Supraventricular tachycardia (SVT) and paroxysmal supraventricular tachycardia (PSVT) are terms often encountered in cardiology. Both describe episodes of abnormally fast heart rhythms originating above the ventricles. These conditions are seen in emergency and outpatient settings, especially in young, otherwise healthy individuals. Understanding the subtle but critical differences between PSVT and SVT on ECG is essential for accurate diagnosis and effective treatment.
Defining SVT And PSVT
What Is SVT?
Supraventricular tachycardia (SVT) is a broad term used to describe tachyarrhythmias that originate above the ventricles. This includes atrial tachycardia, atrial flutter, atrial fibrillation, and atrioventricular nodal reentrant tachycardia (AVNRT).
SVT can be sustained or intermittent and may or may not have symptoms. It is characterized by a heart rate generally between 150–250 beats per minute (bpm) with a narrow QRS complex unless there is pre-existing bundle branch block.
What Is PSVT?
Paroxysmal supraventricular tachycardia (PSVT) is a type of SVT. The term “paroxysmal” indicates that the arrhythmia starts and stops abruptly. PSVT is most commonly associated with AVNRT and atrioventricular reentrant tachycardia (AVRT), and less often with atrial tachycardia.
Episodes of PSVT can occur sporadically, often triggered by stress, caffeine, alcohol, or underlying heart disease. PSVT is not a separate entity from SVT but rather a descriptor of how the rhythm behaves.
Mechanisms Behind PSVT and SVT
SVT Mechanisms
SVT includes various arrhythmias that differ in their reentry circuits or focal activities:
AVNRT: Reentrant circuit within the AV node, the most common cause of PSVT.
AVRT: Involves an accessory pathway, such as in Wolff-Parkinson-White (WPW) syndrome.
Atrial tachycardia: Arises from ectopic atrial foci.
Atrial flutter/fibrillation: Macro-reentrant or chaotic atrial activity.
PSVT Mechanisms
PSVT commonly involves reentrant circuits that are activated under certain conditions. It is characterized by:
- Sudden onset and termination.
- Often initiated by a premature atrial contraction (PAC).
- Triggered by factors like emotion, exertion, or substances.
Key ECG Differences Between PSVT and SVT
PSVT on ECG
On electrocardiogram (ECG), PSVT typically shows:
Regular narrow QRS complexes (duration <120 ms).
Heart rate: Typically 150–250 bpm.
Absent or retrograde P waves: P waves may be buried in or follow the QRS complex.
Sudden onset and sudden cessation: Visible in Holter or telemetry monitoring.
SVT on ECG
SVT as a general category has broader ECG manifestations, depending on the subtype:
Atrial tachycardia: Visible abnormal P waves preceding each QRS.
Atrial flutter: “Sawtooth” flutter waves at a rate of ~300 bpm with variable conduction.
Atrial fibrillation: Irregularly irregular rhythm with no discernible P waves.
AVNRT/AVRT: Similar to PSVT ECG patterns, may require vagal maneuvers for differentiation.
Clinical Presentation of PSVT vs SVT
Symptoms of PSVT
Patients with PSVT often report:
- Palpitations
- Lightheadedness or dizziness
- Shortness of breath
- Chest discomfort
- Fatigue after episodes
Symptoms usually start and end suddenly, and episodes can last from a few seconds to hours.
Symptoms of SVT
SVT symptoms depend on the type and duration:
- Palpitations (especially in atrial tachycardia or AVNRT)
- Fatigue or dyspnea in atrial fibrillation
- Irregular heartbeat in AF or atrial flutter
- Chest pain, especially in patients with coronary artery disease
Triggers and Risk Factors
Common Triggers
For both PSVT and other SVTs, common triggers include:
- Emotional stress
- Excess caffeine or alcohol
- Electrolyte imbalances
- Thyroid disorders
- Congenital heart defects or accessory pathways
Who Is at Risk?
Young, healthy individuals—especially women—are often affected by PSVT. SVT may occur in any population, particularly those with heart disease, structural abnormalities, or metabolic issues.
Diagnostic Approach: Confirming the Type
Initial ECG
The resting ECG is the cornerstone of arrhythmia diagnosis. If the arrhythmia is not captured on a 12-lead ECG, Holter or event monitors can help.
Vagal Maneuvers
In cases of PSVT, vagal maneuvers (such as Valsalva or carotid massage) may terminate the episode. This therapeutic response is also diagnostic.
Adenosine Administration
Intravenous adenosine can terminate AVNRT and AVRT (forms of PSVT), helping to differentiate them from atrial tachycardias that are less responsive.
Management of PSVT vs SVT
Acute Treatment
PSVT: Vagal maneuvers, adenosine, beta-blockers, or calcium channel blockers.
SVT (broadly): Depends on subtype—AF may need rate/rhythm control and anticoagulation, flutter may need cardioversion.
Long-term Treatment
For recurrent PSVT:
- Medications like beta-blockers or antiarrhythmics
- Catheter ablation for curative therapy, especially in AVNRT or AVRT
For SVTs like atrial fibrillation or flutter:
- Chronic anticoagulation if stroke risk is elevated (e.g., CHA2DS2-VASc score)
- Rhythm or rate control strategies
- Ablation or surgical options in refractory cases
Prognosis and Complications
Prognosis of PSVT
PSVT is generally not life-threatening but can affect quality of life. Episodes may become more frequent over time. Catheter ablation offers a high cure rate with minimal risk.
Complications of SVT
Complications vary by type. Atrial fibrillation increases stroke risk. Persistent tachycardias can cause cardiomyopathy if left untreated. Proper diagnosis and treatment significantly reduce long-term risks.
Summary: Comparing PSVT and SVT on ECG
| Feature | PSVT | SVT |
|---|---|---|
| Definition | Subset of SVT with abrupt onset/termination | Broad term for all supraventricular tachycardias |
| ECG Pattern | Regular, narrow QRS; hidden or retrograde P waves | Varies depending on type (AF, flutter, etc.) |
| Rate | 150–250 bpm | Variable |
| Response to Adenosine | Often terminates | May or may not respond |
| Management | Vagal maneuvers, adenosine, ablation | Depends on underlying type |
Conclusion
While PSVT is a specific type of SVT, distinguishing between the two on ECG is vital for choosing the correct treatment pathway. PSVT is notable for its abrupt onset and classic narrow QRS pattern, often amenable to curative ablation. SVT, being an umbrella term, requires thorough evaluation to identify its specific cause. Recognizing these differences improves diagnostic accuracy and patient outcomes.
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