This 55 year old woman presented with chest pain:

There is sinus rhythm.  There is ST depression and there are negative T-waves in V1-V4. There is also STE in aVL, with reciprocal ST depression in II, III, and aVF.  Looks like acute posterolateral MI, no?  See below.

No, it is not acute MI.  Notice that there is a prominent S-wave in lead I (right axis deviation) and a large R-wave in V1.  This is diagnostic of right ventricular hypertrophy, which is an abnormality of depolarization (abnormal QRS) that results in secondary abnormal repolarziation (ST-T wave).  These negative T-waves and abnormal ST segments are entirely due to RV hypertrophy. 

The physician recognized the abnormal QRS and the appropriate ST-T changes and did not activate the cath lab or initiate anti-ischemic or antiplatelet therapy other than aspirin. 

The patient ruled out for MI.  Echocardiogram showed RV hypertrophy and pulmonary hyptertension.

EMS 12-lead has a great discussion of pulmonary pressures and ECG patterns, and they show another example of this.