Ongoing Search for Improved CRT Optimization Technique

October 10, 2007 By Grendel Burrell [mailto:grendel.burrell@gmail.com]

Barcelona, Spain: Currently, the most common approach to optimization of CRT device is echocardiography. However, the ideal measurements are not well standardized, and due to the number of parameters assessed, the procedure is time consuming and personnel intensive. In a study published in the October issue of the Journal of Cardiovascular Electrophysiology, Vidal and colleagues from the Thorax Institute, University of Barcelona, describe a technique for CRT V-V optimization based on electrocardiography rather than echocardiographic assessment. In a previous study, the Thorax Institute group published their observations that epicardial LV pacing generates a “pseudodelta wave” on the surface ECG (1). The “slurring” of the initial QRS upstroke presumably represents transmural myocardial conduction from the pacing site to the endocardial surface. This generally occurs over a 30-40 ms interval.

In their current study, Vidal et al included 31 consecutive patients with refractory LV failure and evidence by electrocardiograph of dyssynchrony who were referred for CRT. All patients were symptomatic NYHA class III-IV on optimal medical therapies for at least two months, had a QRS ≥ 130 ms, LVEF ≤ 35% with an end diastolic diameter ≥ 55mm, and walked < 500 meters on a 6-minute test. All patients received a biventricular pacemaker with the LV lead targeted for placement at the posterolateral LV wall. All patients received a baseline, pre CRT device implantation, transthoracic echo. The same echo exam was performed 24-72 hours post implant.

Mean age of the participants was 68 +/-10 years. 84% were males. Mean LVEF was 23 +/-6%. All patients had LBBB and the mean WRS width was 172 +/- 20 ms.

All patients underwent three optimizations with the first two occurring immediately post implant. These first two were based on electrocardiography. VV timing was assessed at LV -30 ms, simultaneous BiV pacing, and LV +30 ms. In order to determine the “optimal“ VV timing interval the investigators measured the narrowest QRS complex. The second ECG method determined the difference in time between RV stimulation to engagement of the His-Purkinje system as seen on the rapid upstroke of the QRS) and LV stimulation to His-Purkinje engagement. Using the second ECG method, the difference in RV-LV time was identified as the “optimal” V-V offset.

The “optimal” VV offset determined by tissue Doppler echo was compared to both ECG methods in which the narrowest pace QRS was identified and the difference in time between RV and LV pacing and His-Purkinje system engagement occurred.

Using echo, the authors found that 25 (80%) of 31 patients benefited most form LV-early ventricular pacing, and three patients (10%) were optimal with simultaneous BiV pacing, and three patients (10%) were optimal with RV early pacing.

Utilizing the assessment of three different VV intervals, 58% of patients had the narrowest QRS with simultaneous biventricular pacing, 26% with LV preactivation, and 16% with RV preactivation. However, when the authors examined the interventricular activation delay measurement, they found that 68% benefited from LV preactivation, 29% with simultaneous biventricular pacing, and 3% with RV preactivation.

Comparing the VV interval considered “optimal according to echo with the QRS width measurement, the data coincided in 32% of patients. When the echo results were compared with the measurement of interventricular activation delay, the data coincided in 82.6% of patients.

Whether by echo or ECG, the optimal V-V interval in most patients was LV preactivation. All patients had a LBB configuration. In this study, V-V optimization was performed with only three intervals. This was a pilot study, not randomized, and provided no information on clinical outcomes. Another limitation to using the ECG method may be the need to optimize the AV interval.

In an accompanying editorial (2) titled “A Better Mousetrap? The Search for an Improved CRT Optimization Technique”, Drs. David Spragg and Hugh Calkins, Johns Hopkins Hospital, Baltimore, note that the “disconnect between WRS width and true mechanical dyssynchrony is a likely contributor to the 1/3 nonresponder rate reported consistently” in CRT trials. They also state that as Vidal and colleagues identified that “a narrow paced WRS complex is not necessarily indicative of effective resynchronization.” Spragg and Calkins also comment on the significant requirements of time, equipment, and expertise to use echo for optimization and point out that “other techniques are likely needed for true optimization.”

The message of a need for CRT optimization continues in the September issue of American Journal of Cardiology, Vidal and colleagues from the Thorax Institute published another investigation (3) of the clinical impact of cardiac resynchronization device optimization in a series of 100 patients. In the first 49 patients, an empirical atrioventricular delay of 120 ms was set, with simultaneous biventricular stimulation (interventricular [VV] interval=0 ms). In the next 51 patients, systematic atrioventricular optimization was performed, and VV optimization by tissue Doppler-derived wall displacement was also performed, selecting 1 VV delay, either right or left ventricular preactivation (+30 or -30 ms) or simultaneous (VV interval=0 ms). At follow-up, patients who were alive without cardiac transplantation and showed improvement of ≥10% in the distance walked in the 6-minute test were considered responders. At baseline there were no differences between the 2 groups. LVEF improved in the 2 groups, but left ventricular cardiac output improved only in the optimized group. At 6 months, patients with optimized devices walked slightly further in the 6-minute walk test (497+/-167 vs. 393+/-123 m, p<0.01), with no differences in NYHA class or quality of life compared with nonoptimized patients. The number of nonresponders was similar in the 2 groups (27% vs. 23%, p=NS). The authors concluded, “The echocardiographic optimization of cardiac resynchronization devices provided a slight incremental clinical benefit at midterm follow-up. Simple and rapid methods to routinely optimize the devices are warranted.”

References:

 
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 * 1) ref3 pmid=17826387