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CARDIOLOGY*

*The authors acknowledge the special contributions of Binita R. Shah, MD, to prior edition.

BRADYCARDIA

Clinical Summary

Bradycardia is defined as a heart rate below the normal range for age, and its various etiologies are mentioned in Table 5.1. Clinically significant bradycardia is defined as a heart rate <60 beats per minute (bpm) associated with poor systemic perfusion. Signs of circulatory impairment include poor skin perfusion with pallor; cyanosis; cool mottled extremities; prolonged capillary refill; thready, weak, or absent peripheral pulses; and discrepancy in volume between peripheral and central pulses. Patient is irritable, lethargic, and confused, or has decreased level of consciousness. Respiratory difficulty, decreased pulse pressure of >20 mm Hg, hypotension (decompensated shock), and decreased or no urine output can also be found when severe. The spectrum of bradyarrhythmias includes sinus bradycardia, sinus node dysfunction, sinus node arrest with a slow junctional or ventricular escape rhythm, and atrioventricular (AV) block.

An ECG is necessary to exclude second-degree or complete heart block (CHB). Findings on ECG include a slow heart rate with P waves that may or may not be visible. QRS duration may be normal or prolonged (depending on the location of the intrinsic cardiac pacemaker). Dissociation of P waves and QRS is seen in CHB. P wave with a normal PR interval preceding each QRS complex is seen in sinus bradycardia.

Emergency Department Treatment and Disposition

Patients with bradycardia not associated with evidence of poor systemic perfusion need support of ABCs (airway, breathing, and circulation), observation, and reassessment. Hospitalize patient for continued observation, and consult cardiology for asymptomatic bradycardia from drug ingestion, bradycardia resulting from complete AV block or acquired or congenital heart disease (CHD), or patients with refractory bradycardia requiring pacing.

FIGURE 5.1

Sinus Bradycardia. A 12-lead ECG showing a heart rate of 58 bpm. The patient is in sinus rhythm as every QRS complex is preceded by a P wave, a QRS complex follows every P wave, and the P-wave axis is normal. This could be a normal phenomenon in well-trained athletes. (Photo contributor: Shyam K. Sathanandam, MD.)

FIGURE 5.2

Sinus Bradycardia with Junctional Escape Rhythm. A 12-lead ECG showing a heart rate of 53 bpm with junctional escape rhythm (arrows) indicated by narrow QRS complex and no relationship between QRS complex and preceding P waves. The P waves and QRS complex are very close to each other, with occasional P waves embedded within the QRS complex. (Photo contributor: Sushitha Surendran, MD.)

FIGURE 5.3

Differential Diagnosis of Bradycardia. Subarachnoid hemorrhage (SAH) presenting with Cushing triad. A noncontrast head CT scan shows hyperdensity in the basal cisterns in the area of the circle of Willis, with blood in the fourth ventricle (findings typical of SAH) in an adolescent boy presenting to the ED with sudden onset of severe headache, increasing lethargy, and obtundation. Patient had bradycardia, irregular respirations, and hypertension (Cushing triad secondary to ...

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