junctional rhythms/disturbances in rhythm

Question 1

junctional escape rhythms

Answer 1

• rate: 40-60 bpm
• regularity: regular
• early/late beats: none
• P wave morphology: retrograde P waves before or after QRS complexes OR P waves not visible
• AV ratio:
• PR interval: < 120 ms if P waves prior to QRS complexes
• QRS duration and morphology: < 120 ms
• QT interval: less than 1/2 preceding R-R interval
• causes: damage to SA node from MI, ischemia, calcification, valvular heart disease, myocarditis, CHF, digitalis toxicity; beta/Ca++ blockers may reduce automaticity of SA node
• note: AV junction is second line of defense in hierarchy of pacemakers - evidence of junctional rhythm may be protective for pt w impaired SA node automaticity
• concerns: may see sx of low HR/CO
• treatments: tx of all bradycardias guided by sx - not treated if asymptomatic

Question 2

accelerated junctional rhythm and junctional tachycardia

Answer 2

• rate: AJR 60-100 bpm; tachycardia > 100 bpm
• regularity: regular
• early/late beats: none
• P wave morphology: retrograde P waves before or after QRS complexes OR P waves not visible (same as junctional escape rhythm)
• AV ratio:
• PR interval: short if measurable
• QRS duration and morphology: < 120 ms
• QT interval: less than 1/2 preceding R-R interval
• causes: enhance autorhythmicity of junction inc digitalis/theophylline toxicity, catecholamine surge from stress/stimulants, acid base imbalances
• treatments: based on removal of cause & control of HR; meds that limit automaticity of jx - beta/Ca++ blockers, amiodarone

Question 3

premature junctional contractions (PJCs)

Answer 3

• rate: can occur during several different rhythms
• regularity: disrupt underlying rhythms’ regularity - exist as individual beats, pairs and in bi/tri/quadra-geminal patterns (like PACs)
• early/late beats: by definition, PJCs are early beats that originate from junction
• P wave morphology: retrograde P waves before or after QRS complexes OR P waves not visible (same as junctional escape rhythm)
• AV ratio:
• PR interval: (of underlying rhythms) vary - PR interval of early complexes will be short if measurable
• QRS duration and morphology: < 120 ms
• QT interval: less than 1/2 preceding R-R interval
• causes: inc vagal tone, stimulants (caffeine, tobacco), CHF, valvular disease, COPD, hyperthyroidism, electrolyte disturbances (e.g. hypoK+), digitalis toxicity
• concerns: indicate enhance autorhythmicity - infrequently cause sx but some may experience palpitations
• treatments: normally not indicated - removal of stimulants/correction of underlying causes are top priorities

Question 4

supraventricular tachycardia (SVT)

Answer 4

• tachycardia originating above ventricle
• rhythms > 150 bpm difficult to discern - determine rate and width of QRS
• “narrow complex tachycardias” - inc sinus tachycardia, rapid a. fib, rapid a. flutter, atrial tachycardia, multiple atrial tachycardia, junctional tachycardia
• concerns: variation in individual pt response - pt may begin as asymptomatic, but how long can their heart beat at this rate wo physiological consequence?

treatments: dependent on individual pt response
- initial: determine if pt unstable - serious s/sx (hypotension, chest pain, SOB, syncope, loss of consciousness)
- if unstable, prep for immediate synchronized cardioversion OR admin adenosine to slow HR and ID origin of rhythm
- if stable, try non/pharmacological measures to slow ventricular HR (to dx specific rhythm and give rhythm-specific meds) - vagal maneuvers (by advanced practitioner), adenosine, beta/Ca++ blockers