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

CRT Implant

Cardiac resynchronization therapy implant — adds an LV lead through the coronary sinus to a standard pacemaker (CRT-P) or ICD (CRT-D) to restore biventricular synchrony in heart failure with conduction delay.

Typical duration
2–4 h
Sedation
Moderate sedation

Overview

CRT implant adds a third lead — through the coronary sinus into a branch vein on the lateral wall of the left ventricle — to a standard transvenous device. The goal is to pace the LV simultaneously with (or just before) the RV, restoring synchronized contraction in patients whose conduction system can no longer do it on its own.

The first two leads (RA and RV) go in the same way as a dual-chamber pacemaker or ICD. The case lives or dies on the LV lead — coronary sinus anatomy, target vein selection, and stable fixation are the hard parts.

Indications

  • LVEF ≤35% on optimal GDMT for ≥3 months, NYHA II–IV, with LBBB QRS ≥150 ms — strongest indication
  • LVEF ≤35%, QRS 120–149 ms with LBBB or QRS ≥150 ms without LBBB — Class IIa
  • Patients with an existing pacing indication and LVEF ≤35% who would otherwise pace >40% from the RV
  • Upgrade from a chronic RV-paced system with declining LV function

Pre-procedure prep

  • Review most recent echo (LVEF, valve disease, RV function), 12-lead ECG (QRS morphology and duration), and labs
  • Discuss strategy: CRT-P vs CRT-D based on overall ICD indication
  • Hold DOACs per institutional protocol; warfarin uninterrupted is acceptable
  • Cefazolin 2 g IV (vancomycin if MRSA-positive) within 60 minutes of incision
  • Anti-emetic on board — contrast for the venogram is well tolerated but worth pre-empting

Sterile setup

  • Left chest prep, wide and including the axilla
  • Two suction setups
  • Contrast (iodinated, 30–50 mL) on the back table for occlusive venography
  • Antibiotic pocket irrigation
  • Antibiotic envelope opened on the field

Equipment

  • 7–9 Fr peel-away sheaths (×2 for atrial and RV leads)
  • CS guide catheter and inner subselector
  • Occlusive balloon catheter for venography (6 Fr)
  • Quadripolar LV pacing lead (preferred over bipolar — more vectors)
  • RA active-fixation lead, RV pacing or defibrillation lead
  • CRT-P or CRT-D generator
  • Pacing system analyzer with the ability to test each LV pole independently
  • Fluoroscopy with PA, LAO 40°, RAO 30° — both views essential for CS work

Technique

  1. Access and pocket as for a standard implant. Two or three venous punctures depending on the strategy.
  2. RV lead placed first — provides a backup pacing site and a fluoroscopic landmark for CS cannulation.
  3. CS cannulation. Use the LAO 40° view — the CS ostium sits at the 5 o’clock position relative to the tricuspid annulus. Engage with the CS guide and a soft-tip wire.
  4. Occlusive venogram. Inflate the balloon in the proximal CS and inject 10–20 mL contrast. Capture cine in LAO and RAO. Identify lateral and posterolateral branches.
  5. Target vein selection. The ideal branch:
    • Lateral or posterolateral wall
    • Adequate caliber to anchor a quadripolar lead
    • Avoids scar (correlate with prior imaging if available)
    • Distance from phrenic nerve (typically anterior branches sit closer to the phrenic)
  6. Advance the LV lead through the CS guide into the target vein over a wire. Quadripolar leads typically have an active or passive fixation mechanism (lobes, helix, or wedge fit).
  7. Threshold and phrenic testing in every vector:
    • Capture threshold <2.5 V at 0.5 ms is acceptable; <1.5 V ideal
    • Pace at 10 V at 0.5 ms in each available vector and watch for diaphragmatic capture
    • If phrenic capture occurs in any vector, mark and avoid programming that vector
  8. Confirm position in LAO (lead away from spine = lateral) and RAO (mid-ventricular height preferred).
  9. Remove the CS guide with a slitter — do not pull it back without slitting, or the LV lead will dislodge.
  10. RA lead placed last to avoid getting in the way during CS work.
  11. Connect and torque all set-screws; verify with the wrench-back.
  12. Final intraoperative interrogation: confirm biventricular capture on a 12-lead ECG — paced QRS should narrow compared with intrinsic.
  13. Closure in layers as for any device implant.

Threshold and impedance targets

  • LV capture threshold: <2.5 V at 0.5 ms in at least one vector (preferably <1.5 V)
  • LV impedance: 400–1200 ohms
  • No phrenic capture at 10 V in the chosen programming vector
  • QLV (interval from QRS onset to local LV electrogram) >95 ms predicts response

Pitfalls

  • CS dissection from aggressive cannulation — usually self-limited but can prevent that-day completion
  • Phrenic nerve stimulation — the single most common reason for post-implant patient complaint
  • LV lead dislodgement in the first 48 hours, especially from large CS branches
  • Failure to cannulate the CS — escalate to a long sheath, deflectable EP catheter as guidewire, or 3D reconstruction
  • Loss of biventricular pacing percentage from AF with rapid conduction — plan AV node ablation if pacing % is suboptimal

Post-procedure orders

  • CXR PA and lateral to confirm lead positions
  • Telemetry overnight, sling for 24 hours
  • Pre-discharge interrogation:
    • Confirm biventricular capture
    • Test each LV vector for phrenic at 10 V
    • Program the lowest-threshold, phrenic-free vector
    • Set AV delay and VV offset (start nominal, optimize at follow-up if non-responder)
  • Echo at 3 and 6 months to assess response (LVEF, reverse remodeling, MR)
  • Heart failure clinic follow-up within 2 weeks

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.