User Tools

Site Tools


c_sinus_tachycardia

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

common iatrogenic medication causes of sinus tachycardia in the ED

subacute causes of persistent sinus tachycardia

other causes

c_sinus_tachycardia.txt · Last modified: 2019/08/24 22:19 (external edit)