Discussion:
This case presentation reflects the complex nature of VT in patients with LMNA cardiomyopathy. Despite thorough mapping, the full VT circuit was not detected, which was attributed to a hidden mid-myocardial isthmus not detected during activation mapping on opposite surfaces. Previous case series have observed similar findings of extensive intramural substrate in similar patients.10
Mid myocardial substrate dependent arrhythmias are difficult to define but can be suggested by three-dimensional circuit activation with missing complete reentrant patterns during simultaneous endo/epicardial mapping. 11 Other features suggesting intramural ventricular arrhythmias include intramural fibrosis on imaging with CT or MRI. Large areas of earliest activation, during activation mapping, suggest the critical portion of the circuit is not being mapped. Additionally, RF application at the site of earliest activation without termination of VT suggests intramural ventricular arrhythmia. Intramural substrate is not limited to LMNA patients, and has been seen in 44-61% of ischemic and non-ischemic ventricular arrhythmia patients.10,11
The morphology variability encountered in our patient likely reflects the complexity of the intramural reentry circuit with variable cycle lengths and exits with inaccessible substrate in each mapped VT morphology. 11
This phenomenon likely explains the variable VT morphologies and cycle lengths in this patient.12 Not unexpectedly, clinically there is a higher incidence of catheter ablation failure, arrhythmia recurrence and poor prognosis of VT in patients with LMNA cardiomyopathy due to complex intramural substrate.4,5
Complete substrate elimination may not be effective or possible with standard ablation approaches in intramyocardial substrate cases. All attempts to map the arrhythmia may be limited to the encountered inner/outer loops and multiple entrance and exit sites.13
Relying on traditional catheter ablation techniques is often insufficient and carries higher risk of recurrence. Careful coordination between electro-anatomical mapping, VT entrainment results and pre-procedure imaging studies is recommended when possible. Utilizing nonstandard techniques, including half normal saline radiofrequency ablation, bipolar ablation, simultaneous unipolar catheter ablation, or needle catheter ablation could be critical to eliminate deep substrate components and essential for successful ablation. 9Unfortunately, even with the best efforts, recurrent ventricular tachycardia is associated with adverse events in LMNA cardiomyopathy and other advanced heart failure therapies should be considered early for these patients once VT emerges.5