Cardiac Rhythm Device Therapy: Pacemakers and ICDs
What the exam tests
This domain covers indications, programming, and follow-up of pacemakers and ICDs from the allied professional's perspective: recognizing when a device is indicated, interpreting NBG codes and timing cycles, checking lead performance, and troubleshooting malfunctions. Questions often pair a clinical vignette with programmed parameters or a device strip.
Core rules
- Pacemaker indications: symptomatic sinus node dysfunction, high-grade AV block, and selected neurally mediated or post-surgical blocks. ICD secondary prevention after VF or hemodynamically unstable VT; primary prevention when LVEF ≤35% with NYHA II–III symptoms on optimal therapy and >1-year expected survival.
- NBG code positions: I = chamber paced, II = chamber sensed, III = response (I, T, D, O), IV = rate modulation (R), V = multisite pacing. DDDR is common.
- Timing: the lower rate interval sets basic rate; AV delay; PVARP prevents retrograde conduction and pacemaker-mediated tachycardia; blanking avoids oversensing; refractory periods prevent double-counting.
- Sensing/pacing: bipolar leads reduce EMI and crosstalk; check pacing threshold, P/R-wave amplitude, and impedance at implant and follow-up.
- ICD tiers: ATP for organized VT, cardioversion for slower VT, defibrillation for VF/fast VT; DFT testing confirms an adequate safety margin. Detection uses rate plus SVT discriminators (onset, stability, morphology).
- MRI: only “MRI conditional” systems under specified conditions-reprogram, monitor, restore.
Worked example
A 62-year-old with LVEF 30%, NYHA II, LBBB with QRS 160 ms, on GDMT for 3 months. Primary prevention ICD is indicated (LVEF ≤35%, NYHA II). Because LBBB ≥150 ms and QRS ≥130 ms, CRT is also indicated, so choose CRT-D. Program atrial tracking with biventricular pacing, keep PVARP long enough to block retrograde VA conduction, and set ATP before shock in the VT zone.
Traps
Confusing pacing with ICD indications; misordering NBG positions; forgetting PVARP when diagnosing pacemaker-mediated tachycardia; assuming all VT needs a shock (ATP first); treating “MRI conditional” as unconditional; missing impedance trends that signal lead fracture or insulation failure.