36 | Chapter 3 Outcomes All arrhythmic events were adjudicated retrospectively from the time of echocardiographic assessment. Life-threatening ventricular arrhythmia was defined as a documented history of sustained ventricular tachycardia, aborted cardiac arrest or appropriate ICD therapy. The division into three different disease stages was based on the presence of subsets of the 2010 TFC, as described previously.5,6 In brief, subjects in the structural stage presented with minor or major 2010 TFC for structural abnormalities on echocardiography or CMR. Subjects categorized in the electrical stage fulfilled no structural criteria but had minor or major ECG abnormalities (repolarization and/or depolarization) and/or history of ventricular arrhythmias as defined by the 2010 TFC. Subclinical subjects were defined as fulfilling neither structural, nor electrical 2010 TFC. Statistical analysis Analyses were performed with SPSS statistics for Windows 21 (IBM corp., Armonk, New York) and Stata/SE version 16.0 (Statacorp, College Station, Texas). Continuous data were presented as mean ± SD and categorical variables were presented as frequencies (percentage of cases). Continuous variables were compared by independent Student’s t-tests and categorical data by χ2 or Fisher’s exact tests. The association to VA was assessed by the area under the receiver operator characteristics curve (AUC). Odds ratios (OR) and 95% confidence intervals (CI) were calculated for RV deformation patterns and mechanical dispersion using univariable and multivariable logistic regression. The incremental value of combining RV deformation patterns with mechanical dispersion was assessed by reclassification analysis by integrated diagnostic improvement (IDI) and continuous net reclassification improvement (NRI), and the AUCs of different models were compared. Mechanical dispersion was dichotomized at an optimal cutoff derived from a single threshold regression analysis. This threshold was defined as the point estimate that best classified two groups with the most diverging odds ratios. Intra- and interobserver variability was expressed by kappa statistics or intraclass correlation coefficient, as appropriate. P-values were two-sided and values <0.05 were considered significant. RESULTS Clinical characteristics We included 160 patients (55% female, aged 41 ± 17 years), comprising 68 probands and 92 mutation positive family members, from 86 different families. Plakophilin-2 (PKP2) was the most common pathogenic mutation in both the Oslo and Utrecht cohort (90% and 89%, respectively). Most probands (n = 55 (81%)) and part of the family members (n = 42 (46%)) fulfilled a definite 2010 TFC AC diagnosis.5 Life-threatening ventricular arrhythmia had occurred in 47 (29%) of the subjects, with similar rates in the Oslo and Utrecht cohort (25 (31%) vs. 22 (28%), p = 0.60); as documented sustained ventricular tachycardia in 37, aborted cardiac arrest in 8, and appropriate ICD therapy in 2. More patients from the Oslo cohort were categorized in the electrical disease stage (25 (31%) vs. 13 (16%), p = 0.03), whereas the other disease stages were equally represented in both cohorts. (Table 1)
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