24. Intracardiac Electrophysiology Study Tracings and Lewis Ladder Diagrams
Intracardiac electrophysiology studies (EPS) record local bipolar electrical signals directly from endocardial structures to dissect conduction intervals and mechanism of arrhythmias.
1. Multipolar Diagnostic Catheter Placements & Intervals
CATHETER POSITION LOCAL BIPOLAR SIGNALS RECORDED High Right Atrium (HRA) -> Atrial depolarization wavefront (Sinus node region) His Bundle Electrogram (HBE) -> Atrial (A), His Bundle Spike (H), Ventricular (V) Coronary Sinus (CS 1-2 to 9-10) -> Distal-to-proximal left atrial activation sequence Right Ventricular Apex (RVA) -> Right ventricular apical depolarization (V)
| Intracardiac Interval | Normal Value Range | Anatomical Conduction Substrate | Diagnostic Significance |
|---|---|---|---|
| P-A Interval | $25 - 45\text{ ms}$ | High right atrium to low interatrial septum. | Intra-atrial conduction time. |
| A-H Interval | $55 - 125\text{ ms}$ | Compact Atrioventricular Node. | AV nodal conduction time; decremental with pacing; prolonged by beta-blockers. |
| H-V Interval | $35 - 55\text{ ms}$ | Proximal His bundle to ventricular myocardium. | His-Purkinje conduction time; non-decremental; $\ge 100\text{ ms}$ indicates critical infranodal block. |
2. Construction of Lewis Ladder Diagrams
Lewis ladder diagrams use three horizontal tiers to plot the timing and direction of cardiac electrical conduction:
TIER 1: ATRIUM (A) ●─────────●─────────● (P waves) \ \ TIER 2: AV NODE / JUNCTION (AV) \ \ \ (PR interval conduction delay) \ \ TIER 3: VENTRICLE (V) ▼─────────▼─────────▼ (QRS complexes)
Application in Complex Conduction Phenomena:
- Wenckebach AV Block: Progressively angled diagonal lines across the AV tier until an atrial point (●) fails to cross into the ventricular tier (dropped beat).
- AV Dissociation with Capture: Independent horizontal rhythms in Tier 1 and Tier 3 with intermittent diagonal lines crossing from A to V representing captured beats.
- Concealed Conduction: An impulse penetrates partially into the AV tier without reaching the ventricular tier, leaving the AV node refractory for the subsequent impulse.