c_sinus_tachycardia
Table of Contents
sinus tachycardia
see also:
cardiac output = stroke volume x heart rate
mean arterial blood pressure = cardiac output x systemic vascular resistance
thus a reflex tachycardia mediated via baroreceptors attempting to maintain blood pressure will occur if blood pressure falls due to either:
- fall in systemic vascular resistance (eg. vasodilator drugs, ethanol, warm skin such as after a bath)
- reduced cardiac stroke volume (eg. decreased blood volume, decreased venous return to the heart, impaired cardiac pumping)
a sinus tachycardia may also be mediated due to increased sympathetic nervous system activity (eg. hyperthyroidism, circulating adrenaline or sympathomimetic drugs) or blockade of parasympathetic activity (eg. anticholinergics)
introduction
- a sinus tachycardia is generally defined in adults as being a sinus rhythm with rate greater than 100bpm
- while the patient with sinus tachycardia in the ED may just be anxious, in pain or a result of medications such as the asthmatic patient on beta adrenergic agonists such as salbutamol, a sinus tachycardia may be a sign of an acute pathology and even impending death such as via pulseless electrical activity (PEA), or it may be more subacute as in anaemia, cardiac failure or hyperthyroidism.
- most causes of hypotension will result in a reflex sinus tachycardia via a baroreceptor reflex response (unless this reflex is depressed as well such as in certain drug overdoses or neurologic depression)
- such is the potential importance of this sign, that heart rate is incorporated in the ED “vital observations”, and should not be ignored unless a plausible explanation is possible and more serious causes are reasonably excluded.
- the patient with a steadily rising heart rate in ED over hours suggests ongoing deterioration such as from occult blood loss.
- the heart rate itself is usually NOT treated in the ED (such as with beta adrenergic blockers) unless it is likely to exacerbate an underlying problem - hence Rx to slow the heart rate is mainly reserved for acute myocardial infarction (AMI/STEMI/NSTEMI), aortic dissection and thyrotoxic crisis.
- remember that the normal heart rate varies with age:
- infants normal heart rate = 110-150 bpm
- adults normal heart rate = 60-100 bpm although resting HR for most adults is 65-85 bpm
- exercise results in a normal sinus tachycardia response depending on level of exertion, cardiovascular fitness and age:
- maximal exercise heart rate is usually given at 200 - age in years
acute potentially life-threatening causes of sinus tachycardia
- hypercapnia - usually a bounding pulse with vasodilation
- hypovolaemia - eg. dehydration, blood loss (eg. trauma, ectopic pregnancy, upper GIT bleeding, abdominal aortic aneurysm (AAA))
- acute abdominal surgical conditions
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- suggested by electrical alternans and low QRS voltages
- early hypothermia as the body attempts to generate heat by shivering
- metabolic disturbances such as diabetic ketoacidosis (DKA)
common iatrogenic medication causes of sinus tachycardia in the ED
- vasodilators such as nitrates (GTN, etc)
- phenothiazines such as iv chlorpromazine
subacute causes of persistent sinus tachycardia
- congestive cardiac failure including Beri Beri (rare in western countries)
- infective endocarditis (including SBE) - usually CRP is elevated
- fever
other causes
- anxiety
- pain
- caffeine
- smoking - nicotine
- exertion
- cardiac deconditioning
- dysautonomia syndromes such as inappropriate sinus tachycardia (ITS) and postural orthostatic tachycardia syndrome (POTS) - usually in young women and often accompanied by chest pains and SOB.
c_sinus_tachycardia.txt · Last modified: 2026/03/20 23:31 by wh