Left Ventricular Lead Proximity to an Akinetic Segment and Impact on Outcome of Cardiac Resynchronization Therapy

Combining electromagnetic navigation and 3-D mapping to reduce fluoroscopy time and achieve optimal CRT response

Implantation of cardiac resynchronization therapy (CRT) devices can be challenging, time consuming, and associated with high-dose x-ray exposure. We present the technique in which an electromagnetic navigation system (MediGuideTM, St. Jude Medical) and an electroanatomical three-dimensional mapping system (EnSite NavX, St Jude Medical) are usefully combined for implanting implantable cardioverter defibrillator CRT devices with strong reduction of x-ray exposure, and for targeting the most delayed regions in the activation maps avoiding scars for optimal CRT response.

Bi-ventricular pacing improves pump function only with adequate myocardial perfusion in canine hearts with pseudo-left bundle branch block

Bi-ventricular (BiV) pacing is an effective therapy for the treatment of cardiac electromechanical (EM) dysfunction. The reason(s), however, for therapy non-response in approximately one-third of the subjects remains unclear, especially as it relates to myocardial perfusion and pacing location. In this study, we examined how acute BiV pacing response may be related to underlying myocardial perfusion coupled with pacing near or distant to the area of perfusion. In 10 open-chest anesthetized canines, coronary blood flow to the left ventricular (LV) anterior wall (AW: n = 5) and lateral wall (LW: n = 5) was controlled during four pacing conditions: right atrial, right ventricular (pseudo-left bundle branch block; [pseudo-LBBB]), BiV-LW and BiV-AW. Local EM function (piezo-electrical crystals and electrodes), along with global hemodynamic parameters, were measured during all pacing conditions at three coronary perfusion rates (≥0.40 mL/min/g, 0.20-0.40 mL/min/g and <0.20 mL/min/g). A positive BiV therapy response was assessed by a significant increase in the maximum cardiac output compared with the pseudo-LBBB condition. Despite no improvement in QRS duration, BiV-LW pacing improved LV function compared with the pseudo-LBBB pacing condition (P value <0.01). This improvement with BiV-LW pacing was seen above a certain myocardial perfusion threshold and was independent of any increases in regional coronary blood flow with BiV pacing. At lower myocardial perfusion rates, LV function was not improved with BiV pacing at any location. This study underscores the significance of even mild ischemia on BiV pacing response.

Contemporary and future trends in cardiac resynchronization therapy to enhance response

The rationale for cardiac resynchronization therapy (CRT), expectations in terms of patient benefit, patient selection for CRT, selection of a CRT pacemaker (CRT-P) vs CRT plus implantable cardioverter-defibrillator (CRT-D) platform, and studies evaluating device programming to enhance benefit from CRT are reviewed. The notion of an "optimal" left ventricular (LV) pacing site, the rationale for identifying and avoiding LV pacing in regions of scar, the use of anatomic, hemodynamic, and electrical parameters to identify an optimal LV pacing site, and the potential utility of multisite LV pacing to enhance benefit from CRT are discussed. Finally, the advantages and disadvantages of the various methods for LV lead delivery are reviewed.

Myocardial infarction does not preclude electrical and hemodynamic benefits of cardiac resynchronization therapy in dyssynchronous canine hearts

BACKGROUND

Several studies suggest that patients with ischemic cardiomyopathy benefit less from cardiac resynchronization therapy. In a novel animal model of dyssynchronous ischemic cardiomyopathy, we investigated the extent to which the presence of infarction influences the short-term efficacy of cardiac resynchronization therapy.

METHODS AND RESULTS

Experiments were performed in canine hearts with left bundle branch block (LBBB, n=19) and chronic myocardial infarction, created by embolization of the left anterior descending or left circumflex arteries followed by LBBB (LBBB+left anterior descending infarction [LADi; n=11] and LBBB+left circumflex infarction [LCXi; n=7], respectively). Pacing leads were positioned in the right atrium and right ventricle and at 8 sites on the left ventricular (LV) free wall. LV pump function was measured using the conductance catheter technique, and synchrony of electrical activation was measured using epicardial mapping and ECG. Average and maximal improvement in electric resynchronization and LV pump function by right ventricular+LV pacing was similar in the 3 groups; however, the site of optimal electrical and mechanical benefit was LV apical in LBBB hearts, LV midlateral in LBBB+LCXi hearts and LV basal-lateral in LBBB+LADi hearts. The best site of pacing was not the site of latest electrical activation but that providing the largest shortening of the QRS complex. During single-site LV pacing the range of atrioventricular delays yielding > or =70% of maximal hemodynamic effect was approximately 50% smaller in infarcted than noninfarcted LBBB hearts (P<0.05).

CONCLUSIONS

Cardiac resynchronization therapy can improve resynchronization and LV pump function to a similar degree in infarcted and noninfarcted hearts. Optimal lead positioning and timing of LV stimulation, however, require more attention in the infarcted hearts.

The impact of myocardial viability on the clinical outcome of cardiac resynchronization therapy

INTRODUCTION

Around 30% of patients do not respond to cardiac resynchronization therapy (CRT). Nonischemic cardiomyopathy has been identified as an independent predictor of response to CRT, probably due to the absence of compact scar.

METHODS AND RESULTS

The relationship between cardiac scar, ischemia, and hibernation (both at the left-ventricular pacing site and as a total burden) and response to CRT was studied in patients with ischemic cardiomyopathy using the perfusion-viability positron emission tomography (PET) test. Sixty-six patients with ischemic cardiomyopathy and traditional criteria for CRT were included. All patients underwent PET scan prior to CRT. Using PET, the amount and location of scarred, ischemic, and hibernating myocardium were characterized. No revascularization was indicated. Responders were defined by an improvement of left-ventricular ejection fraction (LVEF) >or= 5% and/or New York Heart Association (NYHA) class >or= 1 degree. During a mean follow-up of 26.2 +/- 22.2 months, there was a significant improvement in NYHA class and reverse remodeling in patients with the LV lead inserted remotely from the scar. However, reverse remodeling of a similar degree was present also in patients with extensive scarring including the lateral wall. The presence of ischemia, hibernation, or nontransmural scar at the pacing-site did not significantly modify the outcome of CRT as compared with viable myocardium. There were only 38% of CRT-nonresponders. Neither the extent of scar, ischemia, hibernation, or viability predicted outcome or mortality. Twenty patients died during the follow-up, one patient underwent heart transplant.

CONCLUSIONS

At follow-up, response to CRT is observed regardless of the presence of extensive scarring. Left ventricular (LV) pacing at sites with ischemia, hibernation, or nontransmural scar does not appear to modify the effect of CRT as compared to viable tissue.

Effects of biventricular pacing and scar size in a computational model of the failing heart with left bundle branch block

OBJECTIVES

To study the impact of biventricular pacing (BiV) and scar size on left ventricular (LV) regional and global function using a detailed finite element model of three-dimensional electromechanics in the failing canine heart.

BACKGROUND

Cardiac resynchronization therapy (CRT) clinical trials have demonstrated that up to 30% of patients may be classified as non-responders. The presence of a scar appears to contribute to those that do not respond to CRT. A recent study in patients with myocardial scar showed that LV dyssynchrony was the sole independent predictor of reverse remodeling, and not scar location or size.

METHODS

Two activation sequences were simulated: left bundle branch block (LBBB) and acute simultaneous BiV (with leads in the left and right ventricle) in hearts with chronic scars of various sizes. The dependence of regional function (mean fiber ejection strain, variance of fiber isovolumic strain and fraction of tissue stretched during ejection) and global function (left ventricular dP/dt(max), ejection fraction, stroke work) on scar size and pacing protocol was tested.

RESULTS

Global function and regional function averaged over the whole LV during LBBB and BiV decreased as a function of scar size. In the non-scarred regions, however, regional function was largely independent of scar size for a fixed pacing site.

CONCLUSIONS

The model results suggest that uniformity of mechanical contraction in non-scarred regions in the failing heart during biventricular pacing is independent of scar size for a fixed pacing site.

Future potential of echocardiography in heart failure

Echocardiography represents a convenient, portable and noninvasive method to provide important anatomic and physiologic information to inform the management of heart failure patients. Traditional echo assessments include diagnostic, etiologic and prognostic data from ventricular size, geometry and performance. Newer echocardiographic techniques are receiving greater utilization, however, and promise to further enhance diagnostic abilities in heart failure. This article reviews traditional anatomic assessments, echo-based cardiac hemodynamics, 3D echocardiography, quantification of myocardial tissue mechanics and hand-carried echocardiography. These developments in echocardiography underlie future trends toward echo objectivity, improved imaging of patients with poor acoustic windows, miniaturization and simplicity in focused exams and the expanded application of old and new techniques.

Accelerometer-derived time intervals during various pacing modes in patients with biventricular pacemakers: comparison with normals

INTRODUCTION

Changes due to biventricular pacing have been documented by shortening of QRS duration and echocardiography. Compared to normal ventricular activation, the presence of left bundle branch block (LBBB) results in a significant change in cardiac cycle time intervals. Some of these have been used to quantify the underlying cardiac dyssynchrony, assess the effects of biventricular pacing, and guide programming of ventricular pacing devices. This study evaluates a simple noninvasive method using accelerometers attached to the skin to measure cardiac time intervals in biventricularly paced patients.

METHODS

Ten patients with biventricular pacemakers previously implanted for congestive heart failure were paced in the AAI mode, then in atrioventricular (AV) sequential mode from the right and left ventricles followed by biventricular pacing. Simultaneous recordings were obtained by 2D, Doppler echocardiography as well as by accelerometers. Similar recordings were obtained from 10 gender, aged matched, normal controls during sinus rhythm.

RESULTS

Compared to normals, heart failure patients paced in AAI mode had prolonged isovolumetric contraction time (IVCT), shorter ventricular ejection time (LVET), and prolonged isovolumetric relaxation (IVRT). With biventricular pacing the IVCT decreased, but the LVET and IVRT did not change significantly. There was excellent correlation between the echo and accelerometer-measured intervals.

CONCLUSIONS

Shortening of the IVCT measured by an accelerometer is a consistent time interval change due to biventricular pacing that probably reflects more rapid acceleration of left ventricular ejection. The accelerometer may be useful to assess immediate efficacy of biventricular pacing during device implantation and optimize programmable time intervals such as AV and interventricular (VV) delays.

Using echocardiography in cardiac resynchronization therapy

Cardiac resynchronization therapy has become a therapeutic option for refractory heart failure. Several imaging techniques play an increasingly important role in patient selection during and after implantation. This manuscript reviews the current echocardiographic techniques available for guiding both patient selection and optimization of device programming following implantation.

Relation of left ventricular lead placement in cardiac resynchronization therapy to left ventricular reverse remodeling and to diastolic dyssynchrony

The effects of left ventricular (LV) lead placement for cardiac resynchronization therapy (CRT) on LV remodeling and dyssynchrony are not well defined. Sixty-one patients (age 60 +/- 11 years, 76% men) were evaluated by echocardiography before and 4 +/- 2 months after CRT and grouped by the LV lead placement (lateral, posterolateral, or anterolateral). Echocardiographic measurements included LV volumes and LV ejection fraction. Tissue Doppler imaging was used to assess for inter- and intraventricular systolic and diastolic dyssynchrony. Analysis of variance was used to determine the effect of the LV lead placement on echocardiographic variables after CRT. The LV lead was placed in a lateral cardiac vein in 33 patients (54%), posterolateral in 15 (25%), and anterior in 13 (21%). Lateral LV lead placement was associated with significantly smaller LV volumes compared with the posterolateral lead placement (p <0.01). Diastolic dyssynchrony improved significantly with lateral lead placement compared with the anterior lead location (p <0.05). Improvement in LV ejection fraction and inter- and intraventricular systolic dyssynchrony was similar among the 3 groups. In conclusion, in patients undergoing CRT, a lateral lead location resulted in greater reverse LV remodeling and improved diastolic dyssynchrony compared with other lead placement locations.