Limitations
This was a single centre study. Further validation of the prediction
parameters by other centres would increase the robustness and clinical
utility of these findings. The number of individuals included in the
study is relatively low. However, this is comparable to similar studies
using ECG-morphology based parameters.
In our cohort, the patients had relatively high mean ectopic burdens
(16% for RVOT SOO, 24% for LVOT SOO). Consequently, we cannot be sure
if these two parameters would work consistently in patients with
significantly lower burdens of ectopy, as a low ectopic burden overall
would be likely to increase the chance of any hour having < 50
VE. Nonetheless, it is encouraging that some patients in our cohort did
have VE burdens as low as 0.5% and the prediction parameters were still
diagnostic. Furthermore, despite there being a trend towards lower
ectopic burdens in the RVOT cohort, which may bias towards having a
single hour with < 50 VE, total VE burden was included in the
multivariate model and was not found to be independently associated with
SOO.
Finally, the patient population we used to derive these novel parameters
had robust myocardial function with a mean LVEF of 53.7% and 57.9% for
the RVOT and LVOT VE cohorts, respectively. In the setting of VE-induced
cardiomyopathy with significant LV dysfunction, neuro-hormonal
regulatory changes might alter the behaviour of the VEs, limiting the
applicability of these parameters. This would require further
assessment.