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Microvascular obstruction and missed infarction
  1. J C C Moon,
  2. P J Oldershaw,
  3. D J Pennell
  1. j.moon{at}

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A 68 year old retired physician with no previous cardiac history presented with a four hour history of central crushing chest pain. His pulse was 90 beats/min, blood pressure 170/90 mm Hg, with no evidence of heart failure. His ECG demonstrated right bundle branch block, and the troponin T was raised at 0.4 μg/ml (normal < 0.1 μg/ml). Over the next 24 hours he had further chest pain. Cardiac x ray angiography demonstrated normal left ventricular function and minor non-flow limiting disease of the mid left anterior descending (LAD) and right coronary (RCA) arteries.

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Cardiovascular magnetic resonance (CMR) was performed. The basal septum was akinetic on cine imaging. After gadolinium-DTPA, in the early phase (< 5 minutes) there was extensive microvascular obstruction (arrow) in the territory of the first septal branch of the LAD. During the late phase (> 10 minutes), these areas still persist but with surrounding hyperenhancement (arrows).

Gadolinium-DTPA is a small molecule that diffuses into the extracellular fluid making the tissue appear bright on CMR. It does not cross intact cell membranes. Because of myocyte death, myocardial infarction tissue has an increased volume of extracellular fluid and slower gadolinium kinetics than normal myocardium, so in the late phase after a bolus it appears bright and hyperenhanced. In some infarcts, as in this case, gadolinium may fail to enter the infarct core because of capillary collapse and microvascular obstruction, and this is best seen in the early phase. If microvascular obstruction is extensive there will be no flow down the subtending coronary artery, even if the artery is re-opened—the no-reflow phenomenon. Microvascular obstruction is associated with a worse prognosis. The transmural extent of infarction predicts subsequent functional recovery and the potential for recovery after revascularisation.

In the light of the CMR findings, the x ray angiography was reviewed. The first septal did not opacify and a stump off the LAD was noted.

This case illustrates how CMR can make the diagnosis of coronary disease where angiography proved difficult to interpret because of ostial occlusion of a side branch vessel. The diagnosis was acute myocardial infarction because of occlusion of the first septal artery with microvascular obstruction.