Programming Cardiac Resynchronization Therapy for Electrical Synchrony: Reaching Beyond Left Bundle Branch Block and Left Ventricular Activation Delay

How to maximize QRS narrowing

BACKGROUND

Cardiac resynchronization therapy (CRT) resulting in maximal QRS narrowing may be associated with improved outcomes.

METHODS

Various atrioventricular (AV) delay settings, including the new SyncAV™ algorithm (St. Jude Medical/Abbott, St. Paul, MN, USA), aimed at maximal QRS narrowing were tested in an 81-year old CRT recipient.

RESULTS

Maximal QRS narrowing from 160 to 100 ms was achieved with a manually programmed value of SyncAV™ -30 ms. At 2 months, the patient proved to be a CRT super-responder.

CONCLUSION

SyncAV™ algorithm is a new way for effective QRS narrowing with potentially improved outcomes.

Electrocardiographic optimization techniques in resynchronization therapy

Cardiac resynchronization therapy (CRT) is a cornerstone of therapy for patients with heart failure, reduced left ventricular (LV) ejection fraction, and a wide QRS complex. However, not all patients respond to CRT: 30% of CRT implanted patients are currently considered clinical non-responders and up to 40% do not achieve LV reverse remodelling. In order to achieve the best CRT response, appropriate patient selection, device implantation, and programming are important factors. Optimization of CRT pacing intervals may improve results, increasing the number of responders, and the magnitude of the response. Echocardiography is considered the reference method for atrioventricular and interventricular (VV) intervals optimization but it is time-consuming, complex and it has a large interobserver and intraobserver variability. Previous studies have linked QRS shortening to clinical response, echocardiographic improvement and favourable prognosis. In this review, we describe the electrocardiographic optimization methods available: 12-lead electrocardiogram; fusion-optimized intervals (FOI); intracardiac electrogram-based algorithms; and electrocardiographic imaging. Fusion-optimized intervals is an electrocardiographic method of optimizing CRT based on QRS duration that combines fusion with intrinsic conduction. The FOI method is feasible and fast, further reduces QRS duration, can be performed during implant, improves acute haemodynamic response, and achieves greater LV remodelling compared with nominal programming of CRT.

Maximizing biventricular pacing in patients with rate-controlled atrial fibrillation using ventricular sense response

In patients with atrial fibrillation (AF), cardiac resynchronization therapy (CRT) is challenging because the ventricular rate of conducted AF exceeds the biventricular pacing rate. In the current report, we present a patient who received a CRT device that was programmed to ventricular sense response (VSR) on with VVI 40 beats per minute to allow the AF to be paced as fusion beats. We found that the pacing configuration resulting in the narrowest QRS in this patient was VVI 40 with VSR biventricular fusion pacing during AF. VSR mode allows for CRT delivery without the need to artificially increase heart rate.

Outcome of resynchronization therapy on superficial and endocardial electrophysiological findings

Cardiac resynchronization therapy (CRT) has proven efficacious in the treatment of patients with heart failure and dyssynchronous activation. Currently, we select suitable CRT candidates based on the QRS complex duration (QRSd) and morphology with left bundle branch block being the optimal substrate for resynchronization. To improve CRT response rates, recommendations emphasize attention to electrical parameters both before implant and after it. Therefore, we decided to study activation times before and after CRT on the body surface potential maps (BSPM) and to compare thus obtained results with data from electroanatomical mapping using the CARTO system. Total of 21 CRT recipients with symptomatic heart failure (NYHA II-IV), sinus rhythm, and QRSd >/=150 ms and 7 healthy controls were studied. The maximum QRSd and the longest and shortest activation times (ATmax and ATmin) were set in the BSPM maps and their locations on the chest were compared with CARTO derived time interval and site of the latest (LATmax) and earliest (LATmin) ventricular activation. In CRT patients, all these parameters were measured during both spontaneous rhythm and biventricular pacing (BVP) and compared with the findings during the spontaneous sinus rhythm in the healthy controls. QRSd was 169.7+/-12.1 ms during spontaneous rhythm in the CRT group and 104.3+/-10.2 ms after CRT (p<0.01). In the control group the QRSd was significantly shorter: 95.1+/-5.6 ms (p<0.01). There was a good correlation between LATmin(CARTO) and ATmin(BSPM). Both LATmin and ATmin were shorter in the control group (LATmin(CARTO) 24.8+/-7.1 ms and ATmin(BSPM) 29.6+/-11.3 ms, NS) than in CRT group (LATmin(CARTO) was 48.1+/-6.8 ms and ATmin(BSPM) 51.6+/-10.1 ms, NS). BVP produced shortening compared to the spontaneous rhythm of CRT recipients (LATmin(CARTO) 31.6+/-5.3 ms and ATmin(BSPM) 35.2+/-12.6 ms; p<0.01 spontaneous rhythm versus BVP). ATmax exhibited greater differences between both methods with higher values in BSPM: in the control group LATmax(CARTO) was 72.0+/-4.1 ms and ATmax (BSPM) 92.5+/-9.4 ms (p<0.01), in the CRT candidates LATmax(CARTO) reached only 106.1+/-6.8 ms whereas ATmax(BSPM) 146.0+/-12.1 ms (p<0.05), and BVP paced rhythm in CRT group produced improvement with LATmax(CARTO) 92.2+/-7.1 ms and ATmax(BSPM) 130.9+/-11.0 ms (p<0.01 before and during BVP). With regard to the propagation of ATmin and ATmax on the body surface, earliest activation projected most often frontally in all 3 groups, whereas projection of ATmax on the body surface was more variable. Our results suggest that compared to invasive electroanatomical mapping BSPM reflects well time of the earliest activation, however provides longer time-intervals for sites of late activation. Projection of both early and late activated regions of the heart on the body surface is more variable than expected, very likely due to changed LV geometry and interposed tissues between the heart and superficial ECG electrode.