Maintaining Atrioventricular Intrinsic Conduction During Cardiac Resynchronization Therapy: A Feasibility, Efficiency And Safety Study

Objectives To evaluate the feasibility, efficiency and safety of maintaining atrioventricular(AV) intrinsic conduction during cardiac resynchronization therapyMethods during January 2004-December 2009, forty-four patients (34 male and 10 female), average aged (62.11±9.03) years, twenty-five diagnosed with dilated cardiomyopathy and nineteen with ischemia cardiomyopathy, were included in this study. All corresponded to standard CRT indications, with sinus rhythm and normal AV conduction. They were randomized into two sets, the first group was underwent "3-Chamber & 4-site pacing" (AVN mode) followed by routine optimization postoperatively, the second one is on the contrary. We maintained AV intrinsic conduction on the basis of biventricular pacing to implement "3-Chamber & 4-site pacing". Various AV delay (AVd) were "bi-directional titrated" to get the narrowest "truly fusional" QRS complexes composed of biventricular pacing and AV intrinsic conduction. Routine optimization means programming diverse AVd by echocardiography to get the max transaortic valve flow velocity time integral (VTI). A series of comparisons were made between the two modes after one month, including program time, cost, symptoms, exercise tolerance, life quality, QRS width, echocardiography parameters, and mechanical dyssynchrony parameters. The correlation between above-mentioned parameters and ejection fraction (EF) was also analyzed.Results 1. 44 patients contained 23 CRT-P and 21 CRT-D, including 1 dual-site right ventricular pacing, 3 left ventricular lead reseted and 2 CRT-D had high frequency episodes, no infecting , rehospitalization and death. All patients could maintain AV intrinsic conduction and get the narrowest QRS complexes. Mean follow-up (39.91±10.48 VS.39.64±11.59 days, range 28-90) were similar between the two modes. "3-Chamber 4-site pacing" consumed shorter program time (26.23±10.51 min) and was cheaper (Y50.00) than conventional CRT optimization (112.39±25.28min &￥308.00).2. AVN mode got a litter longer optimal AVd (164.09±35.85ms) and shorter VVd (12.32±11.30ms) than routine optimization (128.18±29.20ms & 15.55±13.56ms, P<0.0001). We observed a direct correlation inter two modes optimal AVd (r=0.585, P<0.001), a positive correlation between intrinsic PR intervals and AVN mode optimal AVd (r=0.541, P<0.0001), also intrinsic PR intervals correlated with routine optimal AVd (r=0.454, P<0.002). The intrinsic PR intervals of 22.73% patients decreased, 43.18% extended, only 34.09% was invariable.3. Under AVN mode, the parameters were constant both in acute and short-term situations, including QRS width, aortic velocity time integral (AVI) and mitral velocity time integral (MVI). But the QRS width prolonged (140.75±18.75ms and 146.35±5.31ms, P=0.024) and AVI grew down (22.15±5.31 and 19.91±5.53, P=0.002 ) after routine optimization, only MVI unchanged ( 17.86±4.63 and 17.36±4.60, P=0.620) . Moreover, "3-Chamber & 4-site pacing" QRS widths (acute and short-term) were shorter than routine optimization ( 117.00±19.47ms and 140.75±18.75ms; 118.35±21.59ms and 146.35±5.31ms, P<0.0001), AVI were lower than acute routine CRT (22.15±5.31与19.39±4.49, P<0.0001) while similar with short-term (19.91±5.53与19.79±5.43, P=0.830), the acute and short-term MVI were similar in both pacing modes (18.13±3.74 and 17.86±4.63, 17.28±4.05 and 17.36±4.60; P>0.05) .4. The mechanical dyssynchrony parameters were constant both in acute and short-term situations.①we used the time of left ventricular filling to evaluate AV mechanical dyssynchrony and observed that AVN mode parameter were longer than acute routine optimization (0.49±0.08 and 0.43±0.07, P=0.001) but similar with short-term (0.47±0.08 and 0.44±0.08, P>0.05).②Inter-ventricular mechanical delay time (IVMD) were adopted to evaluate inter-ventricular mechanical dyssynchrony with the result that IVMD were indifferent under different modes not only acute but also short-term . Further more, AVN mode showed a positive correlation between QRS width and IVMD (r=0.472, P =0.023).③Dyssynchrony index (Ts-SD12) was defined as the SD of the time to peak systolic velocities at 12 left ventricular segments. Both acute and short-term Ts-SD12 under AVN mode were shorter than routine optimization whereas without distinguished statistical variance (55.46±19.25ms and 56.33±32.74 ms, 47.95±25.18ms and 58.35±43.60 ms; P>0.05) .5. After "3-Chamber & 4-site pacing", left ventricular fractional shortening (FS), ejection fraction (EF) and transaortic flow velocity(AR) were higher than routine CRT pacing (17.41±5.97 and 15.66±4.90, 35.50±9.72 and 32.68±9.74,115.00±20.93 and 106.80±20.87, P<0.05), while other usual echocardiography parameters including left ventricle at the end of diastole diameter (LVd) were similar under both modes. Moreover, by multiple linear regression analysis, routine optimal pacing showed negative correlation between LVd and EF (β=-0.513, P=0.021).6. Compared with conventional CRT optimization, "3-Chamber & 4-site pacing" parameters were significantly improved during short term follow-up including NYHA heart functional class, exercise tolerance(372.51±80.88m and 328.66±108.89m, P<0.0001), and quality of life(12.48±6.56 and 18.16±12.25,P<0.0001) . Multiple linear regression analysis showed that AVN mode had a only negative correlation between disease and exercise tolerance (β=-0.702, P<0.001), whereas routine CRT pacing indicated correlation between disease, sex, mitral valve regurgitation (MR), AVI, the time of left ventricular filling and exercise tolerance.Conclusions 1. Conventional CRT has many non-physiological disadvantages due to deserting AVN, so it is necessary to maintain AV intrinsic conduction during CRT.2. Maintaining AV intrinsic conduction during CRT is feasible: sinus rhythm and normal AV conduction ensure the implement of "triple-Chamber 4-site pacing", "bi-directional titrating" AVd can get the "true fusional" QRS complexes composed of biventricular pacing and AV intrinsic conduction, and it costs less time & money.3. Maintaining AV intrinsic conduction during CRT is efficient: "3-Chamber & 4-site pacing" gets the narrowest QRS complexes and improves hemodynamic parameters, NYHA heart functional class, exercise tolerance, and life quality.4. Maintaining AV rintrinsic conduction during CRT is safe: it do not cause drug increasing, infecting, rehospitalization, high frequency episodes, death and so on under "triple-Chamber 4-site pacing" mode.5. The mechanisms of AV intrinsic conduction during CRT may be associated with the following factors: multiple-site pacing, pacing in His bundle, pacing in refractory period, partial or total fulfillment of managed ventricular pacing (MVP), and reducing the defects of CRT hardware.6. Patients with CRT may try the "triple-Chamber 4-site pacing", with following situation: who had sinus rhythm, normal AV conduction, relatively short PR intervals, did not respond to CRT with conventional optimization and with the left leads not located in targeted veins.7. Keys to implement "3-Chamber & 4-site pacing" are: "Bi-directional titrating" AVd by monitoring of 12-lead surface ECG based on biventricular pacing and the narrowest "true fusional" QRS complexes.8. It is difficult to perform "3-Chamber & 4-site pacing" among patients with atrial fibrillation or AV block, and to ensure the "true fusional" QRS complexes after follow-up due to the changes of individual PR disperse.9. This study showed "3-Chamber & 4-site pacing" maintaining AV conduction during CRT could increase the benefits of patients with CRT although with smaller sample, shorter follow-up and less parameters. However, more basic research, clinical trials and evaluation approaches need to be further investigated.