A 33-year-old man presented a complete atrio-ventricular block due to two hydatid cysts localized in the interventricular septum and interrupting both bundle branches. Intracardiac rupture within the right ventricle led to extensive pulmonary hydatidosis and death.

Background LV only pacing is non-inferior to BiV pacing, and recent publications showed that DDD CRT without RV lead is safe in patients with normal atrioventricular (AV) conduction, although there are no device algorithms available for fusion pacing and PR interval variability is understudied in this population. Purpose To analyse AV behaviour in patients with DDD CRT and the impact to effective fusion maintenance. Methods Consecutive patients with right atrium/left ventricle leads DDD CRT pacing system were included. Prospective data were collected at every 6 months follow-up visits: device interrogation, exercise test (ET), echocardiography. CRT assessment during ET analysed loss of LV capture with special focus on maintaining constant fusion pacing during exercise. We defined 2 groups of patients: longer PR interval patients (200–250 ms) and normal PR interval patients (<200 ms). In case of LV loss of capture or unsatisfactory LV fusion pacing, device reprogramming was performed individualised for each patient and BB/ivabradine dose titration was done to achieve stability of PR spontaneous interval. Patients were rescheduled in no later one month to be reassessed by ET. Results 55 patients (29 male) aged 62±11 y.o. were included, 36 patients with normal PR and 19 patients with longer PR. During follow-up (45±19 months), a total of 235 ETs were performed with mean exercise load 118±35 watts. In the normal PR group, 14 patients (39%) had inadequate pacing or loss of LV capture during ET due to physiological shortening of PR interval vs. 4 patients (21%) in the longer PR group. Loss of LV capture by exceeding maximum tracking rate (MTR) was noted in 6 patients (17%) with normal PR vs. 2 patients (11%) with long PR. Post ET device optimisation included: reprogramming rate adaptive AV interval (23±8 ms decrease in normal PR patients vs. 12±7 ms in longer PR patients, p<0.0001) and individualised programming of MTR. BB/ivabradine optimisation was performed in 32% of patients with normal PR vs. 13% of patients with longer PR. Conclusions A lower rate of optimisations after ET was needed in patients with a slightly longer AV conduction to achieve stability of fusion pacing DDD CRT, without device algorithms. Larger studies are needed to assess AV conduction variability and the benefits of fusion pacing CRT in patients with longer PR interval. Funding Acknowledgement Type of funding source: Public Institution(s). Main funding source(s): University of Medicine and Pharmacy “Victor Babes”, Timisoara; Timisoara Institute of Cardiovascular Diseases

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Funding Acknowledgements Type of funding sources: None. Background CRT improves both systolic and diastolic function, thus increasing cardiac output. However, less data is available concerning diastolic dyssynchrony and fusion pacing CRT. The aim of our study was to assess the outcome of LV diastolic asynchrony in a population of fusion pacing CRT without right ventricular (RV)  lead. Methods Prospective data were collected from a cohort of patients (pts) with right atrium/left ventricle leads (RA/LV CRT). Baseline and every 6 months follow-up included standard ETT and classical dyssynchrony parameter measurements. Diastolic dyssynchrony was done by offline speckle-tracking derived TDI timing assesment of the simultaneity of E" and A"  basal septal and lateral wall 4 chamber view. New parameters were introduced: E" and respectively A" time (E"T / A"T) as the time difference between E" (respectively A" ) peaks septal and lateral wall. Exercise tests, drugs optimization and device individual programmimg were systematically performed in order to maintain constant fusion and improve CRT response. Patients were divided in three groups: super-responders (SR), responders (R) and non responders (NR). Results Sixty-two pts (35 male) aged 62 ± 11 y.o. with idiopathic DCM implanted with a RA/LV CRT were analyzed: 34%SR / 61%R / 5%NR. Baseline initial characteristics: QRS 164 ± 18 ms; EF 27 ± 5.2; 29% had type III diastolic dysfunction (DD), 63% type II DD, 8% type I DD. Average follow-up was 45 ± 19 months; mean LVEF at the last follow-up was 37 ± 7.9%. The E"T decreased from 90 ± 20 ms to 25 ± 10 ms in SR with significant LV reverse remodelling (LV end-diastolic volume 193.7 ± 81 vs 243.2 ± 82 ml at baseline, p < 0.0028) and lower LV filling pressures (E/E" 13.2 ± 4.6 vs 11.4 ± 4.5, p =0.0295). DD profile improved in 65% of R with a reduction in E/A ratio (1.46 ± 5.3 vs. 0.82 ± 3.9 at baseline, p= 0.4453). Non-sudden cardiac death occurred in 3 NR pts (2%) with type III DD, severe LA volume and larger E" T /A"T (E"T> 85 msec A"T > 30 msec).  Significant cut off value calculated by ROC curve for LV diastolic dyssynchrony is E"T > 80 ms and A"T of > 25 msec. Conclusions Fusion pacing CRT without RV lead showed a positive outcome; improving LV diastolic dyssynchrony in responders and super-responders patients is obvious. Larger randomized studies are needed to define the role of diastolic asynchronism as a predictor of favorable response in fusion pacing. Abstract Figure. Typical TDI patterns in LV fusion pacing

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