In this episode, I’ll discuss whether a pacemaker or implanted cardiac defibrillator (ICD) protects from medication-induced torsades.
I’ve heard clinicians make this argument several times in my career – that because a patient has a pacemaker or ICD, a QTc prolonging drug interaction has no or little risk compared to a patient without a pacemaker or ICD.
While implantable cardiac devices are given to patients with long QT syndrome and other arrhythmias, there is no data on their use to prevent medication-induced torsades.
The pacemaker component of such devices should in theory help prevent torsades by preventing bradycardia. However, the rate of most pacemakers is not likely to provide protection from torsades. This is because a pacemaker is often set to prevent symptomatic bradycardia and may be set at a rate of only 50 beats per minute. A pacing rate of more than 70 beats per minute may be necessary to prevent the development of torsades.
Furthermore, patients with implanted cardiac devices are likely to have a history of cardiac arrhythmia – something that is generally considered a risk factor for medication-induced torsades. Therefore, the presence of an implanted cardiac device may actually signal an increased risk of medication-induced torsades rather than a protective factor.
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