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294 SECTION III CARDIOvASCuLAR ``CARdIOvASCulAR—PHYSIOlOGY CARDIOvASCuLAR ``CARdIOvASCulAR—PHYSIOlOGY
Torsades de pointes Polymorphic ventricular tachycardia, Drug-induced long QT (ABCDE):
No discernible rhythm characterized by shifting sinusoidal waveforms AntiArrhythmics (class IA, III)
on ECG; can progress to ventricular AntiBiotics (eg, macrolides)
fibrillation (VF). Long QT interval Anti“C”ychotics (eg, haloperidol)
predisposes to torsades de pointes. Caused AntiDepressants (eg, TCAs)
2+
2+
+
by drugs, K , Mg , Ca , congenital AntiEmetics (eg, ondansetron)
abnormalities. Treatment includes magnesium Torsades de pointes = twisting of the points
sulfate.
Congenital long QT Inherited disorder of myocardial repolarization,
syndrome typically due to ion channel defects (most
commonly loss-of-function mutations affecting
+
K channels); risk of sudden cardiac death
(SCD) due to torsades de pointes. Includes:
Romano-Ward syndrome—autosomal
dominant, pure cardiac phenotype (no
deafness).
Jervell and Lange-Nielsen syndrome—
autosomal recessive, sensorineural deafness.
Brugada syndrome Autosomal dominant disorder most common in Asian males. ECG pattern of pseudo-right bundle
branch block and ST elevations in V 1 -V 3 . risk of ventricular tachyarrhythmias and SCD. Prevent
SCD with implantable cardioverter-defibrillator (ICD).
Wolff-Parkinson-White Most common type of ventricular pre-
syndrome excitation syndrome. Abnormal fast accessory
conduction pathway from atria to ventricle
(bundle of Kent) bypasses the rate-slowing
AV node ventricles begin to partially
depolarize earlier characteristic delta wave
with widened QRS complex and shortened PR
interval on ECG. May result in reentry circuit Delta wave
supraventricular tachycardia.
PR interval
Shortened PR interval
Normal PR interval
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