Sinus Tachycardia ECG Review

Sinus tachycardia is recognized on an ECG with a normal upright P wave in lead II preceding every QRS complex.

This indicates that the pacemaker is coming from the sinus node and not elsewhere in the atria, with an atrial rate of greater than 100 beats per minute.

The ventricular rate (indicated by the QRS complex rate) is usually also greater than 100 bpm because, in most cases, the P wave conducts through the atrioventricular node to the ventricles to produce a QRS complex in a 1:1 fashion.

On occasion, the sinus rate can be different rom the ventricular rate ― known as AV dissociation ― such as in ventricular tachycardia or third-degree AV block. Treatment is aimed at the primary cause.

The differential diagnosis for sinus tachycardia includes the following:                                        

  1. Exercise
  2. Anemia
  3. Dehydration or shock
  4. Fever/sepsis/infection
  5. Hypoxia
  6. Chronic pulmonary disease
  7. Hyperthyroidism
  8. Pheochromocytoma
  9. Medications/stimulants
  10. Decompensated congestive heart failure
  11. Pulmonary embolus

Sinus tachycardia is rarely a primary cardiac arrhythmia and almost always caused by one of the above conditions. The syndrome of inappropriate sinus tachycardia has been described and is a form of autonomic dysfunction. Sinus node modification or ablation procedures can be done; however, they pose a risk of causing significant sinus node dysfunction, necessitating pacemaker implantation.

ECG Examples:

1.Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric, 6e
2. Surawicz B, et al. AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram. Circulation. 2009; doi:10.1161/CIRCULATIONAHA.108.191095.