Cardiac Blocks Flashcard

D. Rationale: There is an rsR’ pattern in leads V1 and V2 with broad terminal or “slurred” S waves in the lateral precordial leads V4 to V6, which is indicative of complete right bundle branch block.

Answer choice A – In complete heart block, there is an absence of atrioventricular conduction whereby patients will present with severe bradycardia and independent atrial and ventricular rates.
Answer choice B – When there is an incomplete left bundle branch block, the patient will present with ECG changes consistent with the typical left bundle branch block morphology such as a dominant S wave in V1, a broad monophasic R wave in the lateral leads, and the absence of Q waves in the lateral leads, but with a QRS duration < 120 ms.
Answer choice C – In sick sinus syndrome, the abnormal sinus node function will result in symptomatic bradycardia, sinus arrest, or exit block.

C. Rationale: Left anterior fascicular blocks potentially mask inferior wall and anterior wall STEMI.

B. Rationale: A left BBB produces tall R waves in the lateral leads; leads I and V5–V6.

Answer choice A – Left BBB produces deep S waves in the precordial leads, V1–V3.
Answer choice C – Tall, peaked T waves typically represent hyperkalemia.
Answer choice D – Inverted T waves represent myocardial ischemia.
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D. Rationale: The image represents a bifascicular block of the right bundle branch with a left anterior fascicular block variant. The ‘X’ represents the block at the right bundle branch and at the left anterior fascicle. ECG findings in this bilateral fascicular block include a QRS duration > 120 ms; rsR’ complex in V1, which is typically seen in right bundle-branch block; left axis deviation; small q waves in lead aVL; rS complex in leads II, III, and aVF with positive T waves; and a clockwise rotation in the precordial leads.

Answer choice A – Right axis deviation would manifest as a dominant R wave in leads II, III, and AVF.
Answer choice B – A short PR interval would manifest as a PR interval < 0.12 seconds.
Answer choice C – A bilateral fascicular block would manifest as a counterclockwise rotation in the precordial leads.

A. Rationale: Incomplete right bundle-branch block is commonly seen in young patients. There is a notching in the QRS complex described as an rSr’ pattern.

Answer choices B & C – ST elevation and ST depression indicate coronary artery disease.
Answer choice D – The presence of a delta wave represents pre-excitation syndromes such as Wolff-Parkinson-White syndrome.

D. Rationale: The diagnostic criteria of right bundle branch block include a broad QRS complex, an rsR’ in precordial leads V1–V3, and wide slurred S waves in lateral leads I, aVL, and V5–V6. These findings are brought about by the higher magnitude of impulses from the left ventricular depolarizations than the right ventricular depolarizations.

D. Rationale: Studies have shown that an isolated left posterior fascicular block is most likely produced by an inferior wall myocardial infarction.

Answer choice A – An isolated left anterior fascicular block is most likely caused by left ventricular hypertrophy.
Answer choice B – Fibrosis of the infrahisian conduction system known as Lenégre disease most likely causes an isolated left anterior fascicular block.
Answer choice C – A pulmonary embolism most likely causes right ventricular hypertrophy with an isolated right fascicular block.

A. Rationale: Inferior wall MI is associated with left posterior fascicular block, particularly if the frontal QRS axis is between +50° and +140°. Left posterior fascicular block masks the classic ECG characteristics of myocardial infarction.

Answer choice B – Ventricular tachycardia is a dysrhythmia that is unassociated with left posterior fascicular block.
Answer choice C – Wolff-Parkinson-White syndrome is a disorder in which an extra electrical pathway produces a very rapid heartbeat.
Answer choice D – Torsade’s de pointes is a dysrhythmia associated with low magnesium levels.

D. Rationale: The trifascicular block involves the right bundle branch, left anterior fascicle, and left posterior fascicle. The conduction of impulses is maintained if there is the presence of an atypical medial fascicle located in between the left anterior and left posterior fascicles. However, patients may develop a complete atrioventricular block at any time.