Junctional Rhythms

Premature Junctional Complex (PJC)

• An impulse originating from the AV junction, causing a compensatory pause.
• Aetiology:
  • Medications (antiarrhythmics)
  • Adrenaline
  • Hypoxia
  • Junction toxicity
  • Congestive heart failure
  • Coronary artery disease
  • Post heart attack
  • Enhanced automaticity
  • Re-entry of AV junction
• Clinical significance:
  • Isolated PJCs: Not immediately significant
  • Multiple PJCs: Can cause other dysrhythmias, impact cardiac output, and cause patient anxiety.
  • High frequency: May indicate enhanced automaticity or re-entry, potentially leading to more serious dysrhythmias.
• ECG analysis:
  • Rate: Typically 70 bpm (underlying rhythm)
  • Regularity: Underlying rhythm is normal, irregular during PJC.
    • Couplets: 2 PJCs in a row
    • Juncture tachycardia: 3+ PJCs in a row
  • P wave: Can be absent, buried in QRS, inverted, or before/after QRS, depending on the location of PJC in the AV junction.
    • Proximal: Atrial depolarization before ventricles, inverted P wave.
    • Mid: At the same time as ventricles, P wave buried in QRS.
    • Distal: Ventricular depolarization first or retrograde, inverted P wave or after QRS.
  • PR interval: Can be RP, under 0.5 seconds.
  • QRS and conduction ratio: Should be normal with normal ratio.
    • Bigeminy: One PJC after every QRS
    • Trigeminy: One PJC after every two QRS
    • Quadrigeminy: One PJC after every three QRS.
  • Origin: AV junction

Junctional Escape Rhythm

• Occurs when the AV junction takes over pacing due to absent or infrequent descending impulses from the SA node.
• Aetiology:
  • Severe sinus bradycardia
  • Sinus arrest
  • Sinoatrial exit block
  • AV block
  • Hyperkalaemia
  • Medications e.g. beta blockers, calcium channel blockers
  • Return of spontaneous circulation (ROSC) - AV junction activates first.
• Clinical significance:
  • Slower than SA node, leading to slow heart rate and cardiac output, causing poor cerebral, coronary, and organ perfusion.
  • Isolated: Not significant
  • Combined with pre-existing conditions: Highly significant.
• ECG analysis:
  • Rate: Very slow, generally 40-60 bpm, but can be less.
  • Regularity: Regular.
  • P wave: Depends on the cause of SA node dysfunction.
    • Sinus arrest: No P wave.
    • AV block: No P wave.
    • Random P waves: May be present.
  • PR interval: Under 0.12 seconds.
  • QRS and conduction ratio: Narrow, sharply pointed, abnormal QRS complex due to conduction differences in the left bundle branch. No P wave association with QRS complexes.
  • Origin: AV junction.

Nonparoxysmal Junctional Tachycardia (Accelerated Junctional Rhythm/Junctional Tachycardia)

• Continuous, not sudden onset and cessation
• Occurs when the AV junction rate exceeds the SA node rate.
• Aetiology:
  • Medications
  • Damage to the AV junction (e.g., coronary artery blockage, heart attack)
  • Hyperkalaemia
  • Hypoxia
• Clinical significance: Highly significant after a heart attack, in hypoxia, or with sympathetic drug overdose.
• ECG analysis:
  • Rate:
    • Accelerated Junctional Rhythm: 60-100 bpm
    • Junctional Tachycardia: Over 100 bpm.
  • Regularity: Regular, but fast.
  • P wave: Can be seen before, during, or after QRS.
    • Abnormal: Generally inverted.
    • Normal: Generally unassociated with QRS.
  • PR interval: Under 0.12 seconds in nonparoxysmal tachycardia.
  • QRS and conduction ratio: Sharp, narrow.
  • Origin: AV junction.

Paroxysmal Supraventricular Tachycardia (PSVT)

• Definition:
  • Fast heart rate originating above the ventricles.
  • AVNRT (AV nodal re-entry tachycardia): Irregular refractory periods between fast and slow pathways in the AV node cause constant ventricular contraction.
  • AVRT (AV re-entry tachycardia): Two pathways create a circuit causing contraction.
  • Involves re-entry circuits.
• Aetiology:
  • Premature atrial complex initiating supraventricular tachycardia.
  • Increased sympathetic nervous tone (e.g., amphetamines, cocaine, tobacco, alcohol, coffee).
  • Electrolyte imbalances.
  • Hyperventilation.
• Clinical significance:
  • Treatment: Valsalva maneuver.
• ECG analysis:
  • Rate: 150-250 bpm, abrupt onset and termination.
  • Regularity: Irregular at the start and end, but generally not profoundly irregular.
  • P wave: Typically absent, buried in QRS.
    • If present: Not normal, generally inverted.
  • PR interval: Under 0.12 seconds.
  • QRS and conduction ratio: Narrow QRS complexes, relatively normal ventricular conduction, normal duration, 1:1 ratio if P wave is seen.
  • Origin: AV node or accessory pathway outside the AV node causing a re-entry circuit.

Atrioventricular Block - First Degree

• Conduction delay through the AV node, potentially blocking transmission.
• Aetiology:
  • Damage to the AV node (e.g. Myocardial infarction, ischemic heart disease)
  • Excessive vagal tone
  • Medications (beta blockers, calcium channel blockers)
  • Acute rheumatic fever
  • Electrolyte imbalances.
• Clinical significance:
  • Asymptomatic in isolation, but requires evaluation of the underlying cause.
  • Potential to progress to higher-grade blocks.
• ECG analysis:
  • Rate: Same as underlying rhythm.
  • Regularity: Same as underlying rhythm.
  • P wave: Consistently normal.
  • PR interval: Longer than 0.20 seconds, indicating delayed conduction through the AV node.
  • QRS and conduction ratio: Normal P waves precede each QRS complex.
  • Origin: Sinus.

Atrioventricular Block - Second Degree Type 1 (Mobitz 1/Wenckebach)

• Progressive prolongation of conduction through the AV node leading to absent QRS complexes.
• Aetiology:
  • Damage to the AV node (e.g., Myocardial infarction, ischemic heart disease)
  • Excessive vagal tone
  • Medications (beta blockers, calcium channel blockers)
  • Acute Rheumatic fever
  • Electrolyte imbalances
• Pathophysiology: AV conduction progressively slows until the SA node impulse fails to conduct.
• Clinical significance: Transient and reversible.
• ECG analysis:
  • Rate: Same as underlying rhythm.
  • Regularity: Irregular RR intervals but regular PP intervals.
  • P wave: Normal.
  • PR interval: Progressively long, and absent in the non-conducted beat.
  • QRS and conduction ratio: Narrow, sharp QRS complex, ratio depends on the frequency of non-conducted P waves.
  • PP and RR: Irregular RR intervals.
  • Origin: Sinus.

Atrioventricular Block - Second Degree Type 2 (Mobitz 2/Infranodal)

• Intermittent dropped beats, indicating intermittent complete blocks below the AV node.
• Aetiology: Damage to the anterior wall of the heart affecting bundle branches.
• Clinical significance: Slow ventricular rate leading to low cerebral, coronary, and organ perfusion.
• ECG analysis:
  • Rate: Variable, depending on the frequency of the block.
    • Sinus rate: P wave rate
    • Ventricular rate: QRS complex rate.
  • Regularity: Irregularly irregular.
    • PP: Regular.
    • RR: Irregular
  • P wave: Should be normal.
  • PR interval: Can be normal or excessively delayed (prolonged) depending on the block location.
  • QRS and conduction ratio: Dropped QRS complex, normal QRS complex, wide QRS complex (bundle branch issue). Ratio varies based on the dropped beat frequency (generally 4:3, one more P wave than QRS complex).
  • Origin: Sinus.

Atrioventricular Block - Third Degree - Complete AV Block

• Complete block of descending electrical activity through the heart (AV node, Bundle of His, bundle branches).
• Aetiology: Can be transient and reversible or permanent.
  • Transient: Similar to 1st degree block.
  • Permanent: Severe damage to the AV junction (e.g., myocardial infarction) or chronic degenerative changes in bundle branches.
• ECG analysis:
  • Rate: Varies based on functional pacemaker location.
    • 40-60 bpm: AV junctional escape rhythm.
    • 20-40 bpm: Ventricular escape rhythm.
  • Regularity: Regular.
    • PP: Regular if SA node fires regularly.
    • RR: Regular.
  • P wave: Normal (if SA node firing), flutter, or fibrillation.
  • PR interval: Difficult to determine, variable, no association with QRS.
  • QRS and conduction ratio: No association with P waves.
    • Narrow and sharp: SA node rhythm.
    • Wide: Ventricular pacemaker.
  • Origin:
    • Sinus: If SA node is pacing.
    • Ventricular: If ventricular pacemaker dominates.