MI Scar Burden and ICD Implantation in Cardiomyopathy
MI Scar Burden and ICD Implantation in Cardiomyopathy
We examined 450 consecutive patients with severe ICM (defined as LVEF≤40% with ≥70% stenosis in ≥1 epicardial coronary vessel on angiography and/or history of myocardial infarction or revascularisation) who were referred for DHE-MRI between January 2002 and December 2006. We expanded our previous published studies, which previously included patients who were referred for DHE-MRI between 2003 and 2006. With the addition of 101 patients and longer follow-up, our expanded study population resulted in 1956 additional patient-years and 135 additional primary outcome events. Telephone call follow-up was also performed to capture patients who underwent ICD implantation outside of our institution. Patients with standard CMR contraindications were not imaged.
Clinical and demographic variables were entered prospectively into electronic medical records. The use of cardiac medications, post-CMR revascularisation (percutaneous or surgical), and placement of ICD or cardiac resynchronisation therapy (CRT) were recorded. Echocardiographic data were obtained within 1 month of the DHE-MRI study. Mitral regurgitation (MR) severity was assessed by echocardiography using the vena contracta method. Telephone follow-up was conducted to capture patients undergoing procedures (revascularisation and ICD implantation) outside of our institution. Cardiac MRI viability assessment was used clinically to decide whether to revascularise patients. In patients who did not undergo revascularisation, cardiac MRI LVEF was clinically used to determine candidacy for ICD implantation.
All-cause mortality, ascertained by social security death index, was used as the primary endpoint. This study was approved by the institutional review board.
CMR examinations were performed on 1.5-T MR scanners (Sonata and Avanto, Siemens Medical Solutions, Erlangen, Germany), using 40–45 mT/m maximum gradient strength, 200 T/m/s maximum slew rate with electrocardiographic gating. For assessment of global cardiac function, steady-state free precession (SSFP) images were acquired (slice thickness 8–10 mm in contiguous short-axis images). LV volumes and LVEF were calculated on short-axis SSFP images. DHE-CMR images were obtained in long- and short-axis orientations, approximately 15–20 min after injection of 0.2 mmol/kg of Gadolinium dimenglumine, with segmented inversion-recovery (IR) gradient echo sequences (GRE) for studies performed in 2002–2003 and phase-sensitive IR spoiled GRE sequence for studies performed after 2003 (spatial resolution of 1.5–2.1×1.1–1.4 mm).
DHE-CMR images were analysed using a custom analysis multi-vendor package (Qi Imaging, Redwood City, California, USA). Endocardial and epicardial myocardial edges were manually delineated on DHE-CMR images. Scar was defined by intensity ≥2 SDs above user-defined viable myocardium. Peri-infarct areas were defined as areas 2–3 SD above the user-defined viable myocardium. Areas that were identified as scar by the software but not deemed to be scar by the user were excluded manually by the user. MSB and peri-infarct% were automatically determined as percentage of total myocardium (infarct volume/mass divided by total LV volume/mass). Each study was also semiquantitatively graded using the standard American Heart Association 17-segment, 5-point scale model (0: no DHE; 1: DHE of 1%–25% of LV segment; 2: DHE extending to 26%–50%; 3: DHE extending to 51%–75%; and 4: DHE extending to 76%–100%). CMR analysis was blinded from the clinical analysis.
Baseline demographic data, risk factors and clinical variables were descriptively summarised with continuous variables expressed as mean±SD and categorical data presented as percentage frequency. Groups were compared with the Student t test and analysis of variance for continuous variables and the χ test for categorical variables. All-cause mortality was the primary endpoint.
Propensity analysis, performed to correct for non-randomised treatment assignment, used logistic regression modelling and included age, gender, risk factors, LVEF/RVEF, LV/RV volumes, SB, revascularisation history, medical therapy, QRS duration, MSB and scar location. Cox proportional hazard (CPH) modelling was used to assess the impact of (1) MSB and (2) patient gender on the association between post-test ICD use and outcomes after adjusting for baseline differences and possible confounders. Covariate selection for model inclusion was based on clinical experience and prior publications. ICD implantation was modelled as a time dependent intervening event and was determined to satisfy the proportional hazard assumption. Survival functions stratified by key CMR parameters were plotted using the Kaplan–Meier method and compared using log-rank tests. Predicted survival was graphically depicting for predefined covariate values of interest while holding the remaining covariates constant at typical values. The added value of preidentified interactions to the model (ICD×Scar%, LV end systolic volume index (ESVI)×Scar%, Gender×Scar%, RV ESVI×MR, and ICD×Scar%×Gender) was examined using the likelihood ratio test. The models were examined, when applicable, for proportional hazards assumption, multicollinearity and the additive value of the terms.
Statistical comparisons were performed with SPSS V.16.0 (SPSS Inc, Chicago, Illinois, USA). S-PLUS 2000 (Release 2) software package (Insightful Corp, Seattle, Washington, USA) with supplemental libraries (Hmisc, Design) was used for multivariable analyses. A p<0.05 was considered significant.
Methods
We examined 450 consecutive patients with severe ICM (defined as LVEF≤40% with ≥70% stenosis in ≥1 epicardial coronary vessel on angiography and/or history of myocardial infarction or revascularisation) who were referred for DHE-MRI between January 2002 and December 2006. We expanded our previous published studies, which previously included patients who were referred for DHE-MRI between 2003 and 2006. With the addition of 101 patients and longer follow-up, our expanded study population resulted in 1956 additional patient-years and 135 additional primary outcome events. Telephone call follow-up was also performed to capture patients who underwent ICD implantation outside of our institution. Patients with standard CMR contraindications were not imaged.
Clinical and demographic variables were entered prospectively into electronic medical records. The use of cardiac medications, post-CMR revascularisation (percutaneous or surgical), and placement of ICD or cardiac resynchronisation therapy (CRT) were recorded. Echocardiographic data were obtained within 1 month of the DHE-MRI study. Mitral regurgitation (MR) severity was assessed by echocardiography using the vena contracta method. Telephone follow-up was conducted to capture patients undergoing procedures (revascularisation and ICD implantation) outside of our institution. Cardiac MRI viability assessment was used clinically to decide whether to revascularise patients. In patients who did not undergo revascularisation, cardiac MRI LVEF was clinically used to determine candidacy for ICD implantation.
All-cause mortality, ascertained by social security death index, was used as the primary endpoint. This study was approved by the institutional review board.
CMR Protocol
CMR examinations were performed on 1.5-T MR scanners (Sonata and Avanto, Siemens Medical Solutions, Erlangen, Germany), using 40–45 mT/m maximum gradient strength, 200 T/m/s maximum slew rate with electrocardiographic gating. For assessment of global cardiac function, steady-state free precession (SSFP) images were acquired (slice thickness 8–10 mm in contiguous short-axis images). LV volumes and LVEF were calculated on short-axis SSFP images. DHE-CMR images were obtained in long- and short-axis orientations, approximately 15–20 min after injection of 0.2 mmol/kg of Gadolinium dimenglumine, with segmented inversion-recovery (IR) gradient echo sequences (GRE) for studies performed in 2002–2003 and phase-sensitive IR spoiled GRE sequence for studies performed after 2003 (spatial resolution of 1.5–2.1×1.1–1.4 mm).
DHE-CMR Analysis
DHE-CMR images were analysed using a custom analysis multi-vendor package (Qi Imaging, Redwood City, California, USA). Endocardial and epicardial myocardial edges were manually delineated on DHE-CMR images. Scar was defined by intensity ≥2 SDs above user-defined viable myocardium. Peri-infarct areas were defined as areas 2–3 SD above the user-defined viable myocardium. Areas that were identified as scar by the software but not deemed to be scar by the user were excluded manually by the user. MSB and peri-infarct% were automatically determined as percentage of total myocardium (infarct volume/mass divided by total LV volume/mass). Each study was also semiquantitatively graded using the standard American Heart Association 17-segment, 5-point scale model (0: no DHE; 1: DHE of 1%–25% of LV segment; 2: DHE extending to 26%–50%; 3: DHE extending to 51%–75%; and 4: DHE extending to 76%–100%). CMR analysis was blinded from the clinical analysis.
Statistical Analysis
Baseline demographic data, risk factors and clinical variables were descriptively summarised with continuous variables expressed as mean±SD and categorical data presented as percentage frequency. Groups were compared with the Student t test and analysis of variance for continuous variables and the χ test for categorical variables. All-cause mortality was the primary endpoint.
Propensity analysis, performed to correct for non-randomised treatment assignment, used logistic regression modelling and included age, gender, risk factors, LVEF/RVEF, LV/RV volumes, SB, revascularisation history, medical therapy, QRS duration, MSB and scar location. Cox proportional hazard (CPH) modelling was used to assess the impact of (1) MSB and (2) patient gender on the association between post-test ICD use and outcomes after adjusting for baseline differences and possible confounders. Covariate selection for model inclusion was based on clinical experience and prior publications. ICD implantation was modelled as a time dependent intervening event and was determined to satisfy the proportional hazard assumption. Survival functions stratified by key CMR parameters were plotted using the Kaplan–Meier method and compared using log-rank tests. Predicted survival was graphically depicting for predefined covariate values of interest while holding the remaining covariates constant at typical values. The added value of preidentified interactions to the model (ICD×Scar%, LV end systolic volume index (ESVI)×Scar%, Gender×Scar%, RV ESVI×MR, and ICD×Scar%×Gender) was examined using the likelihood ratio test. The models were examined, when applicable, for proportional hazards assumption, multicollinearity and the additive value of the terms.
Statistical comparisons were performed with SPSS V.16.0 (SPSS Inc, Chicago, Illinois, USA). S-PLUS 2000 (Release 2) software package (Insightful Corp, Seattle, Washington, USA) with supplemental libraries (Hmisc, Design) was used for multivariable analyses. A p<0.05 was considered significant.
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