His-Optimized Cardiac Resynchronization Therapy With Ventricular Fusion Pacing for Electrical Resynchronization in Heart Failure.

OBJECTIVES: This study sought to evaluate the effectiveness of His-optimized cardiac resynchronization therapy (HOT-CRT) for reducing left ventricular activation time (LVAT) compared to His bundle pacing (HBP) and biventricular (BiV) pacing (including multipoint pacing [MPP]), using electrocardiographic (ECG) imaging. BACKGROUND: HBP may correct bundle branch block (BBB) and has shown encouraging results for providing CRT. However, HBP does not correct BBB in all patients and may be combined with univentricular or BiV fusion pacing to deliver HOT-CRT to maximize resynchronization. METHODS: Nineteen patients with a standard indication for CRT, implanted with HBP without correction of BBB and BiV (n = 14) or right ventricular (n = 5) leads, were prospectively enrolled. Patients underwent ECG imaging while pacing in different configurations using different LV electrodes and at different HBP ventricular pacing (VP) delays. The primary endpoint was reduction in LVAT with HOT-CRT, and the secondary endpoints included various other dys-synchrony measurements including right ventricular activation time (RVAT). RESULTS: Compared to HBP, HOT-CRT reduced LVAT by 21% (-17 ms [95% confidence interval [CI]: -25 to -9 ms]; p < 0.001) and outperformed BiV by 24% (-22 ms [95% CI: -33 to -10 ms]; p = 0.002) and MPP by 13% (-11 ms [95% CI: -21 to -1 ms]; p = 0.035). Relative to HBP, HOT-CRT also reduced RVAT by 7% (-5 ms [95% CI: -9 to -1 ms; p = 0.035) in patients with right BBB, whereas RVAT was increased by BiV. The other electrical dyssynchrony measurements also improved with HOT-CRT. CONCLUSIONS: HOT-CRT acutely improves ventricular electrical synchrony beyond BiV and MPP. The impact of this finding needs to be evaluated further in studies with clinical follow-up. (Electrical Resynchronization and Acute Hemodynamic Effects of Direct His Bundle Pacing Compared to Biventricular Pacing; NCT03452462).

Cryoablation vs. radiofrequency ablation of the atrioventricular node in patients with His-bundle pacing.

AIMS: Radiofrequency ablation (RFA) of the atrioventricular node (AVN) with His-bundle pacing (HBP) can cause rise in capture thresholds. Cryoablation (CRYO) may offer reversibility in case of threshold rise but has never been tested for AVN ablation in this setting. Our aim was to compare procedural characteristics and outcome of CRYO compared with RFA for AVN ablation in patients with HBP. METHODS AND RESULTS: Forty-four patients with HBP underwent AVN ablation for an 'ablate and pace' indication. Cryoablation was performed in the first 22 patients and RFA in the following 22 patients. Procedural characteristics, success rates, and change in His capture thresholds were compared between groups. Distance from the ablation site to the His lead was measured using biplane fluoroscopy. Acute success was 100% with both strategies. Median procedural duration was significantly longer for CRYO {50 [interquartile range (IQR) 38-63] min} compared with RFA [36 (IQR, 30-41) min; P = 0.027]. An acute threshold rise of ≥1 V was observed in four CRYO (one complete loss of capture) and three RFA patients (P = 0.38), with all of the applications being within 6 mm of the His lead tip. During follow-up, nine patients had AVN re-conduction (six CRYO vs. three RFA; P = 0.58), but only four patients required a redo procedure (all CRYO; P = 0.09). CONCLUSION: Cryoablation does not offer any advantage over RFA for AVN ablation in patients with HBP and tended to require more redo procedures. If possible, a distance of ≥6 mm should be maintained from the His lead tip to avoid a rise in capture thresholds.

His bundle pacing to avoid electrical dyssynchrony with traditional right ventricular pacing: Importance of heart size.

BACKGROUND: His Bundle Pacing (HBP) is attracting interest as an alternative to traditional right ventricular pacing (RVP) because it avoids electrical dyssynchrony induced by RVP. This study aims to evaluate the effect of heart size on benefit from HBP compared to RVP in terms of achieving electrical synchrony. METHODS: Fifty-nine patients with HBP and a RVP back-up lead underwent pre-implantation echocardiography to measure left ventricular end-diastolic volume (LVEDV). Electrical benefit from HBP was calculated as the difference in QRS duration (QRSd) between RVP and HPB. RESULTS: LVEDV was significantly correlated with RVP QRSd (R = 0.53; p < 0.001). In contrast, LVEDV was unrelated to HBP QRSd (R = 0.16; p = 0.24). Electrical benefit of HBP over RVP was directly related with LVEDV (R = 0.43; p = 0.001). In addition, electrical benefit of HBP was larger for patients with LVEDV above median (99 mL) than below (49 ± 27 ms vs. 34 ± 19 ms, p = 0.014). CONCLUSIONS: This study is the first to demonstrate that patients with larger LV size may benefit most from HBP as a replacement of traditional RVP to avoid electrical dyssynchrony. Our results indicate that LV size impacts QRSd during RVP with slow cell-to-cell conduction, whereas it does not affect electrical synchrony during HBP with fast His-Purkinje conduction.

Electrical parameters with His-bundle pacing: Considerations for automated programming.

BACKGROUND: Programming of His-bundle pacing may be challenging because current implantable pulse generators are not specifically designed for this pacing modality. OBJECTIVE: The purpose of this study was to evaluate electrical parameters in order to propose preset programming options with different configurations. METHODS: Data were collected from 50 patients with His pacing leads connected to various ports (atrial, right ventricular, or left ventricular) of pacemakers and defibrillators during a detailed device interrogation, which included capture thresholds with various pacing vectors, measurement of timing intervals, and performance of automatic threshold algorithms. RESULTS: His-bundle pacing thresholds were significantly lower during unipolar pacing compared to bipolar and extended bipolar polarities. However, current drain was offset due to lower impedance. The His pace-right ventricular sensed intervals were measured at 40-150 ms (mean 85 ± 25 ms), with the longest delays in patients with uncorrected right bundle branch block and selective His capture. This has implications for ventricular safety pacing windows (which were inactivated without evidence of crosstalk) and delays to minimize unnecessary ventricular backup pacing (which was also affected by refractory periods). The measured intervals also impacted the performance of automatic threshold algorithms, which performed differently depending on which port the His lead was connected to and did not distinguish between His and myocardial capture. CONCLUSION: Our report provides data that could serve to configure automated programming settings to simplify management of His-bundle pacing.

Automatic atrial fibrillation and flutter detection by a handheld ECG recorder, and utility of sequential finger and precordial recordings.

BACKGROUND: Handheld ECG recorders may have algorithms which automatically inform the user of presence of arrhythmia. The main objectives of this study were to evaluate the accuracy of the arrhythmia diagnosis algorithm of Beurer ME90 recorder to diagnose atrial fibrillation (AF)/flutter, and to evaluate whether recording technique (finger versus precordial) affects diagnostic performance. METHODS: Consecutive patients admitted at the cardiology ward of a tertiary care hospital were enrolled. Handheld ECG recordings were performed by holding the device between index fingers (lead I), and by applying it to the chest (modified V4, mV4), with 12­lead ECGs serving as the gold standard for presence of arrhythmia. RESULTS: A total of 127 patients were included. The automatic arrhythmia detection algorithm identified all 16 cases of AF, but specificity was poor (62-77%, with slightly better specificity of mV4 compared to lead I). Specificity improved to 84% (95% CI 76-91%) if both lead I and mV4 recordings had to be positive for diagnosis, with a positive predictive value of 48% (95% CI 30-67%). Interpretation of the tracings by an electrophysiologist was 100% specific. Atrial flutter with regular ventricular response was however missed by automatic and manual interpretation. CONCLUSIONS: The automatic arrhythmia algorithm of the BeurerME90 device has excellent sensitivity for diagnosing AF, but with low specificity. Strategies such as first recording lead I (more practical to perform), and in case of arrhythmia detection, confirming with an mV4 recording, may be applied to reduce false positive readings requiring manual confirmation by a healthcare professional.

Diagnostic accuracy of multi-lead ECGs obtained using a pocket-sized bipolar handheld event recorder.

BACKGROUND: Handheld ECG event recorders are useful for rhythm monitoring but only record a single lead, which may limit interpretation. We sought to investigate if a multi-lead ECG may be reconstituted using this device, and aimed to evaluate diagnostic accuracy. METHODS: A commercially-available handheld bipolar ECG event recorder was used to reconstruct a 9-lead ECG (leads I, II and III, V1-6). Tracings were analyzed independently by a cardiologist and a fellow. RESULTS: A total of 52 patients were evaluated. Accuracy was excellent (85-98%) for identifying atrial fibrillation, atrioventricular block, bundle branch block and left ventricular hypertrophy, but lower (77-88%) for ST-segment changes and prolonged QTc. CONCLUSIONS: A 9-lead ECG can be reconstituted using a handheld single-lead ECG event recorder, and provides good diagnostic accuracy for common findings.

RIght VErsus Left Apical transvenous pacing for bradycardia: Results of the RIVELA randomized study.

AIMS: To compare cardiac function when pacing from the right or left ventricular apex in patients with preserved left ventricular systolic function, at 1-year follow-up. METHODS: Prospective, multicentre centre randomizing conventional right ventricular apical (RVA) versus left ventricular apical (LVA) pacing using a coronary sinus lead in patients requiring ventricular pacing for bradycardia. Follow-up was performed using 3D-echocardiography at 6 and 12 months. RESULTS: A total of 36 patients (age 75.4 ± 8.7 years, 21 males) were enrolled (17 patients in the RVA group and 19 patients in the LVA group). A right ventricular lead was implanted in 8 patients in the LVA group, mainly because of high capture thresholds. There were no differences in the primary endpoint of LVEF at 1 year (60.4 ± 7.1% vs 62.1 ± 7.2% for the RVA and LVA groups respectively, P = 0.26) nor in any of the secondary endpoints (left ventricular dimensions, left ventricular diastolic function, right ventricular systolic function and tricuspid/mitral insufficiency). LVEF did not change significantly over follow-up in either group. Capture thresholds were significantly higher in the LVA group, and two patients had unexpected loss of capture of the coronary sinus lead during follow-up. CONCLUSIONS: Left univentricular pacing seems to be comparable to conventional RVA pacing in terms of ventricular function at up to 1 year follow-up, and is an option to consider in selected patients (e.g. those with a tricuspid valve prosthesis).

Low risk of electromagnetic interference between smartphones and contemporary implantable cardioverter defibrillators.

AIMS: Manufacturers of implantable cardioverter defibrillators (ICDs) recommend that cell phones be maintained at a distance of ∼15 cm from the implanted device in order to avoid risk of dysfunction due to electromagnetic interference (EMI). Data relating to this issue are outdated and do not reflect modern technology. Our aim was to evaluate whether EMI is still an issue with contemporary ICDs and smartphones. METHODS AND RESULTS: Consecutive patients implanted with a wireless-enabled ICD were tested for potential interference with two models of recent 4G smartphones in conditions intended to maximize risk of EMI. A magnet effect (due to the phone speakers) was tested by placing the smartphones in the standby mode directly over the ICD generator. The presence of EMI artefacts on the real-time electrograms was evaluated by placing the smartphones in the standby, dialling, and operating modes directly over the generator casing and over the parasternal region in the vicinity of the ventricular lead. A total of 63 patients equipped with 29 different models of single, dual, or biventricular ICDs from five major manufacturers were included. None of the patients showed any evidence of interference with the smartphones during any of the 882 tests. CONCLUSION: The risk of EMI between modern smartphones and contemporary ICDs is low. This is probably due to the filters incorporated in the ICDs and low emission by the phones, as well as the small size of the magnets in the smartphones tested. STUDY REGISTRATION: NCT02330900 (http://www.clinicaltrials.gov).

Pulmonary Vein Isolation for Paroxysmal Atrial Fibrillation Using a Circular Multipolar Ablation Catheter: Safety and Efficacy Using Low-Power Settings.

INTRODUCTION: The circular irrigated decapolar nMARQ ablation catheter designed for treating atrial fibrillation (AF) has recently been recalled following two deaths due to esoatrial fistula. Injury to the esophagus has been previously reported in up to 50% of patients using 20-25 W unipolar radiofrequency (RF) energy. Low power of 15 W has been proposed to prevent this complication, but the efficacy of this strategy to avoid AF recurrence is unknown. METHODS AND RESULTS: Consecutive patients with drug-refractory, symptomatic AF were included. Under electroanatomical navigation, the nMARQ catheter was used to isolate all PVs by applying 15 W of unipolar RF simultaneously from up to 10 poles during 40 seconds. Multiple applications were used for each vein, until isolation was achieved. Follow-up was performed after a 2-month blanking period. A total of 50 patients (37 males, age 58 ± 10 years) were included. All PVs were acutely isolated without requiring touch-up by conventional ablation catheters. Pericardial effusion occurred in two patients, of whom one required periocardiocentesis. Right phrenic nerve palsy occurred in another patient, which partially resolved. There were no cases of esophageal fistula or stroke. After a follow-up of 15 ± 4 months, AF recurred in 27/50 (54%) patients. CONCLUSION: The recurrence rate of AF with 15 W unipolar applications is high. Despite use of low power, complications such as pericardial effusion and phrenic nerve palsy may occur.

Noninvasive pacing study via pacemakers and implantable cardioverter-defibrillators for differentiating right from left atrial flutter.

BACKGROUND: Patients with atrial flutter who are implanted with a pacemaker (PM) or implantable cardioverter-defibrillator (ICD) present with the opportunity to perform a noninvasive pacing study (NIPS) using the right atrial pacing lead to differentiate right from left atrial flutter. OBJECTIVES: The purpose of this study was to study the feasibility and accuracy of NIPS to distinguish right from left atrial flutter. METHODS: We enrolled consecutive patients scheduled for an electrophysiological study or ablation procedure who were in atrial flutter and who were implanted with a PM or ICD with a functional atrial lead in the right atrial appendage. Flutter tachycardia cycle lengths (TCLs) and postpacing intervals (PPIs) were measured noninvasively via the device during the procedure. RESULTS: A total of 48 (67%) patients were studied. Right atrial flutter was present in 32 patients (of whom 29 had typical cavotricuspid isthmus-dependent flutter) and 16 (33%) patients had left atrial flutter. A PPI-TCL interval of >100 ms was 100% specific and 81% sensitive to identify left atrial flutter, with an overall accuracy of 94% and a c statistic of 0.94 (95% confidence interval 0.87-1.00). A PPI-TCL interval of ≤100 ms had a positive predictive value of 86% for diagnosing typical flutter. CONCLUSION: NIPS via PMs and ICDs with a PPI-TCL interval of >100 ms can reliably identify left atrial flutter (although we have only validated this cutoff for leads implanted in the right atrial appendage). This simple maneuver may allow planning for left-sided access and may avoid an unnecessary invasive electrophysiological study if left atrial flutter ablation is not to be considered.

Pacing of the interventricular septum versus the right ventricular apex: a prospective, randomized study.

BACKGROUND: Left ventricular (LV) function may be impaired by right ventricular (RV) apical pacing. The interventricular septum is an alternative pacing site, but randomized data are limited. Our aim was to compare ejection fraction (EF) resulting from pacing the interventricular septum versus the RV apex. METHODS: RV lead implantation was randomized to the apex or the mid-septum. LVEF and RVEF were determined at baseline and after 1 and 4 years by radionuclide angiography. RESULTS: We enrolled 59 patients, of whom 28 were randomized to the apical group and 31 to the septal group, with follow-up available in 47 patients at 1 year and 33 patients at 4 years. LVEF in the apical and in the septal groups was 55 ± 8% vs. 46 ± 15% (p=0.021) at 1 year and 53 ± 12% vs. 47 ± 15% (p=0.20) at 4 years. Echocardiography confirmed a mid-septal lead position in only 54% of patients in the septal group, with an anterior position in the remaining patients. In the septal group, LVEF decreased significantly in patients with an anterior RV lead (-10.0 ± 7.7%, p=0.003 at 1 year and -8.0 ± 9.5%, p=0.035 at 4 years), but not in patients who had a mid-septal lead. Left intraventricular dyssynchrony was significantly increased in case of an anterior RV lead. RVEF was not significantly impaired by RV pacing, regardless of RV lead position. CONCLUSIONS: Pacing at the RV septum confers no advantage in terms of ventricular function compared to the apex. Furthermore, inadvertent placement of the RV lead in an anterior position instead of the mid-septum results in reduced LV function.

Comparison of tools and techniques for implanting pacemaker leads on the ventricular mid-septum.

INTRODUCTION: Many physicians target the interventricular septum for pacemaker implantation, but the lead may inadvertently end up in an anterior position. AIMS: We sought to compare two stylet shapes to achieve mid-septal lead placement, as well as the utility of a novel right anterior oblique (RAO) fluoroscopic landmark. METHODS AND RESULTS: Patients undergoing pacemaker implantation were enrolled into four consecutive groups according to stylet shape: a standard curve [two-dimensional (2D) stylet] or with an additional distal posterior curve [three-dimensional (3D) stylet], and whether RAO fluoroscopy was used. Left oblique anterior (LAO) and postero-anterior (PA) fluoroscopic views were used in all cases. After implantation, validation of right ventricular lead position (septal vs. anterior) was performed by echocardiography. A total of 113 patients were included, of whom lead position could be validated in 106 patients. Septal position was achieved in only 10 of 22 (45%) patients in the 2D stylet group and in 17 of 23 (74%) patients in the 3D stylet group (P = 0.07) when only PA and LAO fluoroscopy were used. Results were significantly improved by additional use of RAO fluoroscopy, with successful septal placement in 25 of 28 (89%) patients in the 2D stylet + RAO group (P = 0.001) and 32 of 33 (97%) patients in the 3D stylet + RAO group (P = 0.015). CONCLUSIONS: A septal lead position was obtained in only about half of the patients when a 2D stylet was used with only LAO and PA fluoroscopic views. A 3D stylet was useful to attain the target position, and additional RAO fluoroscopy significantly improved success rate with both stylet shapes.

Biatrial pacing improves atrial haemodynamics and atrioventricular timing compared with pacing from the right atrial appendage.

AIMS: Patients with interatrial conduction delay may have suboptimal left atrioventricular (AV) timing due to delayed contraction of the left atrium with foreshortening of ventricular filling. This may be an issue in pacemaker patients, especially those requiring resychronization therapy. Pacing from the high interatrial septum (IAS) or the distal or proximal coronary sinus (CSD and CSP) may improve left AV synchrony compared with pacing from the right atrial appendage (RAA). Our aim was to compare haemodynamics of these pacing sites. METHODS AND RESULTS: A total of 24 patients undergoing radiofrequency ablation for paroxysmal atrial fibrillation were studied. Left atrial pressures were recorded in sinus rhythm, and during pacing from the RAA, IAS, CSD, CSP, and with biatrial (BiA) pacing from the IAS + CSD. Amplitudes, +dP/dT(max), and timing of the a-wave were compared between recordings. Left atrial contractility, measured by +dP/dT(max), was greatest during BiA pacing (P ≤ 0.03 for all comparisons). There was a marked reduction in delay to peak a-wave when pacing from all sites compared with the RAA, with BiA pacing yielding the shortest delay (P ≤ 0.001). However, AV conduction was shortened by all alternative pacing sites, which mitigated the anticipation of left atrial contraction with respect to ventricular activation, except for BiA pacing (P < 0.001). Pacing of the IAS did not result in any improvement in haemodynamics or AV synchrony. CONCLUSION: Multisite atrial pacing results in favourable acute atrial haemodynamics and left AV synchrony. This may be a solution in pacemaker patients with interatrial conduction delay.

Utility of the surface electrocardiogram for confirming right ventricular septal pacing: validation using electroanatomical mapping.

AIMS: When targeting the interventricular septum during pacemaker implantation, the lead may inadvertently be positioned on the anterior wall due to imprecise fluoroscopic landmarks. Surface electrocardiogram (ECG) criteria of the paced QRS complex (e.g. negativity in lead I) have been proposed to confirm a septal position, but these criteria have not been properly validated. Our aim was to investigate whether the paced QRS complex may be used to confirm septal lead position. METHODS: Anatomical reconstruction of the right ventricle was performed using a NavX® system in 31 patients (70 ± 11 years, 26 males) to validate pacing sites. Surface 12-lead ECGs were analysed by digital callipers and compared while pacing from a para-Hissian position, from the mid-septum, and from the anterior free wall. RESULTS: Duration of the QRS complex was not significantly shorter when pacing from the mid-septum compared with the other sites. QRS axis was significantly less vertical during mid-septal pacing (18 ± 51°) compared with para-Hissian (38 ± 37°, P = 0.028) and anterior (53 ± 55°, P = 0.003) pacing, and QRS transition was intermediate (4.8 ± 1.3 vs. 3.8 ± 1.3, P < 0.001, and vs. 5.4 ± 0.9, P = 0.045, respectively), although no cut-offs could reliably distinguish sites. A negative QRS or the presence of a q-wave in lead I tended to be more frequent with anterior than with mid-septal pacing (9/31 vs. 3/31, P = 0.2 and 8/31 vs. 1/31, P = 1.0, respectively). CONCLUSION: No single ECG criterion could reliably distinguish pacing the mid-septum from the anterior wall. In particular, a negative QRS complex in lead I is an inaccurate criterion for validating septal pacing.

Right ventricular systolic function and cardiac resynchronization therapy.

AIMS: The effect of cardiac resynchronization therapy (CRT) on right ventricular ejection fraction (RVEF) has not been well studied. Furthermore, it is unclear whether baseline RVEF influences response to CRT. To evaluate the acute and chronic effects of CRT on right ventricular systolic function, and to investigate whether baseline RVEF impacts response to CRT. METHODS AND RESULTS: Forty-four patients with a standard indication for CRT underwent radionuclide angiography at baseline and after at least 6 months' follow-up for measuring RVEF, right ventricular synchrony (using phase analysis), and left ventricular ejection fraction (LVEF). In addition, NYHA functional class and 6-min walking distance (6MWD) were evaluated. There were no significant acute changes in RVEF with CRT. After a mean follow-up of 9 +/- 5 months, RVEF was slightly improved (by 1.9 +/- 5.0% in absolute terms, P = 0.016), and to a lesser extent than LVEF (5.1 +/- 9.0%, P = 0.009 compared with RVEF). Right ventricular dyssynchrony was significantly improved at follow-up (P = 0.016). Patients with a baseline RVEF < or = 0.35 (n = 19) were less likely to improve in NYHA class (P = 0.016), and also tended to improve less in 6MWD and LVEF (P < 0.06). CONCLUSION: Cardiac resynchronization therapy has no acute effect on RVEF, and only slightly improves RVEF at follow-up. Patients with reduced RVEF at baseline were less likely to respond to CRT, indicating that right ventricular systolic dysfunction may play a role in patient selection.

Backup right ventricular pacing with a 0.035'' guidewire during implantation of left ventricular leads.

INTRODUCTION: During implantation of biventricular devices, manipulation of the guiding sheath during localization of the coronary sinus (CS) ostium may result in injury to the right bundle and complete heart block. A preventive measure is to implant the right ventricular (RV) lead first, though this may interfere with manipulation of the guiding sheath and dislodge the permanent lead. We tested the feasibility of backup pacing with a 0.035'' guidewire, advanced through the guiding sheath during CS localization. METHODS: One hundred six consecutive patients (mean age = 70 +/- 11 years, 81 men) undergoing biventricular device implantation were studied. A 0.035'' guidewire with an uncoated tip was advanced into the right ventricle through the guiding sheath, and unipolar capture threshold, R-wave sensing amplitude, and pacing impedance were measured. RESULTS: RV pacing was successful in all patients. The mean capture threshold was 3.8 +/- 2.1 V/0.5 ms, R-wave amplitude 5.4 +/- 4.3 mV, and pacing impedance 226 +/- 78 Omega. No arrhythmia was observed during the tests. Two patients developed complete heart block during the implant procedure and were successfully paced temporarily using the 0.035'' guidewire. CONCLUSION: Temporary RV pacing, using a 0.035'' guidewire within the guiding sheath, is a simple, reliable, and safe method that allows backup pacing in case of traumatic complete heart block, developing during the implantation of biventricular devices.

Improvement in cardiac sympathetic nerve activity in responders to resynchronization therapy.

AIMS: To assess changes in cardiac adrenergic activity with cardiac resynchronization therapy (CRT), and to investigate whether these changes are related to improvement in left ventricular ejection fraction (LVEF). METHODS AND RESULTS: Sixteen patients (13 males, age 66 +/- 7 years) were studied at baseline and after > or =6 months of CRT (mean follow-up 9.2 +/- 3.2 months). LVEF was assessed by nuclear angiography. Responders were defined as patients showing > or =5% absolute increase in LVEF + improvement in > or =1 NYHA class + absence of heart failure hospitalization. Cardiac sympathetic nerve activity was studied by (123)I-metaiodobenzyl-guanidine ((123)I-MIBG) scintigraphy. Responders (n = 8) showed lower (123)I-MIBG washout at follow-up when compared with non-responders (P = 0.002), indicating lower cardiac sympathetic nerve activity. The decrease in (123)I-MIBG washout at follow-up when compared with baseline was only seen in the responder group (P = 0.036). There was a moderate correlation between increase in LVEF and decrease in (123)I-MIBG washout (r = 0.52, P = 0.04). CONCLUSION: CRT induces a reduction in cardiac sympathetic nerve activity in responders, that parallels an improvement in LVEF, whereas non-responders do not show any significant changes.