Definition & Overview
A pacemaker is a small electronic device attached beneath the skin of the clavicle. Its primary function is to control abnormal heart rhythms. It consists of a pulse generator, which connects to a string of leads. The leads act as conductors of electrical impulses generated by the pulse generator and sent to the heart muscles to make them contract. This helps the heart muscles to efficiently pump blood to the lungs and other parts of the body.
The techniques involved in pacemaker installation vary, but one of the most employed is epicardial electrode insertion. This technique employs small cameras that guide doctors during surgery (video-assisted thoracic surgery or VATS).
The heart is enveloped by a double-layered sac called the pericardium. The outer fibrous layer is called parietal pericardium while the inner, serous part is the epicardium. The epicardium is situated closely to the heart muscle. In this medical procedure, the electrodes are attached to the epicardium.
Recently, this technique has been replaced by even less invasive approaches. These include transvenous lead placement in the right atrium and ventricle as well as the placement of leads in the left ventricle via the coronary sinus.
The insertion of epicardial electrode usually requires thoracotomy or surgical incision in the chest wall. At times, median sternotomy is used. This is a surgical procedure where surgeons cut open the sternum and divide it to gain access to the heart. Another technique that can be used is the subxiphoid approach where a 6cm incision is made just below the xiphoid process, which is located at the lower end of the sternum.
Who Should Undergo and Expected Results?
Epicardial electrode insertion is used as a therapeutic or diagnostic procedure since the 1960s. These electrodes are installed in the epicardium and are indicated for the management of tachycardia, a condition where the heart beats faster than the normal rate.
The installation of epicardial pacing wires restores the heart’s ability to beat at a normal rate. This allows for an optimised cardiac output, which is the amount of the blood the heart is able to pump in a single minute. The goal of inserting epicardial electrodes is to optimise and augment cardiac output.
A number of studies and medical documentations show that epicardial permanent lead insertion procedure is suitable for many patients suffering from irregular heartbeats and those with chronic diseases of the heart muscle.
However, the procedure is not recommended in some cases. Some of the contraindications for this procedure are the following:
- Existing infection at the site
- Tendency of the patient to bleed profusely
- Existing bacteria in the blood signifying infection (bacteremia)
- Severe lung disease
The insertion of a temporary or permanent epicardial electrode decreases the morbidity and mortality of patients suffering from heart muscle disorders.
How is the Procedure Performed?
Epicardial electrode insertion only lasts an hour or less. Blood loss is less compared to other similar open incision procedures and often, it produces minor or virtually no complications.
If a minimally invasive procedure, such as transvenous placement of leads, is not possible or applicable, that is the only time that surgeons would perform highly invasive epicardial lead insertion procedures. With this method, the epicardial leads are inserted through a surgical incision in the chest wall (thoracotomy). The leads are burrowed down the skin (subcutaneous) and connected to the pacing generator.
Depending on the need, atrial or ventricle wires are installed. Atrial pacing wires are implanted into the right atrial appendage while the ventricular pacing wires are installed into the right ventricles’ anterior diaphragmatic surface. As soon as these wires are installed into the target location, the wounds are sutured closed to prevent further bleeding.
The wires or leads are then connected to the batteries of the pulse generator so that it can start monitoring the heart’s rhythm and intervene when necessary.
Possible Risks and Complications
Like any other kinds of invasive medical procedure, the insertion of epicardial electrodes also poses some risks and complications. However, these complications are mostly minor and immediately get resolved using appropriate drugs or with medical interventions during surgery.
Bleeding from the site where the wires were inserted is one. To resolve this, surgeons often make additional sutures in the area to prevent further blood loss.
The wires or leads used can irritate the phrenic nerve, a nerve that originates from the neck, and can also unnecessarily stimulate the diaphragm. However, this can be avoided with the correct positioning of pacing wires and by making sure they don’t touch any sensitive organs or tissues.
Surgeons require patients to adhere to their follow-up schedule so that they could carefully monitor the leads and pulse generator. They will also use this time to monitor any improvement in the heart’s cardiac output as well as check for early signs of complications.
Risks and complications abound, but potentially catastrophic ones are rare and usually result from the patient’s pre-existing conditions that are left unchecked.
US National Library of Medicine National Institutes of Health; “Epicardial electrode insertion by means of video-assisted thoracic surgery technique”; https://www.ncbi.nlm.nih.gov/pubmed/15503625
Yasir Abu-Omar, Lorenzo Guerrieri-Wolf, David P. Taggart; “Indications and positioning of temporary pacing wires”; http://mmcts.oxfordjournals.org/content/2006/0512/01248.full.pdf