Clinical Outcome Prediction Model in Tetralogy of Fallot Without Pulmonary Valve Replacement Using Contraction Fraction From the SCOUT-TOF Registry

Abstract

Background: Few large scale prediction models of clinical outcomes in repaired tetralogy of Fallot (rTOF) exist. Further, contraction fraction, a novel parameter indexing stroke volume by mass reflecting myocardial efficiency, has not been studied. The goals of this study were to develop and validate an rTOF prediction model of clinical outcome from a single center, the SCOUT-TOF (Single Center Outcomes Using Cardiac Magnetic Resonance in Tetralogy of Fallot) registry, using readily available cardiac magnetic resonance parameters and explore novel metrics.

Methods and results: We retrospectively reviewed cardiac magnetic resonance parameters of patients with rTOF undergoing cardiac magnetic resonance from 2005 to 2021. Composite outcome 1 (CO1) included death, transplantation, ventricular tachycardia, and pacemaker placement, and composite outcome 2 (CO2) added cardiovascular hospitalizations. An elastic net was used to identify significant variables to enter a best subsets logistic regression. A group of 761 patients with rTOF were studied with a median follow-up of 4.15 years; 31 and 44 CO1 and CO2 events occurred respectively. Right ventricular (RV) contraction fraction was the most significant predictor for CO1 (area under the curve, 0.72; odds ratio [OR], 0.54; P=0.01) and CO2 (area under the curve, 0.69; OR, 0.60; P=0.01). RV contraction fraction was lower for those met that CO1 and CO2 end points (median 1.84 [1.48-2.39] versus 2.34 [1.72-3.02] and 1.88 [1.51-2.53] versus 2.34 [1.72-3.02] cc×cm^2.7/g×m^1.4, P<0.01 respectively). Additional significant predictors for CO1 were indexed RV mass/volume and left ventricular ejection fraction whereas for CO2, left ventricular global function index and left ventricular mass were additional predictors.

Conclusions: In rTOF, RV contraction fraction, a novel biomarker of ventricular efficiency, may be used to possibly improve risk stratification. In addition, not only RV but left ventricular measures of remodeling should be considered in the follow-up of these patients.

Keywords: cardiac magnetic resonance; clinical outcome; contraction fraction; tetralogy of Fallot.

Figure 1. CMR parameters measured or calculated to use as predictors of outcome.

CF indicates contraction fraction; CMR, cardiac magnetic resonance; GFI, global function index; LPA, left pulmonary artery; LV, left ventricle; PA, pulmonary artery; RPA, right pulmonary artery; RV, right ventricle, and VA, ventriculoarterial.

Figure 2. RV endocardial (yellow) and epicardial borders (light blue) as well as LV endocardial (red) and epicardial borders (green) were traced in short axis (left panel); papillary muscles were included in ventricular mass.

The RV outflow tract view (right panel) as well as the RV 2‐chamber view (not shown) were used as cross‐references against the short axis. For example, the short axis in the left panel corresponds to the yellow solid line in the RV outflow tract view in the right panel. Near the RV outflow tract patch, the short axis was contoured and cut perpendicular to flow from the septal wall in that region, using the RV outflow tract view as a guide (dashed red line). LV indicates left ventricular; and RV, right ventricular.

Figure 3. Statistical analysis algorithm.

Data were divided into training and testing data sets, imputing the missing data. An elastic net model was applied to the training set for both composite end points and and best candidate variables underwent a best subsets logistic regression to compute the area under the curve for the training and testing data sets. The data were recombined to determine the odds ratio for each variable. AUC indicates area under the curve.

Figure 4. Receiver operator curves for CO1.

On the left is right ventricular contraction fraction and on the right is RV mass/volume plus left ventricular ejection fraction. AUC indicates area under the curve; CO1, composite outcome 1; LVEF, left ventricular ejection fraction; ROC, receiver operator curve; and RV, right ventricular.

Figure 5. Receiver operator curves for CO2 with one‐variable model.

On the left is right ventricular contraction fraction and on the right is left ventricular global function index (A) and receiver operator curves for CO2 with 2‐variable model for right ventricular contraction fraction and left ventricular mass (B). AUC indicates area under the curve; CO2, composite outcome 2; LV, left ventricular; ROC, receiver operator curve; and RV, right ventricular.