The 6-month period from baseline to ascertainment
of the primary end point might be too
short if a placebo effect declined with time,
though prior studies showed a large effect by
6 months (which was sustained through 3 years);
the patients in our study will be followed for up
to 5 years, including those who did not cross
over. The trial was not powered to detect small
differences in systolic or diastolic blood pressure
or any potential effects in subgroups. An operator
learning curve can affect the success of interventional
procedures, though all procedures were
proctored. We observed no significant difference
in outcomes between operators performing five
or more procedures and those performing fewer
than five procedures, and we found no evidence
of a learning curve for high-volume operators
when earlier procedures were compared with
later ones. There was no direct measurement to
confirm that the renal nerves were in fact denervated
by the procedure, because there is no test
that can be easily performed in a large trial.
However, the Symplicity catheter system allowed
confirmation of energy delivery, and the presence
of angiographic notching indicated a bio-logic effect of energy delivery on the artery.
Finally, the results of this trial are specific to the
catheter tested and cannot necessarily be generalized
to other denervation systems.