Arrhythmia Interpretation and Diagnosis Flashcards

A 65-year-old male with a history of myocardial infarction presents with a regular, wide complex tachycardia at 150 bpm. The ECG shows a QRS duration of 160 ms, a northwest axis, and evidence of AV dissociation. In lead V1, there is a monophasic R wave. Which of the following is the most likely diagnosis?

Answer: Ventricular tachycardia

Ventricular tachycardia (VT) is the most likely diagnosis. Several features in the description strongly suggest VT over a supraventricular rhythm with aberrancy. These include a history of structural heart disease (prior MI), QRS duration >140 ms, a northwest axis (extreme axis deviation), and the presence of AV dissociation. A monophasic R wave in V1 is also a classic morphological criterion for VT.

A 58-year-old patient presents to the clinic for a follow-up visit. They mention having intermittent, crushing chest pain over the past week, but are currently pain-free. The ECG shows deeply inverted, symmetric T-waves in leads V2 and V3, with minimal (<1mm) ST-segment elevation and preserved R-wave progression. What is the most likely diagnosis?

Answer: Wellens' syndrome

The ECG findings described are characteristic of Wellens' syndrome (specifically Type B). This pattern, often seen when the patient is pain-free, is highly specific for a critical, proximal stenosis of the left anterior descending (LAD) artery and indicates a high risk of an impending large anterior wall myocardial infarction.

Which of the following ECG findings is the defining characteristic of a Mobitz Type II second-degree atrioventricular block?

Answer: A constant PR interval in all conducted beats before an unexpected, non-conducted P-wave.

Mobitz Type II second-degree AV block is characterized by a constant and unchanging PR interval in the conducted beats preceding a suddenly dropped QRS complex (a non-conducted P-wave). Unlike Mobitz Type I (Wenckebach), there is no progressive lengthening of the PR interval. This type of block is typically located in the His-Purkinje system and carries a higher risk of progressing to complete heart block.

A patient with a dual-chamber pacemaker presents with palpitations. Device interrogation reveals a tachycardia with a ventricular paced rate at the programmed upper tracking rate. The intracardiac electrogram shows a consistent 1:1 ventriculoatrial (VA) conduction pattern where a ventricular paced event is followed by a retrograde atrial sensed event, which then triggers the next ventricular paced event. What is the most likely diagnosis?

Answer: Pacemaker-mediated tachycardia (PMT)

This scenario describes a classic endless loop or pacemaker-mediated tachycardia (PMT). PMT is a reentrant arrhythmia where the pacemaker forms the antegrade limb (atrial sensing to ventricular pacing) and the patient's native conduction system provides the retrograde limb (ventricle to atrium). The cycle of V-pace -> retrograde P-wave -> A-sense -> V-pace maintains the tachycardia.

Which of the following ECG findings is considered the only potentially diagnostic pattern for Brugada syndrome without provocative testing?

Answer: Coved-type ST-segment elevation of ≥2 mm in at least one right precordial lead (V1-V3) followed by a negative T-wave.

The Type 1 Brugada pattern is the only ECG finding considered diagnostic of Brugada Syndrome when associated with clinical criteria (e.g., syncope, family history of sudden death). It is defined by a coved-type ST-segment elevation of 2 mm or more in at least one of the right precordial leads (V1, V2, or V3), followed by a negative or biphasic T-wave.

In analyzing a narrow complex tachycardia, which of the following findings would most strongly favor a diagnosis of typical atrioventricular nodal reentrant tachycardia (AVNRT) over orthodromic atrioventricular reentrant tachycardia (AVRT)?

Answer: A visible retrograde P-wave (pseudo r' in V1 or pseudo S in inferior leads) immediately following the QRS complex, resulting in a short RP interval.

Typical (slow-fast) AVNRT involves near-simultaneous activation of the atria and ventricles. This results in the retrograde P-wave being buried within the QRS complex or appearing just at the end of it, creating a very short RP interval (often <70-90 ms). This can manifest as a 'pseudo r' wave' in V1 or a 'pseudo S wave' in the inferior leads. In contrast, orthodromic AVRT involves a larger reentry circuit, typically leading to a longer RP interval.