Discussion
The main findings of the present study are the following:
- HCM patients with arrhythmia recurrence exhibit significantly wider
fibrotic areas compared to those who remained in sinus rhythm;
- The presence of fibrotic areas greater than 13.1% (≤0.25 mV voltage
criterion) or 14.1% (≤0.4 mV voltage criterion) predict arrhythmia
recurrence with high sensitivity and specificity;
- LA fibrosis is the only predictor of arrhythmia recurrence following
catheter ablation in patients with obstructive HCM;
- HCM patients with AF display significantly broader fibrotic areas
compared to a PS matched control population of non-HCM patients and
AF.
The development of AF in HCM is multifactorial and has been related to
LA enlargement, increased LA pressure, LVOT obstruction, and LA fibrosis
as detected by late gadolinium enhancement cardiac MR
(LGE-CMR).1,13,14 This complex pathophysiology of AF
in HCM possibly explains the high recurrence rates observed following
catheter ablation of the arrhythmia. In a meta-analysis of five studies,
the single-procedure success rate (free from any atrial arrhythmia) was
only 38.7% in patients with HCM compared to 49.8% in
controls.3 Outcomes after multiple procedures
increased to 51.8% compared to 71.2% in controls. Repeat procedures
and antiarrhythmic drugs are more frequently needed in patients with HCM
to prevent arrhythmia relapse.3
Recent LGE-CMR studies have demonstrated the presence of LA fibrosis in
HCM patients, and especially in those with AF.13,14The extent of LA LGE has been significantly correlated with the extent
of LV LGE, suggesting that either the LA fibrosis is the result of LV
fibrosis or both of them are manifestations of the same pathophysiologic
process.5 Atrial fibrosis is the most important
predictor of ablation failure beyond PV isolation.9 PV
and posterior wall isolation alone have been shown to be insufficient to
obtain satisfactory long-term results.6 In addition,
non-PV triggers have been demonstrated in the majority of HCM patients
with arrhythmia recurrence, a finding that supports the appropriateness
of a more extensive ablation beyond PV isolation to improve the
arrhythmia-free survival.6 These findings are possibly
related to an extensive LA cardiomyopathy in this specific population.
In this high-density EAM study, we evaluated for the first time the
extent of LA fibrosis and its impact on catheter ablation outcomes in
patients with HCM and AF. Irrespective of the bipolar voltage cut-off
value used for fibrosis characterization (≤0.25 mV or ≤0.4 mV), HCM
patients with arrhythmia relapse exhibited wider fibrotic regions
compared to those who remained in sinus rhythm. By using the ≤0.4 mV
bipolar voltage criterion, the presence of low voltage areas more than
14.1% of the total LA area predicted AF recurrence with an excellent
sensitivity (100%) and specificity (100%). We additionally showed that
non-paroxysmal AF patients exhibit significantly wider diseased areas
compared to paroxysmal AF patients. HCM patients exhibited larger low
voltage areas compared to the PS matched control population of non-HCM
patients. These findings have important implications in AF catheter
ablation outcomes. In cases with extensive fibrosis, substrate
modification aiming at scar homogenization or isolation or LA
compartmentalization may be need to improve long term outcomes following
catheter ablation.8,9 The existence of LA voltage
areas ≤0.4 mV more than 10% of the total LA surface area has been shown
to predict arrhythmia recurrence following PVAI even for paroxysmal AF
patients.10 In a similar high-density EAM study, we
have demonstrated that substrate modification aiming specific
electrograms within low voltage areas (≤0.4 mV) leads to AF termination
in 23% of patients with persistent AF and improved long-term
free-survival from any atrial arrhythmia.12