What is AV block?

What is AV block?

The heartbeat comes from the sinus node, which makes the heart beat at 50-100 beats per minute. After the sinus node, the impulse is directed to the ventricles. The impulse conduction system consists of the sinus node, which produces the pulses, the atrioventricular node, the His bundle, and the right and left branches of the His bundle (Fig. 1). 

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Any damage to this system of the heart leads to a reduction or interruption in the production or conduction of the rhythm. This condition is called atrioventricular block. The consequence of this is bradycardia or asystole, from which the patient is at risk. 

Types of atrioventricular block

The lesion may be in the atrioventricular node or less commonly in the His bundle. 

There are 3 degrees of severity of atrioventricular block, depending on the electrocardiographic picture (Fig.2):

Fig.2: The three types of atrioventricular block

• 1st degree: Only conduction delay is recorded on the electrocardiogram.
• 2nd degree: Most impulses pass to the ventricles, but some are lost.
• 3rd degree or full: No stimulus passes into the ventricles.

Symptoms of atrioventricular blockage

Your symptoms depend on the type of atrioventricular blockage. Grade 1 atrioventricular block usually has no symptoms. 

Some of the symptoms of 2nd degree atrioventricular block are:

• Chest pain
• Zalada
• Fainting
• Fatigue
• Shipping
• Dyspnea

Some of the symptoms of 3rd degree atrioventricular block are:

• Cardiac arrest
• Zalada
• Fainting
• Severe fatigue
• Palpitations

When should you visit the doctor?

If you faint, have shortness of breath or chest pain, call for help immediately, even if you are alone. Your priority is to get to the hospital and get medical attention. There are many causes that can lead to atrioventricular block. See a doctor if you or another family member develops symptoms of atrioventricular blockage.

Causes of atrioventricular block

Complete atrioventricular block is usually acquired and in a few cases congenital.

• Acquired blockade is most often due to chronic degenerative lesions of the His bundle and its strands. This chronic complete atrioventricular block is a classic indication for artificial pacemaker placement. 
• Acute myocardial infarction is a second and not uncommon cause of complete atrioventricular block. In this case, the infarct is most commonly inferior. Temporary artificial pacing is recommended, especially if the pulses are below 38-40/min and when arterial hypotension is present or a syncopal crisis has occurred. Other times, complete atrioventricular block is due to acute anterior wall infarction. Here the conduction disturbance is due to damage to His from the extensive myocardial infarction. For this reason, the prognosis is grave, even if the indicated artificial pacemaker is placed. 
• Congenital atrioventricular block is rarely manifested by syncopal attacks or other symptoms, but it is nevertheless prudent to implant a permanent pacemaker because in some cases there is a risk of sudden death. 

Risk factors for atrioventricular blockage

A risk factor is defined as anything that increases a person's chances of developing a particular disease. Factors that may increase the risk of developing atrioventricular block are:

• Old age
• Cardiovascular disease
• High levels of potassium in the blood
• Hyperthyroidism
• Lyme disease 
• Recent open heart surgery

How is the diagnosis made?

• In complete atrioventricular block, with a stable heart rate of 35-40/min or higher, patients often have no symptoms. However, some of them may develop manifestations of heart failure, cerebral ischaemia or even coronary insufficiency if obstructive coronary artery lesions are present. 
• In most patients, the heart rate is unstable and Adams-Stokes attacks occur. These seizures are syncopal, due to ischaemia of the brain and are characterised by loss of consciousness, facial pallor and, if they last more than 15 seconds, cyanosis, deep dysregulated breathing and convulsions. Convulsive seizures lasting more than 60 seconds are usually fatal unless cardiac resuscitation is performed. 
• The final diagnosis is made by electrocardiogram if the lesion is permanent, and by Holter if it is transient and intermittent.

What is the treatment?

Complete atrioventricular block is treated with artificial pacing. In grade 2 or rarely in grade 1 atrioventricular block, there are categories of patients who also need to have an artificial pacemaker implanted. 

What is a pacemaker?

A pacemaker is a device that is implanted under the skin of the chest, in a relatively simple operation. The pacemaker is designed to maintain the rhythm of the heart when there are diseases that disturb the rate at which the heart beats. The implantation is carried out under aseptic conditions, in a haemodynamic laboratory equipped with an X-ray machine and under local anaesthesia. 

How does it work?

It is a small battery operated device. It has one, two or three thin wires, which reach up to the heart and conduct electrical stimulation. The purpose is for the heart to pulse at a specific rate when its own rate falls below a critical threshold, depending on the pacemaker's programming. Pacemakers, in other words, work on demand. 

How does the pacemaker affect the patient's normal activity?

The normal activity of a person with a pacemaker is not substantially affected. Regular medical monitoring is necessary in order to properly adjust the pacemaker and check that it is working properly. Monitoring is carried out by the doctor who implants the device every six months, using a special external machine with a head that analyses all the data from the pacemaker for the period since the last check.  

Battery and pacemaker replacement

The battery of the pacemaker has a lifespan that depends on the type of pacemaker and the patient's needs. Replacement of the pacemaker involves only the generator and not the leads. It is done by opening the area, but the procedure is very quick and the recovery is very fast. 

Types of pacemaker

There are single-cavity and dual-cavity pacemakers. Univentricular pacemakers are needed by patients in permanent atrial fibrillation when they develop bradycardia because the atrium is no longer involved in the contraction of their heart. All other patients who have a functioning sinus node need an interstitial pacemaker (Fig. 1).

Amphibiocaval pacemaker

In the last 20 years, a special pacemaker has been added to our pharmaceutical quiver for patients with heart failure, regardless of whether they have bradycardia. This pacemaker is called a biventricular pacemaker, because it has a third lead that is not placed in a cavity, but in the venous network that takes the blood that feeds the heart away from the heart into the coronary sinus. The coronary sinus is adjacent to the left ventricle and so its electrical stimulation stimulates the left ventricle. In this way, we synchronize the electrical stimulation of the right and left ventricles, which in heart failure become desynchronized, and while normally the left ventricle is stimulated first, in heart failure the right ventricle is stimulated first, resulting in a significant deterioration of cardiac function (Fig. 2).

Wireless pacemaker

Also, in the last 5 years, a wireless pacemaker was added, which is implanted in elderly people with atrial fibrillation, who have an inability to access the veins. It is inserted by a special procedure through the femoral vein and the device stays inside the right ventricle. There is no dual-chamber pacemaker without a lead. Also, it is still unclear what will be done with its replacement (Fig. 3).

What we do at the "Agios Loukas" Clinic

At the "Agios Lukas" Clinic we implant a very large number of pacemakers and biventricular pacemakers per year. There is a huge experience in this field of electrophysiology. 

What can I ask the implant specialist?

To better understand your condition and its symptoms, you can ask the implant doctor some of the following questions. Feel free to make a list of anything else you want to ask your doctor.

• What makes my heart beat slowly?
• What is my condition?
• What tests do I need?
• How dangerous is my situation?
• What do I need to change about my activities?
• Which pacemaker do I need?
• What restrictions will I have in my life?
• What are the complications of the surgery?
• Will I be able to have an MRI scan?

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