Optimal echocardiographic assessment of myocardial dysfunction for arrhythmic risk stratification in PLN p.Arg14del mutation carriers. The ‘45/45’ rule can be used to stratify PLN p.Arg14del mutation carriers into three echocardiographic risk categories. Subjects with LVEF < 45% are classified as having overt LV dysfunction, and are considered to be at high risk to develop sustained VA. In subjects with LVEF ≥45%, LVMD should be additionally measured. In case of normal LVMD (i.e. normal LV function), the risk of developing sustained VA is low. However, in case of LVMD >45 ms (i.e. mechanical LV dysfunction), the risk of developing sustained VA is higher, despite normal LVEF. When LVMD is added on top of the current VA risk prediction model, it provides a high NPV, particularly in the lower risk categories. LVEF, left ventricular ejection fraction; LVMD, left ventricular mechanical dispersion; NPV, negative predictive value; PLN, phospholamban; PPV, positive predictive value; (s)VA, (sustained) ventricular arrhythmia.