Supraventricular Tachycardia (SVT) is a condition characterized by an abnormally rapid heart rhythm originating in the upper chambers of the heart, above the ventricles. This rapid firing disrupts the heart’s normal electrical signaling, causing episodes of palpitations, sometimes accompanied by lightheadedness or shortness of breath. Because SVT episodes are intermittent and unpredictable, confirming the diagnosis requires a systematic approach involving patient evaluation and various levels of monitoring.
Initial Clinical Assessment
The diagnostic process begins with a detailed evaluation of the patient’s medical background and current complaints. The physician conducts a thorough medical history, asking specific questions about the frequency, duration, and triggers of the palpitations. Understanding accompanying symptoms, such as chest discomfort or dizziness, helps assess the severity of the episodes.
Gathering information about family history is important, as some SVT forms have a genetic component. The doctor also inquires about caffeine, alcohol, or medication use, which can act as precipitating factors.
The physical examination involves listening to the heart rhythm and sounds using a stethoscope, which may reveal irregularities if the patient is experiencing an episode. Blood pressure and pulse are measured, and the physician looks for signs of underlying heart disease or other conditions that might contribute to the tachycardia.
Primary Diagnostic Tools
Following the initial assessment, the standard procedure is obtaining a 12-lead Electrocardiogram (EKG or ECG). This non-invasive test places electrodes on the skin to record the electrical signals generated by the heart muscle. The EKG provides a snapshot of the heart’s electrical activity, allowing analysis of the rate, rhythm, and conduction pathways.
If the patient is experiencing an SVT episode, the EKG can capture the rapid rhythm, often showing a narrow QRS complex tachycardia exceeding 100 beats per minute. While capturing the event in real-time is ideal, the EKG frequently appears normal if the patient’s rhythm is stable. Even a normal baseline EKG provides valuable information by ruling out certain structural abnormalities.
Blood tests are often performed alongside the EKG to investigate potential non-cardiac causes. These tests evaluate thyroid function, as hyperthyroidism can mimic SVT. Electrolyte levels, such as potassium and magnesium, are also checked, since imbalances can interfere with cardiac electrical stability and trigger a rhythm disturbance.
Long-Term Monitoring Devices
Since SVT is intermittent, a normal EKG often necessitates monitoring devices to capture brief episodes outside of the clinic. The Holter monitor is common, typically worn for 24 to 48 hours, providing a continuous recording of every heartbeat. This continuous data stream is useful for patients who have daily or near-daily episodes likely to occur within the short monitoring window.
For patients with less frequent symptoms, an Event Recorder is worn for a longer duration, sometimes up to 30 days. The event recorder is patient-activated; the individual presses a button to record the heart rhythm immediately before, during, and after an episode. This targeted recording is effective for rhythms that occur days or weeks apart.
Wearable patch monitors are small, adhesive devices worn on the chest for up to 14 days, balancing continuous recording and extended duration. These patches are less cumbersome than traditional Holter monitors and provide a longer window of uninterrupted data. Analyzing the rhythm data confirms the diagnosis and characterizes the specific nature of the SVT.
If episodes are extremely rare, occurring only a few times a year, an Implantable Loop Recorder (ILR) may be considered. This small device is placed under the skin of the chest and monitors the heart rhythm continuously for up to three years. The ILR automatically detects and stores abnormal rhythms, providing a definitive record for infrequent episodes.
Advanced Electrophysiology Testing
When non-invasive monitoring fails to characterize the SVT, or if treatment planning requires precise anatomical detail, physicians may recommend an Electrophysiology Study (EPS). This invasive procedure is typically performed in a cardiac catheterization laboratory under sedation. The goal of an EPS is to map the heart’s electrical system in high detail.
During the study, thin, flexible wires (catheters) are inserted into blood vessels, usually in the groin, and guided into the heart chambers. These catheters contain electrodes that record electrical signals directly from inside the heart muscle. Positioning these mapping catheters allows the cardiologist to create a three-dimensional map of the heart’s electrical pathways.
A defining feature of the EPS is the ability to intentionally induce the tachycardia episode by delivering precisely timed electrical impulses through the catheters. This controlled environment allows the physician to confirm the exact mechanism, or the abnormal short-circuit, responsible for the SVT. Pinpointing the location of this aberrant pathway is crucial, especially if subsequent treatment, such as catheter ablation, is being considered to interrupt the faulty electrical circuit.