Keywords: electrocardiography, EKG, cardiogenic shock, acute myocardial infarction (PubMed Search)
Here's a nice, simple pearl for cardiogenic shock:
"A normal ECG virtually rules out shock due to myocardial infarction."
Essentially, even though MI may be associated with a normal ECG in approximately 5-8% of cases, if a patient has cardiogenic shock due to MI, the ECG will ALWAYS be abnormal.
Gowda RM, Fox JT, Khan IA. Cardiogenic shock: basics and clinical considerations. Int J Cardiol 2008;123:221-228.