Anatomical Determinants of Papillary Muscle Arrhythmias in Apparently Normal Hearts

Background: Myocardial connections of left ventricular (LV) papillary muscles (PM) are determinants of QRS variability in the case of PM arrhythmias. We investigated the anatomical substrate of monomorphic versus polymorphic LV PM arrhythmias in patients with apparently normal hearts, as well as ablation outcomes. Methods: Thirty-two patients were eligible for analysis. Thirteen patients underwent ablation. With advanced cardiac imaging (cardiac MRI or multidetector CT), we determined the number of PM-PM and PM-surrounding myocardium connections, PM architecture according to the number of strands and the level of LV trabeculation. Results: Combinations of unifocal (monomorphic premature ventricular complexes [PVCs]), multiform PVCs and/or runs of polymorphic PM arrhythmias (>= 3 beats) were recorded in 24 patients. The remaining eight patients had only unifocal monomorphic PVCs. The mean [+/- SD] number of PM connections was higher than that of PM-PM or PM-myocardial connections in patients with multiform PVCs (30 +/- 1.5 versus 4 +/- 1, respectively) or polymorphic arrhythmias (136 +/- 4 versus 26 +/- 3, respectively; p=0.004). Compared with the unifocal group, the frequency of multistranded PMs was higher (1 versus 22, respectively; p<0.001) and LV trabeculation was more pronounced in the group with multiform arrhythmia (multiform PVCs and/or polymorphic arrhythmias). All patients ablated for unifocal PVCs remained free of recurrence, compared with only half of those ablated for multiform PVCs. Conclusion: Patients with multiform PM arrhythmias have more PM connections, PM strands and trabeculation than patients without QRS variability. The long-term effectiveness of catheter ablation in this patient group is limited.