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.