Interventricular delay interval optimization in cardiac resynchronization therapy guided by echocardiography versus guided by electrocardiographic QRS interval width

Pilot study to evaluate left-to-right ventricular offset in biventricular pacing-comparison of electrocardiographic imaging and ECG

INTRODUCTION

Biventricular pacing (BiVp) improves outcomes in systolic heart failure patients with electrical dyssynchrony. BiVp is delivered from epicardial left ventricular (LV) and endocardial right ventricular (RV) electrodes. Acute electrical activation changes with different LV-RV stimulation offsets can help guide individually optimized BiVp programming. We sought to study the BiVp ventricular activation with different LV-RV offsets and compare with 12-lead ECG.

METHODS

In five patients with BiVp (63 ± 17-year-old, 80% male, LV ejection fraction 27 ± 6%), we evaluated acute ventricular epicardial activation, varying LV-RV offsets in 20 ms increments from -40 to 80 ms, using electrocardiographic imaging (ECGI) to obtain absolute ventricular electrical uncoupling (VEUabs, absolute difference in average LV and average RV activation time) and total activation time (TAT). For each patient, we calculated the correlation between ECGI and corresponding ECG (3D-QRS-area and QRS duration) with different LV-RV offsets.

RESULTS

The LV-RV offset to attain minimum VEUabs in individual patients ranged 20-60 ms. In all patients, a larger LV-RV offset was required to achieve minimum VEUabs (36 ± 17 ms) or 3D-QRS-area (40 ± 14 ms) than that for minimum TAT (-4 ± 9 ms) or QRS duration (-8 ± 11 ms). In individual patients, 3D-QRS-area correlated with VEUabs (r 0.65 ± 0.24) and QRS duration correlated with TAT (r 0.95 ± 0.02). Minimum VEUabs and minimum 3D-QRS-area were obtained by LV-RV offset within 20 ms of each other in all five patients.

CONCLUSIONS

LV-RV electrical uncoupling, as assessed by ECGI, can be minimized by optimizing LV-RV stimulation offset. 3D-QRS-area is a surrogate to identify LV-RV offset that minimizes LV-RV uncoupling.

Visualization of the SyncAV® Algorithm for CRT Optimization by Non-invasive Imaging of Cardiac Electrophysiology: NICE-CRT Trial

(1) Background: Periodic repetitive AV interval optimization using a device-based algorithm in cardiac resynchronization therapy (CRT) devices may improve clinical outcomes. There is an unmet need to successfully transform its application into clinical routine. (2) Methods: Non-invasive imaging of cardiac electrophysiology was performed in different device programming settings of the SyncAV^® algorithm in 14 heart failure patients with left bundle branch block and a PR interval ≤ 250 milliseconds to determine the shortest ventricular activation time. (3) Results: the best offset time (to be manually programmed) permitting automatic dynamic adjustment of the paced atrioventricular interval after every 256 heart beats was found to be 30 and 50 milliseconds, decreasing mean native QRS duration from 181.6 ± 23.9 milliseconds to 130.7 ± 10.0 and 130.1 ± 10.5 milliseconds, respectively (p = 0.01); this was followed by an offset of 40 milliseconds (decreasing QRS duration to 130.1 ± 12.2 milliseconds; p = 0.08). (4) Conclusions: The herein presented NICE-CRT study supports the current recommendation to program an offset of 50 milliseconds as default in patients with left bundle branch block and preserved atrioventricular conduction after implantation of a CRT device capable of SyncAV^® optimization. Alternatively, offset programming of 30 milliseconds may also be applied as default programming. In patients with no or poor CRT response, additional efforts should be spent to individualize best offset programming with electrocardiographic optimization techniques.

Prognostic effects of longitudinal changes in left ventricular ejection fraction with cardiac resynchronization therapy

Aims

Left ventricular ejection fraction (LVEF) is considered an indicator of cardiac resynchronization therapy (CRT). Longitudinal studies on the predictive value of LVEF are scarce. We aimed to comprehensively evaluate the prognostic role of LVEF in the outcomes of Chinese patients with CRT.

Methods and results

Three hundred ninety‐two patients were divided into three tertiles of LVEF: ≤25%, 25–30%, and 30–35%, and four groups by LVEF changes: <0% (negative response); ≥0% and ≤5% (non‐response); >5% and ≤15% (response); and >15% (super‐response). One hundred six patients were super‐responders. During a median follow‐up of 3.6 years, 141 reached the composite endpoint. Odds ratios (ORs) for super‐response depicted a reversed U‐shaped relationship for baseline LVEF with a peak at 25–30%. Independent predictors of super‐response were smaller left atrial diameter [odds ratio 0.897, 95% confidence interval (CI) 0.844–0.955, P = 0.001], smaller left ventricular end‐diastolic diameter (OR 0.937, 95% CI 0.889–0.989, P = 0.018), and higher estimated glomerular filtration rate (OR 1.018, 95% CI 1.001–1.035, P = 0.042) in Tertile 1; atrial fibrillation (OR 0.278, 95% CI 0.086–0.901, P = 0.033), left bundle branch block (OR 4.096, 95% CI 1.046–16.037, P = 0.043), and left ventricular end‐diastolic diameter (OR 0.929, 95% CI 0.876–0.986, P = 0.016) in Tertile 2; while female sex (OR 2.778, 95% CI 1.082–7.132, P = 0.034) and higher systolic blood pressure (OR 1.045, 95% CI 1.013–1.079, P = 0.006) in Tertile 3. An inverse association with the composite endpoint was found in Tertile 1 vs. Tertile 2 (hazard ratio 1.934, 95% CI 1.248–2.996, P = 0.003). The prognostic effects of CRT response in Tertile 3 and Tertile 1 varied significantly (P for trend = 0.017 and <0.001). Among three tertiles in super‐responders, event‐free survival was similar (P for trend = 0.143).

Conclusions

Left ventricular ejection fraction of 25–30% is associated with a better prognosis of super‐response. Predictors of super‐response are different for LVEF tertiles. CRT responses would have better prognostic performance than LVEF tertiles at baseline, which should be considered when clinicians screening eligible patients for CRT.

Optimization of Lead Placement in the Right Ventricle During Cardiac Resynchronization Therapy. A Simulation Study

Patients suffering from heart failure and left bundle branch block show electrical ventricular dyssynchrony causing an abnormal blood pumping. Cardiac resynchronization therapy (CRT) is recommended for these patients. Patients with positive therapy response normally present QRS shortening and an increased left ventricle (LV) ejection fraction. However, around one third do not respond favorably. Therefore, optimal location of pacing leads, timing delays between leads and/or choosing related biomarkers is crucial to achieve the best possible degree of ventricular synchrony during CRT application. In this study, computational modeling is used to predict the optimal location and delay of pacing leads to improve CRT response. We use a 3D electrophysiological computational model of the heart and torso to get insight into the changes in the activation patterns obtained when the heart is paced from different regions and for different atrioventricular and interventricular delays. The model represents a heart with left bundle branch block and heart failure, and allows a detailed and accurate analysis of the electrical changes observed simultaneously in the myocardium and in the QRS complex computed in the precordial leads. Computational simulations were performed using a modified version of the O'Hara et al. action potential model, the most recent mathematical model developed for human ventricular electrophysiology. The optimal location for the pacing leads was determined by QRS maximal reduction. Additionally, the influence of Purkinje system on CRT response was assessed and correlation analysis between several parameters of the QRS was made. Simulation results showed that the right ventricle (RV) upper septum near the outflow tract is an alternative location to the RV apical lead. Furthermore, LV endocardial pacing provided better results as compared to epicardial stimulation. Finally, the time to reach the 90% of the QRS area was a good predictor of the instant at which 90% of the ventricular tissue was activated. Thus, the time to reach the 90% of the QRS area is suggested as an additional index to assess CRT effectiveness to improve biventricular synchrony.

Advances in atrioventricular and interventricular optimization of cardiac resynchronization therapy - what's the gold standard?

INTRODUCTION

Cardiac resynchronization therapy (CRT) is one of the most important advances in heart failure management in the last twenty years. Approximately one-third of patients appear not to respond to therapy. Although there are a number of possible mechanisms for non-response, an important factor is suboptimal atrioventricular (AV) and interventricular (VV) timing intervals. There remains controversy over whether routinely optimizing intervals is necessary and there is no agreed gold standard methodology. Optimization has classically been performed using echocardiography which has limits related to resource use, time-cost and variable reproducibility. Newer optimization methods using device-based sensors and algorithms show promise in reducing heart-failure hospitalization compared with echocardiography. Areas covered: This review outlines the rationale for optimization, the principles of AV and VV optimization, the standard echocardiographic approach and newer device-based algorithms and the evidence base for their use. Expert commentary: The incremental gains of optimization are likely to be real, but small, compared to the overall improvement gained from cardiac resynchronization itself. At this time routine optimization may not be mandatory but should be performed where there is no response to CRT. Device-based optimization algorithms appear to be practical and in some cases, deliver superior clinical outcomes compared to echocardiography.

The Role of Atrioventricular and Interventricular Optimization for Cardiac Resynchronization Therapy

Many patients with left ventricular systolic dysfunction may benefit from cardiac resynchronization therapy; however, approximately 30% of patients do not experience significant clinical improvement with this treatment. AV and VV delay optimization techniques have included echocardiography, device-based algorithms, and several other novel noninvasive techniques. Using these techniques to optimize device settings has been shown to improve hemodynamic function acutely; however, the long-term clinical benefit is limited. In most cases, an empiric AV delay with simultaneous biventricular or left ventricular pacing is adequate. The value of optimization of these intervals in "nonresponders" still requires further investigation.

Cardiac resynchronization therapy and cardiac sympathetic function

BACKGROUND

Cardiac resynchronization therapy (CRT) is an established therapy for advanced congestive heart failure, improving both survival and hospitalization. The mechanism beneath these improvements still needs to be defined as about one-third of the patients do not benefit from resynchronization. Restoration of sympatho-vagal function can play a significant role in the process, but available data are limited. In this scenario, positron emission tomography scans with (11) C-hydroxyephedrine, a noradrenaline analogous, has the potential to characterize the modifications of the sympathetic nervous system induced by CRT in decompensated patients.

MATERIALS AND METHODS

Ten patients (six males, age 68 ± 10 years) with primary dilated cardiomyopathy were studied before and after resynchronization (acutely and after 3 months), from a clinical and echocardiographic point of view. Their cardiac sympathetic nerve activity was evaluated by (11) C-hydroxyephedrine positron emission tomography before resynchronization, at short and medium term after resynchronization.

RESULTS

Responders to CRT (patients showing ≥ 15% decrease in left ventricular end-systolic volume) showed a higher level of left ventricular radiotracer uptake both at baseline and after resynchronization with respect to nonresponders. This was coupled with a progressive improvement in homogeneity in left ventricular tracer uptake mainly in responders.

CONCLUSIONS

Cardiac resynchronization therapy improves cardiac sympathetic nerve activity in responders since its activation, while nonresponders do not show any significant change at any time of evaluation. CRT seems to be more effective in those patients with a still structurally preserved, yet functionally impaired, neuroautonomic system.

Cardiac resynchronisation therapy optimisation strategies: systematic classification, detailed analysis, minimum standards and a roadmap for development and testing

In this article an international group of CRT specialists presents a comprehensive classification system for present and future schemes for optimising CRT. This system is neutral to the measurement technology used, but focuses on little-discussed quantitative physiological requirements. We then present a rational roadmap for reliable cost-effective development and evaluation of schemes. A widely recommended approach for AV optimisation is to visually select the ideal pattern of transmitral Doppler flow. Alternatively, one could measure a variable (such as Doppler velocity time integral) and "pick the highest". More complex would be to make measurements across a range of settings and "fit a curve". In this report we provide clinicians with a critical approach to address any recommendations presented to them, as they may be many, indistinct and conflicting. We present a neutral scientific analysis of each scheme, and equip the reader with simple tools for critical evaluation. Optimisation protocols should deliver: (a) singularity, with only one region of optimality rather than several; (b) blinded test-retest reproducibility; (c) plausibility; (d) concordance between independent methods; and (e) transparency, with all steps open to scrutiny. This simple information is still not available for many optimisation schemes. Clinicians developing the habit of asking about each property in turn will find it easier to win now down the broad range of protocols currently promoted. Expectation of a sophisticated enquiry from the clinical community will encourage optimisation protocol-designers to focus on testing early (and cheaply) the basic properties that are vital for any chance of long term efficacy.

Comparison of dyssynchrony parameters for VV-optimization in CRT patients

BACKGROUND

Optimization of the interventricular delay (VV-optimization) in cardiac resynchronization therapy (CRT) patients can be performed by evaluation of mechanical dyssynchrony. However, there is no consensus on which method to use. In this study, three conceptually different methods were evaluated.

METHODS

Thirty consecutive CRT patients were included. At day 1, patients were atrioventricular and VV optimized by left ventricular outflow tract (LVOT) velocity time integral (VTI). At 6 months, 2D strain (2DS) echocardiography and tissue Doppler imaging (TDI) was performed at six different VV-programming delay in steps of 20 ms. LVOT and three indices of dyssynchrony were evaluated at each setting: standard deviation (SD) of time-to-peak strain in 12 segments (2DS-SD), SD of time-to-peak velocities in 12 segments (TDI-SD), and maximal activation delay (AD-max) by cross-correlation analysis (XCA) of TDI-derived myocardial acceleration curves.

RESULTS

Feasibility was 90% for 2DS-SD and TDI-SD and 97% for AD-max. Coefficients of variation for intraobserver variability were 13% for 2DS-SD, 11% for TDI-SD, and 6% for AD-max. A relative increase in LVOT VTI > 10% was observed in 5/12 (42%) nonresponders and 7/18 (39%) responders to CRT. Optimization by all three dyssynchrony indices significantly increased LVOT VTI compared to simultaneous pacing and optimal setting at day 1 (P < 0.05, all). LVOT VTI was highest when using AD-max, and AD-max showed the best agreement (k = 0.71).

CONCLUSION

VV optimization at 6 months acutely benefits both responders and nonresponders; however, dyssynchrony indices do not perform equally well. XCA has a high feasibility and reproducibility and appears to be superior to time-to-peak techniques.

Effect of atrioventricular and ventriculoventricular delay optimization on clinical and echocardiographic outcomes of patients treated with cardiac resynchronization therapy: a meta-analysis

BACKGROUND

Optimization of atrioventricular (AV) and ventriculoventricular (VV) delays of cardiac resynchronization therapy (CRT) devices maximizes left ventricular filling and stroke volume. However, the incremental value of these optimizations over empiric device programming remains unclear. The objective of this analysis was to perform a systematic review and meta-analysis of the effects of AV and VV delay optimization on clinical and echocardiographic end points of patients with heart failure treated with CRT.

METHODS

A standardized search strategy was performed and identified 12 trials comparing AV and/or VV delay optimization and conventional CRT device programming and their effects on various clinical and echocardiographic outcomes. Pooled odds ratios were analyzed using random-effect meta-analysis with Mantel-Haenszel method.

RESULTS

Combined data from a total of 4,356 patients with heart failure treated with CRT showed no differences in clinical or echocardiographic outcomes between patients who underwent AV and/or VV delay optimization and patients who underwent empiric device programming (Mantel-Haenszel odds ratio 0.86 [95% CI 0.68-1.09], P value for overall effect = .21 by intention-to-treat analysis).

CONCLUSION

The current literature suggests that routine AV and/or VV delay optimization has a neutral effect on clinical and echocardiographic outcomes based on pooled data from randomized and nonrandomized studies. Standardization of patient selection and optimization timing and method may help to further define the role of CRT device optimization.

A study of mechanical optimization strategy for cardiac resynchronization therapy based on an electromechanical model

An optimal electrode position and interventricular (VV) delay in cardiac resynchronization therapy (CRT) improves its success. However, the precise quantification of cardiac dyssynchrony and magnitude of resynchronization achieved by biventricular (BiV) pacing therapy with mechanical optimization strategies based on computational models remain scant. The maximum circumferential uniformity ratio estimate (CURE) was used here as mechanical optimization index, which was automatically computed for 6 different electrode positions based on a three-dimensional electromechanical canine model of heart failure (HF) caused by complete left bundle branch block (CLBBB). VV delay timing was adjusted accordingly. The heart excitation propagation was simulated with a monodomain model. The quantification of mechanical intra- and interventricular asynchrony was then investigated with eight-node isoparametric element method. The results showed that (i) the optimal pacing location from maximal CURE of 0.8516 was found at the left ventricle (LV) lateral wall near the equator site with a VV delay of 60 ms, in accordance with current clinical studies, (ii) compared with electrical optimization strategy of E_RMS, the LV synchronous contraction and the hemodynamics improved more with mechanical optimization strategy. Therefore, measures of mechanical dyssynchrony improve the sensitivity and specificity of predicting responders more. The model was subject to validation in future clinical studies.

How to improve outcomes: should we put more emphasis on programming and medical care and less on patient selection?

Many factors contribute to the pathophysiology and progression of heart failure (HF), offering the potential for many synergistic therapeutic approaches to its management. For patients, who have systolic HF, prolonged QRS and receiving guideline-indicated pharmacological therapy, cardiac resynchronization therapy (CRT) may provide additional benefits in terms of symptom improvement and mortality reduction. Nevertheless, in many patients, moderate or severe symptoms may persist or recur after CRT implantation due to either the severity or progression of the underlying disease, the presence of important co-morbidities or suboptimal device programming. Identifying and, where possible, treating the reasons for persistent or recurrent symptoms in patients who have received CRT is an important aspect of patient care. The present review summarizes the available evidence on this topic.

A systematic approach to designing reliable VV optimization methodology: assessment of internal validity of echocardiographic, electrocardiographic and haemodynamic optimization of cardiac resynchronization therapy

Background

In atrial fibrillation (AF), VV optimization of biventricular pacemakers can be examined in isolation. We used this approach to evaluate internal validity of three VV optimization methods by three criteria.

Methods and results

Twenty patients (16 men, age 75 ± 7) in AF were optimized, at two paced heart rates, by LVOT VTI (flow), non-invasive arterial pressure, and ECG (minimizing QRS duration). Each optimization method was evaluated for: singularity (unique peak of function), reproducibility of optimum, and biological plausibility of the distribution of optima.

The reproducibility (standard deviation of the difference, SDD) of the optimal VV delay was 10 ms for pressure, versus 8 ms (p = ns) for QRS and 34 ms (p < 0.01) for flow.

Singularity of optimum was 85% for pressure, 63% for ECG and 45% for flow (Chi² = 10.9, p < 0.005).

The distribution of pressure optima was biologically plausible, with 80% LV pre-excited (p = 0.007). The distributions of ECG (55% LV pre-excitation) and flow (45% LV pre-excitation) optima were no different to random (p = ns).

The pressure-derived optimal VV delay is unaffected by the paced rate: SDD between slow and fast heart rate is 9 ms, no different from the reproducibility SDD at both heart rates.

Conclusions

Using non-invasive arterial pressure, VV delay optimization by parabolic fitting is achievable with good precision, satisfying all 3 criteria of internal validity. VV optimum is unaffected by heart rate. Neither QRS minimization nor LVOT VTI satisfy all validity criteria, and therefore seem weaker candidate modalities for VV optimization. AF, unlinking interventricular from atrioventricular delay, uniquely exposes resynchronization concepts to experimental scrutiny.

Clinical validation of a real-time data processing system for cardiac output and arterial pressure measurement during intraoperative biventricular pacing optimization

Biventricular pacing (BiVP) improves cardiac output (CO) and mean arterial pressure (MAP) after cardiopulmonary bypass (CPB) in selected patients at risk for acute left heart failure after cardiac surgery. Optimization of atrioventricular delay (AVD) and interventricular delay (VVD) to maximize the hemodynamic effect of pacing requires rapid and accurate data processing. Conventional post hoc data processing (PP) is accurate but time-consuming, and infeasible in the intraoperative setting. We created a customized, real-time data processing (RTP) system to improve data processing efficiency, while maintaining accuracy. Biventricular pacing optimization was performed within 1 hour of the conclusion of CPB in 10 patients enrolled in the Biventricular Pacing After Cardiac Surgery trial. Cardiac output, measured by an electromagnetic flow meter, and arterial pressure were recorded as AVD was randomly varied across seven settings and VVD across nine settings. Post hoc data processing values calculated by two observers were compared to RTP-generated outputs for CO and MAP. Interexaminer reliability coefficients were generated to access the dependability of RTP. Interexaminer reliability coefficient values ranged from 0.997 to 0.999, indicating RTP is as reliable as PP for optimization. Real-time data processing is instantaneous and therefore is more practical in a clinical setting than the PP method. Real-time data processing is useful for guiding intraoperative BiVP optimization and merits further development.

Left Ventricular Versus Simultaneous Biventricular Pacing in Patients With Heart Failure and a QRS Complex ≥120 Milliseconds

Background—

Left ventricular (LV) pacing alone may theoretically avoid deleterious effects of right ventricular pacing.

Methods and Results—

In a multicenter, double-blind, crossover trial, we compared the effects of LV and biventricular (BiV) pacing on exercise tolerance and LV remodeling in patients with an LV ejection fraction ≤35%, QRS ≥120 milliseconds, and symptoms of heart failure. A total of 211 patients were recruited from 11 centers. After a run-in period of 2 to 8 weeks, 121 qualifying patients were randomized to LV followed by BiV pacing or vice versa for consecutive 6-month periods. The greatest improvement in New York Heart Association class and 6-minute walk test occurred during the run-in phase before randomization. Exercise duration at 75% of peak V o 2 (primary outcome) increased from 9.3±6.4 to 14.0±11.9 and 14.3±12.5 minutes with LV and BiV pacing, respectively, with no difference between groups ( P =0.4327). LV ejection fraction improved from 24.4±6.3% to 31.9±10.8% and 30.9±9.8% with LV and BiV pacing, respectively, with no difference between groups ( P =0.4530). Reductions in LV end-systolic volume were likewise similar ( P =0.6788). The proportion of clinical responders (≥20% increase in exercise duration) to LV and BiV pacing was 48.0% and 55.1% ( P =0.1615). Positive remodeling responses (≥15% reduction in LV end-systolic volume) were observed in 46.7% and 55.4% ( P =0.0881). Overall, 30.6% of LV nonresponders improved with BiV and 17.1% of BiV nonresponders improved with LV pacing.

Conclusion—

LV pacing is not superior to BiV pacing. However, nonresponders to BiV pacing may respond favorably to LV pacing, suggesting a potential role as tiered therapy.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00901212.

Relation of QRS shortening to cardiac output during temporary resynchronization therapy after cardiac surgery

Cardiac resynchronization therapy (CRT) can improve cardiac function in heart failure without increasing myocardial oxygen consumption. However, CRT optimization based on hemodynamics or echocardiography is difficult. QRS duration (QRSd) is a possible alternative optimization parameter. Accordingly, we assessed QRSd optimization of CRT during cardiac surgery. We hypothesized that QRSd shortening during changes in interventricular pacing delay (VVD) would increase cardiac output (CO). Seven patients undergoing coronary artery bypass, aortic or mitral valve surgery with left ventricular (LV) ejection fraction < or =40%, and QRSd > or =100 msec were studied. CRT was implemented at epicardial pacing sites in the left and right ventricle and right atrium during VVD variation after cardiopulmonary bypass. QRSd was correlated with CO from an electromagnetic aortic flow probe. Both positive and negative correlations were observed. Correlation coefficients ranged from 0.70 to -0.74 during VVD testing. Clear minima in QRSd were observed in four patients and were within 40 msec of maximum CO in two. We conclude that QRSd is not useful for routine optimization of VVD after cardiac surgery but may be useful in selected patients. Decreasing QRSd is associated with decreasing CO in some patients, suggesting that CRT can affect determinants of QRSd and ventricular function independently.

Validation of automated monitoring of cardiac output for biventricular pacing optimization

Biventricular pacing (BiVP) can increase cardiac output (CO) during acute failure of the left ventricle (LV) after cardiac surgery. This CO benefit is maximized by adjustment of atrioventricular (AVD) and interventricular (VVD) pacing delays. Real-time CO calculation could facilitate this optimization. Accordingly, we compared real-time automated analysis (AA) of CO with manual analysis (MA) in an animal model of pressure overload of the right ventricle (RV). In six anesthetized pigs, pacing leads were placed on the right atrium, RV, and LV. Complete heart block was induced with ethanol injection, and RV systolic pressure was doubled with a pulmonary artery snare. Atrioventricular pacing delay was varied over seven common values and VVD over nine, in random sequence. Two LV pacing sites (LVPS) were also tested. Aortic flow velocity, measured by ultrasonic flow probe, was integrated by AA and MA to calculate CO. Interexaminer Reliability Coefficient (IRC) was determined by Analysis of Variance (ANOVA) for two 10-second runs in each animal. Cardiac output-AVD and CO-VVD relations were similar for AA and MA. Interexaminer Reliability Coefficients were 0.997 and 0.994 for MA vs. AA. Automated analysis was available in real-time. Manual analysis was delayed at 2 hours or more. Automated analysis merits development for real-time optimization of intraoperative BiVP.

Measurement precision in the optimization of cardiac resynchronization therapy

BACKGROUND

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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 critical comparison of echocardiographic measurements used for optimizing cardiac resynchronization therapy: stroke distance is best

AIMS

Dyssynchrony assessment in cardiac resynchronization therapy (CRT) is controversial, and there are no standard protocols for optimizing treatment. We studied the feasibility and reproducibility of several echocardiographic measures to optimize CRT pacemaker settings. We also assessed the utility of 'stroke distance' [left ventricular outflow tract velocity-time integral (LVOT VTI)] in performing this function.

METHODS AND RESULTS

Thirty patients underwent the following functional assessments; 6 min walk test distance, peak VO(2) consumption on cardiopulmonary exercise testing (VO(2) peak), quality-of-life scoring, and echocardiography; before and at 3 and 6 months after implantation of the CRT device. At 3 months, patients received LVOT VTI-guided optimization of interventricular (VV) and atrioventricular (AV) delays. The feasibility and reproducibility of each optimization measurement was statistically analysed, and the functional benefits of optimization examined. Left ventricular outflow tract VTI, interventricular mechanical delay (IVMD), and tissue Doppler lateral-septal delay showed good feasibility (>90%), whereas LVOT VTI, IVMD, and the 12-segment tissue Doppler dyssynchrony index showed good reproducibility (coefficient of variation <20%). The most feasible and reproducible measure was LVOT VTI. Our optimization protocol necessitated alteration of AV and/or VV delays in 60% of patients at 3 months and was associated with a 50% improvement in functional responder status between 3 and 6 months.

CONCLUSION

Left ventricular outflow tract VTI provides us with a single, direct measure of global LV function which is robust, and easily applicable in routine clinical practice, and which is effective at improving response to CRT.