Right Ventricular Functional Abnormalities in ARVC | 43 study was the first to enable a direct comparison. Both RV deformation pattern recognition and mechanical dispersion were independently associated with VA. Importantly, the classification of patients with a history of VA significantly improved when adding the RV mechanical dispersion to pattern recognition. This implies that the two techniques are complementary and may reflect different pro-arrhythmogenic properties of the myocardium. We chose the clinically most intuitive approach to first evaluate the categorical parameter (deformation patterns), and add the continuous variable (mechanical dispersion). Although deformation patterns and RV mechanical dispersion are both obtained from longitudinal deformation in the same echocardiographic view, there are two important reasons for their unique value. First, mechanical dispersion focusses on heterogeneity in global RV contraction, whereas the deformation pattern is considered to reflect focal substrates in one segment. The usually less affected interventricular septum is included in RV mechanical dispersion for a more robust calculation of the standard deviation and to detect globally delayed contraction of the RV lateral wall. Second, patterns include information of both timing and strain amplitude, whereas strain amplitude has no direct influence on mechanical dispersion. The two methods, therefore, have independent strengths and weaknesses. The pattern approach is sensitive to subtle abnormalities in the subtricuspid segment which may be associated with increased arrhythmic risk. In both cohorts, the subtricuspid segment showed to be first affected in AC, which is in line with previous reports.27 However, prominent involvement of other RV segments has also been reported in AC28,29 and focussing on one segment is accompanied by the risk of missing information. Importantly, whereas the subtricuspid deformation pattern is not able to detect progression to other RV segments, RV mechanical dispersion will increase along with more extensive disease and helps stratifying between intermediate and high arrhythmic risk. Clinical implications External validation of RV deformation pattern recognition and mechanical dispersion is a crucial step towards including them in routine clinical assessment and in clinical risk stratification in AC patients. This study was the first attempt to externally validate the value of these methods. For external validation of the combined approach, a third cohort will be needed. Current risk stratification tools do not include regional and subtle RV function, but only the global RV function from RVEF by CMR.30 Deformation imaging contributes as a sensitive marker of early structural and functional abnormalities and may improve risk stratification as shown in this study. The overall association with arrhythmia was similar to CMR markers, but the easily available echocardiography has many practical advantages, especially in patients who cannot undergo CMR imaging. The increasing use of cascade genetic screening will confront clinicians with an expanding group of asymptomatic patients and relatives with an important arrhythmic risk.13 We showed that a normal RV deformation pattern can identify low risk subjects with excellent negative predictive value. In clinical practice, an initial impression of the deformation pattern can be determined with a brief qualitative determination. Patients with normal deformation patterns would not require quantitative analysis by mechanical dispersion. In patients with borderline abnormal deformation patterns, RV mechanical dispersion may be used for further stratification. In patients with clearly abnormal deformation patterns, a high mechanical dispersion will imply high risk of ventricular arrhythmias. A stepwise approach using both RV deformation indices is superior as it allows identification of a group of low-risk individuals as well as further arrhythmic risk stratification in others. (Central illustration) 3
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