Ecg findings of supraventricular tachycardia
Ecg findings of supraventricular tachycardia Supraventricular tachycardia (SVT) is a common arrhythmia characterized by an abnormally rapid heart rate originating above the ventricles. Its hallmark is a sudden onset and termination of a rapid, regular rhythm, which can cause symptoms ranging from palpitations and dizziness to more severe manifestations like chest discomfort or syncope. Electrocardiogram (ECG) findings are pivotal in diagnosing SVT, offering insights into the arrhythmia’s mechanism and guiding management.
Typically, the ECG in SVT displays a narrow QRS complex, usually less than 120 milliseconds, indicating that the electrical impulse is traveling through the normal His-Purkinje conduction system. The heart rate often ranges from 150 to 250 beats per minute, producing a rapid, regular rhythm. This high rate causes the P waves to be either obscured within the preceding T wave or appear immediately after the QRS complex, making them challenging to identify distinctly. When visible, P waves often have abnormal relationships to the QRS, such as being inverted in the inferior leads during typical AV nodal reentrant tachycardia (AVNRT).
One of the hallmark ECG features of AVNRT, the most common form of SVT, is the presence of P waves that are either hidden within the QRS complex or appear as pseudo R’ waves in lead V1 or pseudo S waves in inferior leads. This occurs because the atrial and ventricular activation are nearly simultaneous, resulting in a ‘short RP’ interval—meaning the interval from the R wave (ventricular depolarization) to the P wave (atrial depolarization) is brief, often less than 70 milliseconds. Conversely, in some SVT variants like atrioventricular reentrant tachycardia (AVRT), P waves may be more discernible, often appearing after the QRS complex with a longer RP interval.
Another important aspect of ECG analysis is the regularity of the rhythm. SVT is typically very regular, with consistent R-R intervals, which helps differentiate it from other forms of tachycardia such as atrial fibrillation or flutter. The absence of visible P waves or their abnormal position relative to the QRS complex is a significant clue pointing toward an arrhythmia originating above the ventricles.
During episodes of SVT, the QRS complexes are narrow because ventricular conduction is normal. However, the ECG can sometimes show aberrant conduction or pre-existing bundle branch block, leading to widened QRS complexes during the tachycardia. Recognizing these variations is essential for accurate diagnosis.
In summary, the diagnosis of SVT on ECG hinges on recognizing a rapid, regular, narrow-complex tachycardia with P waves either hidden or distorting the QRS complex, and short RP intervals in certain variants. These features not only confirm the presence of SVT but also assist in differentiating it from other supraventricular or ventricular tachycardias, ultimately guiding appropriate treatment strategies.
