Double Clipping: Less-Biased Variance Reduction in Off-Policy Evaluation

"Clipping" (a.k.a. importance weight truncation) is a widely used variance-reduction technique for counterfactual off-policy estimators. Like other variance-reduction techniques, clipping reduces variance at the cost of increased bias. However, unlike other techniques, the bias introduced by clipping is always a downward bias (assuming non-negative rewards), yielding a lower bound on the true expected reward. In this work we propose a simple extension, called $\textit{double clipping}$, which aims to compensate this downward bias and thus reduce the overall bias, while maintaining the variance reduction properties of the original estimator.Comment: Presented at CONSEQUENCES '23 workshop at RecSys 2023 conference in Singapor

Improvement of left ventricular function under cardiac resynchronization therapy goes along with a reduced incidence of ventricular arrhythmia

OBJECTIVES: The beneficial effects of cardiac resynchronization therapy (CRT) are thought to result from favorable left ventricular (LV) reverse remodeling, however CRT is only successful in about 70% of patients. Whether response to CRT is associated with a decrease in ventricular arrhythmias (VA) is still discussed controversially. Therefore, we investigated the incidence of VA in CRT responders in comparison with non-responders. METHODS: In this nonrandomized, two-center, observational study patients with moderate-to-severe heart failure, LV ejection fraction (LVEF) ≤35%, and QRS duration >120 ms undergoing CRT were included. After 6 months patients were classified as CRT responders or non-responders. Incidence of VA was compared between both groups by Kaplan-Meier analysis and Cox regression analysis. ROC analysis was performed to determine the aptitude of LVEF cut-off values to predict VA. RESULTS: In total 126 consecutive patients (64±11 years; 67%male) were included, 74 were classified as responders and 52 as non-responders. While the mean LVEF at baseline was comparable in both groups (25±7% vs. 24±8%; P = 0.4583) only the responder group showed an improvement of LVEF (36±6% vs. 24±7; p<0.0001) under CRT. In total in 56 patients VA were observed during a mean follow-up of 28±14 months, with CRT responders experiencing fewer VA than non-responders (35% vs. 58%, p<0.0061). Secondary preventive CRT implantation was associated with a higher likelihood of VA. As determined by ROC analysis an increase of LVEF by >7% was found to be a predictor of a significantly lower incidence of VA (AUC = 0.606). CONCLUSIONS: Improvement of left ventricular function under cardiac resynchronization therapy goes along with a reduced incidence of ventricular arrhythmia

Comparison of Manual and Automated Preprocedural Segmentation Tools to Predict the Annulus Plane Angulation and C-Arm Positioning for Transcatheter Aortic Valve Replacement

<div><p>Background</p><p>Preprocedural manual multi-slice-CT-segmentation tools (MSCT-ST) define the gold standard for planning transcatheter aortic valve replacement (TAVR). They are able to predict the perpendicular line of the aortic annulus (PPL) and to indicate the corresponding C-arm angulation (CAA). Fully automated planning-tools and their clinical relevance have not been systematically evaluated in a real world setting so far.</p><p>Methods and Results</p><p>The study population consists of an all-comers cohort of 160 consecutive TAVR patients with a drop out of 35 patients for technical and anatomical reasons. 125 TAVR patients underwent preprocedural analysis by manual (M-MSCT) and fully automated MSCT-ST (A-MSCT). Method-comparison was performed for 105 patients (Cohort A). In Cohort A, CAA was defined for each patient, and accordance within 10° between M-MSCT and A-MSCT was considered adequate for concept-proof (95% in LAO/RAO; 94% in CRAN/CAUD). Intraprocedural CAA was defined by repetitive angiograms without utilizing the preprocedural measurements. In Cohort B, intraprocedural CAA was established with the use of A-MSCT (20 patients). Using preprocedural A-MSCT to indicate the corresponding CAA, the levels of contrast medium (ml) and radiation exposure (cine runs) were reduced in Cohort B compared to Cohort A significantly (23.3±10.3 vs. 35.3 ±21.1 ml, p = 0.02; 1.6±0.7 vs. 2.4±1.4 cine runs; p = 0.02) and trends towards more safety in valve-positioning could be demonstrated.</p><p>Conclusions</p><p>A-MSCT-analysis provides precise preprocedural information on CAA for optimal visualization of the aortic annulus compared to the M-MSCT gold standard. Intraprocedural application of this information during TAVR significantly reduces the levels of contrast and radiation exposure.</p><p>Trial Registration</p><p>ClinicalTrials.gov <a href="https://clinicaltrials.gov/ct2/show/NCT01805739" target="_blank">NCT01805739</a></p></div

Comparison of the Mean Perpendicular Valve Angulations.

<p>Comparison of the Mean Perpendicular Valve Angulations.</p

Preprocedural Alignment of the Aortic Root Planes.

<p>Colored lines through selected CT images reflect the 3D schematic reconstructions in several planes using a manual software (M-MSCT) <b>(A, coronal, sagittal and axial planes)</b>. The axial plane presents the basis for the alignment of the hinge point plane, in which no valve structure is visible (hinge points). Three points were set on the axial plane, and the 3D volume-rendered reconstruction was initiated. The angles were determined by manually rotating the 3D aortic reconstructions to reach the appropriate projection with a perpendicular view. The automated software (A-MSCT) automatically places fiducial marks at the hinge points (yellow points), representing the aortic valve plane <b>(B)</b>. The aortic root angiogram displays a perpendicular valve view on the aortic valve annulus <b>(C)</b>. NCC = noncoronary cusp; RCC = right coronary cusp; LCC = left coronary cusp; LAO = left anterior oblique; CAUD = caudal; CRAN = cran; M-MSCT = Manual derived CAA by MSCT; A-MSCT = Automated derived CAA by MSCT; CAA = Intraprocedural C-arm angulation.</p

Comparison of the Mean Deviation of the Perpendicular Valve Angulations and Correspondance in Cohort A.

<p>Comparison of the Mean Deviation of the Perpendicular Valve Angulations and Correspondance in Cohort A.</p

Patient Procedural Characteristics and Outcomes.

<p>Patient Procedural Characteristics and Outcomes.</p

Relationship of the MSCT-derived Prediction of the Perpendicular View Angulation between Automated (A-MSCT) and Manual (M-MSCT) Software (Cohort A, method-comparison).

<p>Bland–Altman plots and linear regression analyses comparing M-MSCT and A-MSCT in the LAO/RAO and CRAN/CAUD directions.</p