Supraventricular tachycardia (SVT) is a collective term for an abnormally fast heart rhythm originating in the upper chambers of the heart (atria) or the atrioventricular (AV) node. This AV node is the electrical junction between the upper and lower chambers. This rapid heart rate, typically exceeding 100 beats per minute (bpm) at rest, is caused by a disruption in the heart’s electrical system, often due to a short-circuiting electrical impulse. While most SVT episodes are not life-threatening, the sudden change in heart rhythm can be alarming and cause noticeable physical symptoms. Episodes often begin and end abruptly, giving the condition a distinct pattern of occurrence.
The Patient Experience
The defining characteristic of an SVT episode is the sudden onset of a rapid, often regular, heartbeat. People frequently describe this sensation as feeling like their heart is “pounding” or “fluttering” in their chest, a symptom known as palpitations. The heart rate typically jumps to a range between 150 and 220 beats per minute, significantly exceeding the normal resting rate.
This rapid pumping action prevents the heart’s lower chambers (ventricles) from fully filling with blood between beats, temporarily reducing circulation to the body. Consequently, individuals often experience lightheadedness, dizziness, or faintness. Mild shortness of breath is also common as the body compensates for less efficient blood flow.
The rapid rhythm can induce anxiety, which compounds the physical discomfort. Episodes can last from a few seconds to several hours, resolving just as abruptly as they began. Some people may also notice a pounding sensation in their neck due to the forceful contraction of the atria against a closed valve.
Clinical Identification on an EKG
Supraventricular tachycardia presents a distinct and recognizable pattern on an electrocardiogram (EKG or ECG). The primary characteristic is a regular, rapid rhythm, with a ventricular rate often falling between 140 and 280 bpm. Rates of 150 to 220 bpm are most common, serving as a clear marker of the abnormal electrical activity.
A defining feature of SVT on an EKG is the narrow QRS complex, which represents the electrical activation of the ventricles. This complex measures less than 120 milliseconds in duration, confirming that the electrical impulse uses the heart’s normal, fast-conducting pathway to reach the ventricles. This narrow width signifies the electrical origin is above the His bundle.
The P wave, which signifies atrial activation, is often obscured or abnormal during an SVT episode. Due to the rapid rate, the P wave is frequently not visible because it is buried within the QRS complex or the T wave. If P waves are visible, they may display a retrograde pattern, appearing inverted in certain EKG leads, or be seen as a subtle notch (pseudo-R’ wave or pseudo-S wave).
Common Triggers and Contributing Factors
SVT is caused by an underlying electrical circuit issue, but specific non-cardiac factors can initiate an episode. High levels of emotional stress or anxiety are frequent triggers, as the resulting release of adrenaline overstimulates the heart’s electrical pathways. The combination of stress and fatigue makes the abnormal electrical circuit more easily activated.
Dietary and lifestyle choices also provoke SVT in susceptible individuals. Excessive consumption of stimulants like caffeine and alcohol, which disrupts heart rhythm stability, are common culprits. Nicotine use also contributes to the onset of an episode.
Certain over-the-counter and prescription medications contain stimulating ingredients that can precipitate an SVT event. Cold and allergy medicines, particularly decongestants containing pseudoephedrine or phenylephrine, are known to increase heart rate and trigger the arrhythmia. Intense physical exertion or dehydration can also initiate the rapid heart rhythm.
Recognizing Emergency Symptoms
Though SVT is usually benign, severe symptoms indicate the heart is struggling to maintain adequate blood circulation and require immediate medical attention. The most serious warning sign is the development of profound chest pain or pressure. This suggests the fast heart rate is depriving the heart muscle of necessary oxygen.
A sudden loss of consciousness (syncope) or a feeling of nearly fainting (presyncope) warrants an emergency call. These symptoms occur when the rapid heart rate causes blood pressure to drop significantly, momentarily starving the brain of blood flow.
Difficulty breathing or severe, prolonged shortness of breath that does not improve quickly can signal serious complications, such as heart failure due to the sustained rapid rate. Any SVT episode lasting many hours or accompanied by weakness should be treated as an emergency to prevent potential damage to the heart muscle.