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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 10–66) or independent of respiration (nonphasic). This is generally not a pathologic arrhythmia and requires no specific cardiac evaluation.

eFigure 10–66.

Sinus arrhythmia with increase in rate during inspiration and decrease during expiration. (Reproduced, with permission, from Goldschlager N, Goldman MJ. Principles of Clinical Electrocardiography, 13th ed. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, 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 especially in patients who are in excellent physical condition, 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 (eFigure 10–67). 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 (eFigure 10–68).

eFigure 10–67.

Atrioventricular junctional rhythm. A regular QRS rhythm at a rate of 47/min is present. The QRS complexes are of normal duration. No atrial activity precedes the QRS complexes. P waves are seen in the T waves following each QRS complex (arrows). The P waves are upright in aVR and inverted in II and aVF, indicating retrograde atrial depolarization. (Reproduced, with permission, from Goldschlager N, Goldman MJ. Principles of Clinical Electrocardiography, 13th ed. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)

eFigure 10–68.

Atrioventricular (AV) junctional rhythm with retrograde atrial activation and reciprocal (echo) beats. Each QRS complex is followed by an inverted ...

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