The Contemporary Role of Echocardiography in Improving Patient Response to Cardiac Resynchronization Therapy

Abstract

Cardiac resynchronization therapy (CRT) is an important therapy for heart failure patients with widened electrocardiographic QRS complexes and depressed ejection fractions, however, approximately one-third do not respond. This article presents a practical contemporary approach to the utility of echocardiography to improve CRT patient response by assessing mechanical dyssynchrony, optimizing left ventricular lead positioning, and performing appropriate echo-Doppler optimization, along with future potential roles. Specifically, recent long-term outcome data are presented that demonstrates that baseline dyssynchrony is a powerful marker associated with CRT response, in particular for patients with narrower QRS duration or non left bundle branch block morphology. Advances in speckle tracking echocardiography to tailor delivery of CRT by guiding LV lead position is discussed, including data from randomized clinical trials supporting targeting the LV lead toward the site of latest activation. In addition, an update on the current role of Doppler echocardiographic device optimization after CRT implantation is reviewed.

Keywords: Doppler; echocardiography; heart failure; pacemaker.

Figure 1

Routine pulsed Doppler examples from the right ventricular (RV) outflow track (top panels) and left ventricular (LV) outflow track (bottom panels) from a patient with dyssynchrony before cardiac resynchronization therapy. The calculation of interventricular mechanical delay (IVMD) is the difference from between LV pre-ejection period (PEP) and RV PEP (arrows).

Figure 2

Examples of color-coded tissue Doppler images from the 4-chamber views (left) and corresponding septal and lateral time-velocity plots (right). The top panels are from a normal subject with similar septal and lateral time-velocity curves. The bottom panels are from a patient with left bundle branch block dyssynchrony before cardiac resynchronization therapy, demonstrating early septal and late lateral wall peak systolic velocities.

Figure 3

Examples of speckle tracking radial strain images from the mid-ventricular short axis plane with corresponding time-strain plots from 6 segments. The top panels are from a normal subject with 6 synchronous time-strain curves. The bottom panels are from a patient with left bundle branch block dyssynchrony before cardiac resynchronization therapy, demonstrating early septal and late posterior and lateral wall peak strain.

Figure 4

Kaplan Meier plots of probability of event free survival free from heart transplant or left ventricular assist device in cardiac resynchronization therapy (CRT) patients with and without radial dyssynchrony by speckle tracking radial strain from the STAR study. The cut-off defined as significant dyssynchrony was a septal to posterior wall delay of at least 130 ms. Significant radial dyssynchrony before CRT was associated with a more favorable clinical outcome.

Figure 5

Kaplan Meier plots of probability of event free survival free from heart transplant or left ventricular assist device in cardiac resynchronization therapy (CRT) patients grouped by those with left bundle branch block (LBBB) and those non-LBBB and with and without radial dyssynchrony. The cut-off defined as significant dyssynchrony was a septal to posterior wall delay of at least 130 ms. Non-LBBB patients with significant radial dyssynchrony before CRT had a more favorable clinical outcome, similar to those with LBBB.

Figure 6

An example of a speckle tracking radial strain image from the mid-ventricular short axis plane with corresponding time-strain plots from 6 segments. The right arrow indicates the posterior wall segment having the latest time to peak strain. The left arrow indicates the corresponding anatomical segment with the latest peak strain for LV lead targeting.

Figure 7

Kaplan Meier plots of freedom from heart failure hospitalization or death from the STARTER trial showing 6 month data extracted as preliminary results. Cardiac resynchronization therapy patients were randomized to either LV lead positioning toward the site of latest activation by speckle tracking radial strain, or routine empiric lead placement as a control. The echo-guided strategy was associated with a significant reduction in heart failure hospitalizations or death.

Figure 8

An example of color-coded three-dimensional speckle tracking strain in a patient with widened QRS who was referred for cardiac resynchronization therapy. The apex down three-dimensional map is on the left and the polar map is on the right. The latest site of peak radial strain, color- coded as red, appears in the mid ventricular inferior-posterior region. This representation has potential to assist in guiding left ventricular lead positioning.