![ELECTROPHYSIOLOGICAL RESPONSES
• Both HBP and BVP significantly shortened 12-lead
ECG QRSd (-33.7 ms; 95% confidence interval [CI]:
46.1 to -21.3 ms; p < 0.001; -17 ms; 95% CI: -27.3 to
-7.1 ms; p = 0.002, respectively).
• HBP resulted in significantly more QRS shortening
compared with BVP: the mean within-patient change
in QRSd from BVP to HBP was -18.6 ms (95% CI: -
31.6 to -5.7 ms; p = 0.007).
• Using noninvasive epicardial mapping, both His
bundle and BVP significantly reduced LVAT-95
compared with intrinsic activation (43.3 ms; 95% CI:
-51.7 to -34.8 ms; p < 0.001; -16.7 ms; 95% CI: -29.1
to -4.4 ms; p = 0.01, respectively).
• HBP reduced LVAT-95 significantly more than BVP:
the mean within-patient change in LVAT-95 from
BVP to HBP was -26.4 ms (95% CI: -41.2 to -11.6
ms; p = 0.02).](https://image.slidesharecdn.com/hisresynchronizationversus-190109143610/85/His-Resynchronization-Versus-Biventricular-Pacing-in-Patients-With-Heart-Failure-and-Left-Bundle-Branch-Block-16-320.jpg)
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His Resynchronization Versus Biventricular Pacing in Patients With Heart Failure and Left Bundle Branch Block
- 1. His Resynchronization Versus Biventricular Pacing in Patients With Heart Failure and Left Bundle Branch Block DOI: 10.1016/j.jacc.2018.09.073 December 18, 2018
- 2. Background • Left bundle branch block (LBBB) is deleterious in patients with heart failure. • Biventricular pacing improves the activation pattern, instantly shortening left ventricular activation time (LVAT) and immediately improving cardiac function. • Relative to native LBBB, biventricular pacing (BVP) was found to shorten QRS duration (QRSd) and left ventricular activation time (LVAT), earning it the moniker of “cardiac resynchronization therapy” (CRT).
- 3. • In fact, BVP results in the fusion of 2 nonphysiological wave fronts, resulting in only modest reductions in QRSd. • His bundle pacing (HBP) has the potential to offer greater ventricular resynchronization because large reductions in QRSd have been observed when stimulating the His-Purkinje system in patients with LBBB. • This study tested the ability of HBP to deliver resynchronization and then compared the electromechanical effects of His resynchronization against conventional BVP, using high-precision hemodynamic assessment and noninvasive epicardial ventricular activation mapping
- 4. METHODS STUDY POPULATION • Patients at a single tertiary cardiac center (Hammersmith Hospital, London, United Kingdom) scheduled for conventional biventricular pacemaker implantation with or without defibrillator were recruited.
- 5. Inclusion Criteria • LBBB with QRSd >130 ms, • Ejection fraction <35%, and • New York Heart Association functional class II to IV
- 6. Exclusion Criteria • Patients who were unable to give consent, • Clinically unstable patients
- 7. NONINVASIVE EPICARDIAL ELECTRICAL MAPPING (ECGI) • Patients were fitted with a 252-electrode ECGI vest (Medtronic, Minneapolis, Minnesota) before the procedure and underwent low-dose thoracic computed tomography to acquire electrode and cardiac positions. • Continuous ECGI recordings were obtained throughout the hemodynamic study. • From the individual electrogram activations, the left ventricular (LV) total activation time was calculated.
- 8. • By calculating the shortest interval that spans 95% of activations recorded from the left ventricle (LVAT-95),the potential skewing of LV total activation time were minimized. • Left ventricular dyssynchrony index (LVDI) was also calculated as the standard deviation of individual activations recorded from the LV, which has been proposed as a measure of intraventricular dyssynchrony. • For each ventricular activation parameter, the average of 5 beats each was taken for AAI pacing, HBP, and BVP.
- 9. PACING • Temporary HBP was achieved via either the femoral or subclavian approach. • If the femoral route was used, a quadripolar electrophysiology catheter was placed on the bundle of His, and a second catheter was positioned in the right atrial appendage for sequential atrial followed by His (AH) pacing. • If the subclavian route was used, a SelectSecure 3830 lead was delivered via either a C304-His deflectable sheath or C315 fixed curve sheath.
- 10. • The atrial lead for the CRT device was used to allow AH sequential pacing. • The atrial and His leads were connected to the Micropace pacing system (Micropace EP, Santa Ana, California) that allowed pacing at selected AH delays. • The Micropace pacing output was programmed to 25 mA for all patients. • HBP was attempted from the right atrium in its typical location at the anteroseptal atrioventricular (AV) groove and the His bundle was located using the electrogram (EGM) signal obtained from the catheter/lead.
- 11. • His bundle capture was confirmed by analysis of the 12-lead surface ECG and the catheter/lead EGM. • If pacing produced a QRS morphology similar to the intrinsic (unpaced) QRS, without shortening of the QRSd, the lead was repositioned. • Data were only included for analysis if HBP resulted in a shortening of LVAT by at least 10 ms. • Biventricular pacing was performed via the CRT device, which was implanted using the standard clinical technique.
- 12. ACUTE HEMODYNAMIC STUDY • Invasive beat-by-beat blood pressure was recorded from the femoral or radial artery, depending on patient preference. • Some patients agreed to the study protocol but declined the additional invasive monitoring. In these patients, noninvasive beat-by-beat blood pressure was acquired. • The hemodynamic data were acquired alongwith surface ECG data using a data acquisition system (National Instruments, Austin, Texas) and recorded using customized software.
- 13. RESULTS • Twenty-three patients were recruited. • In 4 patients, temporary HBP did not shorten LVAT-95 by ≥10 ms, and these patients were therefore excluded from the main analysis. • In 1 patient, a technical fault prevented acquisition of ECGI data, and they were therefore also excluded from the analysis. • Eighteen patients therefore demonstrated the 10-ms LVAT-95 shortening required by definition of His resynchronization. • In 1 of them, ECGI data could be collected during His pacing, but not during BVP & therefore also excluded from the analysis.
- 14. • Therefore, the full dataset of ECGI and hemodynamic data for both HBP and BVP was available in 17 patients. • Six had a history of a previous myocardial infarction, and the remainder were diagnosed with nonischemic cardiomyopathy.
- 16. ELECTROPHYSIOLOGICAL RESPONSES • Both HBP and BVP significantly shortened 12-lead ECG QRSd (-33.7 ms; 95% confidence interval [CI]: 46.1 to -21.3 ms; p < 0.001; -17 ms; 95% CI: -27.3 to -7.1 ms; p = 0.002, respectively). • HBP resulted in significantly more QRS shortening compared with BVP: the mean within-patient change in QRSd from BVP to HBP was -18.6 ms (95% CI: - 31.6 to -5.7 ms; p = 0.007). • Using noninvasive epicardial mapping, both His bundle and BVP significantly reduced LVAT-95 compared with intrinsic activation (43.3 ms; 95% CI: -51.7 to -34.8 ms; p < 0.001; -16.7 ms; 95% CI: -29.1 to -4.4 ms; p = 0.01, respectively). • HBP reduced LVAT-95 significantly more than BVP: the mean within-patient change in LVAT-95 from BVP to HBP was -26.4 ms (95% CI: -41.2 to -11.6 ms; p = 0.02).
- 17. • Using a 1-way analysis of variance, the standard deviation of LVAT-95 measurements during HBP was 6.6 ms, and the standard deviation of the difference for change in LVAT-95 was 9.2 ms. • Both HBP and BVP significantly reduced the LVDI (-17.0 ms; 95% CI:-21.9 to -12.0 ms; p < 0.001; -5.73 ms; 95% CI: -11.1 to -0.3 ms; p=0.04). • HBP reduced LVDI significantly more than BVP: the mean within-patient change in LVDI from BVP to HBP was -11.3 ms (95% CI: -16.8 to -5.6 ms; p < 0.001)
- 18. HEMODYNAMIC RESPONSES • Both His bundle and BVP significantly increased acute SBP compared with AAI pacing (12.4 mm Hg; 95% CI: 8.6 to 16.2 mm Hg; p < 0.001; 7.8 mm Hg; 95% CI: 4.2 to 11.4 mm Hg; p < 0.001, respectively) • The improvement in SBP was significantly higher with HBP than with BVP (4.6 mm Hg; 95% CI: 0.2 to 9.1 mm Hg; p = 0.04)
- 19. RELATIONSHIP BETWEEN ELECTRICAL AND HEMODYNAMIC RESPONSE • There was a significant correlation (R2= 0.49, R = 0.70; p = 0.04) (Figure 7) between the individual patient incremental shortening of LVAT (LVAT-95) achieved by HBP over BVP against the incremental increase in blood pressure achieved by HBP over BVP. • By contrast, the correlation between 12-lead QRSd reduction and hemodynamic response was not significant (p = 0.119).
- 20. DISCUSSION • In this study we have quantified the acute effect of cardiac resynchronization therapy delivered with HBP, using high-precision hemodynamic measurements, and performed within-patient comparisons with BVP. • We found that His resynchronization therapy delivers significantly greater improvements in acute hemodynamic response than BVP. • The additional improvements in hemodynamic function appear to be driven by improvements in ventricular activation time occurring as a result of more effective ventricular resynchronization.
- 21. ACUTE HEMODYNAMIC RESPONSE • We found that HBP successfully delivered ventricular resynchronization in 83% of patients & this His resynchronization therapy resulted in significantly greater improvements in acute hemodynamic function compared with BVP. • His resynchronization therapy delivered approximately a 60% increase in acute SBP, compared with BVP (4.6 mm Hg additional His- resynchronization SBP improvement over the 7.8 mm Hg with BVP). • BVP is the current gold standard method for delivering CRT & Hemodynamic studies have consistently demonstrated acute improvements when BVP is delivered to patients with LBBB and LV impairment and subsequent longer-term studies have confirmed reductions in morbidity and mortality.
- 22. MECHANISM OF IMPROVEMENT WITH HIS RESYNCHRONIZATION THERAPY • The correlation between activation time shortening and acute hemodynamic response suggests that the improved hemodynamic response with HBP is driven by more effective ventricular resynchronization. • BVP therapy appears to deliver some of its beneficial effect by improving atrioventricular timing, and the same would be expected of HBP, which may explain the smaller percentage improvement in hemodynamic response compared with the magnitude of intraventricular electrical synchronization.
- 23. • The ventricular activation maps obtained during His pacing typically showed resolution of the LBBB activation pattern seen during intrinsic conduction & this supports the concept that His resynchronization is achieved by recruiting LV conduction fibers. • By contrast, BVP produces nonphysiological activation patterns & Biventricular pacing is not a perfect resynchronization tool: relying on slow cell-to-cell conduction limits the degree of ventricular resynchronization that can be achieved. • Indeed, BVP induces ventricular dyssynchrony when applied to patients with a narrow QRS, resulting in worse clinical outcomes.
- 24. • His pacing has other potential advantages compared with BVP. It does not require the use of contrast and is not limited by diaphragmatic capture or the constraints of the coronary sinus anatomy.
- 25. POSSIBLE MECHANISMS BY WHICH HBP IMPROVES ACTIVATION TIMES • The simplest explanation is that the pacing lead is positioned distal to the site of block, thus recruiting distal conduction fibers that are longitudinally dissociated(electrical bypass). (This would not explain how shortening is achieved when the lead is apparently located proximal to the block, because HBP is usually achieved from the right atrium, whereas the anatomic site of block may be below the bundle of His, within the ventricles.)
- 26. • Therefore, alternative explanations argue that although the lead is not anatomically distal to the block, electrical energy is nevertheless applied to distal conduction fibers either through a large volume of myocardium encompassed by the pacing stimulus (virtual electrode hypothesis) or high energy (source–sink hypothesis). • Another possible explanation is that distal fibers may unfurl back proximally, closer to the lead, resulting in retrograde activation up these fibers.
- 27. STUDY LIMITATIONS • The study has many fewer patients than a long-term event trial. • This study was not specifically powered to discriminate different responses of ischemic and nonischemic cardiomyopathies to HBP. • This was an acute hemodynamic study. So, we do not know if the significant improvements in activation time and acute hemodynamic response we observed will translate into better hemodynamic outcomes with longer-term follow-up. • Although noninvasive ECGI mapping provides high-resolution data of activation and allows segregation of regional activation, there are potential problems including assumptions of static geometry and interpolation accuracy.
- 28. CONCLUSIONS • CRT delivered using HBP appears to be a very promising alternative to BVP in patients with LBBB and heart failure. • It can deliver larger reductions in ventricular activation time, which leads to significantly greater improvements in acute hemodynamic function. • The magnitude of these improvements suggest that His resynchronization therapy has the potential to produce better clinical outcomes than BVP.
- 29. Thank You
Editor's Notes
- #3: LVAT= Left Ventricular Activation Time