How sensitive is ECG for diagnosis of MI?

Single 12 lead ECG is 50-70% sensitive.
Serial ECGs >80% sensitive.

Characteristics of normal sinus rhythm?

P wave of sinus origin
Constant PR interval
Rate between 60-100/min
Constant P wave configuration
Constant PP or RR INTERVAL

What is Marriot's lead in ECG and what is its importance?

• MCL1 is also known as Marriot's lead

• It is the most important lead at the time of uncertainty
• Best to assess Atrial activity 
• Helps in analysis of QRS
• Best for analysis of PAT with Block

Refer : Practical Electrocardiography

What is BIX RULE?

Described by Harold Bix, a Viennese Cardiologist from Baltimore

If 'P' wave is halfway between ventricular complex , additional 'P' wave is most probably hiding 'within' the QRS complex

Seen in PAT with block
refer http://download.journals.elsevierhealth.com/pdfs/journals/0147-9563/PIIS0147956307002166.pdf