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