Diaphragmatic Pacers: Types, Indications, Mechanism, and Complications

Introduction:

Diaphragmatic pacing is a therapy aiming to select patients with ventilatory failure due to diaphragm paralysis. The typical therapy approach is to pace the diaphragm by stimulating the phrenic nerve at the neck or thorax level. It is a lightweight, battery-powered system that electrically stimulates the diaphragm muscles and nerves.

How Does the Diaphragm Work?

The diaphragm is a muscle of respiration separating the thoracic and abdominal cavities, located just below the lungs. As the diaphragm contracts, a negative pressure is created in the lungs, and the air is driven into the lungs, while as the diaphragm relaxes, the elastic recoil pushes the air out.

What Are the Indications for Diaphragm Pacing?

The procedure is indicated in cases of

• Patients with spinal cord injuries above C3 levels.

• Congenital central alveolar hypoventilation.

• Arnold-chiari malformations.

• Basilar meningitis.

• Brainstem tumors.

• Cerebrovascular accidents.

• Pompe's disease.

• Syringomyelia.

• Meningomyelocele.

What Are the Contraindications for Diaphragm Pacing?

The procedure is contra-indicated in cases of

• Patients who are ventilator dependent either because of muscular dystrophies or motor neuron diseases such as spinal muscular atrophy or polio. For the diaphragm pacing to work, the diaphragm muscle and the phrenic nerves should be functional.

Who Is an Ideal Candidate for Diaphragm Pacing?

A candidate to be considered for diaphragm pacing should have

• Normal diaphragm muscle function.

• Phrenic nerves should be intact and able to signal when stimulated.

• Normal lung function with no lung disease.

What Are the Types of Diaphragmatic Pacers?

There are two types of diaphragmatic pacers:

• Conventional DiaphragmaticPacers- Internal electrodes are attached to the phrenic nerve at the cervical, thoracic or diaphragmatic level. Pacing wires connect this electrode to a receiver under the skin. An external transmitter is placed on the skin's surface above the receiver. This transmitter is the main controlling unit and sends radiofrequency signals.

• Diaphragmatic Pacing System- It consists of :

  • Electrodes are implanted in the diaphragm to provide direct muscle stimulation.

  • The fifth electrode implanted under the skin acts as a grounder.

  • An electrode connector joins the five electrodes exiting the skin into a socket known as an external pulse generator.

What Are the Advantages of Placing a Diaphragm Pacing?

The advantages of placing a diaphragm pacer are as follows:

• It reduces the time spent using a ventilator or other assisted breathing device.

• It reduces the risk of respiratory infections.

• The patient can move about easily and perform daily activities.

• It also reduces the length of hospital stay.

What Are the Pre-operative Tests to Be Done?

The pre-operative test includes:

• Pulmonary Function Test: A restrictive process is seen in a patient with a paralyzed diaphragm. Also, vital capacity is lost, which worsens when measured in the supine position.

• Chest X-Ray: It is more useful in patients with unilateral diaphragmatic paralysis as it shows an elevated level of the hemidiaphragm on the affected side compared to the normal side. However, a chest x-ray does not prove beneficial in bilateral diaphragmatic paralysis as it shows elevated hemidiaphragm on both sides, thus appearing normal.

• Fluoroscopic "Sniff" Test: The patient is asked to sniff/inspire in the supine position. Sniffing ensures diaphragmatic involvement. Diaphragmatic movement can be measured with the help of radio-opaque markers. If a patient has normal phrenic nerves, the sniff test will result in a quick downward movement of the diaphragm. A paradoxical upward movement of the diaphragm confirms the test to be positive for paralysis of the diaphragm.

• Percutaneous Cervical Electrical Stimulation: It is considered the gold standard to test the function of the phrenic nerve. Electrical stimulation is performed by placing the electrodes in the neck. Hemidiaphragm stimulation and contraction are seen in an intact phrenic nerve, whereas a prolonged latency or failure to conduct indicates poor phrenic nerve function.

What Is the Technique for Placing the Electrodes?

There are several approaches to placing the electrodes; they include:

• Cervical Approach- The nerve is first identified in the mid portion of the neck under the scalene fat pad by retraction of the sternocleidomastoid muscle. The nerve is tested with the help of a stimulator, and the muscle is identified by fluoroscopy. Once it is tested, the fascia is dissected, and two electrodes are placed onto the nerve and secured to the underlying connective tissue. A wire is passed subcutaneously on the same side of the chest that connects the electrodes to a pulse generator.

• Thoracic Approach- The right phrenic nerve is posterior to the esophagus, and the left phrenic nerve is located lateral to the pericardium. Once the nerve is identified, the electrodes are placed onto the nerve. The nerve is tested in a similar way as in the cervical approach.

• Diaphragmatic Pacing Approach- The electrodes are attached to the phrenic nerve to the diaphragm.

When Does the Diaphragm Pacing Start Working?

It does not start to work immediately after the placement of the electrodes. Instead, it takes about 6 - 8 weeks after the surgery for the incisions to heal and the formation of scar tissues around the electrodes to stabilize them. The diaphragm signals the phrenic nerve sends with the pacer differ from the natural phrenic nerve impulses. Therefore, it is always necessary to train the diaphragm to accept longer pacing periods without developing fatigue. The time pacing is increased gradually; usually, patients are pacing up to 8-12 hours at a time for about three months.

What Are the Complications of Diaphragm Pacing?

• Damage to the phrenic nerve.

• Acute lung injury.

• Vascular injuries.

• Pericardial and esophageal injuries.

• Diaphragmatic perforation.

• Peritonitis.

• Infection of the implanted components.

Conclusion:

The diaphragm pacing method involves electrical stimulation of the patient's diaphragm muscle and nerve. This causes muscle contraction so that air goes inside the lungs; therefore, it helps the patient to breathe normally. It has proven to be a safe mechanical ventilation method allowing mobility and daily physical activities, thus reducing the dependency on mechanical ventilation. The procedure involves a multidisciplinary approach for which a skilled rehabilitation team consisting of physical medicine and rehabilitation clinician, physical therapist, occupational therapist, and speech therapist is required.