Mannheimer et al looked at the effects of SCS in 20 patients
who were on maximal medical therapy and who were not candidates
for revascularization procedures.8 These patients
had angina and ST depression during a bicycle ergometry test performed
prior to the start of the SCS trial. The investigators used coronary
sinus pacing and blood samples to determine the effects of SCS on
the parameters of lactate production and coronary sinus blood flow.
The investigators evaluated the parameters of coronary sinus blood
flow, lactate metabolism, rate pressure product, time to angina,
time to ST segment depression, recovery time from angina, and ST
segment depression. They measured these parameters before and during
the SCS procedure. The results of this study showed that all parameters
including tolerance to pacing, time to angina, time to ST segment
depression, lactate metabolism, and rate-pressure product improved during
SCS. In addition, recovery time from angina and ST segment depression
was decreased. Perhaps the most important outcome of this study
was that at a maximum pacing rate, all patients experienced anginal
pain and ST segment depression comparable to ST segment changes
seen in the control. Therefore, SCS not only increases cardiac function,
perhaps by decreasing myocardial oxygen consumption, but when there
was myocardial ischemia, SCS did not prevent patients from having
angina and ST segment depression.