Randomized Controlled Trial Comparing Intracoronary Administration of Adenosine or Sodium Nitroprusside to Control for Attenuation of Microvascular Obstruction During Primary Percutaneous Coronary Intervention

>100,000 patients suffering STEMI present in the UK each year. P-PCI in the UK is increasing exponentially. In 2004 there were <1500 P-PCI and in 2007 and 2008 these figures had increased to 5902 and 9224 respectively (BCIS database).

Although P-PCI delivered quickly is more effective than thrombolysis, the efficacy of this, essentially mechanical, technique is limited by the unpredictable phenomenon of no-reflow and the under-stated lesser degrees of MVO. As more UK centres adopt P-PCI the dilemma of how to attenuate MVO will remain. Currently there is no consensus on the optimal management to prevent or attenuate MVO particularly when thrombus laden lesions are treated with P-PCI.

There is divergent clinical practice, even within institutions, in the UK and worldwide. This is because there is no solid evidence base to inform clinicians. The current options for interventional cardiologists are:

1. Routinely aspirate thrombus and give IC vasodilator during the intervention but only in high burden thrombus formation lesions.
2. Perform a standard P-PCI only and then give IV vasodilator if angiographic no-reflow develops.
3. Routinely consider that angiographically silent MVO (i.e a grade below true "no-reflow") may have important impact on infarct size and clinical outcome and treat prophylactically.

Few if any clinicians follow this thinking. Indeed, it appears impossible to predict the incidence of (no-reflow/MVO) from the presenting angiogram (pre- or post- wire or balloon) and it can be argued that irrespective of thrombus burden it would be better to undertake prophylactic treatment in all patients, following the use of aspiration catheter, with delivery of agents able, in theory at least, to reduce (angiographically undetectable) MVO. Several studies of IC adenosine or SNP have shown favourable effects in attenuating MVO. However, the size of effect with either drug and whether indeed there is a difference between them in reducing MVO and infarct size is undetermined.