Diminished Left Ventricular Dyssynchrony and Impact of Resynchronization in Failing Hearts With Right Versus Left Bundle Branch Block

ObjectivesWe compared mechanical dyssynchrony and the impact of cardiac resynchronization therapy (CRT) in failing hearts with a pure right (RBBB) versus left bundle branch block (LBBB).BackgroundCardiac resynchronization therapy is effective for treating failing hearts with conduction delay and discoordinate contraction. Most data pertain to LBBB delays. With RBBB, the lateral wall contracts early so that biventricular (BiV) pre-excitation may not be needed. Furthermore, the magnitude of dyssynchrony and impact of CRT in pure RBBB versus LBBB remains largely unknown.MethodsDogs with tachypacing-induced heart failure combined with right or left bundle branch radiofrequency ablation were studied. Basal dyssynchrony and effects of single and BiV CRT on left ventricular (LV) function were assessed by pressure-volume catheter and tagged magnetic resonance imaging, respectively.ResultsLeft bundle branch block and RBBB induced similar QRS widening, and LV function (ejection fraction, maximum time derivative of LV pressure [dP/dtmax]) was similarly depressed in failing hearts with both conduction delays. Despite this, mechanical dyssynchrony was less in RBBB (circumferential uniformity ratio estimate [CURE] index: 0.80 ± 0.03 vs. 0.58 ± 0.09 for LBBB, p < 0.04; CURE 0→1 is dyssynchronous→synchronous). Cardiac resynchronization therapy had correspondingly less effect on hearts with RBBB than those with LBBB (i.e., 5.5 ± 1.1% vs. 29.5 ± 5.0% increase in dP/dtmax, p < 0.005), despite similar baselines. Furthermore, right ventricular-only pacing enhanced function and synchrony in RBBB as well or better than did BiV, whereas LV-only pacing worsened function.ConclusionsLess mechanical dyssynchrony is induced by RBBB than LBBB in failing hearts, and the corresponding impact of CRT on the former is reduced. Right ventricular-only pacing may be equally efficacious as BiV CRT in hearts with pure right bundle branch conduction delay

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Auto-diuresis predicts return of bowel function

Purpose: Feeding a ventral hernia repair (VHR) patient before the return of bowel function (ROBF) can lead to distention and emesis. Many patients spontaneously diurese after surgery. We hypothesized that this auto-diuresis would signal ROBF. Materials and methods: A total of 395 patients who underwent open, laparoscopic, or mixed VHR were evaluated for correlation between fluid status and ROBF or discharge. ROBF within 24 hours and discharge within 24 hours or 48 hours were used as outcome measures. Results: Patients remained an average 3.59 days after surgery in the hospital and the average ROBF was on day 2.99. The first shift of ≥700 mL of urine predicted ROBF (P=0.03) and discharge (P=0.04) within 24 hours. The first shift output of ≥500 mL predicted discharge within 48 hours (P=0.02). Conclusion: Auto-diuresis after surgery is correlated to ROBF and discharge. Accurate fluid measurement can predict bowel function and allow early diet and discharge