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Shock Factor

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The paramedics arriving on scene found the 79-year-old man acting nervous but alert and oriented. The patient identified himself and said he had called 9-1-1 after his implanted defibrillator had fired 11 times. He denied having any chest pain, dizziness or shortness of breath before the ICD had begun firing. His lungs were clear, vital signs were within normal limits, and the cardiac monitor showed a 100% paced rhythm. A 12-lead ECG was performed with no unusual findings.

Further assessment of the ICD was conducted, and the patient produced an information card stating the ICD was manufactured by Medtronic Inc., and may have been one of the devices recently recalled by the Food and Drug Administration (FDA) due to lead malfunction.

The crew removed him to their ambulance. During transport, the patient received five additional shocks from the ICD as the paramedics were talking with him. The patient remained stable but said he felt uncomfortable, so he was placed on oxygen and given Versed for agitation. It was confirmed at the hospital that his ICD was one of the recently recalled devices.

The Benefits of ICDs

Patients with poor left ventricular function and survivors of prior cardiac arrest are candidates for ICD therapy. ICDs are typically used to prevent sudden cardiac death in patients at risk for ventricular tachycardia or ventricular fibrillation, but are also capable of pacing patients with bradycardic heart rhythms.

An ICD has two main hardware components: a defibrillator and leads. The defibrillator is battery-powered and is surgically placed beneath the patient's skin. The leads are also implanted, with wires running from the defibrillator to the patient's heart muscle. If rapid V-tach or V-fib are detected, the defibrillator will deliver a small electrical shock to the patient's heart.

This process is intended to interrupt the abnormal rhythm and allow the heart to use its natural impulse center to restore normal rhythm. Immediate defibrillation before acidosis build-up and heart tissue death have been shown to decrease patient mortality.

Possible Defects

As with all devices, there's a small risk of malfunction. In a study of 990 patients over 13 years, lead failures were identified in 15% of the study population. The incidence of lead malfunction increased over time, with leads 10 years and older experiencing a 20% failure rate. In the 15% of patients with lead failures, insulation defects were the top reason for complications (58%), followed by lead fractures (12%).

When a lead fracture occurs, the most common presentation, like the patient encounter previously described, is multiple inappropriate shocks. These shocks are painful, have the potential to induce lethal arrhythmias and can be extremely distressful psychologically to the patient.

On Oct. 15, 2007, the FDA issued a class 1 recall (the most serious) of some Medtronic Sprint Fidelis leads (Models 6930, 6931, 6948 and 6949). These devices were recalled due to reports of lead fractures associated with the deaths of five individuals. At that time, 268,000 Sprint Fidelis leads had been implanted worldwide. The recall halted the distribution of these leads, but didn't include a recommendation to remove currently implanted leads. The risk of adverse effects from lead removal were thought to be higher than the risk of lead malfunction (1.4

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