area called the sinus node and travels through right atrial pathways, the atrioventricular node, the His bundle, and finally the Purkinje fibers to stimulate the heart muscles.
Heart cells can be in one of two states – excited or resting. From the resting state, the cell becomes active until it reaches a certain limit which then triggers an action potential. After this action potential, the cell enters a phase called the refractory period, during which it can’t be activated by another trigger. The time taken between two action potentials is referred to as the wavelength or cycle length.
What Causes Reentry Arrhythmia?
Reentry, a common cause of abnormal heart rhythms, can be caused by several factors:
1. Electrolyte imbalances and changes in structures that help move electric charges in the heart (channelopathies) can lead to reentry arrhythmias.
2. Physical actions like a thump to the chest can start but also stop reentry.
3. Long-term overstretching of the heart can lead to changes and scarring that affect the electrical properties of heart cells (myocardiocytes).
4. Scar tissue from a previous heart attack can cause reentry due to changes in the heart’s anatomy.
5. Conditions you’re born with, like congenital heart disease, or surgery to treat it, can cause reentry.
6. Genetic factors have been discovered in reentry conditions.
There’s ongoing research into the link between congenital heart disease and reentry. Either the disease itself, or scars from surgery, can prompt the conditions for reentry. For example, patients with a condition called Ebstein anomaly are more likely to have rapid heart rhythms because of multiple extra electrical pathways in the heart.
In patients with Ebstein anomaly, muscle bridges across the heart can lead to a condition called Wolff-Parkinson-White syndrome. Certain surgical procedures, like the Mustard Senning procedure (for incorrect positioning of the main arteries) or the Fontan Bjork operation (for those with only one functional heart chamber), are known to cause arrhythmias due to reentry. A specific kind of rapid heartbeat (Pericaval intra-atrial reentry tachycardia or IART) is linked to Fontan surgery and can be treated by ablating, or destroying, the problematic heart tissue.
People who have had surgery to repair congenital heart disease can develop a rapid heartbeat that can be traced to specific areas of the heart and treated successfully by ablation.
A condition called Arrhythmogenic right ventricular dysplasia, characterized by abnormal tissues in the right heart chamber, is often accompanied by ventricular arrhythmias. Reentry circuits often cluster in affected areas, like the right ventricular outflow tract and the ring-like structure connecting the right chamber and the right atrium (tricuspid annulus), which are affected by scarring changes.
Risk Factors and Frequency for Reentry Arrhythmia
Arrhythmias, or irregular heartbeats, are health conditions that vary in how common they are. They can range from more common ones like atrial fibrillation to rarer diseases like Wolff-Parkinson-White atrioventricular reentry tachycardia. For instance, atrial fibrillation affects 10% of people over 60 and can be found in 60% of patients undergoing surgery for mitral valve disease.
This condition can lead to an increased death rate due to three key reasons:
- It may cause blood clots leading to stroke,
- It can decrease the heart’s blood pumping ability due to lack of proper heart rhythm, and
- It can cause irregular heartbeat.
Ventricular tachyarrhythmias, another kind of irregular heartbeat, can sometimes lead to sudden death in those with chronic heart failure. It’s also been found that 15% of adult patients with inborn heart disease have accompanying supraventricular tachycardias (SVTs).
On the frequency of SVT, a 2015 guide reports that it happens to 2.29 out of every 1000 people, with around 36 new cases per 100,000 people each year. This totals to about 89,000 new cases yearly and around 570,000 people currently living with SVT. AVNRT is more common in middle-aged or older people, while AVRT is mostly found in teenagers. As for the Wolff-Parkinson-White (WPW) syndrome, it causes noticeable changes in the heart rhythm and can be detected in 0.1 to 0.3% of people.
Signs and Symptoms of Reentry Arrhythmia
Supraventricular Tachycardia (SVT), a rapid heart rate condition, usually begins to show symptoms in young adults. The average age for people noticing symptoms of Atrioventricular Nodal Reentry Tachycardia (AVNRT) is 32 years, while for Atrioventricular Reciprocating Tachycardia (AVRT) it’s 23 years. It’s noteworthy that AVNRT is more common in women.
In addition, the symptoms can vary among individuals with SVT. Here are some symptoms that patients with SVT often report along with the percentage of cases with each symptom:
- Heart palpitations (22%)
- Chest pain (5%)
- Fainting (syncope) (4%)
- Sudden cardiac death (0.4%)
Some patients may also feel panic or anxiety. AVNRT patients frequently experience a pounding feeling in the neck, which could be due to what is known as cannon A waves. AVNRT can also result in increased urine production (polyuria) due to elevated pressure in the right atrium. Certain activities like physical exertion or the consumption of substances such as coffee or alcohol can trigger AVNRT symptoms.
Testing for Reentry Arrhythmia
To understand heart rhythm problems, or arrhythmias, doctors can use different types of EKG (a test that records the heart’s electrical activity) and in-depth electrical studies of the heart using targeted stimuli. Certain EKG features can help doctors differentiate between two specific types of arrhythmias, AVNRT and AVRT. Features that point toward AVRT include a delta wave, elongation of a rhythm cycle when a specific heart condition occurs, and the finding of alternating heartbeats. Features that suggest AVNRT include a pseudo s in lead II or pseudo r’ in lead V1.
There’s an advanced technique called entrainment that is used for diagnosing, mapping, and treating heart rhythm disorders. This involves identifying different elements of the heart rhythm pathway. Successful treatment targets slow conduction areas (zones where the heart’s electrical signals travel slower) and the exit sites.
In-depth electrical studies are recommended for certain heart rhythm disorders. Several measurements help to determine the underlying cause of the rhythm problem. The A-H jump, which is a sudden increase of the interval between atrial excitation and His bundle excitation with a prior stimulus, indicates dual AV node physiology and suggests AVNRT.
There are two specific types of heart conditions, the Wolff-Parkinson-White (WPW) syndrome and Lown-Ganong-Levine (LGL) syndrome, fall under a group of arrhythmias called atrioventricular reentry tachycardias (AVRT). The treatment recommendation for these conditions is ablation (a procedure that uses heat to destroy small areas in your heart that may be causing the rhythm problems) when the refractory period is shorter than 250 ms and in cases of inducible AVRT or symptomatic preexcitation syndrome.
Differentiating types of heart rhythm problems such as AVNRT, AT, and AVNRT can be done using the entrainment technique and observing the heart’s response to pacing. Concealed entrainment (AVNRT) is not the same as entrainment with concealed fusion (AVRT with pacing site close to an accessory pathway). The response to entrainment is dependent on the pacing site.
The idea of resetting the heart’s rhythm is likened to the effect of a ventricular premature beat (an early or extra heartbeat) on continuous stimulation. Josephson described entrainment as the continuous resetting of a heart rhythm problem.
Treatment Options for Reentry Arrhythmia
Supraventricular tachycardia (SVT), a condition characterized by a rapid, abnormal heart rhythm, is often treated based on recommendations from the American Heart Association (AHA), the American College of Cardiology (ACC), and the Heart Rhythm Society (HRS). The recommended procedure typically involves an attempt to normalize the heart rhythm using a technique known as the Valsalva maneuver. This procedure involves deep breathing and straining actions that sometimes help decrease the heart’s electrical activity. In some cases, medications like adenosine may be given if the Valsalva maneuver doesn’t work.
However, if the patient’s condition is critical due to unstable vital signs, an immediate procedure called cardioversion, which uses electricity to reestablish a normal heart rhythm, may be executed.
For ongoing management, medications like beta blockers, calcium channel blockers, and sodium channel blockers can be used, as well as other medications like amiodarone or digoxin, depending on the type of SVT.
Methodologies like the Sicilian Gambit propose a personalized approach to treating arrhythmia, attempting to identify the underlying issue leading to the abnormal heart rhythm and target it with specific treatments.
Another condition called atrial flutter, which is a type of abnormal heartbeat, often requires a procedure called a right atrium pacing to normalize the heartbeat. If unsuccessful, a more invasive procedure like ablation can take place.
In cases where multiple heart rhythm abnormalities are present, the treatment can get even more complex. The treatment might involve a procedure called radiofrequency ablation that uses heat to destroy problematic heart tissue and restore normal heart rhythm.
Finally, in some cases, the focused approach that tracks abnormal electrical signals in the heart (complex fractionated atrial electrograms – CFAE) can be used. When ablation is successful, the regular conduction pattern in the heart can be restored.
Due to the complexity of these conditions, each treatment should be ideally tailored considering individual patient factors, with the common goal being the restoration of a normal heart rhythm for the patient.
What else can Reentry Arrhythmia be?
: Understanding what is causing an irregular heartbeat can be tricky. Different types of activities in the heart, like tiny circuits of electrical activity, slow activity zones, or activities originating from the lung veins, all can appear similar in heart studies.
When equal measurements are found at different points in the heart, it’s possible that a large circuit of electrical activity may be looping across both chambers of the heart. Another type of irregular heartbeat, called multifocal atrial tachycardia (MAT), is often mistaken for atrial fibrillation.
In one study, the correct diagnosis of MAT was only made in 22% of cases. MAT shows at least three different types of electrical wave activity in the heart, a heart rate of over 100 beats per minute, and pauses between these waves. MAT is caused by sudden bursts of activity in the heart.
It’s important to understand the root cause of the irregular heartbeat because that will inform the best course of treatment. For example, treatments that work for other types of irregular heartbeats, such as electrical cardioversion, wouldn’t be effective for MAT. Instead, treatments for MAT may include beta-blockers, calcium channel blockers, and magnesium.
Preventing Reentry Arrhythmia
Reentry is a concept that helps us understand some recurring heart rhythm problems. It is used to diagnose and treat these conditions. Essentially, this model shows us how certain heart rhythm problems can keep happening on their own.
