Defibrillation is an urgent medical procedure that uses an electrical shock to stop an abnormal, life-threatening heart rhythm, specifically ventricular fibrillation or pulseless ventricular tachycardia, allowing the heart’s natural electrical system to reset and resume a normal rhythm. Implanted cardiac devices, such as pacemakers and implantable cardioverter-defibrillators (ICDs), function to monitor and regulate heart rhythm. A pacemaker uses low-energy electrical pulses to treat a slow heartbeat, or bradycardia. An ICD monitors the heart for dangerous, fast rhythms, or tachyarrhythmias, and can deliver a high-energy shock internally to restore a normal rhythm. Both devices are typically small, battery-powered generators implanted beneath the skin, often near the collarbone, and are connected to the heart via thin wires called leads.
The Safety of Defibrillating Patients with Implanted Devices
The direct answer to whether a patient with a pacemaker or ICD can be defibrillated is yes, as saving the patient’s life takes immediate precedence over device integrity. If a patient is in cardiac arrest due to a shockable rhythm, external defibrillation must be performed without delay, regardless of the presence of an implanted device. The primary concern is that the high-energy electrical current from the external defibrillator could potentially damage the internal device’s generator or its leads.
While modern implanted devices are designed with some protection against external electrical interference, the powerful external shock carries a risk of malfunction. This risk includes the device resetting to a default safety mode, changes to the programmed settings, or damage to the internal circuitry. For both pacemakers and ICDs, the immediate need to convert a life-threatening rhythm outweighs the risk of damaging the device, which can be checked and corrected later.
Modified Pad Placement During Emergency Defibrillation
Delivering the life-saving shock while minimizing the risk of device damage requires a modification of the standard electrode pad placement. The cardinal rule is to ensure the defibrillation pads are placed a minimum distance away from the pulse generator, which is the visible bulge under the skin. Current guidelines specify that the pads should be positioned at least 1 inch or 8 centimeters away from the site of the implanted device.
This rule of distance prevents the external electrical current from passing directly through the device generator, which could cause internal damage or electrical arcing. Placing a pad directly over the device could also cause the device to absorb or deflect the energy, preventing the full therapeutic current from reaching the heart muscle to convert the rhythm. If the standard anterior-lateral pad position (one pad below the right collarbone, the other on the left side of the chest) would place a pad too close to the device, alternative positions must be used.
One acceptable alternative is the anterior-posterior placement, where one pad is positioned on the front of the chest over the heart and the other is placed on the back, usually beneath the left shoulder blade. This configuration creates a current pathway that effectively bypasses the device. Another option, depending on the device location, is to shift the pads further away on the same side, ensuring the 1-inch or 8-centimeter clearance is maintained. The goal of any modified placement is to maximize the electrical energy that traverses the heart while avoiding the implanted hardware.
Post-Shock Device Evaluation
Following any successful external defibrillation of a patient with an implanted cardiac device, a mandatory medical action is the post-shock device evaluation. Even if the patient appears stable and the heart rhythm has been successfully restored, the internal device must be interrogated by a cardiologist or specialized device technician. This process involves using an external programmer placed directly over the skin to communicate wirelessly with the implanted generator.
The primary purpose of the interrogation is to check for any functional issues caused by the high-energy external shock. The medical team will check the device’s battery status, looking for any unexpected depletion or temporary voltage reduction. They will also assess the integrity of the leads, ensuring the wires connecting the device to the heart have not been damaged or dislodged. Damage to the leads could impair the device’s ability to pace or sense the heart’s electrical activity.
A further inspection involves reviewing the device’s programmed settings. A strong electrical shock can sometimes cause the device to reset to default factory settings or alter its sensing thresholds. Reprogramming may be necessary to restore the patient’s personalized settings, such as the minimum heart rate for pacing or the detection criteria for a dangerous rhythm. This immediate check ensures the device is functioning correctly and is prepared to continue its life-supporting role after the emergency event.