Tips on Differentiating Between The Different Rhythms

Sinus tachycardia

Sinus tachycardia: Scrutinise the ECG carefully for P waves. These can be difficult to see at faster heart rates. Remember that very fast rates are unlikely in sinus rhythm; maximum heart rate = 220-age is a helpful formula. Direct treatment at the underlying cause (e.g. pain, anxiety, sepsis, shock….). Be wary of discharging a patient with an unresolved tachycardia.

Atrial Flutter

• Look at the rate and suspect flutter if it is 140-160 and stays more or less constant. Look carefully for flutter waves in all leads but especially in leads V1 and II.  Treatment is broadly the same as for atrial fibrillation (see AF later). If symptoms have been present <48 hours than electrical cardioversion is probably the treatment of choice.  Pharmacological cardioversion is generally less effective than in atrial fibrillation. Flecainide can paradoxically lead to an increase in the ventricular rate by causing 1:1 conduction and is best avoided

Re-entrant SVT 

If you cannot spot flutter or P waves that precede the QRS complex then you can safely assume a re-entrant SVT.