What is Atrioventricular Dissociation?
Atrioventricular (AV) dissociation is a type of irregular heart rhythm, or arrhythmia, where the upper and lower parts of the heart beat independently from each other. Normally, a small part of the heart called the sinoatrial (SA) node controls the heart’s rhythm. It sends signals that control the pace of both the atria, or upper chambers, and the ventricles, or lower chambers, through a system known as the His-Purkinje system.
When there are disruptions in these signals, the heart’s upper and lower sections can start to beat at different paces. This can have different effects, ranging from benign in minor cases to life-threatening in severe cases, such as complete heart block, which can be deadly if not treated with a pacemaker. Another major cause of this condition is ventricular tachycardia, which is a dangerously fast heart rhythm that must be quickly diagnosed and treated to avoid fatal consequences.
What Causes Atrioventricular Dissociation?
The speed at which the SA node in the heart sends signals can slow down. This can lead to other pacemakers in the heart system taking over, causing irregular heart rhythms and a disconnect between the upper chambers (atria) and lower chambers (ventricles) of the heart. Things that might lead to this slowdown include a slow heart rate, a high level of relaxation in the body (known as high vagal tone), or certain heart medications like beta blockers and calcium channel blockers.
On the other hand, certain conditions can speed up the pacemakers, leading them to take over the rhythm control. This can happen if there’s not enough blood supply to the heart, an excess of stress hormones in the body, or due to the harmful effects of a heart medicine called digitalis.
There are also various types of irregular heart rhythms, referred to as arrhythmias, that can cause a disconnect between the atria and ventricles. For example, ventricular tachycardia, a fast heart rate that starts in the ventricles, can cause this disconnect. Certain features of ventricular tachycardia, like ‘capture’ and ‘fusion’ beats, are signs that it is likely causing the disconnect. Another type, called bundle branch reentrant ventricular tachycardia, involves circular circuits not involving the atria, leading to a disconnect. Junctional tachycardia, where the junction between the atria and the ventricles can beat faster than the SA node, can also lead to this disconnect. This typically happens in certain conditions like digitalis toxicity, after heart surgery, or following a heart attack.
There’s some disagreement about whether complete heart block, where the signals from the SA node don’t reach the ventricles, falls under this disconnect. The reason for this is that, while all cases of complete heart block involve a disconnect, not all cases of disconnect are a complete heart block. In other words, it’s important not to assume that any given disconnect is the same as a complete heart block.
Risk Factors and Frequency for Atrioventricular Dissociation
AV dissociation, a condition detectable in heart monitoring (ECG) tests, occurs in about 0.48% to 0.68% of all these tests. It’s more commonly found in older adults who also have degenerative heart diseases. If you include cases of complete heart block, a more serious condition, the overall occurrence rate increases.
Signs and Symptoms of Atrioventricular Dissociation
If a patient is suffering from inadequate blood flow, they might experience symptoms like dizziness, fainting, shortness of breath, and chest pain. A general physical examination might reveal abnormal vital signs due to extremely fast or extremely slow heart rhythms, known as tachy- or bradyarrhythmias. In addition, specific physical examination related to heart may show inconsistency in the intensity of the first heart sound, large ‘a’ waves which can indicate abnormal jugular venous pulsation, and an unusual splitting of the second heart sound.
Testing for Atrioventricular Dissociation
When investigating symptoms related to heart issues, a detailed record of the patient’s health history is vital. This would cover any history of heart disease, signs of a blocked heart, recent heart procedures, and a thorough review of the patient’s current medications and dosage. Particular focus would be on heart-related drugs such as beta-blockers, calcium channel blockers, other rate-limiters, anti-arrhythmic drugs like Amiodarone, and others.
To further determine the condition, a 12-lead ECG is needed. This type of ECG features distinct characteristics that can lead to a diagnosis. One of these is P Waves that seem to march through the heart rhythm, which suggests the possibility of a heart block. Other telltale signs are Capture and Fusion Beats, disturbances that occur when normal heart rhythm is disrupted.
Depending on the presence of capture beats, we could classify the heart condition as incomplete or complete AV dissociation. Incomplete implies intermittent disruption, while complete refers to constant disruption.
Two specific types of incomplete AV dissociation are Interference AV Dissociation, which presents with alternating intervals of short and long pulses, and Isorhythmic AV Dissociation. The latter refers to a situation where the heart chambers beat separately but at the same rate.
Complete AV dissociation means the atria and the ventricles are completely independent, and there are no capture beats. Here, the main focus is on the timing of the P waves and not necessarily on the presence of a complete AV block. In proposition with the recent nomenclature revisions, it is recommended that this condition can be classified as AV dissociation with or without capture beats.
Once AV dissociation is confirmed, it’s important to compare the atrial and ventricular rates for the sign of a complete heart block. But a diagnosis of complete heart block should only be made if the ventricular rate is less than 40 beats per minute. It would also be essential to explore reversible causes such as Lyme carditis, Hyperkalemia, hypothyroidism, and viral myocarditis as these conditions can also play a role in causing heart block.
In summary, a comprehensive history of the patient and thorough analyses, including an ECG and comparison of the atrial and ventricular rates, can effectively diagnose a heart condition and enable appropriate treatment.
Treatment Options for Atrioventricular Dissociation
The treatment for atrioventricular dissociation, a condition where the heart’s upper and lower chambers beat independently of each other, usually involves addressing the underlying cause. For example, if it’s caused by an unusually fast heart rate (tachycardia), the goal would be to get the heart rate back to normal.
Care should be taken in treating junctional arrhythmias, irregular heart rhythms that originate in the heart’s junctional area, because stopping the irregular rhythm could also stop the only source of natural heart rhythm. Digitalis toxicity, a side effect of the heart medication digoxin, can be treated with another drug that counteracts the digoxin.
In situations where the heart rate needs to be increased, drugs like isoproterenol and atropine may be used. If someone has a complete heart block, which is when the electrical signals can’t move from the heart’s upper chambers to its lower chambers, atropine may not be effective because it works on the area in the heart that is blocked.
Lyme carditis, a heart complication of Lyme disease, usually resolves on its own but antibiotics can speed up recovery. If signs and lab results show that high potassium levels are causing a complete heart block, immediate steps to lower potassium levels may include using medications, and using insulin, calcium gluconate, and beta 2 agonist agents.
If the heart block can’t be fixed by treating the cause, then a pacemaker may be needed. Pacemakers are medical devices that use electrical impulses to regulate the heart rhythm. If a pacing device that’s attached to the skin isn’t enough to manage the situation, a pacemaker that’s inserted into the vein might be considered.
There are three types of permanent pacemakers:
1. Single chamber pacemakers which have one lead placed in the right upper or lower heart chamber.
2. Dual chamber pacemakers consisting of two leads placed in both right upper and lower heart chambers.
3. Biventricular pacemakers, similar to the dual-chamber but with an additional lead placed in the coronary sinus for left lower heart chamber pacing.
Although the most common and effective pacemaker for treating heart block is the dual-chamber pacemaker, recent studies suggest that the biventricular pacemaker may have an edge in reducing the risk of pacing-induced heart failure.
What else can Atrioventricular Dissociation be?
Atrioventricular (AV) dissociation, a condition where the heart’s atria and ventricles beat separately from each other, could look like other conditions that cause rapid heartbeat. Therefore, health care professionals should be able to recognize similar cardiovascular conditions. Here are some conditions that may present similar symptoms to AV dissociation:
- High-grade Atrioventricular block: A serious type of heart block where the signal from the upper parts of the heart fails to reach the lower parts.
- Atrioventricular nodal re-entrant tachycardia: A type of fast heart rate due to an extra circuit in the heart’s electrical system.
- Supraventricular tachycardia with aberrancy: A rapid heart rate that starts in the upper parts of the heart, with abnormal conduction.
- Orthodromic tachycardia: A type of rapid heartbeat that starts in the lower parts of the heart.
It’s vital for doctors to consider these conditions and use appropriate tests to make a correct diagnosis.
What to expect with Atrioventricular Dissociation
Atrioventricular dissociation, often a temporary condition unless accompanied by a complete heart block, has a prognosis largely determined by the root cause rather than the impact of the dissociation itself. If the initial cause can be resolved, patients usually experience a complete recovery.
Possible Complications When Diagnosed with Atrioventricular Dissociation
Complications related to atrioventricular dissociation, a heart condition, typically come from the associated decrease in the effective circulation of blood. This can often be due to the causes of this condition, including severe slow heartbeat (sinus bradycardia) and fast heartbeat originating from the lower chambers of the heart (ventricular tachycardia). The most common complication is fainting, known as syncope. If left untreated, the decreased flow of blood can lead to serious health issues, such as acute kidney failure (due to less blood reaching the kidneys) or a condition where there’s reduced blood flow to the heart (myocardial ischemia).
Potential complications include:
- Severe slow heartbeat (sinus bradycardia)
- Fast heartbeat from the lower chambers (ventricular tachycardia)
- Fainting (syncope)
- Acute kidney failure due to low blood flow to the kidneys
- Reduced blood flow to the heart (myocardial ischemia)
Preventing Atrioventricular Dissociation
Patients showing symptoms need to understand all the aspects of AV dissociation, including its causes and how it affects daily life. It’s also important to stop taking any medications that might be causing it and to review all other medications being taken. This includes being aware of how much of each medication is being taken, such as the dosage of a drug called digoxin in patients who have kidney problems. Patients should also be made aware of potential interactions between different drugs.
Patients who have a slow heart rate (bradycardia) and AV dissociation can benefit from a device called a pacemaker.
Also, patients must be taught about the risks associated with this procedure. They should also be told about the importance of regular check-ups for the functioning of the pacemaker (lead function) and to check the battery. They also need to be aware of things that can interfere with the pacemaker (electromagnetic interference) and unusual results in imaging tests. They should be advised to be cautious during future evaluations.
