P wave and atrial depolarization US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for P wave and atrial depolarization. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
P wave and atrial depolarization US Medical PG Question 1: A 23-year-old man comes to the emergency department because of palpitations, dizziness, and substernal chest pain for three hours. The day prior, he was at a friend’s wedding, where he consumed seven glasses of wine. The patient appears diaphoretic. His pulse is 220/min and blood pressure is 120/84 mm Hg. Based on the patient's findings on electrocardiography, the physician diagnoses atrial fibrillation with rapid ventricular response and administers verapamil for rate control. Ten minutes later, the patient is unresponsive and loses consciousness. Despite resuscitative efforts, the patient dies. Histopathologic examination of the heart at autopsy shows an accessory atrioventricular conduction pathway. Electrocardiography prior to the onset of this patient's symptoms would most likely have shown which of the following findings?
- A. Epsilon wave following the QRS complex
- B. Prolongation of the QT interval
- C. Cyclic alteration of the QRS axis
- D. Slurred upstroke of the QRS complex (Correct Answer)
- E. Positive Sokolow-Lyon index
P wave and atrial depolarization Explanation: ***Slurred upstroke of the QRS complex***
- The patient's presentation with **atrial fibrillation with rapid ventricular response** and subsequent collapse after verapamil administration—a calcium channel blocker—is classic for a pre-excitation syndrome like **Wolff-Parkinson-White (WPW) syndrome**.
- In WPW, an accessory pathway (bundle of Kent) bypasses the AV node, leading to a **short PR interval** and a **delta wave** (slurred upstroke of the QRS complex) on ECG during normal sinus rhythm.
*Epsilon wave following the QRS complex*
- An **epsilon wave** is characteristic of **arrhythmogenic right ventricular cardiomyopathy (ARVC)**, representing delayed depolarization of the right ventricle.
- While ARVC can cause arrhythmias, it is distinctly different from the pre-excitation syndrome described, which involves an accessory pathway.
*Prolongation of the QT interval*
- **Prolonged QT interval** is associated with an increased risk of **torsades de pointes**, a polymorphic ventricular tachycardia.
- This finding is typical of **long QT syndrome** and does not directly relate to an accessory atrioventricular conduction pathway.
*Cyclic alteration of the QRS axis*
- **Cyclic alteration of the QRS axis** or electrical alternans is seen in conditions causing swings in cardiac position, most notably **pericardial effusion with tamponade**.
- This ECG finding is unrelated to accessory pathways or the mechanisms of pre-excitation syndromes.
*Positive Sokolow-Lyon index*
- A **positive Sokolow-Lyon index** signifies **left ventricular hypertrophy (LVH)**, characterized by large QRS voltages (e.g., SV1 + RV5/V6 ≥ 35 mm).
- While LVH can be associated with various cardiac conditions, it is not a direct ECG manifestation of an accessory atrioventricular conduction pathway.
P wave and atrial depolarization US Medical PG Question 2: A researcher is studying how electrical activity propagates across the heart. In order to do this, he decides to measure the rate at which an action potential moves within various groups of cardiac muscle tissue. In particular, he isolates fibers from areas of the heart with the following characteristics:
A) Dysfunction leads to fixed PR intervals prior to a dropped beat
B) Dysfunction leads to increasing PR intervals prior to a dropped beat
C) Dysfunction leads to tachycardia with a dramatically widened QRS complex
D) Dysfunction leads to tachycardia with a sawtooth pattern on electrocardiogram
Which of the following is the proper order of these tissues from fastest action potential propagation to slowest action potential propagation.
- A. B > D > C > A
- B. D > C > A > B
- C. B > C > D > A
- D. A > D > C > B (Correct Answer)
- E. A > C > D > B
P wave and atrial depolarization Explanation: ***A > D > C > B***
* **Purkinje fibers (A)** have the fastest conduction velocity in the heart to ensure rapid and synchronous ventricular depolarization. The description of "fixed PR intervals prior to a dropped beat" in **Mobitz type II second-degree AV block** indicates an issue with conduction distal to the AV node, often in the His-Purkinje system, while still maintaining typical conduction through the atria and AV node for conducted beats.
* **Atrial muscle (D)** has a faster conduction velocity than the AV node but slower than Purkinje fibers. The "sawtooth pattern on electrocardiogram" unequivocally points to **atrial flutter**, which is characterized by rapid, regular depolarization of the atria.
* **Ventricular muscle (C)** has a conduction velocity slower than Purkinje fibers but faster than the AV node. "Tachycardia with a dramatically widened QRS complex" is characteristic of **ventricular tachycardia (VT)**, which arises from abnormal electrical activity within the ventricles.
* **AV node (B)** has the slowest conduction velocity in the heart, which allows for proper ventricular filling. "Increasing PR intervals prior to a dropped beat" describes **Mobitz type I second-degree AV block (Wenckebach phenomenon)**, which is due to progressive prolongation of conduction delay within the AV node itself.
*B > D > C > A*
* This order incorrectly places the **AV node (B)** as the fastest and **Purkinje fibers (A)** as the slowest, which is contrary to the known conduction velocities in the heart.
* The AV node is critical for delaying the impulse, making it the slowest, while Purkinje fibers are designed for rapid spread, making them the fastest.
*D > C > A > B*
* This option incorrectly places **atrial muscle (D)** as faster than **Purkinje fibers (A)**. Purkinje fibers have the fastest conduction velocity in the heart, considerably faster than atrial muscle.
*B > C > D > A*
* This arrangement incorrectly lists the **AV node (B)** as the fastest and **Purkinje fibers (A)** as the slowest. The AV node is the slowest for its physiological role of delaying ventricular contraction, while Purkinje fibers are optimized for rapid conduction.
*A > C > D > B*
* While placing **Purkinje fibers (A)** as the fastest and the **AV node (B)** as the slowest is correct, this order incorrectly places **ventricular muscle (C)** as faster than **atrial muscle (D)**. Atrial muscle generally conducts faster than ventricular muscle in normal physiology.
P wave and atrial depolarization US Medical PG Question 3: A 42-year-old woman comes to the physician because of 2 episodes of loss of consciousness over the past week. She recovered immediately and was not confused following the episodes. During the past 5 months, she has also had increased shortness of breath and palpitations. She has been unable to carry out her daily activities. She also reports some chest tightness that resolves with rest. She has no history of serious illness and takes no medications. She immigrated with her family from India 10 years ago. Her temperature is 37.3°C (99.1°F), pulse is 115/min and irregular, and blood pressure is 108/70 mm Hg. Examination shows jugular venous distention and pitting edema below the knees. Bilateral crackles are heard at the lung bases. Cardiac examination shows an accentuated and split S2. There is an opening snap followed by a low-pitched diastolic murmur in the fifth left intercostal space at the midclavicular line. An ECG shows atrial fibrillation and right axis deviation. Which of the following is the most likely underlying mechanism of these findings?
- A. Increased left ventricular end diastolic pressure
- B. Increased left to right shunting
- C. Increased systemic arterial resistance
- D. Increased left atrial pressure (Correct Answer)
- E. Decreased left ventricular contractility
P wave and atrial depolarization Explanation: ***Increased left atrial pressure***
- The patient's symptoms (dyspnea, palpitations, chest tightness, volume overload signs like JVD, edema, crackles) and cardiac findings (**accentuated S2, opening snap, diastolic murmur**) are highly suggestive of **mitral stenosis**.
- **Mitral stenosis** causes obstruction of blood flow from the left atrium to the left ventricle, leading to a significant increase in **left atrial pressure** to maintain cardiac output, which can then cause atrial fibrillation and pulmonary hypertension.
*Increased left ventricular end diastolic pressure*
- This is typically seen in conditions like **aortic stenosis**, **aortic regurgitation**, or **decompensated heart failure** where the left ventricle is distended or failing.
- The patient's presentation with an **opening snap** and **diastolic murmur** points away from primary left ventricular pathology causing elevated LVEDP, and more towards a valvular issue upstream.
*Increased left to right shunting*
- This typically occurs in **septal defects** (e.g., VSD, ASD, PDA) and would lead to symptoms of pulmonary hypertension and right heart strain, but the specific murmur and opening snap are not characteristic of a shunt.
- While it can cause right ventricular hypertrophy and pulmonary hypertension, the classic auscultatory findings are distinct from those described here.
*Increased systemic arterial resistance*
- This is characteristic of **hypertension** or conditions causing systemic vasoconstriction, which primarily affect afterload on the left ventricle.
- While it can lead to left ventricular hypertrophy over time, it does not explain the specific findings of an **opening snap** and **diastolic murmur**, or the symptoms of pulmonary congestion in this context.
*Decreased left ventricular contractility*
- This would lead to **systolic heart failure** with reduced ejection fraction, causing symptoms like fatigue and dyspnea, and often a **S3 gallop** with a systolic murmur if mitral regurgitation develops.
- However, it does not explain the specific auscultatory findings of an **opening snap** and **diastolic murmur** that are pathognomonic for mitral stenosis.
P wave and atrial depolarization US Medical PG Question 4: A 42-year-old woman comes to the physician because of a 12 month history of progressive fatigue and shortness of breath with exertion. Five years ago, she emigrated from Eastern Europe. She has smoked one pack of cigarettes daily for 20 years. She has a history of using methamphetamines and cocaine but quit 5 years ago. Vital signs are within normal limits. Physical examination shows jugular venous pulsations 9 cm above the sternal angle. The lungs are clear to auscultation. There is a normal S1 and a loud, split S2. An impulse can be felt with the fingers left of the sternum. The abdomen is soft and nontender. The fingertips are enlarged and the nails are curved. There is pitting edema around the ankles bilaterally. An x-ray of the chest shows pronounced central pulmonary arteries and a prominent right heart border. Which of the following is most likely to confirm the diagnosis?
- A. CT angiography
- B. Serologic testing
- C. Doppler echocardiography
- D. High-resolution CT of the lung
- E. Right-heart catheterization (Correct Answer)
P wave and atrial depolarization Explanation: ***Right-heart catheterization***
- This is the **gold standard** for diagnosing **pulmonary hypertension** by directly measuring pulmonary artery pressure, pulmonary wedge pressure, and cardiac output. The patient's symptoms (fatigue, shortness of breath, loud split S2, prominent right heart border, JVP elevation, peripheral edema, digital clubbing) strongly suggest pulmonary hypertension.
- It helps classify the type of pulmonary hypertension and guides treatment strategies, as **mean pulmonary artery pressure (mPAP) > 20 mmHg** at rest is diagnostic.
*CT angiography*
- Primarily used to diagnose **pulmonary embolism** or to evaluate for chronic thromboembolic pulmonary hypertension (CTEPH). While helpful in some cases of pulmonary hypertension, it does not directly measure pressures.
- It would show emboli or chronic organized thrombi if present but doesn't provide the hemodynamic data needed to confirm the severity and type of pulmonary hypertension.
*Serologic testing*
- Used to identify underlying systemic diseases (e.g., **autoimmune conditions like scleroderma**) that can cause pulmonary hypertension. However, it does not directly confirm the diagnosis of pulmonary hypertension itself.
- While it may uncover **etiological factors**, serological markers are not diagnostic for the presence or severity of pulmonary hypertension.
*Doppler echocardiography*
- A crucial initial screening tool that **estimates pulmonary artery pressure** and assesses right ventricular function, often prompting further investigation for pulmonary hypertension.
- While highly suggestive, it is **indirect and an estimation**, and thus not considered definitive for confirming the diagnosis or for precise hemodynamic measurements.
*High-resolution CT of the lung*
- Used to evaluate for **interstitial lung disease** or other parenchymal lung conditions that can cause secondary pulmonary hypertension.
- It provides detailed images of the lung parenchyma but does not directly measure pulmonary pressures or confirm the diagnosis of pulmonary hypertension.
P wave and atrial depolarization US Medical PG Question 5: A 65-year-old woman comes to the physician because of a 3-month history of intermittent palpitations and shortness of breath. Cardiopulmonary examination shows no other abnormalities. An ECG shows an absence of P waves, an oscillating baseline, and irregular RR intervals at a rate of approximately 95 beats per minute. The difference between atrial and ventricular rates in this patient is most likely due to which of the following?
- A. Prolonged influx through voltage-gated Ca2+ channels in the bundle of His
- B. Transient activation of K+ current in Purkinje fibers
- C. Inhibition of the Na+/K+-ATPase pump in ventricular cells
- D. Limited speed of conduction through the left bundle branch
- E. Temporary inactivation of Na+ channels in the AV node (Correct Answer)
P wave and atrial depolarization Explanation: ***Temporary inactivation of Na+ channels in the AV node***
- The ECG findings are classic for **atrial fibrillation**, characterized by a rapid, irregular atrial rhythm (oscillating baseline with no P waves) and an irregularly irregular ventricular response.
- The **AV node's refractory period** and the number of sodium channels available for conduction dictate the rate at which atrial impulses can pass to the ventricles, preventing a dangerously fast ventricular rate.
*Prolonged influx through voltage-gated Ca2+ channels in the bundle of His*
- The **bundle of His** primarily conducts impulses rather than primarily regulating the rate difference between atria and ventricles through calcium channel kinetics.
- Prolonged calcium influx would generally **slow conduction** or decrease excitability, but it's not the primary mechanism explaining the ventricular rate control in atrial fibrillation.
*Transient activation of K+ current in Purkinje fibers*
- **Purkinje fibers** are involved in rapid ventricular depolarization, but their primary role is not to mediate the rate difference between atria and ventricles in atrial fibrillation.
- Activation of K+ current typically leads to **repolarization**, affecting action potential duration, not the overall filtering of atrial impulses.
*Inhibition of the Na+/K+-ATPase pump in ventricular cells*
- Inhibition of the **Na+/K+-ATPase pump** would lead to intracellular sodium accumulation and depolarization, potentially causing arrhythmias, not regulating the ventricular rate in atrial fibrillation.
- This is the mechanism of action for **digoxin**, which can slow AV nodal conduction but through a different primary pathway affecting the pump.
*Limited speed of conduction through the left bundle branch*
- While conduction system abnormalities can occur, a **limited speed of conduction** specifically in the left bundle branch would cause a wide QRS complex or bundle branch block, not the inherent rate-limiting seen in atrial fibrillation.
- The AV node is the primary regulator of ventricular response rate in atrial fibrillation due to its inherent physiological properties.
P wave and atrial depolarization US Medical PG Question 6: A 41-year-old woman presents to the emergency room with chest pain. She has had progressive substernal chest pain accompanied by weakness and mild shortness of breath for the past 2 hours. Her past medical history is notable for poorly controlled systemic lupus erythematosus (SLE), Sjogren syndrome, and interstitial lung disease. She was hospitalized last year with pericarditis presumed to be from SLE. Her temperature is 98.6°F (37°C), blood pressure is 106/56 mmHg, pulse is 132/min, and respirations are 26/min. On exam, the skin overlying the internal jugular vein fills at 9 cm above the sternal angle and distant heart sounds are appreciated. There is no friction rub. She is given 1000cc of intravenous fluids with no appreciable change in her blood pressure. An electrocardiogram in this patient would most likely reveal which of the following findings?
- A. Polymorphic P waves
- B. ST elevations in leads II, III, and aVF
- C. Peaked T waves
- D. Wide QRS complexes with no P waves
- E. Electrical alternans (Correct Answer)
P wave and atrial depolarization Explanation: ***Electrical alternans***
- The patient's symptoms (chest pain, shortness of breath, **hypotension**, **tachycardia**, **elevated JVP**, and **distant heart sounds**) in the context of a history of **pericarditis** and **SLE** are highly suggestive of **cardiac tamponade.**
- **Electrical alternans**, characterized by alternating QRS complex heights due to the swinging motion of the heart in a large pericardial effusion, is a classic EKG finding for cardiac tamponade.
- This finding reflects the mechanical swinging of the heart within the pericardial fluid, causing beat-to-beat variation in QRS amplitude.
*Polymorphic P waves*
- **Polymorphic P waves** (multifocal atrial tachycardia) occur when there are at least three different P wave morphologies on the EKG, indicating multiple ectopic atrial foci.
- This is typically seen in patients with severe lung disease or other conditions causing increased atrial stretch, but it is not a direct consequence or typical finding of cardiac tamponade.
*ST elevations in leads II, III, and aVF*
- **ST elevations in leads II, III, and aVF** indicate an **inferior myocardial infarction**, which is caused by coronary artery occlusion.
- While chest pain is present, the patient's other signs (elevated JVP, distant heart sounds, hypotension not responding to fluids, history of pericarditis/SLE) point away from an acute MI and strongly towards cardiac tamponade.
*Peaked T waves*
- **Peaked T waves** are characteristic of **hyperkalemia**, a condition of excessively high potassium levels in the blood.
- While hyperkalemia can cause cardiac symptoms, it does not typically present with the specific hemodynamic compromise and physical exam findings (elevated JVP, distant heart sounds) described, which are classic for cardiac tamponade.
*Wide QRS complexes with no P waves*
- **Wide QRS complexes with no P waves** are characteristic of a **ventricular arrhythmia**, such as ventricular tachycardia or idioventricular rhythm.
- While the patient is hypotensive and tachycardic, the presenting symptoms and physical exam findings are not directly indicative of a primary ventricular arrhythmia, but rather suggest an extracardiac compression of the heart due to tamponade.
P wave and atrial depolarization US Medical PG Question 7: 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?
- A. AV node with slow and fast pathway (Correct Answer)
- B. Pre-excitation of the ventricles
- C. Mutations in genes that code for myocyte ion channels
- D. Macroreentrant rhythm in the right atria through cavotricuspid isthmus
- E. Fibrosis of the sinoatrial node and surrounding myocardium
P wave and atrial depolarization Explanation: ***AV node with slow and fast pathway***
- This describes **AV nodal reentrant tachycardia (AVNRT)**, a common cause of **paroxysmal supraventricular tachycardia (PSVT)**. The ECG findings of **narrow QRS (100 ms)**, regular RR-interval, and **absent P waves** (often hidden within the QRS complex) are characteristic of AVNRT.
- The patient's symptoms of recurrent chest pain, racing pulse, dizziness, and spontaneous recovery from loss of consciousness fit the episodic nature of **AVNRT**. The presence of two pathways (slow and fast) within the AV node facilitates the reentrant circuit.
*Pre-excitation of the ventricles*
- **Pre-excitation syndromes** (e.g., Wolff-Parkinson-White syndrome) involve an accessory pathway that bypasses the AV node, leading to a **delta wave** and **short PR interval** on the baseline ECG.
- While they can cause SVT, the ECG during tachycardia would typically show a **wide QRS complex** if the accessory pathway is part of the reentrant circuit (antidromic), or a narrow QRS with a visible P wave if orthodromic and the accessory pathway is used for retrograde conduction, which doesn't fully align with the absent P waves and typically *normal* QRS during tachycardia as described.
*Mutations in genes that code for myocyte ion channels*
- This refers to **channelopathies** (e.g., long QT syndrome, Brugada syndrome), which predispose to **ventricular arrhythmias** like **polymorphic ventricular tachycardia** and **ventricular fibrillation**.
- These conditions typically cause **wide QRS tachycardias** and have distinct ECG patterns (e.g., prolonged QT interval, Brugada pattern) not described here. The narrow QRS and regular rhythm point away from primary ventricular channelopathies as the cause of this specific tachycardia.
*Macroreentrant rhythm in the right atria through cavotricuspid isthmus*
- This describes **atrial flutter**, which typically presents with characteristic **"sawtooth" F waves** on ECG, representing atrial activity.
- While atrial flutter can cause recurrent episodes of rapid heart rate, the ECG description of **absent P waves** and a **narrow QRS complex** without F waves makes atrial flutter less likely.
*Fibrosis of the sinoatrial node and surrounding myocardium*
- **Sinoatrial node dysfunction (sick sinus syndrome)** can lead to bradycardia, sinus pauses, or alternating bradycardia and tachycardia (tachy-brady syndrome).
- It does not primarily cause the described paroxysmal narrow-complex tachycardia with absent P waves. The patient's symptoms are more consistent with an abrupt-onset, regular supraventricular tachycardia.
P wave and atrial depolarization US Medical PG Question 8: 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?
- A. Elevated in patients with full thickness ischemic injury of the heart
- B. Becomes peaked in states of hyperkalemia
- C. Becomes prominent in states of hypokalemia
- D. Normal duration defined as less than 120 milliseconds (Correct Answer)
- E. Normal duration defined as less than 200 milliseconds
P wave and atrial depolarization Explanation: ***Normal duration defined as less than 120 milliseconds***
- The question asks for the representation of **initial ventricular depolarization**, which corresponds to the **QRS complex** on an ECG.
- The normal duration of the **QRS complex** is typically less than **0.12 seconds (120 milliseconds)**, reflecting efficient ventricular depolarization.
*Elevated in patients with full thickness ischemic injury of the heart*
- This description refers to the **ST segment elevation** seen in **ST-segment elevation myocardial infarction (STEMI)**, which represents myocardial injury, not initial ventricular depolarization.
- While related to cardiac electrical activity, **ST segment elevation** is a consequence of injury and refers to repolarization abnormalities, not the QRS complex itself.
*Becomes peaked in states of hyperkalemia*
- **Peaked T waves** are characteristic of **hyperkalemia**, indicating altered ventricular repolarization, not ventricular depolarization.
- The T wave represents ventricular repolarization, and its morphology changes significantly with potassium imbalances.
*Becomes prominent in states of hypokalemia*
- A **prominent U wave** is sometimes observed in **hypokalemia**, which follows the T wave and is thought to represent repolarization of Purkinje fibers.
- The U wave is distinct from the QRS complex and does not represent initial ventricular depolarization.
*Normal duration defined as less than 200 milliseconds*
- A duration of less than 200 milliseconds (0.20 seconds) typically refers to the normal duration of the **PR interval**, which represents atrial depolarization and conduction through the AV node.
- The **QRS complex** (initial ventricular depolarization) has a shorter normal duration, typically less than 120 milliseconds.
P wave and atrial depolarization US Medical PG Question 9: A 44-year-old man comes to the emergency department because of persistent palpitations for the past 2 hours. The day before, he was at a wedding, where he drank several glasses of wine and 9–10 vodka cocktails. He has never had similar symptoms before. He is a manager at a software company and has recently had a lot of work-related stress. He is otherwise healthy and takes no medications. His temperature is 36.5°C (97.7°F), pulse is 90/min and irregularly irregular, respirations are 13/min, and his blood pressure is 128/60 mm Hg. Physical examination shows no other abnormalities. An ECG is performed; no P-waves can be identified. Echocardiography shows no valvular abnormalities and normal ventricular function. One hour later, a repeat ECG shows normal P waves followed by narrow QRS complexes. He is still experiencing occasional palpitations. Which of the following is the most appropriate next step in management?
- A. Electrical cardioversion
- B. Defibrillation
- C. Adenosine injection
- D. Observation (Correct Answer)
- E. Catheter ablation
P wave and atrial depolarization Explanation: ***Observation***
- The patient experienced **paroxysmal atrial fibrillation (AF)** likely triggered by **binge alcohol consumption** (holiday heart syndrome), which has already spontaneously converted to normal sinus rhythm.
- Given his hemodynamic stability, normal ventricular function, and the transient nature of this isolated episode, **close observation** for recurrence is the most appropriate initial step.
*Electrical cardioversion*
- This is primarily used for **hemodynamically unstable AF** or for persistent AF that fails to convert spontaneously.
- The patient is currently **hemodynamically stable** and has already converted to normal sinus rhythm, making cardioversion unnecessary.
*Defibrillation*
- **Defibrillation** is used for life-threatening arrhythmias like **ventricular fibrillation** or **pulseless ventricular tachycardia**.
- It is not indicated for stable atrial fibrillation, and the patient has already converted to sinus rhythm.
*Adenosine injection*
- **Adenosine** is used to terminate **supraventricular tachycardias (SVTs)** by blocking the AV node.
- It is generally **ineffective for atrial fibrillation** and not indicated here as the patient is already in normal sinus rhythm.
*Catheter ablation*
- **Catheter ablation** is a definitive treatment for recurrent symptomatic AF or other arrhythmias that are refractory to medical management.
- This patient has experienced a **first-time episode** that spontaneously resolved, making ablation an overly aggressive and premature intervention.
P wave and atrial depolarization US Medical PG Question 10: A 17-year-old girl suddenly grabs her chest and collapses to the ground while playing volleyball at school. The teacher rushes to evaluate the situation and finds that the girl has no pulse and is not breathing. He starts chest compressions. An automated external defibrillator (AED) is brought to the scene within 3 minutes and a shock is delivered. The girl regains consciousness and regular sinus rhythm. She is rushed to the emergency department. The vital signs include: blood pressure 122/77 mm Hg and pulse 65/min. The pulse is regular. An electrocardiogram (ECG) shows a shortened PR interval, a wide QRS complex, a delta wave, and an inverted T wave. Which of the following is the most likely pathology in the conduction system of this patient’s heart?
- A. Impulse generation by tissue in atrioventricular node
- B. Accessory pathway from atria to ventricles (Correct Answer)
- C. Automatic discharge of irregular impulses in the atria
- D. Wandering atrial pacemaker
- E. Blockage in conduction pathway
P wave and atrial depolarization Explanation: ***Accessory pathway from atria to ventricles***
- The ECG findings of a **shortened PR interval**, **delta wave**, and **wide QRS complex** are characteristic of **Wolff-Parkinson-White (WPW) syndrome**, which involves an **accessory pathway** (Bundle of Kent) bypassing the AV node.
- This accessory pathway allows for pre-excitation of the ventricles, predisposing patients to **tachyarrhythmias** like the one experienced by the patient (sudden cardiac arrest).
*Impulse generation by tissue in atrioventricular node*
- This describes a **junctional rhythm**, which would present with a **normal or long PR interval** and a **narrow QRS complex**, contrasting with the given ECG findings.
- A junctional rhythm typically results in a slower heart rate and is not generally associated with sudden cardiac arrest in healthy individuals.
*Automatic discharge of irregular impulses in the atria*
- This typically refers to **atrial fibrillation** or multifocal atrial tachycardia, which would show an **irregularly irregular rhythm** or multiple P-wave morphologies, not the specific PR and QRS abnormalities seen.
- While atrial fibrillation can occur with WPW, the primary pathology described by the ECG findings is the accessory pathway itself.
*Wandering atrial pacemaker*
- A **wandering atrial pacemaker** is characterized by varying P-wave morphology and PR intervals as the pacemaker shifts between different atrial sites, but it generally maintains a normal QRS duration.
- It is typically a benign arrhythmia and does not cause the pre-excitation or the risk of sudden cardiac death seen in this patient.
*Blockage in conduction pathway*
- A **blockage in the conduction pathway** (e.g., AV block) would result in a **prolonged PR interval** or dropped QRS complexes, which is the opposite of the shortened PR interval observed.
- While heart block can cause syncope, it wouldn't explain the pre-excitation pattern (delta wave, wide QRS) seen in the ECG.
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