When the heart suddenly begins to race, it can be a confusing and frightening experience. Many people hear the terms Supraventricular Tachycardia (SVT) and Atrial Tachycardia (AT) used interchangeably, assuming they are the same condition. While both describe a rapid heart rhythm originating in the upper chambers, their relationship is hierarchical: SVT is the broad category, and AT is a specific example. Understanding this precise connection is necessary for proper diagnosis and treatment. The distinction lies in the exact location and mechanism causing the rapid heart rate.
Defining Supraventricular Tachycardia (SVT)
Supraventricular Tachycardia (SVT) is an umbrella term for any rapid heart rhythm originating at or above the ventricles, meaning within the atria or the atrioventricular (AV) node. The heart rate must exceed 100 beats per minute at rest to be classified as a tachycardia. This rapid rate shortens the time the ventricles have to fill with blood, which reduces the heart’s pumping efficiency.
Individuals experiencing an SVT episode often report symptoms such as sudden-onset palpitations, a fluttering sensation in the chest, lightheadedness, or dizziness. The onset and termination of these episodes are frequently abrupt, a characteristic often referred to as paroxysmal.
SVT encompasses several distinct arrhythmias. Common types include Atrioventricular Nodal Reentrant Tachycardia (AVNRT), which involves a re-entry circuit within the AV node. Another type is Atrioventricular Reciprocating Tachycardia (AVRT), which utilizes an abnormal electrical connection between the atria and ventricles (an accessory pathway). Atrial Tachycardia (AT) is also classified under the SVT umbrella, but its mechanism is localized entirely within the upper chambers.
Understanding Atrial Tachycardia (AT)
Atrial Tachycardia (AT) is a specific type of rapid heart rhythm that originates from a small, localized area within the atria, excluding the sinus node. This origin point is referred to as an ectopic focus, meaning it is outside the heart’s normal pacemaker location. The electrical rate in AT is typically between 100 and 250 beats per minute.
The mechanism driving AT is usually one of three types: enhanced automaticity, triggered activity, or micro-reentry. Enhanced automaticity occurs when a cluster of atrial cells spontaneously fires electrical signals at an abnormally fast rate. Triggered activity involves electrical oscillations that initiate a sustained rapid rhythm.
Micro-reentry involves a localized electrical short circuit within the atrial muscle, causing the impulse to loop continuously. Unlike other common SVTs, AT does not rely on the AV node or an accessory pathway for rhythm maintenance. This independence is a fundamental distinction. AT can be classified as focal or multifocal, involving multiple independently firing foci.
The Relationship Between AT and SVT
The core difference between Atrial Tachycardia (AT) and Supraventricular Tachycardia (SVT) is classification. SVT is the broad category that includes all rapid rhythms originating above the ventricles, and AT is one specific member of that group. Therefore, all Atrial Tachycardias are Supraventricular Tachycardias, but not every SVT is an Atrial Tachycardia.
Clinicians use the electrocardiogram (ECG) to distinguish AT from other SVT types like AVNRT or AVRT, primarily by analyzing the P wave. In AT, the P wave morphology is abnormal because the impulse originates outside the normal sinus node. AT often displays a “long RP” pattern, where the time from the QRS complex to the next P wave (RP interval) is longer than the PR interval.
Conversely, in AVNRT, the P wave is often hidden within or immediately follows the QRS complex, resulting in a “short RP” pattern. This specific differentiation is necessary because treatment strategies vary significantly based on the underlying mechanism.
Diagnostic Tools and Treatment Approaches
Confirming the precise type of Supraventricular Tachycardia requires several diagnostic steps, beginning with a standard 12-lead electrocardiogram (ECG) captured during the episode. The ECG assesses the heart rate, rhythm regularity, and P wave morphology to differentiate AT from other SVTs. For rhythms that occur infrequently, continuous monitoring devices, such as a Holter monitor or an event recorder, are used to capture an episode.
When the diagnosis remains uncertain, or when interventional treatment is planned, an Electrophysiology (EP) study is performed. This invasive procedure involves threading thin catheters into the heart to map the electrical signals and pinpoint the exact location of the ectopic focus or re-entrant circuit. This mapping guides curative procedures.
Treatment for AT and other SVTs follows a spectrum, from medication to interventional procedures. Initial management often involves rate-controlling medications, such as beta-blockers or calcium channel blockers. For patients with recurrent or symptomatic Atrial Tachycardia, catheter ablation is an effective, often curative option. This procedure uses energy to destroy the small area of heart tissue causing the faulty electrical signals, preventing recurrence.