Cardiomyopathies are diseases of the heart muscle. One of them is called arrhythmia-induced cardiomyopathy, where the main heart muscle, the left ventricle, weakens due to abnormal heart rhythms. This condition is potentially reversible.
Some of the Arrhythmias Involved
Abnormal heart rhythms are generally called “arrhythmias”, however, in cases where the heart rate is greater than what is considered normal, they are defined as “tachycardias”.
Atrial (top chambers of the heart) or ventricular (bottom chambers) tachycardias, or frequent early beats from the ventricles may cause that cardiomyopathy. Partial or complete improvement of the left ventricle can be expected once arrhythmia control is achieved.
There are 2 Types of arrhythmia-induced cardiomyopathy:
- Arrhythmia induced: one in which the arrhythmia is the sole reason for cardiomyopathy.
- Arrhythmia-mediated: in this case, the arrhythmia provokes additional damages, that is to say when it further deteriorates heart muscle function and/or worsens the symptoms of heart failure in patients with coexisting heart disease.
A diagnosis can be provided only after recovery and stabilization of a normal heart rhythm or following rigid monitoring of the heart rate in the case of arrhythmia.
What Are the Symptoms and Clinical Features of Arrhythmia-Induced Cardiomyopathy?
The key feature is the simultaneous presence of an abnormal heart rhythm and that of an otherwise unexplained weakened heart muscle (cardiomyopathy).
The relationship between arrhythmia and cardiomyopathy is difficult to establish because arrhythmia may be present for years before it is found and cardiomyopathy develops.
Therefore, symptoms may appear only later on as a result of a weakening of the heart or develop gradually over time with an increasing progression of symptoms.
The Most Common Symptoms
These symptoms are a result of heart failure due to a weakened left ventricle. They include, but are not limited to:
- shortness of breath with exertion or at rest,
- inability to lie down without feeling short of breath,
- swelling of the legs and abdomen,
- increased fatigue and lack of energy.
Symptoms may also be related to the underlying arrhythmia itself:
- persistent rapid or abnormal heartbeats (palpitations),
- lightheadedness and fatigue with effort, among other symptoms.
How Is a Diagnosis of Arrhythmia-Induced Cardiomyopathy Reached?
In addition to a patient visit where the symptoms and particular patient characteristics are assessed, several specific tests are essential in making an arrhythmia-induced cardiomyopathy diagnosis.
- Electrocardiogram (ECG or EKG): persistent tachycardia can be seen on a simple ECG (e.g., atrial fibrillation or tachycardia), or frequent early beats (Supraventricular Extrasystoles (SVES) or Ventricular Extrasystoles (VES).
- Holter monitor: sometimes the arrhythmia or tachycardia is not visible on an ECG.
An the extent and burden of arrhythmia throughout that period.
For example: if the arrhythmia is due to atrial fibrillation, the device can identify the average heart rate and duration of the arrhythmia.
If the problem arrhythmia is made up of frequent early beats of the VES type, the Holter can identify the percentage of PVCs that occurred during the monitoring period.
- Transthoracic Echocardiogram: the echocardiogram in arrythmia-induced cardiomyopathy will invariably detect a weakened left ventricle. Other cavities of the heart may be affected as well.
Specific patient characteristics may suggest a higher likelihood of arrythmia-induced cardiomyopathy. Some patients with arrhythmia-induced cardiomyopathy may have smaller heart dimensions, or more precisely a smaller end-filling left ventricular diameter compared to patients with preexisting cardiomyopathy associated with tachyarrhythmia.
- Cardiac MRI (Magnetic Resonance Imaging): this test may be useful to rule out all other causes such as a weakened left ventricle and to consider the possibility of ruling in an arrhythmia-induced cardiomyopathy diagnosis.
If the cause of arrhythmia is frequent premature ventricular contractions (PVCs), a cardiac MRI may show the presence of a scar, which would refute the aforementioned diagnosis.
- Coronary angiogram: an invasive procedure whereby a catheter is inserted through a wrist or groin artery to inject contrast dye into the arteries surrounding the heart. This test is used to stave off any cause of left ventricular weakness, such as arterial obstruction.
Mechanism and Management of Arrythmia-Induced Cardiomypathy
The treatment of arrythmia-induced cardiomyopathy focuses mainly on the elimination or control of arrhythmia.
A favorable response to treatment establishes the arrhythmia-induced cardiomyopathy diagnosis. There is some controversy regarding the need to continue medications once there is a return to normal heart function.
The Chicken or the Egg?
Finally, it can be difficult to determine whether the arrhythmia is the initiator or the consequence of cardiomyopathy in a patient with tachycardia and heart failure.
Arrhythmia is often considered secondary and is not treated as it should be when in fact arrhythmia control is necessary for a full recovery.
Other Important Issues
Although there is an association between high heart rate and myocardial injury:
- Arrythmia-induced cardiomyopathy is rare or nonexistent in patients with inappropriate sinus tachycardia (IST) and postural orthostatic tachycardia syndrome (POTS), even though the average heart rate during waking hours may be over >100 beats/minute.
Typically, the nocturnal heart rate in these disorders is slower due to the lack of influence of tachycardia-promoting elements, such as the hassles of everyday life during that period.
- There is no specific heart rate cutoff at which can develop. The rate may be age dependent.
- Very little is known about factors that might increase patients’ vulnerability to arrythmia-induced cardiomyopathy, but a genetic link has been suggested.
- Atrial Fibrillation
AF is the most common cause of arrhythmia-induced cardiomyopathy in adults.
Several factors contribute to a weakening heart:
- Due to the rapid and irregular heart rate of AF, there is an impairment of the ventricles which cannot relax completely. As a result, there is a lesser volume of blood that goes into the ventricles and thus less blood is pumped forward.
- Because the atria are fibrillating, there is a lack of an important atrial contribution to filling the lower chambers.
Both of these factors are exacerbated by an increase in heart rate.
Sequence of Operation
The ventricles initially begin to dilate as a way to compensate, but with time spent in the setting of rapid atrial fibrillation, the ventricular function starts to decline as well.
Eventually, with a lack of efficient forward blood flow, the pressure within the cardiac chambers increases. This causes pressure to back up into the lungs, most likely resulting in pulmonary edema, more commonly referred to as "having water in the lungs”.
Treatment includes either pharmacological and/or interventional methods.
- Cardiac Rate Control
A monitoring strategy may be attempted at first, using rate-controlling medications that include beta-blockers, calcium channel blockers, and, less commonly, digoxin.
- Rhythm Control
Restoring and maintaining normal sinus rhythm is an alternative approach to the treatment of arrythmia-induced cardiomyopathy.
Not all patients can be candidates for a rhythm-control approach, which means the end of atrial fibrillation towards a regular rhythm called sinus rhythm. This cardioversion can be done electrically or by the introduction of antiarrhythmic drugs, namely: amiodarone, sotalol, or dofetilide for patients with weakened hearts and rapid atrial fibrillation.
In an increasing number of patients, an interventional approach with a catheter ablation procedure of AF is an excellent option for the maintenance of a normal sinus rhythm.
Additional Interventional Approach
For patients who are unresponsive to medications that control heart rate or who are deemed not suitable for restoration of normal sinus rhythm, a cardiologist may recommend a 2-step intervention:
1. pacemaker implantation,
2. ablation of the atrioventricular (AV) node is performed several weeks-months after the pacemaker insertion.
To fully understand the need for the first step, we must go back to a particular detail in cardiac function.
Atrioventricular (AV) Node Ablation
Electrical transmission between the atria and the ventricles is possible at one location only. At this border post, there is a watchdog or customs officer who monitors the passage.
This role is played by an islet of cells called the atrioventricular node, which allows electricity to move from the atria to the ventricles at maximum frequency.
Pacemaker implantation is necessary to maintain ventricular stimulation as the sole electrical transmission point between the atria and the ventricles, given that it will eventually be destroyed. It is only after a few weeks or months that the ablation can be done safely.
More Involved Arrhythmias
Arrhythmia is atrial fibrillation’s twin sister. They share a great number of similar factors that contribute to a weakening heart, as described earlier.
Identical frequency and rhythm control strategies may be applied.
An Interventional Approach Gives Best Results obtained with an in
Mechanistically, the underlying cause of atrial flutter-induced AIC is similar to that of atrial fibrillation, however, its treatment is different.
Radiofrequency ablation of typical right-sided atrial flutter has a high success rate (>96%) with minimal risk of complications. As a result, ablation is the first-line treatment for arrhythmia-induced cardiomyopathy (AIC).
- Frequent Premature Ventricular Contractions (PVCs)
Frequent PVCs can lead to AIC in patients without known heart disease and conversely can exacerbate a weakened heart in patients who already have heart disease present.
The cause leading to ventricular extrasystole-induced cardiomyopathy is not well known, although some hypotheses are currently raised.
Important Arrythmia-Induced Cardiomyopathy Predictors
The most important predictor of arrythmia-induced cardiomyopathy in patients with frequent PVCs is their heavy daily burden of PVCs. A high PVC burden has been defined as ranging from >10,000 to 25,000 PVCs per day and as >10% to 24% of total heartbeats a day.
The ventricular function can improve if the PVC burden is reduced to <5000 PVCs/day.
A larger number of PVCs recorded on an electrocardiogram is generally associated with a higher risk of AIC than in the case of a smaller quantity of PVCs.
A wider PVC on electrocardiogram typically has a higher associated risk of AIC than a narrower PVC.
The purpose of PVC treatment is to suppress or eliminate them, the two options applying either or both pharmacotherapy and/or interventional therapy.
Normally, therapy will start with a beta-blocker or calcium-channel blocker because these are low-risk therapies, however, they have limited effectiveness.
Should additional or another kind of therapy be required, an antiarrhythmic medication may be initiated. Dofetilide, mexiletine, sotalol, and amiodarone are antiarrhythmic medicines that may be most effective although they have a higher risk of side effects and can be proarrhythmic, i.e., promoting arrhythmias.
Antiarrhythmic drug use is frequently reserved for patients who fail or are reluctant to undergo catheter ablation.
Catheter ablation has emerged as the definitive therapy for PVC-mediated AIC with success rates ranging from 50-90%, depending on the location of the extra beats and the frequency of PVCs on the day of the ablation.