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Revision as of 16:57, 20 August 2013
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Synonyms and keywords: Sinus tach; sinus tachy
Overview
Sinus tachycardia is a rhythm with elevated rate of impulses originating from the sinoatrial node, defined as a rate greater than 100 beats/min in an average adult. The normal heart rate in the average adult ranges from 60–100 beats/min. Note that the normal heart rate varies with age, with infants having normal heart rate of 110–150 bpm to the elderly, who have slower normals.
Causes
Sinus tachycardia is usually a response to normal physiological situations, such as exercise and an increased sympathetic tone with increased catecholamine release—stress, fright, flight, anger. Other causes include:
- Fever
- Anxiety
- Dehydration
- Malignant hyperthermia
- Hypovolemia with hypotension and shock
- Anemia
- Heart failure
- Hyperthyroidism
- Pheochromocytoma
- Sepsis
- Pulmonary embolism
- Acute coronary ischemia and myocardial infarction
- Chronic pulmonary disease
- Hypoxia
- Intake of nicotine, caffeine, or illicit drugs
- Hyperdynamic Circulation
Differentiating Sinus Tachycardia from other Disorders
Usually apparent on the EKG, but if heart rate is above 140 bpm the P wave may be difficult to distinguish from the previous T wave and one may confuse it with a paroxysmal supraventricular tachycardia or atrial flutter with a 2:1 block. Ways to distinguish the three are:
- Vagal maneuvers (such as carotid sinus massage or Valsalva maneuver) to slow the rate and identification of P waves
- Administer AV blockers (e.g., adenosine, verapamil) to identify atrial flutter with 2:1 block
Postural orthostatic tachycardia syndrome (POTS)
Postural orthostatic tachycardia syndrome (POTS) usually occurs in women with no known heart problems. This syndrome is characterized by normal resting heart rate but exaggerated postural sinus tachycardia with or without orthostatic hypotension.
Diagnosis
Symptoms
Sinus tachycardia is often asymptomatic. If the heart rate is too high, cardiac output may fall due to the markedly reduced ventricular filling time. Rapid rates, though they may be compensating for ischemia elsewhere, increase myocardial oxygen demand and reduce coronary blood flow, thus precipitating ischemia or valvular disease. Sinus tachycardia accompanying a myocardial infarction may be indicative of cardiogenic shock.
Electrocardiogram
- Rate: Greater than 100.
- Rhythm: Regular.
- P waves: Upright, consistent, and normal in morphology (if no atrial disease)
- PR interval: Between 0.12–0.20 seconds and shortens with increasing heart rate
- QRS complex: Less than 0.12 seconds, consistent, and normal in morphology
- Pathophysiology: Sinus tachycardia is considered "appropriate" when a reasonable stimulus such as fever, anemia, fright, stress, or physical activity, provokes the tachycardia. This is in distinction to Inappropriate sinus tachycardia where no such stiumulus exists.
EKG Examples
Shown below is an EKG example of sinus tachycardia with a heart rate of 125/min. The rhythm is regular.
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/File:Sinustachycardia.jpg
Shown below is an EKG example of 12 lead EKG showing sinus tachycardia. The heart rate is 150 bpm
Copyleft image obtained courtesy of ECGpedia, http://en.ecgpedia.org/wiki/Main_Page
Treatment
Not required for physiologic sinus tachycardia. Underlying causes are treated if present.
Acute myocardial infarction: Sinus tachycardia can present in more than a third of the patients with AMI but this usually decreases over time. Patients with sustained sinus tachycardia reflects a larger infarct that are more anterior with prominent left ventricular dysfunction, associated with high mortality and morbidity. Tachycardia in the presence of AMI can reduce coronary blood flow and increase myocardial oxygen demand, aggravating the situation. Beta blockers can be used to slow the rate, but most patients are usually already treated with beta blockers as a routine regimen for AMI.
Practically, many studies showed that there is no need for any treatment.
IST and POTS. Beta blockers are useful if the cause is sympathetic overactivity. If the cause is due to decreased vagal activity, it is usually hard to treat and one may consider radiofrequency catheter ablation.
Related Chapters
References
- Hammill S. C. Electrocardiographic diagnoses: Criteria and definitions of abnormalities, Chapter 18, MAYO Clinic, Concise Textbook of Cardiology, 3rd edition, 2007 ISBN 0-8493-9057-5