The role of non-invasive imaging in patient selection

Association between left ventricular mechanical dyssynchrony with myocardial perfusion and functional parameters in patients with left bundle branch block

OBJECTIVE

To identify predictors of left ventricular mechanical dyssynchrony (LVMD) in patients with known left bundle branch block (LBBB) using gated single-photon emission computed tomography (SPECT) phase analysis.

METHODS

81 patients (74% male, 70 ± 10 years) with LBBB and suspected or known coronary artery disease underwent ECG-gated myocardial perfusion SPECT. LV perfusion and functional parameters were measured, and phase analysis was performed to quantify LV-dyssynchrony.

RESULTS

35/81 patients (42%) had prior myocardial infarction (MI), and the mean left ventricular ejection fraction (LVEF) was 49% ± 16%. LVMD was present in 58/81 (72%) patients. The summed thickening score (STS) (P < .001; odds ratio 1.22) emerged as independent predictor for the presence of LVMD in a multivariate regression model. In addition, prior MI, low LVEF, summed stress score, summed rest score, summed motion score, and LAD rest extent were identified as predictors of LVMD in a univariate model. Clinical baseline characteristics, cardiac risk factors, and QRS duration (P = .051) had no influence on the presence of LVMD.

CONCLUSION

In patients with LBBB, the occurrence of LVMD as assessed by gated SPECT phase analysis is mainly influenced by reduced myocardial contractility as expressed by the STS. Proper discrimination between LVMD arising from known electrical conduction delay as opposed to areas of MI causing reduced regional contractility seems to be mandatory for therapy planning in patients with LVMD.

Clinical, laboratory, and pacing predictors of CRT response

A decade of research has established the role of cardiac resynchronization therapy (CRT) in medically refractory, moderate to severe systolic heart failure (HF) with intraventricular conduction delay. CRT is an electrical therapy instituted to reestablish ventricular synchronization in order to improve cardiac function and favorably modulate the neurohormonal system. CRT confers a mortality benefit, improved HF hospitalizations, and functional outcome in this population, but not all patients consistently demonstrate a positive CRT response. The nonresponder rate varies from 20% to 40%, depending on the defined response criteria. Efforts to improve response to CRT have focused on a number of fronts. Methods to optimize the correction of electrical and mechanical dyssynchrony, which is the primary target of CRT, has been the focus of research, in addition to improving patient selection and optimizing post-implant care. However, a major issue in dealing with improving nonresponse rates has been finding an accurate and generally accepted definition of "response" itself. The availability of a standard consensus definition of CRT response would enable the estimation of nonresponder burden accurately and permit the development of strategies to improve CRT response. In this review, we define various aspects of "response" to CRT and outline variability in the definition criteria and the problems with its inconsistencies. We describe clinical, laboratory, and pacing predictors that influence CRT response and outcome and how to optimize response.

Prospective evaluation of electrocardiographic parameters in cardiac resynchronization therapy: detecting nonresponders by left ventricular pacing

BACKGROUND AND OBJECTIVE

The purpose of this prospective evaluation of electrocardiographic (ECG) parameters was to identify predictive parameters for cardiac resynchronization therapy (CRT) response.

METHODS

One hundred two patients undergoing first CRT implantation were evaluated prospectively. Symptomatic response was defined as improvement in New York Heart Association functional class of at least 1 class within 3-month follow-up. Twelve-lead ECG of the intrinsic rhythm during biventricular (BIV), right ventricular (RV), and left ventricular (LV) pacing was obtained and analyzed in terms of QRS width and QRS axis (Datinf Measure Software, Datinf GmbH, Tübingen, Germany). In total, 77.5% (n = 79) of patients fulfilled the predefined clinical criterion for response. Patients with dilated cardiomyopathy were more likely to respond to CRT than were patients with ischemic cardiomyopathy (85% vs 71.8%, P = .034). A shorter QRS duration during LV pacing and, in particular, a shorter LV paced than RV paced QRS width were strong and independent predictors for response (-20.13 ± 33.2 ms in responders vs 6.05 ± 27.3 ms in nonresponders, P = .001). No statistically significant differences were found in RV and BIV paced QRS width or in QRS axis (P >.5).

CONCLUSION

This study describes novel and easily obtainable ECG measurements that can be performed during LV lead positioning to optimize clinical outcome of CRT in heart failure patients.