Sinus Rhythms
The impulse starts in the SA node: every P wave is followed by a QRS
Sinus bradycardia
Treat only if symptomaticRate<60/min
RhythmRegular
P waveNormal, 1 per QRS
PR0.12–0.20 s
QRS<0.12 s
Causes: athletes and sleep (normal), vagal stimulation (vomiting, suctioning, bearing down), hypothermia, hypothyroidism, ↑ICP (Cushing's triad), inferior MI, hyperkalemia, drugs (beta blockers, diltiazem/verapamil, digoxin, amiodarone, opioids).
Symptomatic if: hypotension, dizziness/syncope, altered mental status, chest pain, signs of shock or acute HF.
Symptomatic if: hypotension, dizziness/syncope, altered mental status, chest pain, signs of shock or acute HF.
Treatment (symptomatic):
- Atropine 1 mg IV, repeat every 3–5 min, max 3 mg. Updated (old dose 0.5 mg)
- If atropine fails: transcutaneous pacing, or dopamine 5–20 mcg/kg/min or epinephrine 2–10 mcg/min infusion.
- Treat the cause; hold rate-lowering drugs and notify the prescriber.
Sinus tachycardia
A response, not a disease: find the causeRate>100/min (usually ≤150 at rest)
RhythmRegular
P waveNormal, 1 per QRS
PR0.12–0.20 s
QRS<0.12 s
Causes: fever, pain, anxiety, hypovolemia or bleeding, hypoxia, anemia, sepsis, hyperthyroidism, PE, heart failure, stimulants (caffeine, nicotine, cocaine), drugs (albuterol, epinephrine, atropine), alcohol or drug withdrawal.
Treatment: treat the cause: fluids or blood for volume loss, analgesia, antipyretics, oxygen if hypoxic. Do not try to "convert" sinus tachycardia with adenosine or cardioversion.
Watch for: ↓ filling time → ↓ cardiac output, angina in CAD.
Watch for: ↓ filling time → ↓ cardiac output, angina in CAD.
Sinus arrhythmia
Rate varies with breathing (speeds up on inspiration, slows on expiration). Normal in children and young adults. No treatment.
Sinus arrest / pause
SA node fails to fire: a flat gap with no P, QRS or T. Report long pauses (e.g., >3 sec) and symptoms; may need a pacemaker (sick sinus syndrome).
Priority
Sudden bradycardia after suctioning or during a bowel movement = vagal response: stop the stimulus, assess the patient.
Cushing's triad (↑ICP): bradycardia + widening pulse pressure (rising systolic BP) + irregular respirations. This is a late sign: notify immediately.
Cushing's triad (↑ICP): bradycardia + widening pulse pressure (rising systolic BP) + irregular respirations. This is a late sign: notify immediately.