A 43-year-old woman presents to her primary care provider with shortness of breath. She reports a 4-month history of progressively worsening difficulty breathing with associated occasional chest pain. She is a long-distance runner but has had trouble running recently due to her breathing difficulties. Her past medical history is notable for well-controlled hypertension for which she takes hydrochlorothiazide. She had a tibial osteosarcoma lesion with pulmonary metastases as a child and successfully underwent chemotherapy and surgical resection. She has a 10 pack-year smoking history but quit 15 years ago. She drinks a glass of wine 3 times per week. Her temperature is 98.6°F (37°C), blood pressure is 140/85 mmHg, pulse is 82/min, and respirations are 18/min. On exam, she has increased work of breathing with a normal S1 and loud P2. An echocardiogram in this patient would most likely reveal which of the following?

Right ventricular hypertrophy with a dilated pulmonary artery

Biventricular dilatation with a decreased ejection fraction

Left ventricular dilatation with an incompetent aortic valve

Left atrial dilatation with mitral valve stenosis

Left ventricular hypertrophy with a bicuspid aortic valve

An ECG from an 8-year-old male with neurosensory deafness and a family history of sudden cardiac arrest demonstrates QT-interval prolongation. Which of the following is this patient most at risk of developing?

First degree atrioventricular block

An 8-year-old girl is brought to the physician by her parents for the evaluation of an episode of unconsciousness while at the playground that morning. She was unconscious for about 15 seconds and did not shake, bite her tongue, or lose bowel or bladder control. Her grandfather died suddenly at the age of 29 of an unknown heart condition; her parents are both healthy. An ECG shows sinus rhythm and a QT interval corrected for heart rate (QTc) of 470 milliseconds. Laboratory studies are within normal limits. Which of the following is the most likely additional finding in this patient?

Subvalvular ventricular outflow obstruction murmur

Skin folds between the mastoid process and acromion

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 62-year-old woman presents to the emergency department complaining of fever, worsening fatigue, and muscle weakness for the previous 48 hours. The patient describes her muscle weakness as symmetric and worse in the upper limbs. Her past medical history is significant for long-standing diabetes type 2 complicated by stage 5 chronic kidney disease (CKD) on hemodialysis. She takes lisinopril, verapamil, metformin, and glargine. Today, the patient’s vital signs include: temperature 38.6°C (101.5°F), pulse 80/min, blood pressure 155/89 mm Hg, respirations 24/min, and 95% oxygen saturation on room air. The cardiac and pulmonary exams are unremarkable. The abdomen is soft and non-tender. Her strength is 3/5 in the upper extremities and 4/5 in the lower extremities and her sensation is intact. Deep tendon reflexes are absent in both the upper and lower limbs. A 12-lead electrocardiogram (ECG) is shown in the image below. Blood work is drawn and the patient is admitted and started on continuous cardiac monitoring. Based on the available information, what is the next best step in managing this patient?

Administer IV calcium gluconate

Order a stat serum potassium level

Administer IV sodium bicarbonate

Administer regular insulin and 50% dextrose in water

Inherited arrhythmia syndromes for USMLE Step 3: High-Yield Internal Medicine Lessons

Long QT Syndrome - The Prolonged Pause

Pathophysiology: Inherited disorder of delayed ventricular repolarization from cardiac ion channel mutations (↓ K⁺ efflux or ↑ Na⁺ influx).
ECG Hallmark: Rate-corrected QT interval (QTc) prolongation.
- QTc > 450 ms in males
- QTc > 470 ms in females
Clinical Features: Recurrent syncope, seizures, or sudden cardiac death (SCD), often triggered by exercise, emotion, or auditory stimuli.
Types:
- Romano-Ward Syndrome: Autosomal dominant, pure cardiac phenotype.
- Jervell and Lange-Nielsen Syndrome: Autosomal recessive, includes congenital sensorineural deafness.

⭐ The hallmark arrhythmia is Torsades de Pointes (TdP), a polymorphic ventricular tachycardia often leading to ventricular fibrillation.

Management:
- First-line: Beta-blockers (e.g., nadolol, propranolol).
- High-Risk: Implantable Cardioverter-Defibrillator (ICD).
- AVOID: QT-prolonging drugs (e.g., macrolides, fluoroquinolones, antipsychotics).

Long QT Syndrome and Torsades de Pointes ECG

Brugada Syndrome - Coved Calamity

Pathophysiology: Autosomal dominant loss-of-function mutation in sodium channels (most commonly SCN5A gene), leading to ↓ Na⁺ current.
Epidemiology: More common in males of Southeast Asian descent.
Presentation: Syncope, seizures, or sudden cardiac death (SCD), often nocturnal.

ECG patterns in Brugada syndrome types 1, 2, and 3

ECG Findings: Pseudo-RBBB and persistent ST-segment elevation in V1-V2.
- Type 1: Coved ST elevation (≥2 mm) followed by an inverted T-wave.
- Type 2/3: Saddleback ST elevation.
Triggers: Fever, alcohol, cocaine, and certain medications (e.g., sodium channel blockers, beta-blockers).
Management: Implantable cardioverter-defibrillator (ICD) is the only proven therapy to prevent SCD.

⭐ Often presents as nocturnal sudden unexplained death syndrome (SUNDS), especially in young Asian males.

ARVC & CPVT - The Stress Syndromes

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC):
- Autosomal dominant; mutations in desmosomal proteins (e.g., PKP2).
- Fibrofatty infiltration of the RV myocardium → ventricular arrhythmias & SCD, especially with exertion.
- ECG: T-wave inversions (V1-V3), prolonged S-wave upstroke, and the pathognomonic Epsilon wave.
- Tx: Beta-blockers, ICD placement for high-risk patients.
Catecholaminergic Polymorphic VT (CPVT):
- Genetic disorder of intracellular calcium handling (RyR2, CASQ2 mutations).
- Adrenergic stress (exercise, emotion) → massive Ca²⁺ release → delayed afterdepolarizations.
- Presents with syncope or SCD in childhood/adolescence.
- Tx: High-dose beta-blockers (nadolol), flecainide; ICD.

⭐ CPVT is classically associated with bidirectional ventricular tachycardia during exercise stress testing.

Brugada syndrome shows a coved ST-elevation in leads V1-V3, often triggered by fever.

Long QT Syndrome (LQTS) presents with Torsades de Pointes (TdP); avoid QT-prolonging drugs.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) involves fibrofatty replacement of the RV myocardium and may show an epsilon wave.

Catecholaminergic Polymorphic VT (CPVT) causes bidirectional VT with exercise or emotion.

These are primarily ion channelopathies that increase risk of sudden cardiac death (SCD).

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play