Acute biventricular hemodynamic effects of cardiac resynchronization therapy in right bundle branch block.

BACKGROUND: Controversy remains regarding the use of cardiac resynchronization therapy (CRT) in patients with heart failure with right bundle branch block (RBBB) and reduced left ventricular (LV) ejection fraction. Moreover, little is known about acute hemodynamic changes with CRT in this subgroup as compared with patients with left bundle branch block (LBBB). OBJECTIVE: The purpose of this study was to evaluate the acute biventricular hemodynamic response of CRT and other pacing configurations, including the effects of atrioventricular (AV) delay and atrial pacing, to understand the effects of CRT in RBBB. METHODS: Forty patients (9 with RBBB and 31 with LBBB) undergoing CRT implantation underwent temporary pacing with varying configurations and AV delay. The acute hemodynamic response was assessed via invasive measurements of dP/dtmax (maximal rate of change in pressure) in the left ventricle (LV) as well as the right ventricle (RV) in patients with RBBB. RESULTS: Patients with LBBB had a greater LV dP/dtmax response to CRT than did patients with RBBB. In patients with RBBB, single- or dual-site RV pacing configurations resulted in greater increases in RV dP/dtmax than did biventricular pacing. Optimal AV delays that maximized RV dP/dtmax were shorter than optimal AV delays for LV dP/dtmax. Furthermore, AV delays chosen to maximize improvement in RV dP/dtmax frequently resulted in negative effects on LV dP/dtmax. CONCLUSION: These findings demonstrate a complex relationship between pacing configuration, AV delay, and hemodynamic responses. The biventricular hemodynamic response in patients with heart failure with RBBB might be improved by optimizing pacing modalities and AV delays. This may be particularly important in patients with diseases in whom RV failure predominates, such as patients with pulmonary hypertension and LV assist device.

The Effect of Chronic Kidney Disease on Mortality with Cardiac Resynchronization Therapy.

BACKGROUND: Cardiac resynchronization therapy (CRT) improves functional status, reduces heart failure hospitalizations, and decreases mortality. Several comorbidities including renal function affect outcomes with CRT. However, moderate to severe chronic kidney disease (CKD) was an exclusion criterion in the large randomized control trials. OBJECTIVE: To evaluate the association of renal function on survival following CRT implantation. METHODS: This was a retrospective analysis of 432 consecutive patients implanted with an implantable cardioverter defibrillator with CRT (CRT-D). The primary end point was defined as death by any cause, and it was determined using hospital records and the U.S. Social Security Death Index. A Kaplan-Meier analysis was performed separating renal dysfunction into renal stage based on glomerular filtration rate. Multivariate analysis was performed to assess the clinical predictors of mortality. RESULTS: Patients were followed for up to 12 years with a mean follow-up time of 4.3 ± 3.2 years. A total of 164 patients (39.3%) died over the course of the study. Patients with normal and mild renal diseases (Stages 1 and 2) had improved survival compared with those with moderate-, severe-, or end-stage (Stages 3-5) renal disease. This effect remained statistically significant after multivariate analysis. The estimated 5-year mortality was 36.3% for stage 1, 33.4% for stage 2, 40.6% for stage 3, and 62.1% for stage 4/5 kidney disease (P = 0.004 by log-rank test). CONCLUSION: CKD is a strong and an independent predictor of long-term mortality among patients undergoing CRT-D implantation.

The effect of left ventricular electrical delay on the acute hemodynamic response with cardiac resynchronization therapy.

INTRODUCTION: Cardiac resynchronization therapy (CRT) improves hemodynamic function, as well as reduces hospitalizations and mortality among patients with systolic dysfunction, QRS prolongation, and heart failure. The magnitude of the hemodynamic response is associated with improved outcomes, so optimization of this parameter is a goal of therapy. The purpose of this study was to evaluate the effect of left ventricular (LV) electrical delay, as assessed by the QLV interval, on the acute hemodynamic response to CRT. METHODS AND RESULTS: This study included 31 patients undergoing biventricular ICD placement. At implant, invasive LV dP/dt was measured by a micromanometer catheter during biventricular (BV) or LV only pacing. Both atrial sensing (AS) and atrial pacing (AP) modes were evaluated at 5 different AV delays, tested in randomized order. The QLV interval was measured at the LV pacing site. Compared with intrinsic rhythm, CRT increased LV dP/dtmax by 9.5 ± 8.8% with BV pacing and 10.0 ± 9.2% with LV pacing (P = 0.38) during AS. With AP, CRT increased LV dP/dtmax by 16.0 ± 10.8% and 15.3 ± 11.1%, respectively (P = 0.47). QLV was strongly correlated with the hemodynamic response in all pacing configurations. Multivariate analysis showed that with BV pacing QLV was an independent predictor of the hemodynamic response with a 1.7% increase in %LV dP/dt for every 10 milliseconds prolongation of QLV. CONCLUSIONS: LV electrical delay is a strong predictor of the acute hemodynamic response to CRT. This relationship is independent of pacing mode.

Safety of continuous anticoagulation with dabigatran during implantation of cardiac rhythm devices.

The perioperative bleeding risk associated with therapeutic anticoagulation at cardiac implantable electronic device implantation has previously been demonstrated to vary by the specific anticoagulant used. Although uninterrupted anticoagulation with warfarin appears to be safe, heparin products have been shown to increase the risk of perioperative bleeding. However, the risk associated with cardiac implantable electronic device implantation with anticoagulation using dabigatran, a novel oral direct thrombin inhibitor, is not known. We performed a prospective observational study of patients receiving dabigatran for anticoagulation who underwent cardiac implantable electronic device implantation from June 2011 through May 2012. The study end points included thromboembolic and bleeding complications within 30 days of surgery. Major bleeding complications were defined as bleeding requiring surgical intervention, prolongation of hospitalization, and discontinuation of the anticoagulant or transfusion of blood products within 30 days of surgery. Minor bleeding complications included the development of a hematoma not requiring additional intervention. The thrombotic end points included stroke, transient ischemic attack, myocardial infarction, pulmonary embolism, and deep vein thrombosis. A total of 25 patients were identified for inclusion. During the index hospitalization, no thromboembolic or bleeding complications developed. No major bleeding complications occurred within 30 days of surgery. One minor bleeding event (4%) occurred within 30 days of surgery in 1 patient who was also receiving dual antiplatelet therapy. In conclusion, although no thromboembolic or major bleeding events were observed, additional studies are required to define the optimal antithrombotic management in the perioperative period.

Is defibrillation testing of ICDs necessary?

Defibrillation testing during implantation of cardioverter­defibrillators is controversial because of potential safety concerns and a lack of evidence for the effectiveness of the procedure. New data from the SAFE-ICD study is helpful, but does not completely resolve the issue.

Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: the START study.

BACKGROUND: The development of a totally subcutaneous implantable defibrillator (S-ICD) system requires a new approach for arrhythmia detection. To evaluate arrhythmia discrimination of one such system, the Subcutaneous versus Transvenous Arrhythmia Recognition Testing (START) study was designed as a prospective, multicenter trial comparing simulated sensing performances of the S-ICD system with single- (SC-TV) and dual-chamber transvenous (DC-TV) implantable cardioverter-defibrillator (ICD) systems. METHODS: At ICD implantation, induced ventricular and atrial arrhythmias were recorded simultaneously in transvenous (right ventricular [RV] → superior vena cava [SVC]+ Coil) and cutaneous electrode configurations. Recorded signals of ventricular (n = 46) and atrial arrhythmias (n = 50) with ventricular rates >170 bpm from 64 patients were used to compare detection performance of the S-ICD system with TV-ICD systems from 3 manufacturers. Appropriate detection of ventricular tachyarrhythmias was assessed with devices programmed in single-zone (rate ≥ 170 bpm) and dual-zone configurations (ventricular fibrillation ≥ 240 bpm; ventricular tachycardia ≥ 170 bpm). S-ICD specificity performance for supraventricular arrhythmias was compared to single- and dual-chamber devices in a dual-zone configuration. RESULTS: Appropriate detection of ventricular tachyarrhythmias for subcutaneous and TV devices in single- and dual-zone configurations was 100% and >99%, respectively. Specificity for supraventricular arrhythmias was significantly better for the S-ICD system compared to 2 of 3 TV systems, as well as the composite of TV devices (98.0%[S-ICD] vs 76.7%[SC-TV range: 64.0-92.0%] vs 68.0%[DC-TV range: 32.7-89.8%; P < 0.001]). CONCLUSION: Appropriate ventricular arrhythmia detection is excellent for all ICD systems evaluated; however, specificity of supraventricular arrhythmia discrimination by the S-ICD system is better than discrimination by 2 of 3 TV systems.

A prospective, randomized comparison of the acute hemodynamic effects of biventricular and left ventricular pacing with cardiac resynchronization therapy.

BACKGROUND: Cardiac resynchronization therapy (CRT) is most commonly performed with biventricular (BiV) pacing. Left ventricular (LV) only pacing is an alternative pacing configuration for CRT, but comparative studies with BiV pacing have shown inconsistent results. This may be due to differences in LV activation pattern, which could be differentially affected by atriventricular (AV) programming or atrial pacing (AP). OBJECTIVE: The purpose of this study was to compare AV optimization and the effect of atrial overdrive pacing on the acute hemodynamic response of LV and BiV CRT. METHODS: This study included 28 patients undergoing CRT. At implant, invasive LV dP/dt was measured by a micromanometer catheter during BiV or LV pacing in atrial sensing (AS) and AP modes at five different AV delays (AVDs), tested in randomized order. RESULTS: Compared with intrinsic rhythm, CRT with AS increased LV dP/dt by 12% ± 10% during LV pacing and by 11% ± 11% during BiV pacing (P = .15). With atrial overdrive pacing, CRT increased LV dP/dt by 17% ± 10% with LV pacing and by 17% ± 11% during BiV pacing (P = NS vs. LV; P <.001 vs. AS). The optimal AVD was significantly longer with AP (LV 202 ± 63 ms vs. 131 ± 42 ms during AS; BiV 195 ± 71 ms vs. 134 ± 43 ms during AS) but did not differ between LV and BiV pacing. CONCLUSION: In this study, AP increases LV dP/dt during CRT but requires a substantially longer AVD. However, the optimal AVDs were similar for LV and BiV as were the magnitudes of the responses during CRT, suggesting that programmed AVDs are interchangeable in these two configurations.

Defibrillation thresholds in hypertrophic cardiomyopathy.

BACKGROUND: Defibrillation threshold (DFT) testing is performed in part to ensure an adequate safety margin for the termination of spontaneous ventricular arrhythmias. Left ventricular mass is a predictor of high DFTs, so patients with hypertrophic cardiomyopathy (HCM) are often considered to be at risk for increased defibrillation energy requirements. However, there are little prospective data addressing this issue. OBJECTIVE: To assess DFTs in patients with HCM and evaluate the clinical predictors of elevated DFTs. METHODS: Eighty-nine consecutive patients with HCM and 600 control patients with ischemic or nonischemic cardiomyopathy underwent a uniform modified step-down DFT testing protocol. DFT was compared between the control and HCM populations. Predictors of elevated DFT were evaluated in the HCM group. RESULTS: There was no difference in DFT between HCM and control groups (10.4 ± 5.8 J vs 11.2 ± 5.6 J, respectively). Among patients with HCM, clinical parameters such as left ventricular ejection fraction, interventricular septal thickness, left ventricular mass, and QRS duration were not predictive of an elevated DFT. Only 3 patients (3.4%) with HCM had a DFT >20 J. CONCLUSION: Patients with HCM do not have elevated DFTs as compared to more typical populations undergoing implantable cardioverter-defibrillator implant; high-energy devices or complex lead systems are not needed routinely in this population.

Randomized comparison of defibrillation thresholds from the right ventricular apex and outflow tract.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) leads are traditionally placed in the right ventricular apex (RVA), in part because this is considered the preferred vector for minimizing defibrillation threshold (DFT). However, if adequate DFT safety margins are attainable, ICD leads placed in the right ventricular outflow tract (RVOT) might confer advantages if frequent ventricular pacing is anticipated. OBJECTIVE: The purpose of this study was to compare RVA with RVOT transvenous ICD lead position on DFT. METHODS: This was a prospective, randomized, crossover study of RVA versus RVOT DFT in 33 patients undergoing left pectoral ICD placement. A binary search algorithm was used to measure DFT, with initial lead position tested in randomized order. The relationship between RVOT position and DFT was assessed by evaluation of the distance between RVA and RVOT. RESULTS: The study population had a mean age of 59 ± 12 years and ejection fraction of 33% ± 14%. Mean DFT in the RVA was 9.8 ± 7.3 J versus 10.8 ± 7.2 J in the RVOT (P = .53), with no correlation between RVOT location and DFT. CONCLUSION: The study found no evidence that ICD lead placement in the RVOT is associated with significantly higher DFT than lead placement in the RVA.

Role of transesophageal echocardiography among patients with atrial fibrillation undergoing electrophysiology testing.

External or internal shocks administered to terminate ventricular arrhythmias as a part of electrophysiology or implantable cardioverter-defibrillator testing, can inadvertently cardiovert atrial fibrillation (AF). Moreover, anticoagulation therapy is often withheld in these patients in anticipation of an invasive procedure. The risk of embolic events during these procedures has not been well described. Accordingly, the present study was a prospective evaluation of the incidence of left atrial (LA) thrombus and AF cardioversion among patients undergoing ventricular arrhythmia assessment. Transesophageal echocardiography was routinely performed on 44 consecutive patients in AF with subtherapeutic anticoagulation undergoing electrophysiology or implantable cardioverter-defibrillator testing. Arrhythmia induction was not performed when LA thrombus was present. The incidence and clinical predictors of thrombus, the inadvertent cardioversion of AF, and adverse events related to the procedure were assessed during the subsequent 4 to 6 weeks. Left atrial thrombus was observed in 12 patients (27%). Sinus rhythm was restored in 29 patients (91%), at least transiently, who underwent testing with a shock delivered. No adverse neurologic or hemorrhagic complications were observed. Univariate analysis identified no predictors of LA thrombus or cardioversion to sinus rhythm. In conclusion, LA thrombus and cardioversion to sinus rhythm are common among patients with AF undergoing an evaluation of ventricular arrhythmias. Transesophageal echocardiography performed before the procedure in patients with subtherapeutic anticoagulation is warranted to minimize embolic complications. This strategy appears to be a safe method to guide diagnostic testing in this patient population.

The effect of dofetilide on ventricular defibrillation thresholds.

INTRODUCTION: High defibrillation threshold (DFT) with an inadequate defibrillation safety margin remains an infrequent but troubling problem associated with defibrillator implantation. Dofetilide is a selective class III antiarrhythmic drug that reduces DFTs in a canine model. We hypothesized that dofetilide would reduce DFTs in humans, obviating the need for complex lead systems. METHODS AND RESULTS: Sixteen consecutive patients with DFTs > or =20 J delivered energy at implant-received dofetilide therapy and underwent follow-up DFT testing acutely following drug loading and/or chronically (128 +/- 94 days). Amiodarone was discontinued in four patients at implantation. With dofetilide, DFTs decreased from 28 +/- 4 J to 19 +/- 7 J (P < 0.0001), resulting in a safety margin of 15 +/- 8 J for the implanted devices. Five patients subsequently had spontaneous arrhythmias terminated successfully with shocks. CONCLUSION: Dofetilide reduces DFTs sufficiently to prevent the need for more complex lead systems. This strategy should be considered when an inadequate defibrillation safety margin is present.

Implantable cardioverter-defibrillator therapy for primary prevention of sudden death after alcohol septal ablation of hypertrophic cardiomyopathy.

OBJECTIVES: The purpose of this study was to examine the effects of alcohol septal ablation (ASA) on ventricular arrhythmias among patients with obstructive hypertrophic cardiomyopathy (HCM), as measured by appropriate implantable cardioverter-defibrillator (ICD) discharges. BACKGROUND: Alcohol septal ablation is an effective therapy for patients with symptomatic HCM. However, concern has been raised that ASA may be proarrhythmic secondary to the iatrogenic scar created during the procedure. The impact of ASA on ventricular arrhythmias has not been well described. METHODS: This prospective study included 123 consecutive patients with obstructive HCM who underwent ASA and had an ICD implanted for primary prevention of sudden cardiac death (SCD). The ICDs were implanted based on commonly accepted risk factors for SCD in the HCM population. Data from ICD interrogations during routine follow-up were collected. RESULTS: Nine appropriate ICD shocks were recorded over a mean follow-up of 2.9 years in the cohort, which had a mean of 1.5 +/- 0.9 risk factors for SCD. Using Kaplan-Meier survival analysis, the estimated annual event rate was 2.8% over 3-year follow-up. There were no significant differences in the incidence of risk factors between patients who did and did not receive appropriate shocks. CONCLUSIONS: The annual rate of appropriate ICD discharges after ASA is low and less than that reported previously for primary prevention of SCD in HCM. This suggests that ASA is not proarrhythmic. Traditional SCD risk factors did not predict ICD shocks in this cohort.

A prospective comparison of AV delay programming methods for hemodynamic optimization during cardiac resynchronization therapy.

INTRODUCTION: There are several methods for programming the optimal AV delay (AVD) during cardiac resynchronization therapy (CRT). These include Doppler echocardiographic measurements of mitral inflow or aortic outflow velocities, an arbitrarily fixed AVD, and calculations based on intracardiac electrogram (EGM) intervals. The present study was designed to compare the acute effects of AVD programming methods during CRT. METHODS AND RESULTS: We studied 28 patients at CRT implant with invasive measurements of LV dP/dt to determine the effect of AVD during atrial sensed (AS) and atrial paced (AP) modes. The optimal AVD, defined as that resulting in the maximal LV dP/dt, was then compared with that predicted by several noninvasive methods. CRT increased LV dP/dt 11% +/- 11% during AS (heart rate: 73 +/- 14 bpm) and 17% +/- 12% during AP (heart rate: 86 +/- 12 bpm) (P < 0.001 vs AS). There was an excellent correlation between the EGM method and the maximum achievable LV dP/dt (AS: R2 = 0.99, P < 0.0001, AP: R2 = 0.96, P < 0.0001) and this method performed better than other techniques. CONCLUSIONS: An electrogram-based optimization method accurately predicts the optimal AVD among patients over a wide range of QRS intervals during CRT in both AS and AP modes. This simple technique may obviate the need for echocardiography for AVD programming.