A 50-year-old man is brought to the emergency room with substernal chest pain. An electrocardiogram

Discussion in 'USMLE STEP 1' started by samuel, Dec 21, 2014.

  1. samuel

    samuel New Member

    A 50-year-old man is brought
    to the emergency room with substernal chest pain. An electrocardiogram is
    performed, which demonstrates ST segment elevation and T wave inversion. Several hours later the patient
    develops an arrhythmia. The electrocardiogram shows random electrical activity without recognizable QRS
    complexes. Which of the following descriptions best describes this arrhythmia?


    A. Accelerated idioventricular rhythm

    B. Accelerated junctional rhythm

    C. Premature ventricular contraction

    D. Ventricular fibrillation

    E. Ventricular tachycardia
  2. samuel

    samuel New Member

    The answer is D. The rhythm described is that of ventricular fibrillation, which is a feared complication of
    myocardial infarction that must be corrected immediately (CPR, defibrillation, IV and intracardiac drugs
    including epinephrine, lidocaine, or procainamide) if the patient is to survive.

    In an accelerated idioventricular rhythm (choice A), a normal latent pacemaker in the ventricles depolarizes at a
    regular, accelerated rate of 50 to 100/min, each time producing unusually shaped (but similar to each other)
    QRS complexes. P waves related to the complexes are not seen.

    In an accelerated junctional rhythm (choice B), the P waves are typically inverted and may precede, follow, or
    be hidden within regular QRS complexes that occur at a rate of 60 to 150/min.

    In a premature ventricular contraction (choice C), an ectopic ventricular pacemaker inserts an ectopic beat
    (typically with a wide and bizarre QRS complex) before the next sinus beat occurs.

    In ventricular tachycardia (choice E), wide and bizarre, but recognizable, QRS complexes occur at an
    accelerated rate.

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