RECOVERY OF MICROVASCULAR MYOCARDIAL RESISTANCE AFTER ST ELEVATION MYOCARDIAL INFARCTION AND ITS RELATION TO OUTCOME

In acute myocardial infarction, early restoration of blood flow to the
jeopardized myocardium is of paramount importance to limit infarct size and to
improve long term outcome. Primary percutaneous coronary intervention (PPCI) is
the treatment of choice in these patients1. Despite achievement of adequate
epicardial coronary artery reperfusion in many patients, transient or
persistent myocardial microvascular dysfunction is often present, also referred
to as the no-reflow phenomenon. This microvascular dysfunction and the time
course during which it recovers, is most likely also related to long term
outcome.If microvascular reperfusion is still limited immediately after
myocardial infarction but recovers quickly in the days thereafter, this might
be beneficial for long term prognosis. Several treatments have been suggested
to limit microvascular injury and to improve microvascular reperfusion in the
acute phase of myocardial infarction (such as intra aortic balloon pumping,
glycoprotein IIB/IIIA inhibitors, adenosine, verapamil, nitroglycerine,
cyclosporine, or gap-junction-inhibitors), but it has been difficult to assess
the effect of such treatment due to the simple fact that no methodology has
been available for quantitative assessment of the microcirculation of the
heart.
Assessment of microvascular perfusion and function has been very difficult so
far and has been hampered by a number of methodological and technical
shortcomings. Recently, measurement of absolute blood flow in the infarcted
area and true quantitative calculation of absolute resistance in acute
myocardial infarction, has been performed in a small group of patients using a
technique with thermodilution and continuous infusion of small amounts of
saline. Technical performance of such measurements was difficult so far because
of a complex instrumentation and the necessity of additional administration of
intravenous adenosine. Recently, this technique has been largely simplified by
the introduction of a new multipurpose monorail infusion catheter (RayFlow®,
Hexacath, Paris) and the observation that saline infusion of 15-20 ml/min in
itself already ensures maximum coronary hyperemia. Finally, easy to handle
software has been developed for online interpretation of such measurements.
Consequently, measurement of absolute blood flow and myocardial resistance has
become easy to perform now and the complete measurements only take a few
minutes in addition to a regular PCI or FFR measurement. The measurements are
absolutely safe, reproducible, only a small amount of saline (100 ml at room
temperature) is needed, no additional medication is necessary, the patient
doesn*t experience any discomfort of the measurement and the measurements can
be repeated multiple times within minutes. Therefore, a window is opened for
further examination and quantitative assessment of the microcirculation of the
heart. The purpose of the present study is to evaluate changes in myocardial
resistance over time in STEMI patients, both in the early stage and the
subacute phase. Furthermore, the course of such changes and recovery of the
microcirculation will be correlated to long-term outcome as assessed by MRI
measurements and final infarct size. It is hypothesized that patients can be
divided into 3 groups:
A. Patients with an (almost) normal resistance and flow immediately after PPCI
B. Patients with still elevated resistance and decreased flow immediately after
PPCI, but (partial) recovery in the next days
C. Patients with elevated resistance and decreased flow immediately after PPCI
which do not recover at all.

1) To evaluate changes in microvascular resistance of the infarcted area in the
first hours after ST-elevation myocardial infarction and during the recovery
period (<5 days)
2) To classify patients according to recovery of microvascular resistance
3) To relate (recovery of) microvascular resistance to outcome and preservation
of left ventricular function (MRI, echo, clinical FU at 1 yr)

Propective cohort study, single centre and single arm of 50 STEMI patients

There are no specific benefits expected for the patients. The patient just
undergoes the best possible state-of-the-art treatment for the disease.
Inconvenience and risk associated with participation in this study is
minimal.In the acute phase, the patient has to stay for 30 extra minutes in the
catheterization laboratory to perform the initial measurements. But that extra
period of 30 minutes is applicable to the situation after the stent has been
placed, when the patient is mostly relieved from chest pain and feels
comfortable again.
In some patients, an observation period of 10-30 minutes in the catheterization
laboratory might be desirable anyway for clinical reasons.
The procedure of performing the absolute flow and resistance measurements,
carries a neglectable risk. In our experience in more than 300 patients, we
have never seen any noticeable complication related to this procedure. The same
holds true for the follow-up procedure after three to five days. In the study,
only those patients are participating in whom the indication for a second
procedure and instrumentation of the coronary artery is necessary anyway
(presence of additional coronary stenoses). The study related measurement, only
means a prolongation of that procedure by 10-15 minutes. Undergoing
echocardiography is routine in the period after myocardial infarction.
Undergoing MRI is not routine in all patients, but is completely harmless and
without side effects. MRI assessment might have some benefits for the patient
on the longer term.