Interventional electrophysiology and cardiac resynchronization therapy: delivering electrical therapies for heart failure

Charting the Course for Careers in Interventional Heart Failure: Training, Challenges, and Future Directions

Interventional heart failure (IHF) has emerged as a critical subspecialty due to the increasing complexity of heart failure (HF) treatment now spanning both pharmacological and nonpharmacological device-based therapies. Although initially existing at the intersection of interventional cardiology and advanced HF, IHF has expanded to encompass multiple domains of cardiology including cardiogenic shock (CS), transcatheter valve therapies, relief of increased left atrial pressures, and coronary intervention in low ejection fraction and after heart transplant. Although rapidly growing, training pathways remain elusive, and existing training pathways are not well equipped to deliver necessary training components and encourage growth in the field. Those with a career in IHF can be divided into 3 main phenotypes. Those who are not formally interventional trained, but might implant pressure sensors, perform endomyocardial biopsies, and place nonlarge bore devices. Those who have formal interventional cardiology training might focus on coronary interventions, shock calls, and large-bore devices. Those with structural training might focus on transcatheter valve therapies and structural procedures in HF. There are several possible training pathways for IHF and we propose 5 focuses for training. Finally, we describe areas of interest and growth for careers in IHF. The field of IHF has been misunderstood as one of "jack of all trades" but actually represents the trend of increasing specialization for careers within cardiology due to the increasing complexity of therapeutic options within cardiovascular disease. By addressing current training challenges, the field is poised to make significant strides. Trainees entering this specialty will have the opportunity to be at the forefront of cardiovascular care, contributing to innovative treatments and improving outcomes for patients with complex HF.

Prominent crista terminalis mimicking a right atrial mass: a systematic literature review and meta-analysis

The crista terminalis is an anatomical structure localized on the posterolateral wall of the right atrium (RA). We performed a systematic review of the literature and meta-analysis concerning cases of unusual prominent crista terminalis mimicking RA mass. Moreover, we described the differential diagnosis of cardiac masses with the use of echocardiography, computed tomography, and cardiac magnetic resonance (CMR). We also emphasize the potential importance of this structure in electrophysiological procedures, including its role in exaggerated arrhythmias. Prominent crista terminalis may be a potential obstacle during invasive cardiac procedures or catheter ablation target. In analyzed cases, the crista terminalis was often erroneously interpreted as pathologic and at first confused with a thrombus or tumor during transthoracic echocardiography examination. The correct final diagnoses were mostly made with used transesophageal echocardiography or CMR. The most important imaging findings suggestive of prominent crista terminalis rather than tumor were a similar echogenicity/intensity with adjacent myocardium, the location on posterolateral wall of the RA, the phasic change in size, and no enhancement after contrast injection. We describe up to date and detailed imaging features for the differential diagnostics of selected intracardiac masses using various imaging techniques, including multimodality cardiac imaging. Familiarity with the anatomy and the imaging findings of the prominent crista terminalis will reduce misdiagnosis and avoid additional tests and unwarranted clinical interventions, while in patients considered for invasive cardiac procedures it might increase their efficacy and safety.

Is interventional technique better than the traditional over-the-wire method for left ventricular lead implantation in cardiac resynchronization therapy?

Background

Interventional cardiac resynchronization therapy (I-CRT) for left ventricular lead (LVL) placement works as a supplement to traditional (over-the-wire) cardiac resynchronization therapy (T-CRT). It has been argued that I-CRT is a time-consuming and complicated procedure.

Objective

The purpose of this study was to investigate differences in procedure-related, perioperative, postoperative, and clinical endpoints between I-CRT and T-CRT.

Methods

This single-center, retrospective, cohort study included all consecutive patients receiving a CRT-pacemaker/defibrillator between January 1, 2012, and August 31, 2018. Patients underwent T-CRT from January 1, 2012, to June 1, 2015, and I-CRT from January 1, 2016, to August 31, 2018. We obtained data from patient record files, fluoroscopic images, and the Danish Pacemaker and ICD Register. Data were analyzed using Wilcoxon rank-sum/linear regression for continuous variables and the Pearson χ2/Fisher exact for categorical variables.

Results

Optimal LVL placement was achieved in 82.7% of the I-CRT group and 76.8% of the T-CRT group (P = .015). In the I-CRT group, 99.0% of LVLs were quadripolar vs 55.3% in the T-CRT group (P <.001). Two or more leads were used during the procedure in 0.7% and 10.5% of all cases in the I-CRT and T-CRT groups, respectively (P <.001). Total implantation time was 81.0 minutes in the I-CRT group and 83.0 minutes in the T-CRT group (P = .41). Time with catheters in the coronary sinus was 45.0 minutes for the I-CRT group vs 37.0 minutes in the T-CRT group, respectively (P <.001).

Conclusion

I-CRT did not prolong total implantation time despite longer time with catheters in the coronary sinus. I-CRT allowed more optimal LVL placement, wider use of quadripolar leads, and use of fewer leads during the procedure.

Troubleshooting the difficult left ventricular lead placement in cardiac resynchronization therapy: current status and future perspectives

INTRODUCTION

Cardiac resynchronization therapy (CRT) is an important option in modern cardiac implantable electronic device (CIED) treatment. Techniques for left ventricular (LV) lead placement in the coronary sinus and its tributaries are neither well described nor studied systematically, despite attention regarding where to place the LV lead.

AREAS COVERED

This review presents specialized tools and techniques to overcome some of the most common problems encountered in LV lead placement in CRT. These tools and techniques are termed Interventional-CRT (I-CRT), as they share technology with other interventional procedures. The main principle in I-CRT, compared to the traditional Over-The-Wire technique, is to add better support for delivery of the LV lead through dedicated inner catheters that also allows more flexibility with use of more guidewires and better imaging with direct venography in the target vein.

EXPERT OPINION

Even though CRT is an established therapeutic option, there are still many challenges in the implementation of the therapy. The cornerstone should be an ease of delivering the CRT and specifically implantation of the LV lead. Therefore, knowledge of the principles in I-CRT, as I-CRT could make implantation simpler in general and easier to reach the optimal LV pacing site.

Comparison of Speckle Tracking Echocardiography During Different Pacing Modalities for Cardiac Resynchronization Therapy Response Prediction

Background: The aim of this study was to evaluate left ventricular mechanical activation pattern by speckle tracking echocardiography (STE) as a predictor of response to cardiac resynchronization therapy (CRT) in patients with heart failure. Methods: Echocardiography was performed during no pacing, right ventricular pacing (RVP), biventricular pacing (BVP) and multipolar pacing (MPP) immediately after CRT implantation in 16 patients at a single centre. Seven patients were diagnosed as responders and 9 patients as non-responders after 6 months of standard CRT pacing. All had adequate short axis views, and 1 CRT responder and 2 CRT non-responders had limited longitudinal views. Results: Longitudinal and circumferential global strain (GS) and global strain rate (GSR) or their change analysis, did not yield any CRT response prediction. However, the longitudinal BVP/RVP GS ratio was significantly higher in the responder group (1.32 ± 0.2%, 2.0 ± 0.4% and 1.9 ± 0.4%), compared with the non-responder group (1.06 ± 0.2%, 1.1 ± 0.4% and 1.2 ± 0.4%) in the apical two-chamber, APLAX and four-chamber views, respectively. Similarly, the longitudinal BVP/RVP GSR at active systolic phase (GSRs) was significantly higher in the responder group (1.9 ± 0.9% and 1.7 ± 0.4%) compared with the non-responder group (1.0 ± 0.4% and 1.1 ± 0.2%) in the apical APLAX and four-chamber views, respectively. Measurements of the strain delay index showed predictive power regarding CRT response in non-paced patients. Conclusion: Post implantation, longitudinal BVP/RVP GS and GSRs ratios of 1.4% and above may be useful as a CRT response prediction tool. Furthermore, our findings support the usefulness of strain delay index prior to CRT implantation in non-paced patients.

Clinical impact of increasing left ventricular pacing output in cardiac resynchronization therapy - the new optimization strategy

We report a patient who did not improve after standard optimization of atrioventricular and intraventricular pacing timing, but showed response to cardiac resynchronization therapy (CRT) after increasing left ventricular (LV) pacing output. Increasing LV pacing output is one of the useful optimization methods for CRT nonresponder.

Clinical value of cardiovascular magnetic resonance in patients with MR-conditional pacemakers

AIMS

Magnetic resonance (MR) conditional pacemakers are increasingly implanted into patients who may need cardiovascular MR (CMR) subsequent to device implantation. We assessed the added value of CMR for diagnosis and management in this population.

METHODS AND RESULTS

CMR and pacing data from consecutive patients with MR conditional pacemakers were retrospectively reviewed. Images were acquired at 1.5 T (Siemens Magnetom Avanto). The indication for CMR and any resulting change in management was recorded. The quality of CMR was rated by an observer blinded to clinical details, and data on pacemaker and lead parameters were collected pre- and post-CMR. Seventy-two CMR scans on 69 patients performed between 2011 and 2015 were assessed. All scans were completed successfully with no significant change in lead thresholds or pacing parameters. Steady-state free precession (SSFP) cine imaging resulted in a greater frequency of non-diagnostic imaging (22 vs. 1%, P < 0.01) compared with gradient echo sequences (GRE). Right-sided pacemakers were associated with less artefact than left-sided pacemakers. Late gadolinium enhancement imaging was performed in 59 scans with only 2% of segments rated of non-diagnostic quality. The CMR data resulted in a new diagnosis in 27 (38%) of examinations; clinical management was changed in a further 18 (25%).

CONCLUSIONS

CMR in patients with MR conditional pacemakers provided diagnostic or management-changing information in the majority (63%) of our cohort. The use of gradient echo cine sequences can reduce rates of non-diagnostic imaging. Right-sided device implantation may be considered in patients likely to require CMR examination.

Echocardiographic assessment of left ventricular dyssynchrony in Egyptian children with congestive heart failure due to dilated cardiomyopathy

OBJECTIVE

To evaluate the presence of cardiac dyssynchrony in Egyptian children with congestive heart failure due to dilated cardiomyopathy.

MATERIALS AND METHODS

A total of 30 children with congestive cardiac failure due to dilated cardiomyopathy and 30 healthy age-matched controls were examined with conventional echocardiography, tissue Doppler, and speckle tracking imaging.

RESULTS

Conventional Doppler echocardiography demonstrated significant left ventricular systolic and diastolic dysfunction in the patient group. Tissue Doppler showed significant decrease in S-wave velocity and E'/A' ratio, and prolonged isovolumic contraction and relaxation times of mitral annulus as well as significant prolongation in mean difference between time-to-peak systolic strain of the basal septal and basal lateral segments in the patient group compared with the control group (p<0.005). Speckle tracking imaging demonstrated significant prolongation in mean difference between time-to-peak systolic strain of anteroseptal and posterior segments in both circumferential and radial strain analysis in the patient group than in the control group (p<0.005). It also demonstrated significant prolongation in the mean difference between time-to-peak systolic strain of the basal septal and basal lateral segments in longitudinal strain analysis in the patient group than in the control group (p<0.005). A significant increase in the standard deviation of time-to-peak strain, as a marker of increased intra-ventricular dyssynchrony, was present in the patient group compared with the control group (p=0.008).

CONCLUSION

Children with congestive heart failure due to dilated cardiomyopathy usually suffer from significant intra-ventricular dyssynchrony. Tissue Doppler imaging and speckle tracking imaging strain analysis are helpful tools to detect the presence of cardiac dyssynchrony.

Improvement in hemodynamic response using a quadripolar LV lead

BACKGROUND

The Quartet quadripolar lead (St. Jude Medical Inc., St. Paul, MN, USA) offers 10 different left ventricle pacing configurations that may further influence hemodynamic parameters compared to traditional bipolar pacing configurations. The purpose of this study was to evaluate whether pacing from additional quadripolar lead vectors could enhance cardiac output (CO).

METHODS

For each patient, CO was measured in "no-pacing" and in all the 10 configurations available, within 7 days of implantation of the device. Tip-ring, tip-right ventricular coil (RVC), and ring-RVC vectors were considered as traditional vectors. The seven additional configurations available in the quadripolar lead were considered as nontraditional vectors. CO was measured by ECHO. The best configuration was defined as the one presenting the highest CO measurement within configurations, which have a capture threshold <3 V and a safety margin between the capture and the phrenic nerve stimulation thresholds.

RESULTS

Fifty-one standard cardiac resynchronization therapy patients were enrolled. The mean of each patient's best CO obtained with traditional vectors was higher than the baseline nonpaced CO (4.16 L/min vs 3.64 L/min). The mean of each patient's best CO, including all 10 available configurations, was also higher than the baseline nonpaced CO (4.33 L/min vs 3.64 L/min). In addition, the mean of each patient's best CO obtained with the best configuration available through a quadripolar lead was better than the mean of each patient's best CO obtained with a traditional configuration. In 53% of patients, the best CO was obtained with a nontraditional vector unique to the quadripolar lead.

CONCLUSIONS

A quadripolar lead offers multiple additional pacing options to increase CO acutely compared to conventional bipolar leads.

Anatomical reconstructions of the human cardiac venous system using contrast-computed tomography of perfusion-fixed specimens

A detailed understanding of the complexity and relative variability within the human cardiac venous system is crucial for the development of cardiac devices that require access to these vessels. For example, cardiac venous anatomy is known to be one of the key limitations for the proper delivery of cardiac resynchronization therapy (CRT)(1) Therefore, the development of a database of anatomical parameters for human cardiac venous systems can aid in the design of CRT delivery devices to overcome such a limitation. In this research project, the anatomical parameters were obtained from 3D reconstructions of the venous system using contrast-computed tomography (CT) imaging and modeling software (Materialise, Leuven, Belgium). The following parameters were assessed for each vein: arc length, tortuousity, branching angle, distance to the coronary sinus ostium, and vessel diameter. CRT is a potential treatment for patients with electromechanical dyssynchrony. Approximately 10-20% of heart failure patients may benefit from CRT(2). Electromechanical dyssynchrony implies that parts of the myocardium activate and contract earlier or later than the normal conduction pathway of the heart. In CRT, dyssynchronous areas of the myocardium are treated with electrical stimulation. CRT pacing typically involves pacing leads that stimulate the right atrium (RA), right ventricle (RV), and left ventricle (LV) to produce more resynchronized rhythms. The LV lead is typically implanted within a cardiac vein, with the aim to overlay it within the site of latest myocardial activation. We believe that the models obtained and the analyses thereof will promote the anatomical education for patients, students, clinicians, and medical device designers. The methodologies employed here can also be utilized to study other anatomical features of our human heart specimens, such as the coronary arteries. To further encourage the educational value of this research, we have shared the venous models on our free access website: www.vhlab.umn.edu/atlas.

Real-time CT-guided percutaneous placement of LV pacing leads

OBJECTIVES

The aim of this study was to assess the feasibility of real-time computed tomographic (CT) imaging to guide the percutaneous placement of left ventricular (LV) leads in an animal model.

BACKGROUND

Cardiac resynchronization therapy has been shown to improve morbidity and mortality in patients with chronic heart failure. However, placement of the coronary sinus lead can be challenging and may require a more aggressive surgical approach.

METHODS

Nine swine were placed in a real-time CT scanner to define the safest percutaneous access strategy. Under real-time CT guidance, a 3.5-F pacing lead was placed percutaneously in the anterolateral LV epicardium (n = 6 swine) or to the posterolateral wall after the creation of intentional left pneumothorax (n = 3 swine) in a tangential (n = 12) or perpendicular (n = 1) approach. Pacing parameters and CT images were assessed during 30-min follow-up. Necropsy findings were compared with real-time CT images.

RESULTS

CT imaging successfully defined the safest percutaneous access route in all 13 lead placements and guided the therapeutic creation of pneumothoraces. Needle trajectory remained within 5 mm of the access route defined on CT imaging. LV lead placement under CT guidance was successful in all attempts within 19 ± 7 min. The mean pacing thresholds was 2.5 ± 1.5 V, the mean R wave amplitude was 11.2 ± 5.6 mV, and the mean impedance was 686 ± 103 Ω and remained unchanged after tangential placement during 30-min follow-up. Although no cardiac complications were observed with tangential lead placement (12 of 12), the perpendicular approach resulted in a pericardial effusion requiring pericardiocentesis. At necropsy, CT images correlated well with the in situ pathological results.

CONCLUSIONS

Percutaneous placement of LV pacing leads under CT guidance is feasible and might offer an alternative to more invasive surgical approaches in patients with complicated coronary sinus lead placement.

Variance in coronary venous anatomy: a critical determinant in optimal candidate selection for cardiac resynchronization therapy

BACKGROUND

Knowledge of coronary sinus (CS) anatomy and its variations is one of the important factors determining the final position of left ventricle pacing lead during cardiac resynchronization therapy.

METHODS

Coronary venous system anatomy, including number, diameter, and opening angles of tributaries, was studied in 50 normal formalin-fixed adult cadaveric hearts.

RESULTS

Thebesian valve (TV) and Vieussens valve were present in 64% and 60% cases, respectively. CS ostium coverage of ≥75% by TV was seen in 25% (8/32) cases. Number of prominent tributaries lying between anterior interventricular vein and middle cardiac vein varied from 1-4. In 28% of hearts, only one prominent tributary was present. Midlateral vein (average diameter 1.75 ± 0.66 mm) with an average distance of 43.5 ± 12.2 mm from coronary ostium was present in 58% (29/50) hearts, of which it formed an acute angle with CS axis in four (13.39%) cases. Posterolateral vein (average diameter 1.62 ± 0.45 mm) with an average distance of 33.4 ± 11.7 mm from coronary ostium was found in 72% (36/50) cases and formed an acute angle with CS in three (8.33%) cases.

CONCLUSIONS

Restrictive TV covering ≥75% CS ostium (25% cases), presence of single prominent tributary (28% cases), and formation of acute angle of tributary with CS axis (1/4 cases with anterolateral vein, 4/29 cases with midlateral vein, 3/36 cases with posterolateral vein, and 3/28 cases with posterior veins of the left ventricle) can impede successful cannulation of CS.

Prognostic value of plasma renin activity in heart failure

The prognostic role of specific biomarkers of the renin-angiotensin-aldosterone system and sympathetic activation pathways in heart failure has never been investigated in populations with current evidence-weighted treatment. To establish whether the plasma renin activity (PRA), among several neurohormonal biomarkers, is able to predict cardiac events in a population of patients with heart failure on up-to-date treatment, we selected 996 consecutive patients with systolic left ventricular dysfunction (ejection fraction <50%, mean age 65 ± 13 years), who underwent a complete clinical and humoral characterization and were then followed up (median 36 months, range 0 to 72) for cardiac death and appropriate implantable cardioverter device shock. We recorded 170 cardiac deaths and 27 shocks. On Cox multivariate analysis, only ejection fraction (hazard ratio 0.962, 95% confidence interval 0.938 to 0.986), N-terminal pro-brain natriuretic peptide (NT-proBNP; hazard ratio 1.729, 95% confidence interval 1.383 to 2.161) and PRA (hazard ratio 1.201, 95% confidence interval 1.024 to 1.408) were independent predictors of cardiac death. Receiver operating characteristic curve analysis identified a cutoff value for PRA of 2.30 ng/ml/hour that best predicted cardiac mortality. Independent predictors of PRA were ejection fraction, functional class, sodium, potassium, NT-proBNP, norepinephrine, aldosterone, C-reactive protein, and medical therapy. The association of high NT-proBNP and high PRA identified a subgroup (22% of the study population) with the greatest risk of cardiac death. In conclusion, PRA resulted an independent prognostic marker in patients with systolic heart failure additive to NT-proBNP level and ejection fraction. PRA might help to select those patients needing an enhanced therapeutic effort, possibly targeting incomplete renin-angiotensin-aldosterone system blockade.

Event-free survival following CRT with surgically implanted LV leads versus standard transvenous approach

BACKGROUND

While surgical epicardial lead placement is performed in a subset of cardiac resynchronization therapy patients, data comparing survival following surgical versus transvenous lead placement are limited. We hypothesized that surgical procedures would be associated with increased mortality risk.

METHODS

Long-term event-free survival was assessed for 480 consecutive patients undergoing surgical (48) or percutaneous (432) left ventricle (LV) lead placement at our institution from January 2000 to September 2008.

RESULTS

Baseline clinical and demographic characteristics were similar between groups. While there was no statistically significant difference in overall event-free survival (P = 0.13), when analysis was restricted to surgical patients with isolated surgical lead placement (n = 28), event-free survival was significantly lower in surgical patients (P = 0.015). There appeared to be an early risk (first approximately 3 months postimplantation) with surgical lead placement, primarily in LV lead-only patients. Event rates were significantly higher in LV lead-only surgical patients than in transvenous patients in the first 3 months (P = 0.006). In proportional hazards analysis comparing isolated surgical LV lead placement to transvenous lead placement, adjusted hazard ratios were 1.8 ([1.1,2.7] P = 0.02) and 1.3 ([1.0,1.7] P = 0.07) for the first 3 months and for the full duration of follow-up, respectively.

CONCLUSIONS

Isolated surgical LV lead placement appears to carry a small but significant upfront mortality cost, with risk extending beyond the immediate postoperative period. Long-term survival is similar, suggesting those surviving beyond this period of early risk derive the same benefit as coronary sinus lead recipients. Further work is needed to identify risk factors associated with early mortality following surgical lead placement.

Balloon-facilitated delivery of a left ventricular pacing lead

While modern implant tools have contributed greatly to the success of cardiac resynchronization therapy, technical challenges remain. A common problem is the inability to advance left ventricular pacing leads into branch veins that are tortuous or arise at steep angles. In these cases, advancement of the lead causes it to buckle and prolapse into the coronary sinus or great cardiac vein. Lead prolapsed can be avoided by employing a balloon to temporarily obstruct the coronary sinus or great cardiac vein just upstream from the branch vein. The balloon redirects the force of advancement laterally into the branch vein, facilitating delivery.

Can optimization of pacing settings compensate for a non-optimal left ventricular pacing site?

AIMS

Optimal left ventricular (LV) lead position improves the response to cardiac resynchronization therapy (CRT). However, in some patients it is not possible to position the LV lead at an optimal pacing site. The aim of this study was to determine whether optimization of the pacing settings atrioventricular delay (AVD) and interventricular delay (VVD) can compensate for a non-optimal LV pacing site.

METHODS AND RESULTS

In 16 patients with heart failure [New York Heart Association class III (13) or IV (3), median QRS duration of 172 ms and median LV ejection fraction of 20%] the acute haemodynamic effect of biventricular pacing was assessed at > or =2 pacing sites by the increase in maximum rate of LV pressure rise (%dP/dt(max)). At each site the AVD and VVD were optimized. Biventricular pacing with nominal settings at a non-optimal LV pacing site improved dP/dt(max) by 12.8% (-0.5 to 23.2%). This could be further improved by 6.5 percentage points (1.2-13.9) by optimization of pacing settings (P = 0.001) and by 9.9 percentage points (3.7-13.3, P = 0.004) by optimization of pacing site. Optimization of the LV pacing site and pacing settings together improved %dP/dt(max) by 16.2 per cent points (10.0-21.8, P < 0.001).

CONCLUSION

Optimization of the AVD and VVD can partly compensate for a non-optimal LV pacing site. However, a combination of an optimal LV pacing site and optimized pacing settings gives the best acute haemodynamic response.

Utility of QRS width and echocardiography parameters in an integrative algorithm for selecting heart failure patients with cardiac dyssynchrony

BACKGROUND

Cardiac resynchronization therapy (CRT) is an effective treatment in dilated cardiomyopathy (DCM). However, it has been demonstrated that mechanical dyssynchrony is not related to electrical dyssynchrony. We hypothesized that a new QRS width cutoff could be easier to use as a first step in the selection of patients with inter- and intraventricular dyssynchrony.

METHODS

We included 58 patients with DCM. Electrocardiographic (PR interval and QRS width) and echocardiographic (left ventricular dimensions, systolic and diastolic function, dyssynchrony parameters) data were evaluated in all patients.

RESULTS

According to QRS width, we divided the study population in two groups: Group 1, 25 patients having a narrow QRS (<or=120 ms), and Group 2, 33 patients having a wide QRS (>120 ms). Patients in Group 2 had larger left ventricles, with similar systolic function and more severe diastolic dysfunction than patients with narrow QRS. Interventricular dyssynchrony was more frequent in group 2 (54.5% vs 20%, p=0.01), while intraventricular dyssynchrony was highly prevalent in both groups (82.1% vs 72%, p=0.48). A QRS>140 ms best predicted the presence of interventricular dyssynchrony (sensitivity 78.2% and specificity 63.6%), while a QRS>150 ms best predicts intraventricular dyssynchrony (sensitivity 48.6% and specificity 80%).

CONCLUSIONS

Intraventricular dyssynchrony has a high prevalence in patients with DCM, irrespective of the QRS width. Using a higher QRS width cutoff (150 ms) might help in patient selection for CRT. Electrocardiography and echocardiography can be combined into a selection algorithm for patients receiving resynchronization therapy.

Biventricular pacing and defibrillator use in chronic heart failure

Since the 1970s when the implantable cardioverter defibrillator (ICD) was developed, multiple clinical trials have documented survival benefits in certain high-risk subsets of heart failure patients. Over the past decade, cardiac resynchronization therapy (CRT) emerged as an important therapy in carefully selected patients with ongoing symptoms despite optimized pharmacological therapy. ICDs should be considered first-line therapy for survivors of life-threatening ventricular arrhythmic events. Subsets of patients with both ischemic and nonischemic dilated cardiomyopathy appear to have a survival benefit from primary ICD therapy. CRT has resulted in substantial symptomatic improvement and survival benefits in a subgroup of chronic heart failure patients. CRT should be considered in heart failure patients undergoing ICD implantation who have evidence of ventricular dyssynchrony.