SA node rhythms

Question 1

sinus rhythm

Answer 1

• rate: 60-100 bpm
• regularity: regular
• early/late beats: none
• P wave morphology: uniform upright P waves
• AV ratio: 1:1
• PR interval: 120-200 ms
• QRS duration and morphology: < 120 ms, identical morphology
• QT interval: less than 1/2 preceding R-R interval
• causes: none
• treatments: none

Question 2

sinus bradycardia

Answer 2

• rate: < 60 bpm - regularity: regular - early/late beats: none - P wave morphology: uniform upright P waves - AV ratio: 1:1 - PR interval: 120-200 ms - QRS duration and morphology: < 120 ms, identical morphology - QT interval: less than 1/2 preceding R-R interval - causes: inc vagal tone; desired effect of beta-adrenergic blockers/other meds c negative chronotropic effects (decrease SA node rate) - e.g. Ca++ channel blockers, digitalis preparations; may be normal variant esp in athletes; hypothyroidism - concerns: sudden onset can severely dec CO and lead to dizziness, lightheadedness, syncope, etc; common early rhythm in early inferior MI; may be presenting rhythm c increased ICP - treatments: only treated if symptomatic (SOB, chest pain, diaphoresis, hypotension, change in LOC) - tx algorithm: atropine, transcutaneous pacing (painful!), dopamine or epinephrine infusion (NOT push)

Question 3

sinus tachycardia

Answer 3

• rate: 100-160 bpm - regularity: regular - early/late beats: none - P wave morphology: uniform upright P waves - AV ratio: 1:1 - PR interval: 120-200 ms - QRS duration and morphology: < 120 ms, identical morphology - QT interval: less than 1/2 preceding R-R interval - causes: exertion, exercise, fever, pain, anxiety, stimulants (e.g. caffeine, nicotine, cocaine), meds that dec parasympathetic tone (atropine, glycopyrrolate) or inc sympathetic tone (epi, dopamine, dobutamine, tricyclic antidepressants), hypoxia, hypo- or hypervolemia, CHF, hyperthyroidism, PE - concerns: inc HR improves CO but inc work of heart - coronary arteries suffer impaired filling above 120 bpm - treatments: correct cause - if pt develops sx of dec CO (rare), use beta blockers/Ca++ blockers

Question 4

sinus arrhythmia

Answer 4

• rate: can be sinus bradyarrhythmia or tachyarrhythmia - regularity: regularly or irregularly irregular - early/late beats: beats occur at variable intervals - P wave morphology: uniform upright P waves - AV ratio: 1:1 - PR interval: 120-200 ms - QRS duration and morphology: < 120 ms, identical morphology - QT interval: less than 1/2 preceding R-R interval - causes: normal variation in rhythm - variations in autonomic tone (for young pts, esp in relation to resp cycle - inc on inspiration, dec on expiration in the young) - treatments: does not req tx if rate is 60-100 bpm/producing adequate CO; sinus bradyarrhythmia/tachyarrhythmia treated as sinus bradycardia/tachycardia