MedEducation Flix – SVT & ECG Case-Based Self-Assessment (31 Questions)

This ECG demonstrates **supraventricular tachycardia (SVT)**. It is characterized by a narrow-complex regular rhythm, typically >150 bpm, with absent or retrograde P waves. The clinical context and abrupt onset/termination help distinguish it from sinus tachycardia.

The most common mechanism is AV nodal reentrant tachycardia (AVNRT), caused by dual AV nodal pathways creating a reentrant circuit.

AVRT (atrioventricular reentrant tachycardia) involves an accessory pathway (e.g., in Wolff-Parkinson-White syndrome) connecting the atria and ventricles, whereas AVNRT is confined to the AV node.

A narrow QRS tachycardia with a short RP interval and retrograde P waves, often seen after the QRS complex.

Palpitations, dizziness, chest discomfort, dyspnea, and occasionally syncope, often with sudden onset and termination.

Vagal maneuvers such as Valsalva, carotid sinus massage, and facial immersion in cold water can increase vagal tone and terminate AVNRT.

Adenosine is first-line pharmacologic treatment for acute termination of narrow-complex SVT (especially AVNRT and AVRT) if vagal maneuvers fail.

Ensure the rhythm is not atrial fibrillation with an accessory pathway, as adenosine may precipitate ventricular fibrillation. Also monitor for bronchospasm in asthmatics.

Start with 6 mg rapid IV push followed by saline flush; if ineffective, escalate to 12 mg. A second 12 mg dose can be used if needed.

Flushing, chest discomfort, dyspnea, transient AV block, and a brief feeling of doom, all resolving quickly due to its short half-life.

Verapamil or diltiazem are effective calcium channel blockers, particularly in patients with bronchospasm or adenosine intolerance.

SVT often has abrupt onset/termination and a fixed rate (usually >150 bpm), whereas sinus tachycardia has a gradual onset and rate variation with activity.

If the patient is hemodynamically unstable, has chest pain, hypotension, or altered mental status, or if pharmacologic measures fail.

50–100 J is generally effective for narrow-complex tachycardias.

Regular narrow-complex tachycardia with absent or retrograde P waves; RP interval can help differentiate subtypes.

Catheter ablation of the slow AV nodal pathway is highly effective (>95%) and is preferred over long-term medical therapy.

Wolff-Parkinson-White syndrome involves a congenital accessory pathway (Bundle of Kent) causing pre-excitation and a risk of AVRT or pre-excited AF.

Short PR interval, delta wave (slurred QRS upstroke), and widened QRS complex.

It can block AV nodal conduction, increasing conduction through the accessory pathway and precipitating VF.

Use procainamide or flecainide (if no structural heart disease); avoid AV nodal blockers. If unstable, perform synchronized cardioversion.

Atrial tachycardia originates from a single ectopic atrial focus and often shows a warm-up and cool-down pattern; P waves are often visible and dissociated from QRS.

An irregularly irregular rhythm with ≥3 different P wave morphologies, often associated with COPD and hypoxia.

Correct underlying causes (e.g., hypoxia, electrolyte imbalance). Use rate control with beta-blockers or calcium channel blockers; avoid antiarrhythmics.

Structural heart disease, hyperthyroidism, electrolyte imbalance, stimulant use (e.g., caffeine, cocaine), and pregnancy.

Pregnancy increases SVT risk due to hormonal and volume changes. Manage conservatively with vagal maneuvers, adenosine, and avoid teratogenic drugs. Consider ablation postpartum.

An automatic focus from the AV junction, often post-surgery or drug-induced. ECG shows narrow QRS and inverted P waves in II, III, aVF if visible.

To confirm diagnosis, identify the circuit, and perform ablation in recurrent or drug-refractory SVT cases.

Risk of AV block requiring pacemaker (<1%), vascular complications, pericardial effusion, and rare stroke or infection.

Avoid stimulants (caffeine, energy drinks), manage stress, ensure adequate sleep, and correct underlying medical conditions.

Useful in capturing intermittent episodes, particularly in palpitations with unclear cause. Devices include Holter monitors and patch ECGs.

Short RP (<70 ms) suggests AVNRT; long RP (>70 ms) favors AVRT or atrial tachycardia. Helps distinguish reentrant from focal mechanisms.