Discussion
Pacemaker or ICD implantation is one of the most common cardiac interventions utilized today. They are used to treat cardiac arrythmias, including bradycardia and tachycardia. As such, indications for pacemaker implantation are numerous. ICD and pacemakers are most used to treat Sinus Node Dysfunction (SND) and Atrioventricular block. They can also treat chronic bifascicular block, hypertrophic cardiomyopathy, or patients with congenital heart disease.1 The need for a pacemaker can easily be determined using ECG or EP studies. However, as manifested by this case, a high degree of skepticism is required, including situations with young patients or those who have few cardiac studies.
Pacemaker implantation is a minimally invasive procedure, but still carries risks. Nearly a third of all complications are due to lead dislodgement or malposition.2 A proper ventricular lead is one placed in the right ventricular (RV) cavity; however, leads can migrate to the left ventricle (LV) through several pathways. Passage through an atrial septal defect is most common but can also occur through a patent foramen ovale or a ventricular septal defect.3 An RV lead in the LV is a serious and likely under-reported complication of pacemaker implantation. Leads in the LV can lead to dangerous thromboembolic events, which can occur anywhere from months to years after lead migration.2
A misplaced ventricular lead must quickly be diagnosed to prevent adverse events, and thus a high degree of scrutiny is required. The most important tool to recognize a lead in the LV is an ECG; on ventricular pacing, a misplaced lead will display a right bundle branch block (RBBB) morphology rather than the expected left bundle branch block (LBBB).4 However, this method is limited in cases such as SND in the absence of AV node disease, as the patient would likely only have atrial pacing or no pacing at baseline.2Adjunctive imaging is used to further confirm a misplaced lead, with AP and lateral X-rays as the primary techniques. A correctly positioned RV lead on an AP chest X-ray should have a smooth right lateral course with slight bowing at the RV apex (Figure 9). A lateral chest X-ray should display the tip of an ICD lead projected anteriorly (Figure 10); in a mispositioned LV lead, this tip is projected posteriorly.5 It may be difficult to differentiate between a lead in the LV from those in the middle cardiac vein or coronary sinuses. Thus, CT imaging or TEE can be used to visualize lead migration.