EP Staff Education Clinical Staff Ilyas Colombowala, MD, FACC, FHRS →
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Procedure

EP Study

Diagnostic electrophysiology study to characterize sinus node function, AV conduction, accessory pathways, and inducible arrhythmias. Foundation case for the lab — every fellow does dozens before they ablate.

Typical duration
1–1.5 h
Sedation
Moderate sedation

Overview

The EP study is our diagnostic workhorse. Whether the patient is here for unexplained syncope, documented SVT, wide-complex tachycardia, or risk stratification for an inherited arrhythmia, the workflow is largely the same: place catheters in standard intracardiac positions, record baseline intervals, perform programmed stimulation in the atrium and ventricle, and interpret what we induce.

A diagnostic EP study often transitions directly to an ablation in the same setting once the mechanism is identified.

Indications

  • Documented but unclassified SVT
  • Wide-complex tachycardia of uncertain mechanism
  • Syncope with structural heart disease or bifascicular block (HV interval assessment)
  • Risk stratification in Brugada, HCM (selected), congenital heart disease
  • Pre-ablation mapping of AF, atrial flutter, VT
  • Suspected sinus node dysfunction with non-diagnostic ambulatory monitoring

Pre-procedure prep

  • Hold antiarrhythmics for at least 5 half-lives (amiodarone is the exception — clinical judgment)
  • NPO 6–8 hours; large-bore IV
  • Continue anticoagulation if indicated; INR target 2.0–3.0 for left-sided procedures
  • Baseline 12-lead ECG in the chart
  • Review prior monitor strips — bring tracings into the lab for comparison during induction

Sterile setup

  • Bilateral groin prep — most cases use right femoral access for two or three sheaths, left femoral for the CS catheter
  • Ultrasound-guided venous access is standard
  • Sterile drape with windows over both groins; chest exposed for surface ECG and external pacing pads
  • Set up the EP recording system with 12-lead surface ECG and intracardiac channels labeled HRA, His proximal/mid/distal, RV, CS 1-2 through 9-10

Equipment

  • Multipolar diagnostic catheters: quadripolar (HRA, RV), decapolar (CS), quadripolar His
  • 5–8 Fr femoral venous sheaths (typically 3–4)
  • EP recording system with stimulator
  • Programmable stimulator (built into the recording system in most labs)
  • Fluoroscopy with PA, LAO 40°, RAO 30°
  • Isoproterenol drip ready (start 1–2 mcg/min, titrate to HR 120–150)
  • External defibrillator pads in place before any ventricular stimulation
  • ACLS cart at the bedside

Technique

Catheter placement

  1. HRA catheter — straightforward placement in the high right atrium near the SVC junction. Confirms sinus node region.
  2. His catheter — anterior tricuspid annulus. Look for the classic A-H-V signal with H sandwiched between A and V. Adjust until you see a robust His potential 35–55 ms before V.
  3. RV catheter — RV apex is standard; mid-septum acceptable. Use for V-pacing and V-extrastimuli.
  4. CS catheter — engage the CS ostium in LAO 40°. Advance distally so the decapole spans the mitral annulus from proximal (right) to distal (left lateral).

Baseline measurements

  • PR, QRS, QT from surface ECG
  • Sinus cycle length (baseline and after autonomic blockade if indicated)
  • AH interval — atrial signal on the His catheter to His deflection; normal 60–125 ms
  • HV interval — His deflection to earliest ventricular signal; normal 35–55 ms

Atrial stimulation

  • Sinus node recovery time (SNRT) — pace the HRA at progressively faster rates (600, 500, 400, 350 ms) for 30 seconds; measure pause after pacing stops. cSNRT >550 ms is abnormal.
  • AV conduction Wenckebach point — pace the atrium with progressively shorter cycle lengths; document the cycle length at which AV block first occurs. Normal ≤500 ms (≥120 bpm).
  • Atrial ERP — drive train of 8 S1 beats at 600 ms, then S2 starting at 350 ms and decrementing by 10 ms until the atrium fails to capture.

Ventricular stimulation

  • Programmed ventricular stimulation — drive train (S1 at 600 ms, then 400 ms) followed by S2, S3, and S4 extrastimuli at progressively shorter coupling intervals.
  • Used for VT induction in patients with structural heart disease or syncope.
  • Document HV interval during ventricular pacing if assessing retrograde conduction.

Tachycardia induction

  • If no tachycardia at baseline, repeat atrial and ventricular stimulation on isoproterenol (1–4 mcg/min, target HR 120–150).
  • During induced tachycardia, assess:
    • Atrial-ventricular relationship (1:1, more A than V, more V than A)
    • VA interval and septal-vs-lateral activation
    • Response to pacing maneuvers (PPI-TCL, His-refractory PVCs, V-A-V vs V-A-A-V)

Threshold and endpoint considerations

  • Tachycardia inducibility is the diagnostic endpoint — if we cannot induce, the study is limited.
  • Document everything inducible — non-clinical tachycardias matter for ablation planning.
  • A truly negative study after full protocol on iso has clinical value: it argues against an inducible mechanism in patients with syncope.

Pitfalls

  • Catheter-induced ectopy obscuring the rhythm — pause stimulation and let the patient settle
  • Mistaking catheter trauma RBBB for clinical bundle branch block
  • Inducing sustained VT in a patient without external pads in place
  • Iso-induced sinus tachycardia masquerading as SVT — always look for warm-up and cool-down
  • Failing to perform left-sided assessment (CS pacing maneuvers) in suspected AVRT

Post-procedure orders

  • Bed rest 2–4 hours with groin pressure
  • Resume anticoagulation per protocol; antiarrhythmics held until ablation strategy is finalized
  • Discharge same day for most diagnostic studies
  • Document findings in the lab report with intervals, induced rhythms, and pacing maneuvers performed

Last reviewed by Dr. Colombowala on May 22, 2026.

Not medical advice. This page is educational. Your situation may differ — discuss it with Dr. Colombowala or your treating physician before making decisions.