Results

Patients

35 patients were enrolled (Table 1) in the study. Over two thirds had a CRT indication and one third had ischemic cardiomyopathy. Left bundle area pacing was achieved in 30/35 (86%) of patients.

Septal scar quantification

Late gadolinium enhancement was present in the basal septum in 26 of the 35 patients. There was considerable variation in extent, between 1% and 74% (Figure 3). Figure 3 shows a representative basal short axis slice in all 35 patients.
25 patients had both bright blood and dark blood images. In 9 patients (of whom 7 had ischemic cardiomyopathy), the dark blood revealed more scar. In 1 patient with amyloid the bright blood revealed more scar. In the rest bright blood and dark blood scar extent was equivalent.

Lead advancement, capture, and achievement of narrow QRS

Advancement to the left side of the septum was achieved in 30/35 patients (86%). Amongst those, left bundle capture was achieved in 30/30 (100%) patients.
In the 5 patients where lead advancement was not achieved, device indication was CRT in 5/5 (100%). In this group, 3/5 (60%) had ischaemic cardiomyopathy, 1/5 (20%) had dual pathology and 1/5 (20%) had amyloid. All 5 patients went on to have successful biventricular pacing devices.
In the 30 patients where lead advancement was achieved, device indication was CRT in 21/30 (70%) and bradycardia pacing in 9/30 (30%). In this group, 7/30 (23%) had ischaemic cardiomyopathy, 15/30 (50%) had non-ischaemic cardiomyopathy and 2/30 (7%) had dual pathology.
Narrow QRS (<130ms) was achieved in 28 of the 30 (93%) patients in whom the left bundle was captured. It was not achieved in two patients. In one, with left bundle branch block and extensive ischemic scar (39% of total myocardium), the QRS remained 140ms despite left bundle capture. In the other, with right bundle branch block and a very broad intrinsic QRS (206ms), the QRS did shorten substantially but only to 150ms.

Basal septal scar and success of lead advancement

There was significantly more basal septal scar in the patients where lead advancement failed (median 67% of myocardium, IQR 58 to 69.5) than patients where lead advancement was successful (median 10% of myocardium, IQR 0 to 20, p = 0.0006, Figure 4).

Basal septal scar and electrical response

The paced QRS duration showed no significant relationship (Figure 5) with the extent of scar in the basal septum (r = .06, 95% CI: -0.3-0.4, p = 0.75) and only a non-significant trend with scar in the whole left ventricle (r = 0.3, 95% CI:-0.06-0.6, p = 0.1).

Predicting advance ability of the lead from extent of basal septal scar

We constructed an exploratory analysis of the likelihood of delivering a lead, predicted from the extent of basal septal scar.