Background It is not obvious which is a better echocardiographic marker for optimisation of AV or VV delay: stroke distance (VTI) or peak velocity. The biggest problem is genuine physiological variability between beats. Because optimisation of VV delay requires detection of persistent changes in cardiac function (“signal”), which may be small in relation to beat-to-beat variability (“noise”), we should choose measurements with the best signal-to-noise ratio and reproducibility. The standard echocardiographic method of choice for VV delay optimisation is to maximise left ventricular outflow tract velocity time integral (LVOT VTI). An alternative is peak velocity instead of VTI as the parameter to be measured. But surely VTI, which is encompassing and cumulating more data, is more immune to disruption by spontaneous variability between beats, and therefore simply using peak velocity might give a less reliable optimum? Surely the time saved by using peak would have a price to pay in poorer reproducibility of the optimum? In this study, we evaluate whether peak velocity is a suitable alternative to VTI, having regard to both time consumed and reproducibility. We also examine whether averaging multiple replicate measurements improves optimisation.
Methods & Results VV optimisation was performed on 40 subjects with biventricular pacemakers using LVOT velocity (VTI or peak) as the echocardiographic marker being maximised. Importantly, 6 successive replicate optimisations were performed per patient at a single session. Scatter of apparent VV optimum between repeat optimisations was threefold smaller for peak than VTI (p<0.03), with a single measurement for each. Peak velocity had a higher intraclass correlation coefficient (ICC) than VTI (0.66 vs 0.53, p=0.003). Scatter between replicate optimisations is reduced if, instead of single measurements, we use pairs, or triplicates (ANOVA p<0.0001). This benefit occurs with both peak and VTI (p<0.001 among each). Time taken for acquisition and analysis of a single optimisation (6 settings) was 17.5 s for peak and 57.5 s for VTI (p<0.0001).
Conclusions Doppler optimisation of VV delay using peak velocity rather than VTI is (as expected) quicker but (surprisingly) more accurate. Making replicate measurements further improves reproducibility. Perhaps guidelines should favour peak over VTI and mandate multi-replicate averaging? These data suggest a rare opportunity to reduce labour while increasing reliability of optimisation. Indeed, triplicate peak velocity assessment takes the same amount of time as a single VTI, and identifies the VV optimum 3 times more confidently. While VTI measurement remains essential for assessing stroke volume and cardiac output, for optimisation purposes it comparison of peak velocity between different settings is both faster and more reliable.
- Cardiac resynchronisation theraphy
- LVOT velocity time integral