Role of Endothelin in Microvascular Dysfunction Following PCI for NSTEMI

Percutaneous coronary intervention (PCI) for acute coronary syndromes frequently fails to restore myocardial perfusion despite establishing epicardial vessel patency. Endothelin-1 (ET-1) is a potent vasoconstrictor and its expression is increased in atherosclerotic coronary arteries. Our hypothesis is that increased activity of the endogenous endothelin system contributes to microvascular dysfunction, and adjunctive therapy with an endothelin receptor antagonist will result in improved microvascular blood flow.

Aims: The aims of the study are to assess in patients with non ST-elevation myocardial infarction, whether: 1) PCI causes an increase in coronary blood ET-1 level; 2) an endothelin receptor antagonist acutely improves coronary microvascular blood flow following PCI.

Non-ST segment elevation myocardial infarction (NSTEMI) is one type of heart attack. It is defined as the development of heart muscle necrosis results from an acute interruption of blood supply to a part of the heart which is demonstrated by an elevation of cardiac markers Creatinine Kinase Isoenzyme Muscle/Brain Type (CK-MB) in the blood and the absence of ST-segment elevation in ECG (electrocardiography). ST-segment is a portion of ECG, its elevation indicates full thickness damage of heart muscle. Absence of ST-segment elevation in NSTEMI indicates partial thickness damage of heart muscle occurs. Therefore, NSTEMI is less severe type of heart attack compared to STEMI (ST-segment elevation myocardial infarction) in which full thickness damage of heart muscle occurs.

Our hypothesis is that the endogenous endothelin system contributes to microvascular dysfunction and impaired myocardial reperfusion following successful PCI for non ST-elevation MI, and that endothelin receptor antagonism will improve microvascular flow. The study will provide new insight into the humoral regulation of the microcirculation in patients presenting with acute coronary syndromes.

General methods: This section describes our approach to investigating the specific aims. The study is a prospective, double blind, placebo-controlled trial to assess the efficacy of a selective endothelin type A receptor antagonist (BQ-123), as adjunctive therapy for PCI for non ST elevation MI. The control group will receive placebo rather than another vasodilator in order to specifically elucidate the role of the endogenous endothelin system.

Eligibility Criteria:
Inclusion Criteria:

* Age ≥ 18 years
* Clinical diagnosis of unstable angina or non ST-elevation myocardial infarction, and requiring clinically indicated PCI for the management of non ST elevation acute coronary syndrome.

Exclusion Criteria:

* Systemic hypotension (systolic \<90 mmHg)
* Heart failure or known ejection fraction \< 30%
* Left main disease
* Culprit lesion is in a saphenous vein graft
* 100% occlusion of the culprit vessel or culprit is an ostial right coronary stenosis
* Currently enrolled in other active cardiovascular investigational studies
* Severe endocrine, hepatic, or renal disorders
* Pregnancy or lactation
* Federal Medical Center inmates
* Inability or unwillingness to provide informed consent