Optimal Atrioventricular Interval Research Articles

Feasibility study on cardiac resynchronization in the treatment of heart failure by single left bundle branch pacing

To examine the feasibility of single left bundle branch pacing for cardiac resynchronization therapy (CRT) by carrying out a frequency adaptive atrioventricular delay (RAAVD) algorithm and automatic optimization of the single left bundle branch pacing atrioventricular interval (AVI) based on the right atrioventricular interval (RAS–RVS). Thirty-six patients with CRT class Ia indications according to the European Society of Cardiology 2016 guidelines and implanted with RAAVD functional three-chamber pacemakers were prospectively enrolled in this study. Patients were divided into a single left bundle branch pacing group (n = 21) and a standard biventricular pacing group (n = 15). The optimization of the two groups was performed under standard cardiac colour Doppler ultrasound, followed by the comparison of the QRS width, cardiac function improvement, and echocardiography indicators. The ratio of AVI to the right atrial-right ventricular interval (RAS–RVS) after single LV pacing optimization was defined as the single left bundle branch pacing coefficient (LUBBPε). In comparison to the BVP, the QRS was significantly narrowed (P = 0.017), accompanied by a significantly increased proportion of patients with NYHA class I and II, as well as the 6MWT. Compared with standard biventricular pacing, LVEDD was significantly shortened (P = 0.045), accompanied by significantly improved LAD, AVVTI, EA distance/RR, IVMD, and TS-SD after the operation. RAS–RVS was 156 ± 33 ms, the optimized AVI was 102 ± 10 ms, and LUBBPε was calculated to be 0.66 ± 0.06. Depending on the LUBBPε, a three-chamber pacemaker with a single left bundle branch pacing system was developed based on RAS–RVS-optimized AVI automatically. A three-chamber pacemaker with single left bundle branch pacing can achieve CRT based on RAS–RVS, reaching the optimal AVI of 66% of RAS–RVS.

Programming Algorithms for Cardiac Resynchronization Therapy.

Current cardiac resynchronization therapy (CRT) implant guidelines emphasize the presence of electrical dyssynchrony (left bundle branch block (LBBB) and QRS> 150 ms) yet have modest predictive value for response and have not reduced the 30% nonresponse rate. Optimized programming to optimize CRT delivery has promised much but to date has largely been ineffective. What is missing is the understanding of LV paced effects (which are unpredictable) and optimal paced AV interval (that can be conserved during physiologic variations) that then can be incorporated into an individualized programming prescription. Automatic device-based algorithms that deliver electrical optimization and maintain this during ambulatory fluctuations in AV interval are discussed.

Optimal Pacing Mode in Dual Chamber Pacing with Long AV-Intervals:A Pressure Volume Loop Study

Objectives: This study aimed to assess if dual chamber pacemaker patients with prolonged atrioventricular (AV-) intervals at rest and maintained LV function will benefit from spontaneous AV-conduction compared to AV synchronous pacing at optimized AV-intervals (DDD-OPT). Background: AV-hysteresis and mode change algorithms allow very long AV-intervals to avoid right ventricular pacing, however, the optimal long AV interval remains undefined. Methods: LV pressure volume loops were obtained via a conductance catheter in 19 dual chamber pacemakers patients with resting AV-intervals >250 ms. Hemodynamic data were recorded during atrial pacing at 70/min (AAI) and DDD-OPT. The optimal AV-interval was defined by the largest consequent stroke work. Results: Mean AV-interval during atrial pacing was 302{±}32 ms. Systolic parameters were not different between pacing modes with the exception of +dp/dt max (AAI: 1398{±}393 mmHg/s; DDD-OPT 1319{±}377 mmHg/s; p=0.006). Stroke work was higher in 9/19 patients with AAI and in 10/19 with DDD-OPT. The diastolic parameters tau (DDD-OPT: 38{±}8 ms; AAI: 35{±}8 ms; p=0.002) and peak filling rate (DDD-OPT: 832{±}450 ml/s; AAI: 627{±}231 ml/s; p=0.001) showed superior results for DDD-OPT. Differential values between the two modes for stroke work and +dp/dtmax correlated significantly with the resting AV-interval ( 320 ms favored DDD-OPT whereas AV-intervals <280ms favored AAI. Conclusion: In dual chamber pacemaker patients with long resting AV-intervals there is a trade-off between pacing-induced LV systolic dysfunction and impaired diastolic filling. Maintaining spontaneous AV-conduction at all cost might not be the preferred option in this patient group.

179-02: First-degree atrioventricular Block, Atrioventricular (Dys)synchrony and Dual-chamber pacing. A long PR interval or a wide QRS? That is the dilemma

Background: In modern DDD pacemakers, strategies to minimize artificial right ventricular activation seek to avoid the potential but well-studied deleterious effects of cardiac pacing. While these mechanisms maintain electrical atrioventricular (AV) sequence, if significant 1st. degree AV block (1st.AVB) coexists, paradoxically AV mechanical dyssynchrony could be promoted. Apparently, atrioventricular sequence differs from atrioventricular synchrony. The purpose of this study was to elucidate clinical and hemodynamic results of long AV delays - narrow intrinsic QRS against DDD pacing with optimized AV interval - paced wide QRS. Methods: Prospectively included 32 adult patients with DDD pacemakers implanted for sick sinus node disease (SSND) and 1st.AVB. Study protocol demanded septal right ventricular lead, demonstrated <5% of ventricular pacing overall since implantation, normal QRS duration, preserved left ventricular ejection fraction (LVEF), no prosthetic valves and no history of atrial fibrillation (AF). Using Doppler echocardiography diastolic and systolic performances were verified in AAI pacing 10 beats/min faster than sinus rhythm, intrinsic long AV delay and native QRS (Ap-Vs), against the hemodynamic results (VTi, LVEF and Mitral regurgitation obtained by iteratively shortening the programmed AV delay (DDD pacing - Ap-Vp) at same cardiac rate. By Mitral valve inflow analysis (E/A waves measurements) optimal diastolic function (AV synchrony) was verified. Best left ventricular contractility and function was assessed by means of higher aortic flow time velocity integral (VTi) and LVEF. Optimal AV delay was defined by maximal separation of E/A waves, higher VTi and best LVEF with less Mitral valve regurgitation. AV dyssinchrony was determined by fused E + A waves, or E + A duration <40% of cardiac cycle. This patients were kept to ventricular pacing at the optimal AV interval (optimized AV – OAV group) for further comparison. The non-optimized AV (NOAV) group was formed by those whose best cardiac function was found at the intrinsic PR interval-native QRS. This group was kept to minimal ventricular pacing at the baseline PR interval. Follow-up included clinical evaluation and cardiac structure and function assessment at 3 and 6 months for both groups of patients. Results: Our cohort so far (mean= 73,6 + /-11,8 years) confirmed the existence of 2 separate groups from the diastolic function point of view: those showing AV dyssynchrony requiring AV optimization (OAV group: 18/32) and those with no AV dyssynchrony (no need for AV optimization - NOAV group: 14/32); p= 0.003. No other statistical differences were found in age, gender, symptoms, NYHA functional class, medication use, and structural heart disease, baseline PR interval or LVEF between groups. AAI pacing rate for echo measurements was 65 + /-9bpm for the OAV group vs. 67,5 + /-6,7bpm of their counterparts (p= NS). Remarkably, the AV interval when exceeded 263ms in the OAV group was 72% sensitive and 73% specific to demonstrate AV dyssynchrony. Moreover, in the OAV group, under optimized AV delay and artificial ventricular pacing, after 6 months of follow-up, LVEF is noticed to significantly decline (p= 0.002) and detrimental changes of cardiac structure with significant increase in left ventricular systolic (p= 0.04) and diastolic (p= 0.02) dimensions are noticed. No other statistical differences at follow-up were found in clinical outcomes (incidence of new AF episodes, electronic arrhythmias, pacemaker syndrome-like symptoms, NYHA functional class or hospitalizations) between groups. Conclusion: Our results preliminarily suggest that 1st.AVB with non-physiologically prolonged AV conduction (when ≥263ms) is highly associated with disturbed AV synchrony. However, this AV dyssynchrony when corrected by echocardiographycally optimized AV delays and forced ventricular pacing is negatively affected by the detrimental consequences of continual right ventricular artificial activation. Alternative-pacing strategies such as biventricular-pacing in this scenario merit further investigation.

Effects of AV Delay and VV Delay on Left Atrial Pressure and Waveform in Ambulant Heart Failure Patients: Insights into CRT Optimization

We hypothesized that left atrial pressure (LAP) obtained by a permanent implantable sensor is sensitive to changes in cardiac resynchronization therapy (CRT) settings and could guide CRT optimization to improve the response rate. We investigated the effect of CRT optimization on LAP and its waveform parameters in ambulant heart failure (HF) patients. CRT optimization was performed in eight ambulant HF patients, using echocardiography as reference. LAP waveform was acquired at each of eight atrioventricular (AV) intervals and five inter-ventricular (VV) intervals. Selected waveform parameters were also evaluated for their sensitivity to CRT changes and agreement with echocardiography-guided optimal settings. Optimal AV and VV intervals varied considerably between patients. All patients exhibited significant changes in waveform morphology with AV optimization. Optimal AV delay determined from echocardiography ranged between 140 ms and 225 ms. Mean LAP tended to be lower at optimal setting 14 ± 3 mmHg compared to shorter (<100 ms) or longer (>160 ms) AV settings (P = 0.16). There were clear trends to smaller peak a-wave (P = 0.11) and gentler positive a-slope (P = 0.15) and positive v-slope (P = 0.09) with longer AV delays. Mean LAP and negative v-wave slope correlated well with echo-guided optimal setting, r = 0.91 (P = 0.001) and 0.79 (P = 0.03), respectively. No significant effects on LAP or waveform were seen during VV optimization. LAP and its waveform changes considerably with AV optimization. There is good agreement between echo-guided optimal setting and LAP. LAP could provide an objective guide to CRT optimization. (Clinical Trial Registry information: URL: http://www.clinicaltrials.gov. Unique Identifier: NCT00632372).

The QRS narrowing index for easy and early identification of responder to cardiac resynchronization therapy

The QRS narrowing index for easy and early identification of responder to cardiac resynchronization therapy

Three‐Dimensional Echocardiographic Optimization Improves Outcome in Cardiac Resynchronization Therapy Compared to ECG Optimization: A Randomized Comparison

There is little consensus on optimal atrioventricular (AV) and ventricular-to-ventricular (VV) intervals in cardiac resynchronization therapy (CRT). The aim of this study was to examine a novel combination of Doppler echocardiography (DE) and three-dimensional echocardiography (3DE) for individualized AV- and VV-interval optimization compared to conventional electrocardiogram (ECG) optimization. In this double-blind, randomized controlled trial, 77 patients (male: 57, age: 68 ± 10 years) with severely reduced ejection fraction (EF), New York Heart Association (NYHA) class III or IV, and wide QRS complex (>120 ms) have been included. Patients were randomized to either AV- and VV-interval optimization using DE and 3DE (group 1, n = 39) or ECG (group 2, n = 38). 3DE was performed in all patients for the evaluation of left ventricular (LV) dimensions, EF and systolic dyssynchrony index (SDI), and NYHA class obtained before CRT and after 3 months. Primary endpoint of the study was clinical response to CRT, defined as a reduction of NYHA class by ≥1 score. Secondary endpoints were change of EF, LV volumes, and SDI. There were significantly more responders in group 1 (82%) than in group 2 (58%, P = 0.021). Similarly, group 1 showed a larger increase in EF (7.0 ± 6.0% vs 3.4 ± 5.6%, P = 0.015) and a more pronounced reduction of SDI (-4.5 ± 5.9% vs -1.5 ± 5.6%, P = 0.039) than group 2. Compared with conventional ECG optimization, this novel echocardiographic optimization protocol resulted in a significantly higher response rate, improved LV systolic function, and may be used to select the optimal AV and VV intervals in CRT.

Goldilocks and the importance of AV intervals in cardiac resynchronization—How to best find the AV interval that is not too long, not too short, but just right for patients

Long before cardiac resynchronization (CRT) became standard therapy for patients with QRS prolongation and drug-refractory heart failure, standard dual chamber pacing in the right atrium and right ventricle using short atrioventricular (AV) delays was undertaken. The proponents of this procedure performed in patients without traditional bradycardia indications for pacing theorized that a shortened AV delay would decrease symptoms of heart failure by decreasing mitral and tricuspid valve regurgitation. Several case reports and case studies demonstrated favorable outcomes of improvement in cardiac output and decrease in symptoms of breathlessness in patients randomized to right ventricular pacing with short AV intervals. 1,2 Right ventricular pacing solely to improve symptomatic heart failure in patients without bradycardia was no longer thought useful after the publication of a double-blind randomized crossover trial of 12 patients, which demonstrated no difference in hemodynamic parameters or symptoms of heart failure between the times spent in the backup VVI 40 beats/min mode vs the VDD mode with an AV delay of 100 ms. The importance of AV intervals was realized even in the early days of left ventricular pacing for the treatment of heart failure. In a substudy of the Pacing Therapies in Congestive Heart Failure (PATH-CHF) trial, patients with a left bundle branch block treated with an epicardial left ventricular lead had significant differences in acute hemodynamic parameters as the AV interval was varied. There were significant variations in the optimal AV interval among individual patients, but the greatest benefit was seen as improvements in aortic pulse pressure, aortic systolic pressure, and left ventricular contractility if the AV interval was not too short and not too long. 3

Letter by van Gelder and Bracke Regarding Article, “Left Ventricular Versus Simultaneous Biventricular Pacing in Patients With Heart Failure and a QRS Complex &gt;120 Milliseconds”

To the Editor: We read with interest the article by Thibault et al1 comparing the effect of left ventricular (LV) pacing versus simultaneous biventricular pacing, a study with a crossover design between both pacing modes. Submaximal exercise was used as an elegant method of qualification of the clinical response. The optimal atrioventricular intervals (atrial sensed-ventricular paced and atrial paced-ventricular paced) were determined during LV pacing and defined as the longest atrioventricular interval that fully captured the ventricle (no fusion with intrinsic conduction). This atrioventricular delay was used for LV and biventricular pacing, along with the rate-adaptive atrioventricular delay feature, and was …

Towards a Personalized and Dynamic CRT-D

In spite of cardiac resynchronization therapy (CRT) benefits, 25-30% of patients are still non responders. One of the possible reasons could be the non optimal atrioventricular (AV) and interventricular (VV) intervals settings. Our aim was to exploit a numerical model of cardiovascular system for AV and VV intervals optimization in CRT. A numerical model of the cardiovascular system CRT-dedicated was previously developed. Echocardiographic parameters, Systemic aortic pressure and ECG were collected in 20 consecutive patients before and after CRT. Patient data were simulated by the model that was used to optimize and set into the device the intervals at the baseline and at the follow up. The optimal AV and VV intervals were chosen to optimize the simulated selected variable/s on the base of both echocardiographic and electrocardiographic parameters. Intervals were different for each patient and in most cases, they changed at follow up. The model can well reproduce clinical data as verified with Bland Altman analysis and T-test (p > 0.05). Left ventricular remodeling was 38.7% and left ventricular ejection fraction increasing was 11% against the 15% and 6% reported in literature, respectively. The developed numerical model could reproduce patients conditions at the baseline and at the follow up including the CRT effects. The model could be used to optimize AV and VV intervals at the baseline and at the follow up realizing a personalized and dynamic CRT. A patient tailored CRT could improve patients outcome in comparison to literature data.

Discordant electrical and mechanical atrial delays affect intracavitary electrogram-based cardiac resynchronization therapy optimization

It has been shown that atrioventricular (AV) delay optimization improves cardiac resynchronization therapy (CRT) response. Recently, an automatic algorithm (QuickOpt™, St Jude Medical), able to quickly identify the individual optimal AV interval, has been developed. The algorithm suggests an AV delay based on atrial intracavitary electrogram (IEGM) duration. We hypothesized that the difference between electrical and mechanical atrial delays could affect the effectiveness of QuickOpt method. The aim of this study was to test this hypothesis in 23 CRT patients who were recipients of St. Jude Medical devices. Using echocardiography, aortic flow velocity time integral (VTI) was evaluated at baseline, at QuickOpt suggested AV delay and after reducing it by 25 and 50%. Mechanical inter-atrial delay (MIAD) derived from echo/Doppler and electrical inter-atrial delay (EIAD) derived from IEGM were also analysed. Optimal AV delay was identified by the maximal VTI. In 11 patients (Group 1) the maximal VTI was achieved at the AV delay suggested by the algorithm, in 6 patients (Group 2) after a 25% reduction, and in 6 patients (Group 3) after a 50% reduction. While EIAD was similar among the three groups, MIAD was significantly different (P< 0.001). MIAD was longer than EIAD in Group 1 (P= 0.028) and shorter than EIAD in Groups 2 (P= 0.028) and 3. (P< 0.001). Mechanical inter-atrial delay was the only independent predictor of the AV interval associated with the best VTI (R(2) = 0.77; P< 0.001). Our results show that MIAD plays the main role in determining the optimal AV delay, thus caution should be taken when optimizing AV by IEGM-based methods.

Influence of Atrial Function and Mechanical Synchrony on LV Hemodynamic Status in Heart Failure Patients on Resynchronization Therapy

The aim of this study was to evaluate atrial and ventricular function in patients undergoing cardiac resynchronization therapy (CRT). Right atrial pacing (AP) in CRT induces delays in electrical and mechanical activation of the left atrium. The influence of atrial sensing (AS) versus AP on ventricular performance in CRT and the mechanisms underlying the differences between AS and AP in CRT have not been fully elucidated. Fifty-five patients with heart failure undergoing CRT for 9 ± 12.5 months and 22 control subjects without heart failure were enrolled. Conventional and tissue Doppler echocardiography was performed to examine atrial and ventricular mechanics and hemodynamic status. The optimal atrioventricular interval was shorter in AS compared with AP mode (126 ± 19 ms vs. 155 ± 20 ms, p < 0.0001). Left ventricular (LV) outflow tract time-velocity integral (22 ± 7 cm vs. 20 ± 7 cm, p < 0.001), diastolic filling period (468 ± 124 ms vs. 380 ± 93 ms, p < 0.001), and global strain (-32 ± 24% vs. -27 ± 22%, p = 0.001) were greater in AS compared with AP mode. Atrial strain was higher in AS compared with AP mode in the right atrium (-28.2 ± 8.6% vs. -22.6 ± 7.6%, p = 0.0007), interatrial septum (-17.1 ± 6.5% vs. -13.2 ± 5.4%, p = 0.002), and left atrium (-16.4 ± 11.0% vs. -13.6 ± 8.5%, p = 0.02). There was no difference in intraventricular dyssynchrony but significantly lower atrial dyssynchrony in AS compared with AP mode (31 ± 19 ms vs. 42 ± 24 ms, p = 0.0002). AS is associated with preserved atrial contractility and atrial synchrony, resulting in optimal LV diastolic filling, stroke volume, and LV systolic mechanics. This pacing mode maximizes LV performance and the hemodynamic benefit of CRT in patients with heart failure.

Measurement Precision in the Optimization of Cardiac Resynchronization Therapy

Cardiac resynchronization therapy improves morbidity and mortality in appropriately selected patients. Whether atrioventricular (AV) and interventricular (VV) pacing interval optimization confers further clinical improvement remains unclear. A variety of techniques are used to estimate optimum AV/VV intervals; however, the precision of their estimates and the ramifications of an imprecise estimate have not been characterized previously. An objective methodology for quantifying the precision of estimated optimum AV/VV intervals was developed, allowing physiologic effects to be distinguished from measurement variability. Optimization using multiple conventional techniques was conducted in individual sessions with 20 patients. Measures of stroke volume and dyssynchrony were obtained using impedance cardiography and echocardiographic methods, specifically, aortic velocity-time integral, mitral velocity-time integral, A-wave truncation, and septal-posterior wall motion delay. Echocardiographic methods yielded statistically insignificant data in the majority of patients (62%-82%). In contrast, impedance cardiography yielded statistically significant results in 84% and 75% of patients for AV and VV interval optimization, respectively. Individual cases demonstrated that accepting a plausible but statistically insignificant estimated optimum AV or VV interval can result in worse cardiac function than default values. Consideration of statistical significance is critical for validating clinical optimization data in individual patients and for comparing competing optimization techniques. Accepting an estimated optimum without knowledge of its precision can result in worse cardiac function than default settings and a misinterpretation of observed changes over time. In this study, only impedance cardiography yielded statistically significant AV and VV interval optimization data in the majority of patients.

A prospective comparison of echocardiography and device algorithms for atrioventricular and interventricular interval optimization in cardiac resynchronization therapy

Echocardiographic optimization of atrioventricular (AV) and interventricular (VV) intervals in cardiac resynchronization therapy (CRT) is costly, time-consuming, and requires skill and expertise so is usually undertaken only in 'non-responder' patients. An algorithm in St Jude Medical CRT devices (QuickOpt) claims to optimize these settings automatically. The aim of this study was to compare the two optimization techniques. Optimization of AV and VV intervals was performed a month after CRT device implantation in 26 patients with heart failure, first by echocardiography then by QuickOpt. The left ventricular outflow tract (LVOT) velocity-time integral (VTI) was measured after optimization by each method. Agreement between the optimization methods was assessed by the Bland-Altman analysis and correlation by Pearson's correlation coefficient. There was good correlation between the LVOT VTI following optimization by both methods (R2 = 0.77, P < 0.001). However, agreement between the two methods was poor, with 15 of 26 and 10 of 26 patients having a >20 ms difference in the optimal AV and VV interval values, respectively. Left ventricular outflow tract VTI was significantly better (22 of 26 patients; P < 0.001) in patients optimized by echocardiography than by QuickOpt. There is a poor agreement in optimal AV and VV intervals determined by echocardiography and QuickOpt, with echocardiographic optimization giving a superior haemodynamic outcome.

Echocardiography for Determining the Optimal Atrioventricular Interval in Patients with Dual Chamber Pacemakers

We investigated the clinical value of Doppler echocardiography for determining the optimal setting of atrioventricular interval in patients with dual chamber pacemakers (DDD). In 38 patients with complete atrioventricular block and DDD pacemakers, the atrioventricular interval was prolonged in a stepwise fashion by 20 ms, from 90 to 250 ms, and cardiac stroke volume and transmitral flow were measured by pulsed Doppler echocardiography. The optimal atrioventricular interval at which the cardiac stroke volume was maximal was 168.9 +/- 15.6 ms. The atrioventricular interval was 178.4 +/- 23.4 ms when the end of the A wave coincided with complete closure of the mitral valve. There was a significant linear relationship between the optimal atrioventricular interval and the predicted optimal atrioventricular interval (Y = 86.2 +/- 0.5X, r = 0.70, standard error of the estimate [SEE] = 11.5, P < 0.01). The optimal atrioventricular interval setting for DDD pacing can be successfully determined using Doppler echocardiography, which is a noninvasive, repeatable, and simple approach.

Echo optimization of cardiac resynchronization therapy

Echocardiography has a prominent role in the era of cardiac resynchronization therapy (CRT) by virtue of its noninvasive nature with high feasibility and reproducibility. More importantly, it permits serial assessment for optimization of the therapy before and after device implantation [1]. First, echocardiography can optimize selection of CRT candidates by baseline evaluation of left ventricular (LV) dyssynchrony and myocardial contractility reserve. Second, it may be used to guide the LV lead position in order to avoid those areas with extensive scar. Finally, it is important in optimization of device programming, including atrioventricular (AV) and interventricular (VV) intervals. Although the clinical and echocardiographic benefits of CRT have been well demonstrated, about one-third of patients did not respond to the therapy, in whom the lack of systolic dyssynchrony before device implantation is mainly attributable [1,2]. Various advanced echo techniques, such as tissue Doppler imaging (TDI) and its postprocessing modalities, real-time 3-dimensional echocardiography (RT3DE) and 2-dimensional speckle tracking, have been proved to be able to detect LV dyssynchrony and predict acute or chronic favorable responses after CRT [3−5]. In addition, a certain myocardial reserve might also be necessary, as reflected by a positive result in stress echo or a preserved circumferential strain at baseline [6,7]. With rapidly evolving new technologies, more accurate identification of responders to CRT by echocardiography would be expected so as to reduce the number of nonresponders and improve the cost effectiveness of the therapy. Despite the presence of pre-implant LV dyssynchrony, recent data from MRI have demonstrated that patients with scar tissue in the posterolateral LV segments, where the LV lead is usually located, failed to show clinical and echocardiographic responses after CRT [8]. It suggests the importance of deploying the LV lead away from scar areas. However, it is unclear whether the assessment of scar region by use of echo methods would have predictive value, though the extent of scar tissue by contrast echo was shown to be inversely related to CRT responses [9]. It also needs more information whether discordance between the site of latest activation and the position of LV lead would give rise to a lesser degree of improvement after CRT, though being suggestive in observational and registry studies. Improvement of AV dyssynchrony is one of the mechanisms of benefit from CRT, which is particularly helpful in those patients with 1st AV block where diastolic filling time will be in further jeopardy [2]. Optimization of AV interval is in attempt to ensure AV synchrony and near 100% ventricular pacing in individual patient, which results in decrease in pre-systolic time, abolishment of diastolic mitral regurgitation, increase in LV filling time and gain in cardiac output. The two commonly employed methods by Doppler echocardiography are based on the principles of optimal LV diastolic filling or maximal cardiac output. Usually, AV interval optimization is performed shortly after the device implantation, ie. at the pre-discharge period. However, re-optimization of AV interval at intermediate (e.g. 3 months) and long-term (e.g.12−18 months) follow up may be necessary to further improvement in cardiac performance.[10] VV Optimization may further reduce ventricular dyssynchrony and hence improve systolic function. Currently, optimization of VV interval is commonly based on the reiterative cardiac output method, which is very time-consuming. However, the benefit of VV timing over conventional simultaneous biventricular pacing needs to be confirmed by large, prospective, randomized studies [11].

Comparison of different approaches for optimization of atrioventricular and interventricular delay in biventricular pacing

It has been shown that optimizing atrioventricular (AV) and interventricular (VV) delay improves cardiac performance in patients with biventricular pacemakers. However, there is no standard method for optimization available yet. The aim of this study was to compare echocardiographic parameters-displacement imaging, A wave duration, and aortic velocity time integral (VTI)-and acoustic cardiography derived electromechanical activation time (EMAT) using different approaches of AV and VV delay optimization. We tested whether the initial optimization of the AV interval followed by VV optimization at that optimal AV interval or initial optimization of the VV interval followed by AV optimization at the determined optimal VV interval was accurate and consistent, and how this compared to testing every conceivable combination of AV and VV intervals available. A group of 20 patients with biventricular pacemakers was included. Displacement imaging, A wave duration, and aortic VTI were determined at different combinations of AV (100, 150, 200, 250 ms) and VV (RV40, 0, LV40 ms) intervals. If AV duration was determined first, displacement imaging identified the best setting in 8/20, aortic VTI in 10/20, A duration in 13/20, and EMAT in 18/20 patients. With VV duration determined first, the best setting was more difficult to identify regardless of the method used. There was a poor agreement in optimal AV and VV delays of the different methods, and there was no single patient in whom all four methods yielded the same delay combination. It is advisable to measure a full grid of AV and VV delays to identify optimal settings rather than optimizing one of the two delays first. Different techniques for delay optimization resulted in different optimal delay combinations.

Impedance cardiography: a useful and reliable tool in optimization of cardiac resynchronization devices

Optimizing cardiac resynchronization therapy (CRT) devices has become more complex since modification of both atrioventricular (AV) and interventricular (VV) stimulation intervals has become possible. The current paper presents data from the routine use of impedance cardiography (IC)-based cardiac output (CO) measurements to guide the optimization of AV- and VV-interval timing of CRT devices. Forty-six patients with heart failure (left ventricular ejection fraction <35%, New York Heart Association (NYHA) III-IV) and left bundle branch block (>130 ms) in sinus rhythm were evaluated 3-5 days after implantation of a CRT device by means of IC. CO was measured without pacing and with biventricular pacing using a standard protocol of VV- and AV-interval modification from -60 to +60 ms and 80 to 140 ms, respectively, in 20 ms steps. Mean CO without pacing was 3.66 +/- 0.85 L/min and significantly increased to 4.40 +/- 1.1 L/min (P<0.05) with simultaneous biventricular pacing and an AV interval of 120 ms. 'Optimizing' both VV and AV intervals further increased CO to 4.86 +/- 1.1 L/min (P<0.05). Maximum CO was measured in most patients with left ventricular pre-excitation. The proportion of 'non-responders' to CRT was reduced by 56% following AV- and VV-interval modification using IC guidance. Modification of both AV and VV intervals in patients with a CRT device significantly improves CO compared with standard simultaneous biventricular pacing and no pacing. IC is a useful non-invasive technique for guiding this modification. Marked variability of optimal AV and VV intervals between patients requires optimization of these intervals for each patient individually.

The role of repeating optimization of atrioventricular interval during interim and long-term follow-up after cardiac resynchronization therapy

Background: Cardiac resynchronization therapy (CRT) is an effective therapy for heart failure patients with electromechanical delay. Optimization of atrioventricular interval (AVI) is a cardinal component for the benefits. However, it is unknown if the AVI needs to be re-optimized during long-term follow-up. Methods: Thirty-one patients (66 ± 11 years, 20 males) with sinus rhythm who received CRT underwent serial optimization of AVI at day 1, 3-month and during long-term follow-up by pulse Doppler echocardiography (PDE). At long-term follow-up, the optimal AVI and cardiac output (CO) estimated by non-invasive impedance cardiography (ICG) were compared with those by PDE. Results: The follow-up was 16 ± 11 months. There was no significant difference in the mean optimal AVI when compared between any 2 time points among day 1 (99 ± 30 ms), 3-month (97 ± 28 ms) and long-term follow-up (94 ± 28 ms). However, in individual patient, the optimal AVI remained unchanged only in 14 patients (44%), and was shortened in 12 (38%) and lengthened in 6 patients (18%). During long-term follow-up, although the mean optimal AVIs obtained by PDE or ICG (94 ± 28 vs. 92 ± 29 ms) were not different, a discrepancy was found in 14 patients (45%). For the same AVI, the CO measured by ICG was systematically higher than that by PDE (3.5 ± 0.8 Vs. 2.7 ± 0.6 L/min, p < 0.001). Conclusion: Optimization of AVI after CRT appears necessary during follow-up as it was readjusted in 55% of patients. Although AVI optimization by ICG was feasible, further studies are needed to confirm its role in optimizing AVI after CRT.

Avoidance of Right Ventricular Pacing in Cardiac Resynchronization Therapy Improves Right Ventricular Hemodynamics in Heart Failure Patients

Cardiac resynchronization therapy (CRT) applied by pacing the left and right ventricles (BiV) has been shown to provide synchronous left ventricular (LV) contraction in heart failure patients. CRT may also be accomplished through synchronization of a properly timed LV pacing impulse with intrinsically conducted activation wave fronts. Elimination of right ventricular (RV) pacing may provide a more physiological RV contraction pattern and reduce device current drain. We evaluated the effects of LV and BiV pacing over a range of atrioventricular intervals on the performance of both ventricles. Acute LV and RV hemodynamic data from 17 patients with heart failure (EF = 30 +/- 1%) and a wide QRS (138 +/- 25 msec) or mechanical dyssynchrony were acquired during intrinsic rhythm, BiV, and LV pacing. The highest LV dP/dt(max) was achieved during LV pre- (LV paced prior to an RV sense) and BiV pacing, followed by that obtained during LV post-pacing (LV paced after an RV sense) and the lowest LV dP/dt(max) was recorded during intrinsic rhythm. Compared with BiV pacing, LV pre-pacing significantly improved RV dP/dt(max) (378 +/- 136 mmHg/second vs 397 +/- 136 mmHg/second, P < 0.05) and preserved RV cycle efficiency (61.6 +/- 14.6% vs 68.6 +/- 11.4%, P < 0.05) and stroke volume (6.6 +/- 4.4 mL vs 9.0 +/- 6.3 mL, P < 0.05). Based on LV dP/dt(max), the optimal atrioventricular interval could be estimated by subtracting 30 msec from the intrinsic atrial to sensed RV interval. Synchronized LV pacing produces acute LV and systemic hemodynamic benefits similar to BiV pacing. LV pacing at an appropriate atrioventricular interval prior to the RV sensed impulse provides superior RV hemodynamics compared with BiV pacing.