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Sinus Bradycardia/Tachycardia Including Respiratory Variablity

Scott Goldston

Sinus Tachycardia

Clinical Highlights

Normal adult heart rates are 60 to 100 beats per minute (bpm). See Chap. 8, section on Normal ECG at Age Intervals for discussion of childhood norms. Sinus tachycardia is a rapid heart rate that originates from the sinus node. Diagnostic criteria include normal P-wave morphology (normal for the patient), normal PR intervals (0.12–0.2 s), and a 1-to-1 P wave to QRS relationship. Rate is usually less than 160 except in critically ill patients. Occasionally, sinus tachycardia cannot be confirmed and other rhythm diagnoses must be considered. There are numerous causes, including fever, dehydration, hypoxia, stimulants (ie, coffee, nicotine, and illicit drugs), pulmonary embolism, anemia, anxiety, hyperthyroidism, hypotension/shock, sepsis, and many more.


(A) ECG showing sinus tachycardia with the rate of 123 bpm. If there is suspicion that the P-wave morphology is abnormal on the tachycardic rhythm, compare the P wave with the patient’s normal resting ECG. (B) ECG lead V1 detail of P wave and QRS morphology from the same patient in A at a rate within the normal range. The P wave and QRS complexes are identical in V1 leads


(A) ECG showing rhythm of 169 bpm in a patient with a prior episode of atrial flutter complaining of palpitations and generalized weakness. The computer, the emergency physician, and the cardiologist initially read the ECG as sinus tachycardia (look at lead V3). (B) An ECG lead V3 from an ECG 2 months before presentation. Only after ruling out other causes was the patient successfully slowed with diltiazem, and cardioverted to normal sinus rhythm from atrial flutter.

ED Care and Disposition

Sinus tachycardia may be perceived as a fast or “pounding” heartbeat. Usually symptoms are felt if there is underlying cardiac disease. Treating the underlying disorder will typically resolve the tachycardia and success can be gauged by the trend toward a normal rate. Consider airway, breathing, and circulation first; oxygen, fluids, airway intervention, or specific therapy are often required.

Pearls and Pitfalls

  • Sinus tachycardia is always 1:1 P wave to QRS conduction.

  • There is no specific treatment for sinus tachycardia, treat the underlying cause.

  • If you have trouble identifying P waves in rhythms over 120/minute, consider running the electrocardiogram (ECG) at double speed.

  • If workup and treatment of suspected sinus tachycardia fail to prove useful, pursue other rhythm diagnoses.

Sinus Bradycardia

Clinical Highlights

Sinus bradycardia is a heart rate that is ...

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