Background Left bundle area pacing is growing in use both for bradycardia pacing and cardiac resynchronization, but implants are not always successful. We prospectively studied consecutive patients to determine whether septal scar contributes to implant failure. Methods Patients scheduled for left bundle area pacing, using the 3830 Selectsecure lead were prospectively enrolled. All patients underwent standardized scar assessment by cardiac MRI with late gadolinium enhancement imaging. Scar burden was quantified as the proportion of basal septal segments showing late enhancement. Results 35 patients were recruited: 29 male, mean age 68 years, 10 with ischemic and 16 with dilated cardiomyopathy. Pacing indication was bradycardia in 26% and cardiac resynchronization in 74%. In 5/35 (14%) it was not possible to advance the lead through the ventricular septum. Basal septal late gadolinium enhancement was significantly more extensive in these patients (median 67%, IQR 58-69.5) compared to the other 30 (median 10%, IQR 0-20, p = 0.0006). There was no significant correlation between the paced QRS duration achieved and the extent of basal septal scar (r = 0.06, P = 0.75). Conclusions Failure to deliver a lead to the left bundle area is strongly associated with a (very) high burden of scar in the basal septum. Once the lead is delivered, however, the electrical response is independent of scar burden. This suggests that it would be worth developing delivery tools to tackle scarred basal septa, because if the lead could be delivered the electrical capture might still achieve a narrow QRS.

Aims: A prolonged PR interval may adversely affect ventricular filling and therefore cardiac function. AV delay can be corrected using right-ventricular-pacing (RVP) but this induces ventricular dyssynchrony, itself harmful. Therefore, in intermittent heart-block, pacing-avoidance algorithms are often implemented. We tested His-bundle pacing (HBP) as an alternative. Methods: Out-patients with a long PR interval(>200ms) and intermittent need for ventricular pacing were recruited. We measured within patient differences in high-precision haemodynamics between AV-optimized RVP, and HBP, as well as a pacing-avoidance algorithm [Managed Ventricular Pacing (MVP)]. Results We recruited 18 patients. Mean left ventricular ejection fraction was 44.3±9%. Mean intrinsic PR interval was 266±42ms and QRS duration was 123±29ms. RVP lengthened QRS duration(+54 ms, 95%CI 42 to 67ms, p<0.0001) whilst HBP delivered a shorter QRS duration than RVP(-56 ms, 95%CI -67 to -46ms, p<0.0001). HBP did not increase QRS duration(-2ms 95%CI -8 to 13ms, p=0.6). HBP improved acute systolic blood pressure by mean of 5.0 mmHg(95%CI 2.8 to 7.1mmHg, p<0.0001) compared to RVP and by 3.5 mmHg(95%CI 1.9 to 5.0mmHg, p=0.0002) compared to the pacing avoidance algorithm. There was no significant difference in haemodynamics between RVP and ventricular pacing avoidance (p=0.055). Conclusions HBP provides better acute cardiac function than pacing avoidance algorithms and RVP, in patients with prolonged PR intervals. HBP allows normalisation of prolonged AV delays (unlike pacing avoidance) and does not cause ventricular dyssynchrony (unlike RVP). Clinical trials may be justified to assess whether these acute improvements translate into longer term clinical benefits in patients with bradycardia indications for pacing.