Methods

The design and results of the MADIT-CRT study have been reported previously. Briefly, 1,820 patients with ischemic cardiomyopathy (New York Heart Association [NYHA] functional class I or II) or nonischemic cardiomyopathy (NYHA functional class II), left ventricular ejection fraction (LVEF) ≤0.30%, and prolonged intraventricular conduction with QRS duration ≥130 ms were randomized to receive either CRT-D or implantable cardioverter difibrillator therapy in a 3:2 ratio. Screened patients were excluded from enrollment if they had an existing indication for CRT, NYHA functional class III/IV in the past 90 days before enrollment, an implanted pacemaker, coronary artery bypass graft surgery, percutaneous coronary intervention, or myocardial infarction within the past 90 days before enrollment. Echocardiograms were obtained according to a study-specific protocol, at baseline before device implantation and at 1 year. We studied the effect of PP in 754 patients with CRT-D and LBBB in this post hoc analysis of MADIT-CRT study.

This population was chosen to preserve the clinical applicability of this study as recent updated guidelines recommend the use of CRT-D in patients with poor LV function and mild HF symptoms only in the presence of LBBB based on evidence that the presence of LBBB conduction at baseline plays a central role in determining the efficacy of CRT-D. Paired echocardiographic data with the device turned on were available for 529 patients in the CTR-D arm with LBBB. Two-dimensional echocardiographic parameters were measured in the core echocardiography laboratory according to the established American Society of Echocardiography protocols. LV volumes were measured by Simpson’s method. LVEF and LV mass were calculated according to a standard method. LV mechanical dyssynchrony was measured using B-mode speckle tracking software (TomTec, 1.0; Amid Cardiac Performance Imaging, Unterschleissheim, Germany) and analyzed offline, as reported previously. LV mechanical dyssynchrony was defined as the SD of regional time-to-peak transverse strain, measured in the 12 segments of the left ventricle in the apical 4- and 2-chamber views (septum, lateral, anterior, and inferior walls; all of them subdivided into basal, mid, and apical segments). The intra- and interobserver variability for LV dyssynchrony was 13.8% and 15.4% for time-to-peak transverse strain, as reported elsewhere. Before randomization, baseline demographics and clinical data were obtained including systolic and diastolic BP. The BP measurements were taken at the discretion of individual center’s protocol.

PP, which was determined by subtracting the diastolic BP from systolic BP, was the primary focus of this present study. LBBB was defined with QRS duration ≥130 ms, QS or rS in lead V1, and broad (frequently notched or slurred) R waves in lead I, AVL, V5, and V6, and absent Q waves in lead I, V5, and V6. The diagnosis of HF required signs and symptoms consistent with CHF that was responsive to intravenous decongestive therapy on an outpatient basis or an augmented decongestive regimen with oral or parenteral medications during an in-hospital stay.

An echocardiographic response was defined as the percentage of reduction in left ventricular end-systolic volumes (LVESVs) between enrollment and at 1 year (calculated as the difference between 1-year cardiac volumes and baseline cardiac volumes divided by baseline cardiac volumes). We used the 15% reduction in LVESV in the CRT-D and LBBB patients as a threshold for the definition of echocardiographic response. The change in these echocardiographic variables was evaluated both as a continuous measure and as a dichotomous measure. The primary end point of the present study was echocardiographic response to CRT-D (defined as >15% reduction in LVESV at 1 year), and secondary end points included (i) percent change in LVESV, LVEDV, LVEF, and LV mechanical dyssynchrony between enrollment and 1 year and (ii) the first occurrence of HF or death and all-cause mortality after the assessment of the echocardiographic response. Patients were divided into quartiles according to the baseline PP values. Kaplan-Meier cumulative mortality curves were plotted to display trends in mortality over time, and patients were grouped into low PP (Q1) and high PP (Q2 to Q4). Baseline characteristics in CRT-D/LBBB low and high PP were compared with Kruskal-Wallis tests for continuous variables and chi-square test for categorical variables.

The association of baseline PP and echocardiographic response (LVESV >15% response) was carried out with multivariate logistic regression models with adjustment for age, gender, LVEF, LVESV, and etiology of cardiomyopathy. These variables were prespecified. Separate models were created for unit change in PP by 10 mm Hg (as continuous) and categorical variable (high vs low PP). Linear regression was used to assess the relation of baseline PP with percent change in the LVESV, LVEDV, and measure of dyssynchrony with adjustment for age, gender, LVEF, LVESV, and etiology of cardiomyopathy. Separate models were created for unit change in PP by 10 mm Hg (as continuous) and categorical variable (high vs low PP). The relation between unit changes in PP and high versus low PP at 1 year and occurrence of primary end points subsequent to the 1 year of study follow-up (land mark–type analysis) was assessed using Cox proportional hazards methods. The following prespecified variables including age, gender, LVEF, and history of ischemic cardiomyopathy were included in the model. All p values were 2 sided, and a p-value of ≤0.05 was considered significant. Analyses were conducted with SAS software, version 9.2 (SAS Institute, Cary, North Carolina).

Results

There were 754 patients with CRT-D with LBBB enrolled in MADIT-CRT who were included in the study. The mean ± SD of baseline PP was 51.5 ± 13.9 mm Hg. Distribution of baseline PP in the study population is shown in Figure 1 . The mean ± SD of 12-month PP was 51.1 ± 13.6 mm Hg. The mean ± SD change in PP between the 2 time points was −0.31 ± 15.9 (range: −50.00 to 57.00) mm Hg.

Distribution of baseline PP in CRT-D and LBBB patients.

Baseline PP quartiles were ≤40 mm Hg (Q1), 41 to 49 mm Hg (Q2), 50 to 59 mm Hg (Q3), and ≥60 mm Hg (Q4). Patients were divided into 2 groups: low PP (≤40 mm Hg; Q1) and high PP (>40 mm Hg; Q2 to Q4). Baseline characteristics of the patient population according to low versus high PP group are presented in Table 1 . The mean PP for 188 study patients with low PP was 35.5 ± 5.3 mm Hg and for 566 patients with high PP was 56.8 ± 11.6 mm Hg (p <0.001). Patients with low PP were younger, with low baseline systolic BP, and higher mean heart rate compared with patients with high PP ( Table 1 ). In contrast, patients with high PP were more often female with higher frequency of hypertension. Baseline LV volumes were significantly greater in patients with low PP. There was no difference in the baseline LV dyssynchrony between the 2 groups. During follow-up, 134 (18%) patients died or had HF event.

We found strong positive correlation between systolic BP and baseline PP (r = 0.8; p <0.001); therefore, separate models were created to evaluate the relation between systolic BP and PP on echocardiographic response. PP was found to be a stronger predictor of the echocardiographic response than systolic BP. Baseline high PP was associated with a significantly higher echocardiographic response compared with low PP ( Table 2 ). Every 10 mm Hg increment in baseline PP was associated with 40% (p = 0.011) increase in the likelihood of a positive echocardiographic response to CRT. Patients with high PP (>lower quartile) had a 3.4-fold (p = 0.002) increase in the likelihood of having a positive echocardiographic response. These results were consistent in separate multivariate analysis including all variables with p <0.1 from Table 1 . Furthermore, analyzing the association between baseline PP and improvement in echocardiographic parameters (measured as continuous variables) showed a direct relation between baseline PP and the magnitude of reverse remodeling and improvement in dyssynchrony ( Table 3 and Figure 2 ). Patients with high PP compared with low PP had 4.5% (p = 0.02) further reduction in LVESV, 3.2% reduction in LVEDV, and 17.6% (p = 0.005) reduction in LV dyssynchrony (% change in SD of regional time to peak transverse strain).

Table 2

Baseline pulse pressure and echocardiographic response (>15% reduction in left ventricular end systolic volume) ^∗

	Odds Ratio	95% CI	p Value
For each 10 mm Hg increment in baseline pulse pressure	1.42	1.08–1.87	0.011
High pulse pressure (>40 mm Hg) vs. low pulse pressure (≤40 mm Hg)	3.48	1.80–6.73	0.002

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