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Key Clinical Updates in Sinus Arrhythmia, Bradycardia, & Tachycardia

In patients without evidence of atrioventricular nodal or bundle branch conduction abnormality, a single chamber atrial pacemaker is reasonable.

ESSENTIALS OF DIAGNOSIS

  • Wide variation in sinus rate is common in young, healthy individuals and generally not pathologic.

  • Symptomatic bradycardia may require permanent pacemaker implantation, especially in the elderly or patients with underlying heart disease.

  • Sinus tachycardia is usually secondary to another underlying process (ie, fever, pain, anemia, alcohol withdrawal).

  • Sick sinus syndrome manifests as sinus bradycardia, pauses, or inadequate heart rate response to physiologic demands (chronotropic incompetence).

GENERAL CONSIDERATIONS

Sinus arrhythmia is an irregularity of the normal heart rate defined as variation in the PP interval of more than 120 ms. This occurs commonly in young, healthy people due to changes in vagal influence on the sinus node during respiration (phasic) (eFigure 10–56) or independent of respiration (nonphasic). This is generally not a pathologic arrhythmia and requires no specific cardiac evaluation.

eFigure 10–56.

The rhythm tracing displays the normal heart rate variability with respiration. There is a normal increase in heart rate during inspiration. This sinus arrhythmia is a natural response and is more commonly seen in children than adults. (Reproduced with permission from Coté CJ, Lerman J, Anderson BJ. A Practice of Anesthesia for Infants and Children, 6th ed. Elsevier; 2019. Copyright © Elsevier Inc.)

Sinus bradycardia is defined as a heart rate slower than 60 beats/min and may be due to increased vagal influence on the normal sinoatrial pacemaker or organic disease of the sinus node. In healthy individuals, and particularly in well-trained athletes, sinus bradycardia to rates of 50 beats/min or lower especially during sleep is a normal finding. However, in elderly patients and individuals with heart disease sinus bradycardia may be an indication of true sinus node pathology. When the sinus rate slows severely, the atrial-nodal junction or the nodal-His bundle junction may assume pacemaker activity for the heart, usually at a rate of 35–60 beats/min. This rhythm may also occur in patients with myocarditis, CAD, and digitalis toxicity as well as in individuals with normal hearts. The rate responds normally to exercise, and the diagnosis is often an incidental finding on ECG monitoring, but it can be suspected if the jugular venous pulse shows cannon a waves.

Sinus tachycardia is defined as a heart rate faster than 100 beats/min that is caused by rapid impulse formation from the sinoatrial node. It is a normal physiologic response to exercise or other conditions in which catecholamine release is increased. The rate infrequently exceeds 160 beats/min but may reach 180 beats/min in young persons. The rhythm is generally regular, but serial 1-minute counts of the heart rate indicate that it varies five or more beats per minute with changes in position, with breath ...

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