THE EFFlCACY OF SPlNAL CORD STlMULATlON IN THE TREATMENT OF

REFRACTORY ANGlNA PECTORIS: A CRlTlCAL REVlEW

N.Franco, M.Marzaloni, F.Bologna, W.Raffaeli°

Cardiology Dept. and Anaesthesia and lntensive Care Dept. -Pain Unit°

lnfermi Hospital, Rimini AUSL, ltaly

The improvement of long-term prognosis of patients (pts) affected by ischemic

cardiomyopathy, thanks to better secondary prevention and achievements in the

field of revascularization procedures, will lead in the future to an increasing number

of pts with end-stage Coronary Artery Disease (CAD), suffering from the so-called

refractory angina pectoris.

The application of Spinal Cord Stirnulation (SCS) to the pts complaining of severe

and disabling angina pectoris, refractory to medical therapy and unsuitable of

conventional surgical treatment, is aimed at a reduction of the thoracic pain (number

of episodes and intensity), lower nitrates' consumption, higher angor and ST

threshold and at an increase in functional capacity.

Despite the substantially positive results given by this method at a clinical level, still

a series of doubts, unresolved by large-scale controlled studies, exist.

What are the exact mechanisms of action involved? Is SCS just a powerful

anaesthetic? Has the analgesic effect been evaluated with tests of proven accuracy

and reliability? Has sufficient consideration been given to exclude the placebo

effect?

Is the assessment of the presumed antiischemic effect based on reliable

parameters?

Different mechanisms were proposed to explain the effect of neurostimulation jn pts

with CAD: as regards the antiischemic effect , at present is reasonable to believe in

a blood-flow homogeneization (PET results) instead of in an increase of myocardial

perfusion. More detailed analyses on the reduction of 02 consumption must

therefore be made; the complete range of haemodynamic effects of SCS has not yet

unambiguously ascertained; because of the relatively small number of cases,

together with the frequent lack of randomization, is often impossible to obtain a

reliable comparison. Experimental blinding is not feasible, considering the fact that

the presence of paraesthesia in the treated area represents an unequivocal and may

be unavoidable signal of activity for the pt. Do we then just observe a modification of

the sequence of events triggered by the onset of anginal pain instead of a direct

action on the causes of ischemia?

Many studies supported the antiischemic effed of SCS evaluating the reduction of

ST down-sloping as a signal of diminished myocardial ischemia; unfortunately it is

known equally well that the sensitivity of the exercise test is low in the context of a

population certainly affected by chronic ischemic cardiopathy. Other assessment

methods should therefore be adopted to test the efficacy of SCS. Promising in this

field could be the technique of atrial pacing, even if the design has already been

criticized, as atrial pacing itself could be a cause of ischemic preconditioning.

Modern stimulators have a wide range of stimulation modes, but on the use of these

there are still large gaps in our knowledge. Should the stimulation be intermittent or

continuous? And if intermittent how many times and for what duration? Many

available data derive from experience acquired in the field of peripheral

vasculopathies, but they would not seem to represent an adequate model for the

comprehension of the complex regulation of myocardial circulation.

It is generally known that the placebo effect accounts for the efficacy in the 30-40%

of therapeutic medical treatments, and this remain true even when objective criteria

for the assessment of ischemia are applied; it has also been claimed that it tends to

decline with time; it has thus been derived that since the action of SCS lasts much

longer, it cannot be correlated to placebo effect. Is this always true?

Few references in literature are found as it regards cost-benefit analysis for SCS

application. The fundamental issue in safety at present, considering surgical

advances in the procedure and newer devices, concerns the potential reduction of

tha warning signal of anginal pain of stimulated pts. Recent reports in literature

would tend to give full reassurance about it, as no increase in mortality was

observed and no symptoms of myocardial infarction were masked in the pts treated

with SCS.

Conclusions: prospective polycentric controlled studies are needed to clarify the

various hypothesis suggested by literature analysis on SCS; therefore it remains true

that an hypothesis can assume an universal nature only after every attempt has

been made to demonstrate ist falsity and therein lies the utility of "controversies".