Q wave in lead V1-V2

A 60-year old male presented with acute dyspnea and chest pain. He was tachypnic and ill looking. Here is the ECG:

Sinus rhythm @100bpm. Incomplete RBBB. Q wave in lead V1 

What is the likely diagnosis? Septal MI (old)? But the patient has acute onset dyspnea and chest pain.

What is the significance of Q wave in lead V1-V2?

QS pattern in V1-2 usually is associated with a septal infarct, but it can occur with anatomic changes (vertical axis) due to lung disease or LVH and with intraventricular conduction defects such as LAFB, LBBB, and WPW or with hypertrophic cardiomyopathy.

In one study (http://www.ncbi.nlm.nih.gov/pubmed/14731215), 99 cases having QS deflections in both leads V1 and V2 but no other ECG abnormality were studied and reported that prior MI, or presence of clinical CAD was present in only about 20% of the cases. Authors further concluded that QS deflections in leads V1-V2 appeared most often to be an artifact of precordial lead placement.

Patient in the present case had large mobile thrombus in the right heart chamber leading to Acute Pulmonary Embolism. Patient was managed by intravenous tPA and improved rapidly.  (ECG courtesy: Dr Stephen W Smith)

Final note

If the history does not suggest a MI or another explanation, the ECG should be repeated with anatomically correct electrode placement. If the patient has pulmonary disease as an explanation, other ECG findings of lung disease should be present. The diagnosis of septal infarction should not be made if LAFB, LBBB or WPW are present.