BACKGROUND: Quantification of left ventricular (LV) dyssynchrony allows for objective measures of resynchronization therapy (CRT) effectiveness. We tested the hypothesis that site of LV pacing, fusion beats and baseline contractility alter contraction synchrony as quantified by regional and global measures of LV performance. METHODS AND RESULTS: In 8 open-chested pentobarbital-anesthetized canine preparations we compared the effects of right atrial (RA), RA-high right ventricular (RV) free wall, as a model of left bundle branch block contraction pattern, RA-LV apex (LVa), RA-LV free wall (LVfw), and RA-RV-apical LV (CRTa) and RA-RV-free wall LV (CRTfw), as CRT. LV pressure-volume loops recorded using high-fidelity pressure and conductance catheters and echocardiographic angle-corrected color-coded strain imaging of mid-LV short axis views analyzed radial strain from six segments. To control for contractile state esmolol-induced beta blockage was studied, and in 5 dogs to control for RA and ventricular pacing fusion beat artifacts, repeat studies were done following AV node ablation. RA-RV pacing reduced stroke work (SW) (57±18 to 33±13* mmHg·mL,*p<0.05 vs RA pacing), decreased LV end-diastolic volume and induced marked radial dyssynchrony (maximal time difference between peak segmental strain) from 31±15 to 234±60* ms. Changes in radial dyssynchrony correlated significantly with changes in SW (r=-0.53, p<0.01). Dyssynchrony improved with both CRTa and CRTfw (69*±31 and 98*±63 ms, respectively) while SW only improved with CRTa (62±22* and 37±13 mmHg·mL, respectively * p<0.05 vs RV pacing). CRTa also tended to increased LV end-diastolic volume over RA-RV. Esmolol slowed HR from 118±10 to 108±10 beats/min* and tended to decrease contractility (end-systolic elastance (Ees) from 12.1±7.9 to 8.9±3.9 mmHg/ml, p=0.167) but did not alter the degree of RV-pacing induced dyssynchrony. AV ablation had no effect on the observed apical and free wall contraction differences seen during baseline conditions. CONCLUSION: Although both CRTa and CRTfw reduced contraction dyssynchrony, CRTa tended to improve global LV performance more by increasing end-diastolic volume. Thus, CRT may improve global LV performance differently, depending on the LV pacing site.

The objective of the study is to determine factors that influence the outcome of long stay patients in a general intensive care unit (ICU) and/or high-dependency unit (HDU) in a New Zealand teaching hospital. 10-bed general ICU and 4-bed surgical HDU in a 400-bed hospital. Population based retrospective cohort study. All patients with prolonged stay in a high resource area (>7 days in the ICU or >14 days in either the ICU or HDU) between 2000 and 2003 were reviewed. Demographic data, co-morbidities, diagnoses, clinical events, hospital and 1-year mortality data were obtained using available databases and patient records. Multiple logistic regression analysis was performed to identify which variables are associated with death among patients with a prolonged stay in a high-resource unit (ICU/HDU). 207 patients were included in the study. Twenty eight percent died before hospital discharge and 40% died within one year of their admission. Univariate analysis showed that increasing age, APACHE II score, admission post cardiac arrest, inpatient cardiac arrest, development of sepsis and requirement for renal support therapy were all risk factors for increased mortality. However, when adjusted for age, gender and APACHE II score the only risk factor strongly associated with death was having a cardiac arrest in the ICU. Prolonged ICU and/or HDU stay is associated with a high mortality rate particularly in patients with advancing age and increasing severity of illness. In this study, only cardiac arrest after a prolonged stay in the ICU and/or HDU is a strong predictor of death independent of the age and the APACHE II score.