Supraventricular Tachycardia (SVT) is an abnormally fast heart rhythm that begins in the upper chambers of the heart, above the ventricles. During an episode, the heart rate can suddenly jump to between 150 and 220 beats per minute, or even higher, which is significantly faster than the normal resting rate of 60 to 100 beats per minute. This rapid rhythm is caused by a malfunction in the heart’s electrical system, often due to a short-circuit pathway.
Understanding SVT Symptoms
The most common sign of an SVT episode is a sudden onset of a racing or pounding heart, often described as palpitations. This rapid beating can last from a few minutes to several hours, and the heart rate typically remains fixed throughout the episode. The quickened pace prevents the heart’s lower chambers from filling completely, temporarily reducing the amount of blood pumped out to the body.
This reduction in output often leads to symptoms like dizziness, lightheadedness, mild shortness of breath, or fatigue. If these symptoms are transient and resolve quickly when the heart rhythm returns to normal, immediate hospital intervention is usually not necessary. However, new or worsening symptoms should always prompt contact with a healthcare provider.
Immediate Action: Vagal Maneuvers
For individuals experiencing a stable SVT episode, specific physical actions known as vagal maneuvers are the first line of defense. These maneuvers stimulate the vagus nerve, which helps slow electrical impulses traveling through the heart’s atrioventricular (AV) node, attempting to break the short-circuit rhythm. Success rates for restoring a normal rhythm range from about 20% to over 40%, especially with the modified approach.
The most commonly recommended technique is the modified Valsalva maneuver, which involves bearing down while exhaling against a closed airway. To perform this, a person should blow into an object like a syringe plunger for about 15 seconds. Immediately after straining, the person is laid flat, and their legs are raised to a 45-degree angle for about 45 seconds to increase blood return to the heart, which significantly boosts the maneuver’s effectiveness.
Alternative maneuvers include coughing forcefully or applying an ice-cold, wet towel to the face. These self-management steps should only be attempted if the patient feels stable and is not experiencing any severe symptoms.
Critical Indicators: When Emergency Intervention is Necessary
The decision to seek emergency care is based on “red flag” symptoms, which indicate the rapid heart rate is compromising the body’s circulation. These signs of hemodynamic instability require immediate activation of emergency services, such as calling 911. A sudden and persistent heart rate over 150 beats per minute, especially if accompanied by other severe symptoms, is a cause for serious concern.
Immediate medical attention is necessary if the SVT episode includes any of the following critical indicators:
- Chest pain or pressure resembling angina.
- Fainting (syncope) or near-fainting (pre-syncope), indicating insufficient blood flow to the brain.
- Severe or sudden shortness of breath, potentially signaling heart failure.
- Signs of shock, such as confusion, cold and clammy skin, or a sudden drop in blood pressure.
If the rapid heart rhythm persists for more than 20 to 30 minutes, even without these severe symptoms, medical evaluation is warranted, particularly if vagal maneuvers have failed.
Hospital Protocol: What to Expect Upon Arrival
Upon arrival at the emergency department, the patient will immediately be placed on continuous cardiac monitoring, and an electrocardiogram (ECG) will be performed to confirm the rhythm. Intravenous (IV) access will be established quickly for the rapid administration of medications. In a stable patient, the first pharmacological agent used is typically adenosine, given as a rapid IV bolus that temporarily blocks the AV node to chemically “reset” the heart’s electrical circuit.
If the patient is hemodynamically unstable, showing signs like low blood pressure or altered mental status, the protocol shifts immediately to synchronized electrical cardioversion. This procedure delivers a controlled, timed electrical shock to the heart to instantly restore a normal rhythm. For stable patients where adenosine fails, other IV medications, such as calcium channel blockers (e.g., diltiazem) or beta-blockers, may be used as a second-line treatment to slow the heart rate.