How to identify supraventricular tachycardia on ecg
How to identify supraventricular tachycardia on ecg Supraventricular tachycardia (SVT) is a rapid heart rhythm originating above the ventricles, commonly involving the atria or the AV node. Recognizing SVT on an electrocardiogram (ECG) is crucial for prompt diagnosis and management. One of the key features of SVT is a sudden onset and termination of the tachycardia, often with a heart rate ranging from 150 to 250 beats per minute. The ECG during SVT typically shows a narrow QRS complex, which indicates that the electrical conduction is occurring through the normal His-Purkinje system, as opposed to wide complexes seen in ventricular tachycardia.
The first hallmark to identify SVT is a rapid, regular rhythm. On the ECG, the rhythm will appear remarkably consistent, with each P wave followed by a QRS complex at a regular interval. However, P waves may be hidden within the preceding T waves or may be difficult to discern due to the rapid rate. In many cases, the P wave is either superimposed on the QRS complex or appears just after it, which can complicate interpretation. Recognizing the P wave position relative to the QRS is vital; in typical SVT, the P wave often appears inverted in the inferior leads (II, III, aVF) if the origin is from the atria or within the AV node.
Another important feature is the narrow QRS complex, which suggests that the conduction pathway is normal. Wide QRS complexes often point toward ventricular origin or aberrant conduction, which are not characteristic of typical SVT. The QRS duration in SVT usually measures less than 120 milliseconds. Additionally, the PR interval may be shortened or absent, especially in cases of atrioventricular nodal reentrant tachycardia (AVNRT), the most common type of SVT.
The onset and termination of SVT are abrupt, which can sometimes be demonstrated on the ECG as sudden changes in the rhythm. During episodes, the heart rate can accelerate rapidly, and when the episode terminates, the rhythm reverts to the baseline sinus rhythm. The P wave morphology and its relationship to the QRS complex are key clues; for example, in AVNRT, the P wave is often retrograde and seen just after the QRS complex, producing a pseudo R’ wave in lead V1 or a pseudo S wave in inferior leads.
In some cases, the ECG shows specific features like a “short PR interval” or “pseudo R’ wave,” which are characteristic of certain SVT subtypes. The presence of these features, alongside the clinical context of sudden onset and termination of palpitations, helps confirm the diagnosis. It is also essential to differentiate SVT from other rapid rhythms such as atrial flutter with 2:1 conduction or atrial fibrillation, which typically have irregular rhythms or wider QRS complexes.
In summary, identifying SVT on ECG involves looking for a regular, narrow QRS complex tachycardia with a high heart rate, often with P waves that are either hidden or appear in unusual positions relative to the QRS complex. Recognizing these patterns enables clinicians to distinguish SVT from other arrhythmias and to plan appropriate treatment strategies, which may include vagal maneuvers, medications, or electrical cardioversion.
