P245 Acute ST segment elevation MI in a patient following negative dobuatmine stress echocardiography: Possible mechanisms and lessons to learn
Authors: Lwin T S , Alama M , Farooq M , Shaukat N 
Published: January 2020

Abstract

Funding Acknowledgements
No Funding

Background
Dobutamine stress echocardiography (DSE) has been used as a safe stress modality for assessing myocardial ischemia. Acute myocardial infarction is one of the rare complications of DSE. In this report, we will discuss a case of a 60 year old lady who developed anterior ST-segment elevation myocardial infarction(STEMI) after a negative DSE.

Case report
60 year old lady with a background of PCI to LAD in 2009 presented with angina , a repeat angiogram showed mild to moderate in stent restenosis (ISR) within the LAD but instant wave-free ratio (IFR ) was 0.94 , Fractional Flow Reserve(FFR) 0.84 and negative IVUS studies. Despite that, the patient continued to have chest pain with effort and therefore a DSE was requested. The patient was stressed with intravenous Dobutamine with a maximum dose of 40mcg/kg/min plus 600mcg of atropine. There was no evidence of ischemia. The Patient developed chest pain 15 minutes later. ECG was done and showed ST elevation in anterior leads. Urgent angiography was undertaken which showed acute thrombotic occlusion in the mid LAD with TIMI 0 flow (within the area where ISR had been seen previously) (fig1) . Percutaneous intervention was undertaken and TIMI III flow was restored.

Discussion
Acute STEMI within a few hours after normal DSE is very rare with an incidence of 0.02% (range 0.00% to 0.10%) Plaque destabilisation and rupture are the possible underlying mechanisms behind coronary occlusion. Interestingly, most of the cases happen within 30 mins after the test.
The activation of sympathetic nervous system leads to increased catecholamines, blood viscosity, arterial pressure and heart rate, which are accompanied by detectable increase in platelet aggregation and decrease in fibrinolytic activity that both tend to favour thrombosis. This could lead to propagation of mural thrombus overlying a small plaque erosion that might otherwise have been harmless.
Another interesting learning point is the correlation between chronotropic incompetence (CI) and myocardial ischaemia. Low basal heart rate is one of the predictors of CI (baseline average heart rate of 60 bpm in our case, and she managed to achieve only 81% of target Heart rate (THR) despite the maximum dose of dobutamine and atropine). Many studies examined the significance of CI. Impaired Chronotropic response is associated with an increased risk of mortality and MI. Possible explanation is that patients with CI fail to demonstrate or underestimate extent of ischemia.
With the experience of our case and similar cases from the literature, we suggest symptoms of chest pain should be seriously attended even after a normal DSE. The risk of life-threatening complication should be informed to patients and enough time should be taken for observation post stress test.
More research is needed to clarify the role of DSE in CI patients on account of its potential normal result with submaximal THR and risk of life threatening cardiac event.
Abstract P245 Figure. Coronary Angiogram fig1