An electrocardiogram (EKG) is a non-invasive test that records the heart’s electrical activity. This diagnostic tool translates these signals into a visual tracing to assess heart health. Supraventricular Tachycardia (SVT) is a fast heart rhythm originating in the upper chambers, above the ventricles. Understanding SVT’s appearance on an EKG provides insight into this common cardiac rhythm disturbance.
The Basics of an EKG
A normal EKG tracing displays distinct waves and intervals, each representing a specific electrical event in the heart. The P wave signifies atrial depolarization, the electrical activation leading to the contraction of the heart’s upper chambers. Following the P wave, the QRS complex represents ventricular depolarization, indicating the electrical activation that causes the contraction of the lower chambers. The T wave then illustrates ventricular repolarization, the electrical recovery of the ventricles.
The PR interval measures the time it takes for an electrical impulse to travel from the atria to the ventricles. This segment reflects a conduction delay in the heart’s electrical system, ensuring proper ventricular filling. The QT interval encompasses the entire duration of ventricular depolarization and repolarization. Heart rate is calculated by measuring the time between consecutive QRS complexes, while the regularity of these complexes determines the heart’s rhythm. A normal EKG establishes a baseline for comparison, making it possible to identify deviations caused by various cardiac conditions.
The EKG Signature of SVT
SVT on an EKG tracing exhibits several characteristic features. A primary indicator is a rapid heart rate, typically ranging from 150 to 250 beats per minute. This accelerated rate results from fast electrical impulses originating from above the ventricles. Another defining feature is a narrow QRS complex, appearing slender on the EKG. This narrow appearance indicates the electrical impulse travels through the heart’s normal conduction pathways to activate the ventricles.
The rhythm in SVT is usually very regular, presenting a consistent pattern of narrow QRS complexes at a rapid rate. Identifying P waves in SVT can be challenging due to the rapid heart rate. These atrial electrical signals may be hidden within or immediately after the QRS complex, making them difficult to discern. In some cases, P waves might appear inverted or even seem absent on the EKG.
The PR interval is also often difficult to measure accurately because the P waves are frequently obscured by the rapid rhythm. While not primary diagnostic features, changes in the ST segment or T wave can sometimes be observed during SVT. These changes might result from the increased heart rate, potentially indicating rate-related oxygen demand issues or alterations in the heart’s electrical recovery.
Differentiating SVT from Similar Rhythms
Distinguishing SVT from other fast heart rhythms on an EKG involves recognizing key differences in their electrical signatures. Sinus tachycardia, for example, also presents with a fast heart rate, but it maintains normal P waves that consistently precede every QRS complex. Furthermore, the maximum rate in sinus tachycardia is typically slower than that seen in SVT. These clear P waves and a generally lower peak rate help differentiate it from SVT.
Atrial fibrillation with a rapid ventricular response (RVR) is another condition that can cause a fast heart rate. However, atrial fibrillation is characterized by a chaotic and irregular rhythm, contrasting sharply with the consistent regularity of SVT. Additionally, atrial fibrillation lacks distinct, organized P waves, instead showing a wavy baseline or fine fibrillatory waves. This absence of clear P waves and the irregular ventricular response help distinguish it from SVT.
Ventricular tachycardia (VT) represents a serious fast heart rhythm. A distinguishing feature of VT is a wide QRS complex, which is broader than the narrow QRS complex seen in SVT. This wide QRS indicates that the electrical impulse is originating from within the ventricles themselves, leading to an abnormal and slower conduction through the heart muscle. Recognizing this difference in QRS width is important for patient management and safety.
When to Seek Medical Attention
Interpreting EKG tracings requires specialized medical knowledge and training. Individuals should not attempt to self-diagnose based solely on information from articles or general knowledge. If experiencing symptoms such as a racing heart, palpitations, dizziness, shortness of breath, chest pain, or fainting, it is important to seek prompt medical attention. These symptoms could indicate an underlying heart rhythm issue that requires professional evaluation. A healthcare professional can accurately diagnose the specific type of heart rhythm disturbance and recommend appropriate management or treatment.