Introduction Tissue Doppler imaging (TDI) is widely used for the selection of patients for cardiac resynchronisation therapy (CRT). A number of cut-off values has been produced by investigators to aid selection but values have varied between groups. Cut-off values have traditionally been calculated by recruiting a group of normal controls, calculating the mean value and standard deviation (SD) and stating that values greater than mean ± 2 SD are abnormal. We aimed to assess dyssynchrony both at rest and during exercise so as to assess the prevalence of dyssynchrony using established cut-off values, calculate new cut-off values with our population and assess the effect of increasing heart on dyssynchrony indices.
Methods 40 healthy individuals aged over 18 years were recruited. Individuals with a history of diabetes, cardiac or respiratory disease were excluded. All subjects had a QRS duration of less than 110 ms. Assessments of left ventricular pre-ejection interval (LVPEI), interventricular dyssynchrony (IVMD) and SD of time to peak systolic velocity (Ts SD) for six basal and six mid-left ventricular segments were taken at rest and during submaximal exercise using a supine bicycle ergometer. All analysis was performed off line by one operator. Positive dyssynchrony was assigned using established cut-offs: LVPEI >140 ms, IVMD >40 ms, Ts SD >33 ms (as calculated by Yu with mean 17 ± 8).
Results See table.
Conclusion Our study suggests that current TDI cut-off values for dyssynchrony may be inappropriately low. Mean levels of Ts SD are similar to those originally produced by Yu, but the SD is significantly higher and this has large effects on the calculated cut-off values. IVMD and Ts SD do not appear to reduce significantly with increasing heart rate but there was a large reduction in LVPEI on exercise. LVPEI is rate dependent and this has implications for the assessment of patients for CRT.