Iterative Cardiac Output Measurement for Optimizing Cardiac Resynchronization Therapy: A Randomized, Blinded, Crossover Study

The incidence and outcomes of delayed response to cardiac resynchronization therapy

BACKGROUND

The incidence and clinical outcomes of delayed response to cardiac resynchronization therapy (CRT) have not been well clarified. We aimed to observe the incidence and prognosis of delayed response and to identify its possible mechanisms.

METHODS

A total of 115 CRT patients were retrospectively analyzed in our study. Patients who met the enrollment criteria were divided into two groups: group A, conventional responders who showed response at 1-year follow-up, and group B, delayed responders who showed response after 1-year follow-up. CRT response was defined as an absolute increase of ≥10% in left ventricular ejection fraction.

RESULTS

Fifty-two patients (61 ± 12 years, 37 male) experienced conventional response to CRT and 17 patients (63 ± 11 years, 10 male) experienced delayed response. The mean follow-up time was 5.2 ± 2.4 years. The incidence of delayed response was 14.8% (17/115). All-cause mortality and hospitalization rates for heart failure were similar for delayed and conventional responders. Multivariate logistic regression analysis revealed that scar burden > 35% was an independent predictor of CRT delayed response (odds ratio 8.794, P  =  0.038).

CONCLUSIONS

A significant proportion of patients demonstrated delayed response to CRT. The delayed responders had a good prognosis that was similar to that of conventional responders. More scar burden might be related to the incidence of delayed response.

Hemodynamic benefit of rest and exercise optimization of cardiac resynchronization therapy

The optimal method of cardiac resynchronization therapy (CRT) optimization is as yet unknown. We sought to investigate the responses of optimization at rest and on exercise. This 2 stage study involved 59 patients (age 65 ± 10, 75% male), who had all recently undergone successful CRT implantation. In the first stage, the 6-month response was compared between 30 individuals who underwent resting echocardiographic optimization of CRT [atrioventricular (AV delay) plus ventriculo-ventricular delays (VV delay)], compared with the 29 who did not. In the second stage, a subset of 37 patients from the original cohort were randomized (double-blind) to either resting echocardiographic optimization (n = 20) or exercise echocardiographic optimization (n = 17) and followed for a further 6 months. Clinical and echocardiographic data were collected at each stage. Patients undergoing rest optimization demonstrated improvement in almost all variables and significantly in B-type natriuretic peptide (BNP) in contrast to those without optimization. In a linear regression model, the only significant predictor of BNP change was whether an individual underwent resting optimization or not (β = 0.38, P = 0.04). In those undergoing resting optimization, the degree of change in AV delay was correlated with improvement in left ventricle (LV) end-diastolic volume (r(2)  = 0.33, P < 0.01). Optimization on exercise was associated with a significant decrease in 6-minute walk test compared to those randomized to rest optimization possibly due to inducing nonoptimization at rest. In conclusion, echocardiographic optimization of CRT at rest is superior to no optimization or optimization on exercise. Patients with the greatest change in AV delay to reach optimal may undergo greater LV remodeling.

Optimization of the atrioventricular delay during cardiac resynchronization therapy using a device for non-invasive measurement of cardiac index at rest and during exercise

AIMS

It is not clear whether cardiac resynchronization therapy (CRT) should only be optimized at rest or whether it is necessary to perform CRT optimization during exercise. Our study aims to answer this question by using an inert gas rebreathing method (Innocor®).

METHODS AND RESULTS

Twenty-seven patients with congestive heart failure and implanted CRT devices were included in the study. The aetiology of the heart failure was ischaemic in nine (33%) patients. Patients had low left ventricular ejection fraction (29 ± 8%) and enlarged LV end-diastolic diameters (63 ± 7 mm). Atrioventricular delay (AVD) was optimized at rest according to cardiac index (CI), measured by inert gas rebreathing (Innocor®). Thereafter, patients performed standardized, steady-state bicycle exercise at 30 W in sitting body position. Three AVDs were tested during exercise in a random sequence: optimized resting AVD (AVD(opt)) according to baseline measurement; AVD(opt) - 30 ms; and AVD(opt) + 30 ms. Cardiac index was measured in each AVD by inert gas rebreathing. Cardiac index increased significantly during exercise. However, neither AVD(opt) shortening nor prolongation during exercise had significant effect on CI (shortening of AVD(opt) - 30 ms was accompanied by a reduction of CI of 4.8%, prolongation of AVD(opt) + 30 ms was accompanied by a reduction of CI of 7.7%).

CONCLUSION

Shortening or lengthening of the AVD during exercise has no impact on CI in CRT patients. On the basis of our results, we conclude that in CRT patients the AVD should be programmed, fixed even during exercise.