Abnormal Rate Or Rhythm
Michael D. Puchalski, MD
DIFFERENTIAL DIAGNOSIS
Common
Premature Atrial Contraction
Transient Bradycardia
Less Common
Complete Heart Block
Supraventricular Tachycardia
Atrial Flutter
ESSENTIAL INFORMATION
Key Differential Diagnosis Issues
Normal heart rate: 100-180 beats per minute (bpm)
Irregular rhythm in this range most often benign premature atrial contractions (PACs)
Bradyarrhythmia is HR < 100 bpm
Tachyarrhythmia is HR > 180 bpm
Supraventricular tachycardia (SVT): HR 220-280 bpm
Atrial flutter: HR 300-600 bpm
Helpful Clues for Common Diagnoses
Premature Atrial Contraction
Atrial contraction not conducted to ventricle,
Heart rate normal unless blocked PACs → ↓ ventricular rate
< 5% may develop SVT
Transient Bradycardia
Anatomically normal heart, due to excessive transducer pressure
Helpful Clues for Less Common Diagnoses
Complete Heart Block
Bradyarrhythmia with slow independent ventricular rate
Look for heterotaxy: Left atrial isomerism → no sinoatrial node
Look for ventricular inversion (i.e., corrected transposition of great arteries)
Check maternal history for connective tissue disease, Ro/La antibody status
Antibodies cross placenta → immune complex-mediated damage to conduction system
Supraventricular Tachycardia
1:1 AV relationship, intermittent or incessant, starts/stops in 1 beat
Atrial Flutter
Atrial rate > ventricular rate, incessant with no variation in atrial rate
Variable degrees of AV block: Most common 2:1
Other Essential Information
PACs account for 85% of cases: Typically resolve without treatment
Bradycardia is difficult to treat, often requires pacing after birth
Poor prognosis with congenital heart disease
Complete heart block associated with in-utero fetal demise
Transplacental drug therapy highly successful for tachycardia
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