A 29-year-old woman with Wolff-Parkinson-White syndrome presents to her cardiologist’s office for a follow-up visit. She collapsed at her job and made a trip to the emergency department 1 week ago. At that time, she received a diagnosis of atrial fibrillation with rapid ventricular response and hemodynamic instability. While in the emergency department, she underwent direct-current cardioversion to return her heart to sinus rhythm. Her current medications include procainamide. At the cardiologist’s office, her heart rate is 61/min, respiratory rate is 16/min, the temperature is 36.5°C (97.7°F), and blood pressure is 118/60 mm Hg. Her cardiac examination reveals a regular rhythm and a I/VI systolic ejection murmur best heard at the right upper sternal border. An ECG obtained in the clinic is shown. Which of the following is the most appropriate treatment to prevent further episodes of tachyarrhythmia?

Refer her for electrophysiology (EP) study and ablation

Begin anticoagulation with dabigatran

Add verapamil to her medication regimen

Begin anticoagulation with warfarin

Refer her for right heart catheterization

A 51-year-old woman with a history of paroxysmal atrial fibrillation comes to the physician for a follow-up visit. She feels well and wants to discuss pausing her only current medication, flecainide. Her pulse is 75/min and regular, blood pressure is 125/75 mm Hg. Physical examination shows no abnormalities. An ECG shows a PR interval of 180 ms, QRS time of 120 ms, and corrected QT interval of 440 ms. Which of the following ECG changes is most likely to be seen on cardiac stress testing in this patient?

False-positive ST-segment depression

A cardiologist is studying how a new virus that infects the heart affects the electrical conduction system of the cardiac myocytes. He decides to obtain electrocardiograms on patients with this disease in order to see how the wave patterns and durations change over time. While studying these records, he asks a medical student who is working with him to interpret the traces. Specifically, he asks her to identify the part that represents initial ventricular depolarization. Which of the following characteristics is most consistent with this feature of the electrocardiogram?

Normal duration defined as less than 120 milliseconds

Elevated in patients with full thickness ischemic injury of the heart

Becomes peaked in states of hyperkalemia

Becomes prominent in states of hypokalemia

Normal duration defined as less than 200 milliseconds

A 40-year-old woman comes to the physician for a 6-month history of recurrent episodes of chest pain, racing pulse, dizziness, and difficulty breathing. The episodes last up to several minutes. She also reports urinary urgency and two episodes of loss of consciousness followed by spontaneous recovery. There is no personal or family history of serious illness. She does not smoke or drink alcohol. Vitals signs are within normal limits. Cardiopulmonary examination shows no abnormalities. Holter monitoring is performed. ECG recordings during episodes of tachycardia show a QRS duration of 100 ms, regular RR-interval, and absent P waves. Which of the following is the most likely underlying cause of this patient's condition?

AV node with slow and fast pathway

Pre-excitation of the ventricles

Mutations in genes that code for myocyte ion channels

Macroreentrant rhythm in the right atria through cavotricuspid isthmus

Fibrosis of the sinoatrial node and surrounding myocardium

A 58-year-old man is diagnosed with right lower lobe pneumonia and has been admitted to a tertiary care hospital. His laboratory investigations suggest that he acquired an infection from the hospital where he underwent an elective abdominal surgery 3 weeks ago. His past medical records reveal a history of deep vein thrombosis and pulmonary embolism one year prior. After a steady clinical improvement over 5 days of inpatient treatment, he develops a cough, breathlessness, and hemoptysis on the 6th day. His temperature is 38.6°C (101.5°F), the pulse is 112/min, the blood pressure is 130/84 mm Hg, and the respiratory rate is 28/min. A general examination shows the presence of edema over the right leg and tenderness over the right calf region. Auscultation of the chest reveals localized crackles over the left mammary region and right infrascapular region. However, his heart sounds are normal, except for the presence of tachycardia, and there are no murmurs. Which of the following is the investigation of choice as the immediate next step in this patient’s management?

Contrast-enhanced computed tomography (CECT) of chest

Serum brain natriuretic peptide

Supraventricular tachycardias for USMLE Step 3: High-Yield Internal Medicine Lessons

SVT Overview - The Heart's Short Circuits

SVT: Atrial Tachycardia, AVNRT, and AVRT Pathways

Definition: Rapid, regular tachyarrhythmias originating above the His bundle.
ECG Hallmark: Narrow QRS complex (<0.12s) is characteristic, unless there's aberrant conduction.
Mechanism: Most commonly caused by a re-entrant circuit in the atria or AV node, creating a "short circuit."
Primary Types:
- AV Nodal Re-entrant Tachycardia (AVNRT): A circuit within the AV node.
- AV Re-entrant Tachycardia (AVRT): Involves an accessory pathway (e.g., WPW syndrome).
- Atrial Tachycardia (AT): An ectopic focus within the atria.

⭐ AVNRT is the most common form of paroxysmal SVT (~60% of cases), frequently presenting in young adults without structural heart disease.

ECG Diagnosis - Reading the Rhythm

Rate: >100 bpm, regular rhythm.
QRS: Narrow (<0.12s) unless pre-existing bundle branch block.
P waves: Key to diagnosis. Assess morphology & relation to QRS (RP interval).

Rhythm	P wave	RP Interval	Key Feature
AVNRT	Buried in QRS or retrograde (inverted in II, III, aVF)	Short RP (<90ms)	Pseudo R' in V1 or S in inferior leads
AVRT	Retrograde, after QRS	Short or Long RP	Look for delta waves (WPW) on baseline ECG
AT	Abnormal axis (non-sinus)	Long RP (>90ms)	Warm-up/cool-down phenomenon

⭐ Vagal maneuvers or adenosine can terminate AVNRT/AVRT by blocking the AV node. In atrial tachycardia or flutter, they will slow the ventricular rate and unmask the underlying atrial activity.

Acute Management - Taming the Tachycardia

Assess Stability: First, determine if the patient is hemodynamically unstable (e.g., hypotension, altered mental status, shock, ischemic chest pain, acute heart failure).

📌 Stable SVT Meds: Adenosine → Beta-blocker → Calcium Channel Blocker.

⭐ In patients with known Wolff-Parkinson-White (WPW) syndrome, avoid AV nodal blockers (adenosine, CCBs, beta-blockers) if they present with an irregular wide-complex tachycardia (AFib with WPW), as this can precipitate VFib. Consider procainamide.

Chronic Control - Preventing Future Flutters

Pharmacologic Prophylaxis:
- First-line: Beta-blockers (e.g., metoprolol) or non-dihydropyridine calcium channel blockers (verapamil, diltiazem).
- Second-line: Class Ic antiarrhythmics (flecainide, propafenone) for patients without structural or ischemic heart disease.
- Class III agents (sotalol, amiodarone) are also options.
Definitive Therapy: Catheter Ablation
- Curative treatment of choice for most recurrent, symptomatic SVTs (AVNRT, AVRT, Atrial Flutter).
- High success rate (>95%) and low complication risk.
- Especially indicated for Wolff-Parkinson-White (WPW) syndrome.

⭐ In patients with pre-excitation (WPW) and atrial fibrillation, AV nodal blocking agents are contraindicated as they can precipitate ventricular fibrillation.

SVT is any regular, narrow-complex tachycardia originating above the His bundle.

AVNRT is the most common type, caused by a reentrant circuit within the AV node.

AVRT (e.g., WPW syndrome) involves an accessory pathway; look for a delta wave and short PR interval on baseline EKG.

Atrial flutter classically presents with a "sawtooth" pattern of P-waves.

Acute management of stable SVT: attempt vagal maneuvers, then give IV adenosine.

Any unstable patient requires immediate synchronized cardioversion.

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