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JUNCTIONAL RHYTHM

Comprehensive MD Medicine Notes

Sources: Tintinalli's Emergency Medicine | Harrison's Principles of Internal Medicine 22E | Braunwald's Heart Disease | Goldman-Cecil Medicine | Rosen's Emergency Medicine | Katzung's Basic & Clinical Pharmacology | Harriet Lane Handbook | Frameworks for Internal Medicine

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SECTION 1: DEFINITION

1.1 Definition of Junctional Rhythm

• Escape mechanism: the SA node fires too slowly or fails, and the AV junction assumes pacemaker function
• Enhanced automaticity: the AV junction fires faster than the SA node, overriding it

"Under normal circumstances, the SA node discharges at a faster rate than the AV node, so the pacemaker function of the AV node and all other slower pacemakers are suppressed." - Tintinalli's Emergency Medicine

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1.2 Anatomy and Physiology of the AV Junction

Atrial myocardium
        |
   [AV Node] ← compact node, located in Koch's triangle
        |         (bounded by: tendon of Todaro, tricuspid annulus,
        |          orifice of coronary sinus)
   [Bundle of His] ← penetrates the central fibrous body
        |
   [Bundle Branches] → Left + Right
        |
   [Purkinje fibers]

• 90%: Right coronary artery (posterior descending branch) - hence inferior MI affects it
• 10%: Left circumflex artery

• Rich autonomic innervation: parasympathetic (vagal) slows, sympathetic speeds
• Intrinsic rate of AV junction: 40-60 bpm

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1.3 Normal Pacemaker Hierarchy

┌─────────────────────────────────────────────────────────┐
│              NORMAL PACEMAKER HIERARCHY                 │
├──────────────────┬────────────────┬─────────────────────┤
│   Pacemaker      │   Location     │   Intrinsic Rate    │
├──────────────────┼────────────────┼─────────────────────┤
│   SA Node        │  Right atrium  │   60-100 bpm ← BOSS │
│   AV Junction    │  AV node/His   │   40-60 bpm          │
│   Purkinje/Vent. │  Ventricles    │   20-40 bpm          │
└──────────────────┴────────────────┴─────────────────────┘

• The SA node is primary pacemaker because it has the fastest spontaneous depolarization
• Subsidiary pacemakers are suppressed by overdrive suppression - when a faster pacemaker depolarizes them, they reset
• If the SA node slows or fails, the AV junction "escapes" and becomes the dominant pacemaker

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1.4 Escape Rhythm vs Accelerated Rhythm

Pearl: Junctional escape is a life-saving protective response. Never suppress it without ensuring another pacemaker is present.

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SECTION 2: ELECTROPHYSIOLOGY

2.1 Automaticity of the AV Junction

• Automaticity = ability of cardiac cells to spontaneously depolarize during phase 4 of the action potential (slow diastolic depolarization via the "funny current" - If)
• AV nodal cells have less steep phase 4 slope compared to SA node → slower intrinsic rate (40-60 bpm)
• AV nodal cells use L-type calcium channels for phase 0 (slow action potential) unlike atrial/ventricular cells (fast Na+ channels)

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2.2 Escape Mechanism

1. AV junction cells are no longer suppressed by overdrive
2. They complete their own intrinsic phase 4 depolarization
3. An escape beat fires at 40-60 bpm
4. If this continues: junctional escape rhythm

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2.3 Enhanced Automaticity

• Catecholamines, ischemia, digoxin toxicity, or electrolyte disturbances steepen phase 4 slope of AV junction cells
• This causes the junction to fire faster than the SA node
• Results in: accelerated junctional rhythm (60-100 bpm) or junctional tachycardia (>100 bpm)
• Mechanism: increased If current, enhanced Ca2+ influx, or decreased K+ efflux

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2.4 Re-entry Mechanism

         ATRIUM
           |
    ┌──────┴──────┐
    │ FAST pathway │ (alpha, short refractory)
    │              │
    │  SLOW pathway│ (beta, long refractory)
    └──────┬──────┘
           |
        VENTRICLE

• Anterograde: down slow pathway
• Retrograde: up fast pathway
• Creates a rapid circuit → P wave buried in or just after QRS

Note: True junctional tachycardia (focal JT) is automatic, NOT re-entrant - this distinguishes it from AVNRT.

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2.5 Influence of Autonomic Tone

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SECTION 3: CLASSIFICATION

3.1 Overview Table

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3.2 Junctional Escape Rhythm (40-60 bpm)

Lead II:
          ___         ___         ___
         /   \       /   \       /   \
________/     \_____/     \_____/     \____
    No P wave          No P wave

Rate: 40-60 bpm | Regular | Narrow QRS | No preceding P wave

• Rate: 40-60 bpm
• Regular rhythm
• Narrow QRS (<120 ms) unless aberrant conduction
• No P wave before QRS, or inverted P in inferior leads (retrograde)
• If retrograde: P wave immediately BEFORE QRS (very short PR, <120 ms) OR AFTER QRS

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3.3 Accelerated Junctional Rhythm (60-100 bpm)

Lead II:
    P' P'         P' P'         P' P'
   /\_            /\_            /\_
__/   \__________/   \__________/   \__
  (inverted/retrograde P waves near QRS)

Rate: 60-100 bpm | Regular | Narrow QRS

• Rate: 60-100 bpm (faster than normal junctional escape, but not tachycardia)
• Regular
• Narrow QRS
• P waves: inverted in II, III, aVF; may be before, within, or after QRS
• AV dissociation may be present if SA node continues firing independently

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3.4 Junctional Tachycardia (>100 bpm)

Lead II:
P'P'P'P'P'P'P'P'P'
|__|__|__|__|__|__|
  [narrow QRS complexes, ~120-130 bpm]
P' = inverted/buried, retrograde

Rate: >100 bpm | Regular | Narrow QRS

"Junctional tachycardia (ectopic junctional tachycardia) is a rare form of SVT in which the ECG resembles AVNRT but is distinct in that (1) the mechanism is automatic, not reentrant, and (2) the atrium is clearly not involved in the tachycardia. This disorder is most often observed in young healthy individuals, in women more often than in men, and is usually catecholamine dependent."

"JT shows sustained ventricular rates but rarely exceeds 130 bpm. JT is associated with structural heart disease, metabolic disturbances, or drug toxicity."

• AVNRT: re-entrant, onset/offset paroxysmal, adenosine terminates
• JT: automatic, gradual onset (warm-up), adenosine may transiently suppress but does NOT terminate

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3.5 Non-Paroxysmal Junctional Tachycardia (NPJT)

• Rate: 70-130 bpm (most commonly 70-130)
• Onset and termination: gradual (not abrupt - "warm up/cool down" pattern)
• Mechanism: enhanced automaticity
• Classic cause: digitalis toxicity (especially when combined with atrial fibrillation - fibrillatory baseline with regular QRS = NPJT)
• Also: inferior MI, acute rheumatic fever, myocarditis, post-cardiac surgery
• ECG: regular narrow QRS, retrograde P waves, AV dissociation possible
• Treatment: remove offending drug (digoxin), treat underlying cause

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3.6 Congenital Junctional Ectopic Tachycardia (Congenital JET)

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3.7 Postoperative Junctional Ectopic Tachycardia (Postoperative JET)

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SECTION 4: ETIOLOGY

4.1 Comprehensive Etiologic Classification Table

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4.2 Memory Aid - "DISCHARGE" Mnemonic for Junctional Rhythm Causes

D - Digitalis toxicity I - Ischemia (inferior MI), Idiopathic S - Sick sinus syndrome, Surgery (cardiac), Sleep apnea C - Calcium channel blockers, Congenital HD H - Hyperkalemia, Hypokalemia, Hypoxia A - Athletes (physiological), Amiodarone R - Rheumatic fever, Reperfusion G - (vagal) Greater vagal tone E - Electrolyte abnormalities

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SECTION 5: ECG DIAGNOSIS (DETAILED)

5.1 Stepwise ECG Interpretation

STEP 1: RATE
  ├── Count QRS complexes in 6-second strip × 10
  ├── OR 300 ÷ (large boxes between QRS)
  └── Junctional: 40-60 (escape), 60-100 (accelerated), >100 (JT)

STEP 2: RHYTHM REGULARITY
  ├── Measure R-R intervals
  └── Junctional rhythm = REGULAR (unlike AF)

STEP 3: P WAVE ANALYSIS (KEY!)
  ├── Is there a P wave?
  ├── Is P wave UPRIGHT in leads I, II, aVF? → Sinus origin
  ├── Is P wave INVERTED in II, III, aVF? → Retrograde (junctional)
  ├── Where is P relative to QRS?
  │     ├── BEFORE QRS (PR < 120 ms) → Junctional with retrograde atrial activation
  │     ├── WITHIN QRS (buried) → P not visible; QRS appears P-waveless
  │     └── AFTER QRS (RP < 200 ms) → Junctional with retrograde conduction after ventricles
  └── No P wave visible at all → Buried or absent retrograde conduction

STEP 4: PR INTERVAL
  ├── Normal sinus: 120-200 ms
  ├── Junctional: If P before QRS → PR <120 ms (retrograde)
  └── AV dissociation: Variable PR (no fixed relationship)

STEP 5: QRS DURATION
  ├── Narrow (<120 ms) = Junctional (supraventricular)
  └── Wide (>120 ms) = Aberrant conduction OR ventricular origin

STEP 6: LOOK FOR AV DISSOCIATION
  └── P waves and QRS independent, with junctional rate > atrial rate

STEP 7: CAPTURE AND FUSION BEATS
  ├── Capture beat: occasional sinus impulse "captures" ventricle → normal-looking QRS
  └── Fusion beat: simultaneous activation from SA and junctional → hybrid QRS morphology

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5.2 ECG Diagrams - All P Wave Patterns

Pattern A: No P Wave (P buried in QRS)

Lead II
         |         |         |         |
─────────|─────────|─────────|─────────|──────
        /|\       /|\       /|\       /|\
       / | \     / | \     / | \     / | \
──────/  |  \───/  |  \───/  |  \───/  |  \──
      QRS  (no P visible - buried inside QRS)

Rate: ~50 bpm | No P waves discernible | Narrow QRS
DIAGNOSIS: Junctional rhythm with P wave buried in QRS

Pattern B: Inverted P BEFORE QRS (short PR)

Lead II
    P'      P'      P'      P'
    |        |        |        |
─v──|──/\─v──|──/\─v──|──/\─v──|──/\──
   QRS      QRS      QRS      QRS

P' = inverted (negative) in II, III, aVF
PR interval < 120 ms (retrograde fast conduction)
DIAGNOSIS: Junctional with retrograde P before QRS

Pattern C: Inverted P AFTER QRS (short RP)

Lead II
   /\   P'   /\   P'   /\   P'   /\   P'
──/  \─\──v─/  \─\──v─/  \─\──v─/  \─\──v─
  QRS       QRS       QRS       QRS
       RP interval < 200 ms

DIAGNOSIS: Junctional rhythm with retrograde P after QRS (most common pattern)

Pattern D: P Wave Simultaneous with QRS (P in QRS)

     ↕P merged with QRS
─────/\/\──────/\/\──────/\/\───
   QRS+P     QRS+P     QRS+P

Cannot see P wave on surface ECG
DIAGNOSIS: Synchronous retrograde activation - P hidden in QRS

Pattern E: AV Dissociation (P waves walking through QRS)

Lead II showing AV dissociation:

P  P  P  P  P  P  P  P  P  P  P   (atrial rate: 60 bpm - slower)
|  |  |  |  |  |  |  |  |  |  |
|     |     |     |     |     |
   J     J     J     J     J       (junctional rate: 80 bpm - faster)
   /\    /\    /\    /\    /\

P waves march THROUGH QRS complexes
P-QRS relationship constantly changing
DIAGNOSIS: Accelerated junctional rhythm with AV dissociation
                                         ↑
                              Capture beat here (P happens to precede 
                              QRS with appropriate PR → normal-looking beat)

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5.3 Key ECG Parameters Summary Table

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5.4 Retrograde Atrial Activation

• AV junction impulse travels RETROGRADE from AV node up to atria
• Atria activated from below upward (inferior to superior)
• Results in:
  • Lead II, III, aVF: Inverted P wave (negative)
  • Lead aVR: Positive P wave
  • Lead I: Usually isoelectric or slightly negative

Normal sinus:          Retrograde:
    +P in II                -P in II
     ↓                       ↑
Atria activate          Atria activate
 top → bottom           bottom → top
(SA node high)         (AV node low)

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5.5 Capture and Fusion Beats

• During AV dissociation, an occasional sinus P wave arrives at the ventricles at just the right time (outside junctional refractory period)
• The sinus impulse "captures" the ventricles → produces a normal-looking narrow QRS
• Confirms AV dissociation is NOT complete
• Importance: Capture beats PROVE that the rhythm is ventricular (if in VT) or junctional (if in accelerated JR)

• Simultaneous activation of ventricles from BOTH the junctional pacemaker AND a descending sinus impulse
• Produces a QRS morphology intermediate between normal sinus QRS and junctional QRS
• Confirms: two competing pacemakers

Fusion beat morphology:
  Sinus alone:  Normal QRS
  Junctional alone: Also narrow QRS (same morphology in junctional)
  Fusion: Hybrid - often subtle difference in morphology

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5.6 Diagnostic Flowchart for ECG Interpretation

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SECTION 6: ECG DIFFERENTIAL DIAGNOSIS

6.1 Master Differential Comparison Table

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6.2 Junctional vs Sinus Bradycardia

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6.3 Junctional vs Complete Heart Block

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6.4 Junctional Tachycardia vs AVNRT

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6.5 Junctional vs Accelerated Idioventricular Rhythm (AIVR)

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SECTION 7: CLINICAL FEATURES

7.1 Symptoms

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7.2 Signs

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7.3 Hemodynamic Effects and Cannon A Waves

• When P and QRS are dissociated, atria may contract AGAINST CLOSED AV VALVES
• This produces: Cannon A waves in JVP (visible neck pulsation)
• Loss of atrial kick → reduces CO by 20-30% in patients with poor LV function

Cannon A Wave Physiology:
  
  Atrium contracts ──→ Tricuspid CLOSED (ventricle already contracting)
                  ──→ Blood forced BACKWARD into vena cava
                  ──→ Giant pulsation in jugular vein = CANNON A WAVE
                  
Classic causes of cannon A waves:
  • AV dissociation (junctional rhythm, VT, CHB)
  • Tricuspid stenosis
  • Right heart failure (giant "a" waves)

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SECTION 8: DIAGNOSTIC EVALUATION

8.1 History

• Onset (gradual vs sudden), duration, triggers
• Associated symptoms (syncope, chest pain, dyspnea)
• Drug history: digoxin, beta-blockers, CCBs, amiodarone
• Cardiac history: previous MI (especially inferior), CHD, cardiac surgery
• Symptoms of hypothyroidism, electrolyte disorders
• Family history (congenital JET)
• Athletic history

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8.2 Physical Examination

• Vital signs: HR, BP, SpO2, RR
• Pulse: rate, rhythm (regular in junctional)
• JVP: cannon A waves (AV dissociation), elevated (heart failure)
• Carotid sinus massage (CSM): may slow or reveal underlying atrial activity
• Cardiac auscultation: variable S1 intensity (AV dissociation), S3/S4 (heart failure)
• Signs of digoxin toxicity: GI, neurological (yellow-green vision)

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8.3 Laboratory Investigations

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8.4 Cardiac Investigations

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SECTION 9: APPROACH TO JUNCTIONAL RHYTHM

9.1 Clinical Algorithm / Flowchart

┌─────────────────────────────────────────────────────────────────┐
│          PATIENT PRESENTING WITH JUNCTIONAL RHYTHM              │
└──────────────────────────┬──────────────────────────────────────┘
                           ↓
              ┌────────────────────────┐
              │   12-LEAD ECG + VITALS │
              └────────────┬───────────┘
                           ↓
          ┌────────────────┴────────────────┐
          ↓                                  ↓
   UNSTABLE PATIENT                   STABLE PATIENT
   (SBP <90, altered MS,            (Alert, BP adequate,
    chest pain, severe HF)           no shock)
          │                                  │
          ↓                                  ↓
   IMMEDIATE:                      IDENTIFY SUBTYPE:
   • IV access                     • Escape (40-60 bpm)?
   • O2 supplementation            • Accelerated (60-100)?
   • Monitoring                    • JT (>100 bpm)?
   • Atropine 0.5mg IV                        │
   • If no response:               IDENTIFY CAUSE:
     Transcutaneous pacing         • Check digoxin level
   • Prepare for transvenous       • Electrolytes
     pacing                        • Troponin
          │                        • Echocardiogram
          ↓                                   │
   TREAT CAUSE                     TREAT REVERSIBLE CAUSE
   (adjust/stop offending           (stop drug, correct electrolyte,
    drugs, reperfuse if MI)          treat ischemia/infection)
          │                                   │
          ↓                                   ↓
   PERSISTENT SYMPTOMATIC          REASSESS:
   BRADYCARDIA?                    • Rhythm resolved? → Follow-up
          │                        • Persists symptomatically? →
          ↓                          Consider permanent pacemaker
   PERMANENT PACEMAKER             • Ablation if JT refractory
   (see indications below)

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SECTION 10: ACUTE MANAGEMENT

10.1 ACC/AHA/ESC Guideline-Based Management

Stable Patient

STABLE JUNCTIONAL RHYTHM
        ↓
Is the rate adequate (>40 bpm with no symptoms)?
        |
       YES → Monitor, identify cause, no immediate treatment
        |
        NO (symptomatic bradycardia from escape rhythm)
        ↓
┌──────────────────────────────────┐
│ 1. O2 (maintain SpO2 >94%)       │
│ 2. IV access                     │
│ 3. Cardiac monitoring            │
│ 4. 12-lead ECG, labs             │
│ 5. TREAT UNDERLYING CAUSE        │
│    • Stop digoxin                │
│    • Correct hypokalemia         │
│    • Treat inferior MI           │
└──────────────────────────────────┘
        ↓
If symptomatic (lightheaded, low BP):
ATROPINE 0.5 mg IV → repeat q3-5 min → max 3 mg
        ↓
Response? → Observe, monitor
No response? → Consider temporary pacing

Unstable Patient

UNSTABLE PATIENT (hypotension, syncope, altered consciousness, 
                   angina, acute pulmonary edema)
        ↓
┌──────────────────────────────────────────┐
│ IMMEDIATE STABILIZATION                  │
│ 1. O2 via face mask / intubate if needed │
│ 2. IV access (large bore, bilateral)     │
│ 3. Continuous ECG monitoring             │
│ 4. 12-lead ECG                           │
└──────────────────────┬───────────────────┘
                       ↓
              ATROPINE 0.5 mg IV
         Repeat every 3-5 min, max 3 mg
                       ↓
              Response?
           YES ─────────────────→ Monitor, treat cause
              NO
               ↓
   ┌─────────────────────────────────────┐
   │ TRANSCUTANEOUS PACING (TCP)        │
   │ • Start immediately while          │
   │   arranging transvenous pacing     │
   │ • Rate: 60-80 bpm initially        │
   │ • Output: start at 60 mA,          │
   │   increase to capture              │
   │ • Analgesia/sedation essential     │
   └──────────────────┬──────────────────┘
                      ↓
   While awaiting pacing or if TCP ineffective:
   ┌──────────────────────────────────────────┐
   │ PHARMACOLOGICAL BRIDGE                   │
   │ • DOPAMINE 2-10 mcg/kg/min IV infusion  │
   │ • EPINEPHRINE 2-10 mcg/min IV infusion  │
   │ • ISOPROTERENOL (rare, for beta-blocker  │
   │   or CCB overdose) 2-10 mcg/min         │
   └──────────────────────────────────────────┘
                      ↓
   TRANSVENOUS PACING (TVP)
   - Definitive emergency pacing
   - Via right internal jugular or subclavian vein
   - Float electrode to RV apex
   - Confirm capture on ECG

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10.2 Drug Summary Table

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10.3 Pacing Indications and Technique

Transcutaneous Pacing (TCP)

• Indication: Hemodynamically unstable symptomatic bradycardia not responding to atropine
• Technique: Anterior-posterior pad placement, rate 60-80, increase output until capture
• Limitation: Painful, not for long-term use, may fail to capture

Transvenous Pacing (TVP)

• Indication: Persistent symptomatic bradycardia, TCP failure, high-degree AV block
• Route: Right internal jugular, right subclavian, femoral
• Target: RV apex (float-through or fluoroscopy guided)
• Confirm capture: Paced spike → wide QRS in ECG, pulse corresponding to pacing

Permanent Pacemaker Indications (ACC/AHA Class I)

• Symptomatic sinus bradycardia (including junctional escape as secondary pacemaker)
• Sick sinus syndrome with symptomatic bradycardia
• Complete (3rd degree) AV block at any anatomic level
• Symptomatic Mobitz II 2nd degree AV block
• Symptomatic bradycardia not responding to other treatments
• Drug-induced bradycardia when drug cannot be stopped

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SECTION 11: LONG-TERM TREATMENT

11.1 Treat Underlying Cause

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11.2 Permanent Pacemaker Decision

SYMPTOMATIC JUNCTIONAL RHYTHM / ESCAPE RHYTHM
            ↓
Is the cause reversible?
  YES → Treat cause, re-evaluate
  NO → Is the patient symptomatic with bradycardia?
            ↓
           YES
            ↓
PERMANENT PACEMAKER IMPLANTATION
  • VVIR (single chamber) - sufficient for isolated junctional escape
  • DDDR (dual chamber) - preferred if AV synchrony beneficial
  • Consider CRT if LVEF <35% and LBBB pattern

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11.3 Catheter Ablation for Junctional Tachycardia

• Reserved for drug-refractory symptomatic JT
• Target: focus near His bundle / AV node
• Risk: Complete heart block requiring pacemaker >5% (Braunwald's)
• Success rate: lower than for AVNRT (~80-85%)
• Preferred approach: careful mapping with His potential monitoring

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SECTION 12: DRUG-INDUCED JUNCTIONAL RHYTHM

12.1 Detailed Drug Table

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12.2 Digoxin Toxicity - Special Emphasis

• Atrial fibrillation with REGULAR QRS complexes (NPJT + AF = "regularized AF")
• Bidirectional ventricular tachycardia (pathognomonic)
• PAT with block (atrial tachycardia at 150-250 bpm with 2:1 AV block)

Digoxin Toxicity + Junctional Rhythm
        ↓
STOP DIGOXIN
Monitor K+ (correct hypokalemia to K+ >4 mEq/L)
        ↓
Mild (NPJT, asymptomatic): Monitor, hold digoxin
        ↓
Moderate (hemodynamically unstable): Digoxin-specific Fab fragments
        ↓
Severe (life-threatening arrhythmia, K+ >5 in acute overdose): 
  Digoxin-specific Fab, AVOID cardioversion (risk of VF),
  AVOID calcium (can worsen stone heart)

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SECTION 13: JUNCTIONAL RHYTHM IN SPECIAL SITUATIONS

13.1 Inferior Wall MI

• AV node supplied by posterior descending artery (PDA) from RCA in 90% of people
• Inferior MI (ST elevation in II, III, aVF) → ischemia of AV node → junctional escape
• Features:
  • Usually transient (hours to days)
  • Narrow QRS junctional escape if below bundle of His not involved
  • May progress to Mobitz I (Wenckebach) → complete AV block
  • Management: PCI/reperfusion (primary treatment); atropine if hemodynamically compromised; temporary pacing rarely needed
  • Prognosis: usually resolves after reperfusion; rarely needs permanent pacemaker

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13.2 Digoxin Toxicity

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13.3 Post-Cardiac Surgery

• Common in first 24-48 hours post-cardiac surgery (especially in children)
• Mechanism: edema and trauma to His bundle during VSD repair, Tetralogy of Fallot repair, Fontan procedure
• Management:
  • Avoid catecholamines if possible (worsen automaticity)
  • Hypothermia (36°C): reduces automaticity
  • Amiodarone IV loading dose
  • Atrial pacing faster than JET rate to restore AV synchrony
  • Dexmedetomidine (alpha-2 agonist) - reduces sympathetic tone
  • Usually transient (resolves in 24-72 hours)

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13.4 Athletes

• Sinus bradycardia (40-55 bpm) very common
• High resting vagal tone → junctional escape (benign)
• ECG: absent P waves at rest, HR 45-55 bpm, narrow QRS
• Rate increases normally with exercise (distinguishes from pathological SA node disease)
• No treatment required - this is a normal physiological variant
• Reassurance is key

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13.5 Pregnancy

• Pregnancy generally causes sinus tachycardia (↑ sympathetic tone)
• Junctional rhythm in pregnancy: consider inferior MI, peripartum cardiomyopathy, drug effect
• Management: treat underlying cause; atropine safe for acute use; avoid isoproterenol (uteroplacental effects); temporary pacing if severely symptomatic

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13.6 Pediatric Patients

• Congenital JET: most important; see Section 3.6
• Junctional escape common after cardiac surgery
• Normal range for pediatric HR higher than adults; junctional rhythm diagnosed relative to age-appropriate normal rates

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13.7 ICU Patients

• Multiple contributing factors: sedatives, electrolytes, hypoxia, cardiac ischemia, sepsis
• Strategy:
  • Correct electrolytes first (K+, Mg2+, Ca2+)
  • Review all medications
  • Treat underlying critical illness
  • Continuous telemetry monitoring

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13.8 Electrolyte Abnormalities

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SECTION 14: COMPLICATIONS

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SECTION 15: PROGNOSIS

15.1 Benign vs Pathological Junctional Rhythm

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15.2 Prognostic Factors

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15.3 Specific Prognostic Scenarios

• With successful PCI: AV conduction usually recovers within 24-72 hours
• Rarely progresses to permanent complete heart block
• Prognosis determined by infarct size, not the rhythm itself

• High mortality if untreated (heart failure, hydrops in infants)
• With amiodarone ± ablation: most survive but risk of complete heart block from ablation

• Historically 10-15% mortality; modern management (cooling, amiodarone) reduces this
• Usually transient (24-48 hours)
• Recurrence rare after healing

• Excellent prognosis after drug withdrawal and Fab treatment
• Recurrence prevented by avoiding digoxin

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CLINICAL PEARLS SUMMARY

Pearl 1: Junctional rhythm is NARROW QRS (unless bundle branch block coexists). If you see a wide-complex escape rhythm, think ventricular escape.

Pearl 2: In AV dissociation with junctional rhythm, look for cannon A waves in JVP - they are pathognomonic of atria contracting against closed tricuspid.

Pearl 3: NEVER suppress a junctional escape rhythm without ensuring another adequate pacemaker is present. It may be the only thing keeping the patient alive.

Pearl 4: "Regularized AF" (AF with regular R-R intervals) = junctional tachycardia from digoxin toxicity until proven otherwise.

Pearl 5: Focal junctional tachycardia has GRADUAL onset (warm-up), while AVNRT starts ABRUPTLY. Adenosine terminates AVNRT but only transiently slows JT.

Pearl 6: Inferior MI affects the AV node (RCA supplies in 90%) → transient junctional escape expected. Reperfuse first; most will resolve without pacing.

Pearl 7: Atropine is ineffective in heart transplant recipients (denervated heart) and may paradoxically worsen Mobitz II or CHB.

Pearl 8: Postoperative JET treatment priorities: cooling > amiodarone > atrial pacing (faster than JET to restore AV synchrony). Emerging evidence: ivabradine (PMID: 41845224) may reduce JET rate.

Pearl 9: In complete heart block, narrow QRS escape = junctional escape (above bifurcation, 40-60 bpm, more stable). Wide QRS escape = ventricular escape (below bifurcation, 20-40 bpm, less stable, needs urgent pacing).

Pearl 10: ECG hallmark of junctional rhythm: inverted P waves in II, III, aVF (retrograde) either before QRS (PR < 120 ms), within QRS (not visible), or after QRS (RP < 200 ms).

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KEY ECG SUMMARY DIAGRAM

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REFERENCES

• Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th ed. - Chapter 18: Dysrhythmia Management
• Harrison's Principles of Internal Medicine, 22nd Edition (2025) - Chapter 253: Supraventricular Arrhythmias
• Braunwald's Heart Disease, 2 Vol Set - Chapter on Catheter Ablation of Arrhythmias
• Goldman-Cecil Medicine International Edition - Chapter 52: Junctional Tachycardia
• Rosen's Emergency Medicine, 9th ed. - Chapter 65: Arrhythmias
• Katzung's Basic and Clinical Pharmacology, 16th Edition - Chapter on Digoxin
• Harriet Lane Handbook, 23rd ed. - Chapter 7: Arrhythmias
• Frameworks for Internal Medicine - Junctional Escape Rhythm
• Balweel H et al. Potential use of ivabradine in postoperative junctional ectopic tachycardia: a systematic review and meta-analysis. BMC Cardiovasc Disord. 2026 (PMID: 41845224)
• Carmona-Puerta R et al. Junctional ectopic tachycardia revisited. Postgrad Med. 2025 (PMID: 40143746)