Supraventricular tachycardia (SVT) represents a type of abnormally fast heart rhythm that originates in the upper chambers of the heart, above the ventricles. These episodes can cause the heart to beat at rates significantly higher than normal. For many individuals experiencing SVT, adenosine is a common and effective medication used to restore a regular heart rhythm. This medication works by targeting specific electrical pathways within the heart to interrupt the abnormal rhythm.
Understanding Supraventricular Tachycardia
The heart’s electrical system typically controls its rhythmic beating, starting with a signal from the sinoatrial (SA) node, the natural pacemaker, which then travels through the atria to the atrioventricular (AV) node and into the ventricles. Supraventricular tachycardia occurs when there is a disruption in this organized electrical activity, causing the heart to beat rapidly.
This rapid heartbeat often results from an electrical “short circuit” or a re-entry pathway within the heart’s electrical system. Instead of the signal traveling in a normal, linear fashion, it gets caught in a loop, continuously re-exciting the heart muscle. Many types of SVT involve the atrioventricular (AV) node, which acts as a gatekeeper for electrical signals passing from the atria to the ventricles.
When this re-entry circuit forms, the heart rate can suddenly jump to 150 beats per minute or higher, even at rest. This can prevent the heart from filling adequately with blood between beats, potentially leading to symptoms like lightheadedness or dizziness.
What is Adenosine?
Adenosine is a compound found naturally in every cell of the human body, where it plays diverse roles in cellular function and energy transfer. This widespread presence underscores its biological significance in various physiological processes.
As a medication, adenosine is a pharmaceutical preparation of this naturally occurring substance, specifically formulated for medical purposes. It is primarily utilized for its effects on the cardiovascular system, particularly in managing certain heart rhythm disturbances. A notable characteristic of pharmaceutical adenosine is its extremely rapid action and very short half-life, typically less than 10 seconds.
This rapid onset and quick dissipation make it suitable for acute interventions, allowing for precise control during medical procedures. Its short half-life also contributes to its safety profile, as any potential side effects are generally short-lived.
How Adenosine Works to Stop SVT
The primary action of adenosine in stopping SVT centers on its effect on the atrioventricular (AV) node, a critical junction in the heart’s electrical conduction system. When administered, adenosine binds to specific receptors, known as A1 receptors, located on the surface of heart cells, particularly concentrated within the AV node.
Upon binding to these A1 receptors, adenosine initiates a cascade of cellular events that lead to a temporary slowing of electrical conduction through the AV node. This slowing is achieved by opening potassium channels and inhibiting calcium channels in the cells, making them less excitable and prolonging the time it takes for electrical signals to pass through this region.
By transiently blocking or significantly slowing conduction through the AV node, adenosine can interrupt the re-entry electrical circuit that sustains most types of SVT. This interruption effectively “resets” the heart’s electrical system, allowing the normal pacemaker (SA node) to regain control and restore a regular sinus rhythm. The success rate for terminating SVT with adenosine ranges between 78% and 96%.
The Experience of Adenosine Administration
Adenosine is administered intravenously, meaning it is injected directly into a vein, typically as a rapid push. Because of its swift action, patients often experience immediate, albeit temporary, physiological changes.
Patients commonly report a sensation of flushing or warmth, chest pressure, and a feeling of shortness of breath. Some individuals may describe a transient feeling of impending doom or a brief moment where their heart feels like it stops. This sensation is due to the medication causing a brief period of asystole (a flatline on the electrocardiogram) or a very slow heart rate, which is a sign that the medication is working to interrupt the abnormal rhythm.
While alarming, these effects are expected and indicate the medication is successfully targeting the electrical pathway responsible for the SVT. Medical professionals closely monitor patients during administration to manage these temporary side effects and confirm the return to a normal heart rhythm.