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IBHRE CEPS: Cardiac Rhythm Devices

IBHRE CEPS · Work through your exam, one topic at a time.

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Cardiac Rhythm Devices

Cardiac Rhythm Devices

The device domain tests timing cycles, detection algorithms, and troubleshooting rather than catalog memorization. Expect pacemaker mode switching, AV timing, ICD discrimination, CRT response, and EMI/MRI questions.

Core rules

  • NBG code: position I paced chamber, II sensed chamber, III response (I, T, D), IV rate modulation, V multisite pacing. DDDR means dual-chamber pacing and sensing, dual response, rate responsive.
  • Pacemaker timing: the lower rate sets the escape interval; the upper rate limits ventricular pacing. A short PVARP can permit retrograde P-wave sensing and initiate pacemaker-mediated tachycardia; a long PVARP reduces the maximum tracking rate. Ventricular safety pacing prevents crosstalk from an atrial pacing artifact.
  • Mode switch: when the atrial rate exceeds the mode-switch threshold, the device switches from DDD(R) to DDIR or VDIR to avoid tracking atrial fibrillation or flutter.
  • ICD detection: VF zone usually >200–220 bpm; VT zones are programmable. Supraventricular tachycardia discriminators include sudden onset, cycle-length stability, morphology, and atrial/ventricular relationship. Inappropriate shocks usually reflect atrial fibrillation, sinus tachycardia, or oversensing.
  • CRT: candidates typically have HFrEF, LVEF ≤35%, LBBB with QRS ≥150 ms, and NYHA class II–IV. An LV lead in a lateral or posterolateral vein with a long QLV interval predicts response.

Worked example

A dual-chamber pacemaker patient has atrial flutter at 260 bpm. The programmed mode is DDDR, mode-switch rate 170 bpm, lower rate 60 bpm. The surface ECG shows paced ventricular complexes at 60–70 bpm while the atrial electrogram shows rapid regular atrial activity. The device has mode-switched to DDIR and is pacing at the lower rate. The correct interpretation is appropriate mode-switch behavior, not atrial undersensing or pacemaker failure.

Traps

  • Calling mode switch undersensing when the atrial channel is sensing appropriately.
  • Missing ventriculoatrial conduction that causes pacemaker-mediated tachycardia.
  • Confusing T-wave oversensing with true ventricular fibrillation in an ICD.
  • Programming a short PVARP in a patient with intact VA conduction.
  • Assuming CRT response from QRS narrowing alone; assess symptoms, LVEF, and LV pacing percentage.