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Pacemakers and Indications for Pacing

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💡 Students often get confused about pacemaker coding. Remember: the paced chamber always comes first — without a paced chamber, it’s not truly a pacemaker. ⚠️ True pacemaker malfunction is rare; pseudo-malfunction (misinterpreting pacing artefacts, undersensing, or oversensing) is far more common.

🔧 About Pacemaker Codes

A pacemaker has a pulse generator + pacing leads.
Leads usually pass through the venous system and attach to the endocardium by screw or tine fixation.
Some are epicardial leads, sewn or screwed onto the heart surface during surgery.
⚡ Standard dual-chamber pacemaker = RA lead + RV lead. (Dual-chamber ICD adds a defibrillator coil in RV).
❤️‍🔥 Biventricular pacing (CRT) uses 3 leads (RA, RV, LV via coronary sinus) → restores synchrony, improves haemodynamics, relieves heart failure symptoms.
🔁 Dual chamber devices can be programmed for triggered pacing (sense in atrium → pace ventricle after a delay).

📊 NBG Pacemaker Codes

Written in a 5-letter code (chamber paced ➝ chamber sensed ➝ response ➝ programmability ➝ anti-tachy function).
Example: DDDR = Dual-chamber paced, Dual-chamber sensed, Dual response, Rate modulated.
Historic codes & detail: NASPE

Chambers Paced 1	Chambers Sensed 2	Mode of Response 3	Programmable Functions 4	Anti-Tachycardia 5
V = Ventricle	V = Ventricle	T = Triggered	R = Rate Modulated	O = None
A = Atrium	A = Atrium	I = Inhibited	C = Communicating	P = Paced
D = Dual (A&V)	D = Dual (A&V)	D = Dual (T+I)	M = Multi-programmable	S = Shocks
O = None	O = None	O = None	P = Simple programmable	D = Dual (P+S)
---	---	---	O = None	---

🩺 Pacemaker Types

Type	Indications	Notes
Single-Chamber (AAI or VVI)	AAI: Sinus node disease with intact AV conduction. VVI: Chronic AF with bradycardia or AV block.	One lead (RA or RV). ✅ Simple, fewer complications. ❌ No AV synchrony.
Dual-Chamber (DDD)	AV block (2° or 3°). Sinus node dysfunction + bradycardia. Maintains AV synchrony.	Two leads (RA + RV). Better haemodynamics than single-chamber. Most common modern pacemaker.
Biventricular (CRT)	Heart failure + reduced EF. Wide QRS / LBBB + persistent symptoms (NYHA II–IV).	Leads in RA, RV, + LV via coronary sinus. Resynchronises ventricles → ↑ CO. Improves survival & QOL in HFrEF.
Leadless Pacemaker	Symptomatic bradycardia. High infection risk or venous access issues.	Implanted directly in RV. Lower infection/lead complications. ❌ Limited to VVI pacing.
ICD with Pacing	High SCD risk (e.g., VT/VF, post-MI, low EF). Also manages bradycardia.	Defibrillator + pacing in one device. Delivers shocks & prevents bradyarrhythmias. Regular follow-up needed.

⏱️ Hysteresis

Allows heart to use intrinsic rhythm → conserves battery.
Set below base rate (e.g., Base 60, Hysteresis 50 → no pacing until HR < 50, then pace at 60).
Useful for physiologic rate changes (e.g., slower HR during sleep).

⚙️ Pacemaker Insertion

📋 Pre-op: Hx, exam, ECG, echo, bloods, informed consent.
💉 Antibiotic prophylaxis (e.g., cefazolin).
🔪 Pocket created under clavicle; leads placed via subclavian/cephalic vein.
⚡ Leads tested & generator implanted in pocket.
✅ Pacemaker programmed & wound closed.

🛡️ Post-Procedure Care

Monitor on telemetry.
CXR → confirm leads & exclude pneumothorax.
Wound care & infection precautions.
Restrict arm movement/lifting for several weeks.

⚠️ Complications

Infection (pocket/endocarditis).
Lead displacement.
Pneumothorax (venous access).
Bleeding/hematoma.
Pacing failure (over/undersensing).
Venous thrombosis (rare).

📍 Indications – Temporary Pacing

Asystole or complete heart block.
Severe bradycardia with haemodynamic compromise.
Bradycardia-dependent arrhythmias (e.g., Torsades).
Overdrive pacing for VT, AF, flutter.
Acute MI + 2°/3° heart block.

📍 Indications – Permanent Pacing

Symptomatic bradycardia (syncope, fatigue).
2° or 3° AV block.
Sick sinus syndrome.
AF with slow ventricular response.
HFrEF + ventricular dyssynchrony → CRT.
Post-MI conduction disturbance.

📚 Exam tip: Learn the common codes (VVI, AAI, DDD, DDDR, CRT). True malfunction is rare → always rule out pseudo-malfunction first (lead displacement, oversensing, battery depletion).

PLEASE NOTE LEGAL ADVICE: The contents are under continuing development and improvements and may contain errors of omission or fact. Feedback vital and always welcome at drokane at gmail.com. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice. It is only for educational purposes. Please adhere to your local protocols. If you are unwell please seek healthcare advice from your doctor. This does not replace senior or specialist advice. If you do not accept this then please do not use the website. If you need medical advice, please consult a doctor or other appropriate medical professional. If you are a medical professional and you need advice then speak to your senior or colleagues.

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