Sinus tachycardia

• common causes:
  • the normal response to exercise
  • conditions in which catecholamine release is physiologically enhanced: flight, fright, anger, or stress. 
• other factors may be responsible in selected cases including:
  • Hyperthyroidism
  • Fever
  • Effective volume depletion
  • Anxiety
  • Pheochromocytoma
  • Sepsis
  • Anemia
  • Hypotension and shock
  • Pulmonary embolism
  • Acute coronary ischemia and myocardial infarction
  • Heart failure
  • Chronic pulmonary disease
  • Hypoxia
  • Exposure to stimulants (nicotine, caffeine) or illicit drugs

DIAGNOSIS 

ECG

• P waves may be difficult to identify at heart rates above 140 beats per minute, since they are often superimposed on the preceding T wave 

•  As a result, a sinus tachycardia can be confused with a paroxysmal supraventricular tachycardia or atrial flutter with 2:1 block.
• Carotid sinus massage, other vagal maneuvers, or intravenous AV nodal blocking agents (eg, adenosine, verapamil ) may help in the identification of the arrhythmia by inducing one or more of the following:
  • Slowing the sinus rate to allow proper identification of the sinus P waves
  • Causing transient AV nodal block to make atrial flutter with 2:1 block apparent
  • Termination of a paroxysmal supraventricular tachycardia (atrioventricular nodal reentrant tachycardia or atrioventricular reentrant tachycardia)

Inappropriate sinus tachycardia (IST)

• Aka chronic nonparoxysmal sinus tachycardia
• occurs in individuals without apparent heart disease or other cause for sinus tachycardia, such as hyperthyroidism or fever
• Affected patients have an elevated resting heart rate and/or an exaggerated heart rate response to exercise; many patients have both.
• The cause of IST is unknown, but abnormal autonomic control is thought to be important. 
• Many patients with IST work in the healthcare field.
• One study suggested that this tachycardia is related to a
  • primary sinus node abnormality, characterized by a high intrinsic heart rate,
  • depressed efferent cardiovagal reflex
  • eta-adrenergic hypersensitivity

Postural orthostatic tachycardia syndrome (POTS)

• predominantly in young women with normal hearts, who have a normal resting heart rate
• Symptoms
  • reports dizziness, lightheadedness, weakness, blurred vision, and fatigue upon standing
  • orthostatic symptoms: palpitations, tremulousness, and anxiety
  • Gastrointestinal symptoms such as nausea, abdominal cramps, early satiety, bloating, constipation, and diarrhea may be particularly problematic in some
• diagnosis:
  • increase in heart rate on tilt table testing or standing 
  • usually no orthostatic hypotension
• TREATMENT
  • No therapy is required for a physiologic sinus tachycardia and, in most settings, treatment is directed at the underlying disease.
  • UptoDate suggest suggest volume repletion and fludrocortisone (0.1 to 0.4 mg per day) as the first line of therapy