Can a bedside echocardiogram help rule out STEMI in patients with suspicious ECG?
No, it can’t (Though, it may be tempting to use a rapid echo to look for wall motion defect to rule out ACS )
If your answer is No, probably you don’t need to read any further in this post.
Diagnosis of STEMI* is based on
*Please note, two of the most popular investigations namely Echo and Coronary angiogram are missing in the list.
Though, echocardiography, a great noninvasive imaging tool at the point of care, it stands almost helpless in the diagnosis of the commonest cardiac emergency ie ACS. It can be called as mother of all paradox even visualizing the myocardium directly with high-quality imaging will not tell you, whether there is ongoing ACS or not.
Relying on wall motion defects without diagnostic ECG changes to diagnose STEMI can be misleading for the simple reason, both unstable angina and old MI can be a 100 % confounding effect. Similarly, absence of WMA doesn’t rule out an evolving STEM(Apart from the bizarre behavior of Ischemic cascade, In the early hours only subendocardial wall stress is noted, that is not good enough to cause visible WMA)
Role of CAG in the diagnosis of STEMI
Urgent CAG is an easy way out in confusing coronary conundrums. But, unless you know the background info even a CTO can be mistaken for ATO/ STEMI . So it is essentially new ST/T shifts (corroborated with CAG) will be the guiding force.
The humble Clinical examination and ECG will prevail over all other modalities in the diagnosis of ACS. Mind you, ECG findings are built within the diagnosis of myocardial infarction ie STEMI (ST-segment) so can’t diagnose it with Echo. Further, an indication of thrombolysis or PCI goes with ECG finding only.
*Having said that, there is a key role for echocardiography in the ER to diagnose alternate cardiac emergencies like Aortic dissection, Acute pulmonary embolism or ACS mimickers like HOCM, etc. Further, echocardiography is used in a big way, in the risk stratification or identifying complication during the ACS management.
In patients with atypical presentations, pacemaker rhythms, LBBB, especially elderly, comorbid, ECG can be quiet normal or non-diagnostic. Here, echo and angiogram may have some adjunct diagnostic roles.
What about newer echo Imaging modalities?
** There has been a suggestion, that regression of Global longitudinal strain(GLS) or new-onset regional loss of myocardial strain, detected by speckle tracked echo is a powerful and the earliest sign of myocardial ischemia.
GLS is proposed to be used in coronary units to rule out ACS. In spite of its Initial promise, we understand it has not been accurate enough to be included as criteria to diagnose ACS . So, as of now, it appears unlikely for echo criteria to be included in the diagnose of STEMI.