Temporary Pacing

In depth

The one-page summary above is what the PDF prints. These sections go further.

Conduction physiology and what pacing restores

The sinus node fires at 60 to 100/min and the impulse crosses the AV node (the PR delay). If the sinus node fails, the AV junction escapes at 40 to 60/min with a narrow QRS; below the His bundle a ventricular focus escapes at 20 to 40/min, wide and unreliable. The right coronary artery supplies the AV node in about 90% of people, so inferior MI gives nodal block that usually resolves and anterior MI gives infranodal block from septal necrosis that often does not.

Cardiac output is rate times stroke volume, and a stiff, stunned or ischemic ventricle cannot raise stroke volume, so output falls with the rate. Atrial contraction adds 15% to 30% of stroke volume, more in diastolic dysfunction, aortic stenosis and the first hours after bypass, so DDD or AAI beats VVI at the same rate; BJA Educ 2023 gives 70 to 90/min as the usual post-bypass target. VVI with retrograde conduction gives cannon A waves and hypotension (pacemaker syndrome), so AAI is preferred when AV conduction is intact. Hyperkalemia, acidosis, hypoxia, ischemia, hypothermia, class IC antiarrhythmics and electrode fibrosis raise the capture threshold, mostly in the first 48 hours.

Indications and the 2018 ACC/AHA/HRS guideline

Symptoms and hemodynamics decide, not the rate: the 2025 AHA algorithm names hypotension, altered mentation, shock, ischemic chest pain and acute heart failure. Infranodal block (Mobitz II, alternating bundle branch block, wide-QRS complete block, most anterior-MI block) can go to asystole without warning.

After cardiac surgery 0.8% to 24% of patients need temporary pacing, most after valve surgery, and conduction usually recovers over 5 to 7 days (2018 guideline). Overdrive pacing: rapid atrial pacing for atrial flutter runs 20 to 30/min above the flutter rate, about 260 to 340/min, for up to 20 seconds through atrial wires only (BJA Educ 2023); RAP on the Medtronic 5392 runs to 800 ppm and can accelerate the rhythm or start atrial fibrillation, so a defibrillator is at hand.

• Class I (B-NR): temporary pacing for refractory symptomatic or hemodynamically significant bradycardia in acute MI; a waiting period, then a permanent device for Mobitz II, high-grade, alternating bundle branch block or persistent or infranodal complete block; block that resolves gets no device (III: Harm).
• Class IIa (B-NR): temporary transvenous pacing for AV block refractory to drugs; an externalized active-fixation lead when pacing will be prolonged. IIb (B-R): transcutaneous pacing as a bridge. SND: transvenous IIa, transcutaneous IIb; minimal symptoms, no temporary pacing (III: Harm).
• Drugs: atropine IIa for SND and AV-nodal block, including in acute MI; beta agonists (isoproterenol, dopamine, dobutamine, epinephrine) IIb when ischemia is unlikely; aminophylline IIb in inferior MI, IIa after heart transplant or spinal cord injury; atropine after heart transplant III: Harm.

The NBG code and the modes nurses use

The NASPE/BPEG code (Bernstein 2002): position I is the chamber paced, II the chamber sensed (O none, A atrium, V ventricle, D both), III the response to sensing: I inhibited (no pulse), T triggered (a pulse), D both (a sensed P inhibits the atrial output and triggers a ventricular pulse after the AV interval). IV and V are O on temporary generators, so three letters are used.

DDD timing: the lower rate; the AV interval or paced PR (20 to 300 ms on the Medtronic 5392, usually 150 to 200); the upper rate (80 to 230 ppm), the fastest the ventricle is paced in answer to sensed P waves; and the PVARP (150 to 500 ms), during which the atrial channel ignores everything after a ventricular event, so retrograde P waves are not tracked. On the 5392, DDI is DDD with A Tracking off.

Transcutaneous pacing in practice

Transcutaneous current crosses the chest wall, so most of it is spent in skeletal muscle and the adult threshold is 40 to 80 mA, higher with obesity, hyperinflation, a large effusion, acidosis or hypoxia. Anterior pad left of the sternum over the apex, posterior pad between the left scapula and spine (anterior-lateral if the patient cannot be turned); clip hair, dry the skin.

1. Separate ECG electrodes: LIFEPAK 15 and ZOLL X Series pads cannot sense while pacing.
2. Demand mode, 60 to 80/min (ZOLL: 10 to 20 above the intrinsic rate, or 100 if none).
3. Raise the current until every spike is followed by a wide QRS and a broad opposite T wave (electrical capture); artifact can mimic a QRS, so look for the T wave.
4. Confirm mechanical capture: femoral pulse at the paced rate, arterial waveform or SpO₂ plethysmograph matching the spikes; twitching makes the carotid unreliable.
5. Set the output just above threshold (about 10%; older ACLS text 2 mA, StatPearls 5 to 10 mA) and recheck capture after every move.

Pacing is painful within minutes. The 2018 guideline and AHA 2025 say analgesia, anxiolysis or sedation and name no drug; small titrated IV doses of fentanyl (25 to 50 mcg) or midazolam (0.5 to 2 mg) are common, and each can drop a marginal pressure. Do not delay pacing to sedate a deteriorating patient. Check the skin under the pads every few hours: this is a bridge measured in hours.

Transvenous pacing: insertion, position and daily care

A 5 Fr balloon-tipped catheter passes through a 6 Fr introducer to the right ventricular apex. The right internal jugular gives the straightest path and fewer complications (2018 guideline); the femoral vein needs fluoroscopy and in older series carried venous thrombosis in 18% to 85% and pulmonary emboli in 50% to 60%. In the right atrium the balloon is inflated and the lead advanced under fluoroscopy, echo or ECG guidance (injury current on the distal electrode), or paced at 10 to 20 mA in VOO until capture appears. Then: balloon down, threshold measured (under 1 mA is good contact, above 2 mA a floating tip), output at least two to three times threshold, lead and sheath sutured, hub length recorded, chest radiograph for position and pneumothorax.

Each shift: thresholds, hub length, site and dressing, paced QRS shape, presence of an escape rhythm; limit movement on the access side, bed rest with a femoral lead. Complications rise after 48 hours (2018 guideline), so the plan for a permanent device or an externalized active-fixation lead is made early. Rising thresholds, a changed QRS, loss of capture with position, pericardial pain, a rub, hiccups or diaphragmatic twitching and hypotension mean dislodgement or perforation: 12-lead, echo, team.

Epicardial pacing after cardiac surgery, adult and pediatric

Epicardial wires are sutured to the right atrium and right ventricle before closure and brought out through the skin, atrial right of the sternum and ventricular left by convention (PA Patient Safety Advisory 2006, PCICS). Two wires per chamber are bipolar; a single wire is unipolar and needs an indifferent skin electrode on the positive terminal. BJA Educ 2023: a capture threshold under 5 mA at surgery is acceptable, 5 to 10 mA means discussing repositioning, above 10 mA is unacceptable.

Off bypass the usual settings are 70 to 90/min with an AV interval of 160 to 200 ms (BJA Educ 2023). Tune the AV interval at the bedside: shorten it until the paced QRS shows no fusion, then adjust while watching the arterial pressure. AAI at 80 to 90/min is first choice with intact AV conduction and lowers postoperative atrial fibrillation; DDD for AV block, VVI for atrial fibrillation or no atrial wires, DDI for AV block with a fibrillating atrium.

• Thresholds drift most in the first 48 hours; check at least daily (BJA Educ 2023). By day 5 to 7 fibrosis often makes capture and sensing unreliable; a patient whose wires sense poorly should not go to the ward on backup pacing.
• Idle wires: coil, cap every exposed end, label, dress, handle with gloves (PCICS). Spare generator and battery at the bedside, pads on a dependent patient, generator pouched out of the patient's reach (Medtronic).
• Document each shift: mode, rate, outputs, sensitivities, AV interval, thresholds, intrinsic rhythm, dependence.

Children: prophylactic wires are routine in infants, after valve surgery and in single-ventricle repairs (PCICS). PACES 2021 recommends a permanent device when postoperative advanced block persists beyond 7 days. Junctional ectopic tachycardia gets cooling, fewer catecholamines and amiodarone, plus atrial pacing just above the junctional rate to restore AV synchrony (PCICS). A 50 mA high-output generator exists for infants who lose capture at the standard 25 mA maximum (PCICS).

Generator settings and threshold testing step by step

The 5392 locks itself 60 seconds after the last adjustment; the DOO/EMERGENCY key works even when locked and starts high-output asynchronous pacing, and the enter key returns it to demand mode. Manual values are lost at power-off, so write them down.

1. Sensing threshold first, only with an adequate intrinsic rhythm and never in a dependent patient: rate at least 10/min below intrinsic, output 0.1 mA so the unit cannot pace competitively (Medtronic).
2. Turn the mV number up until the sense light stops and the pace light flashes, then down until the sense light returns: the sensing threshold. Set sensitivity at half that or less (6 mV: set 3 mV).
3. Capture next: restore the output, rate at least 10/min above intrinsic, lower the output until a spike has no complex, raise it until every spike captures: the stimulation threshold.
4. Output at least two to three times threshold (2 mA: 4 to 6 mA or more), rate restored, thresholds and time recorded; repeat daily and after any change in rhythm or capture.

Troubleshooting problem by problem

Work every problem the same way: the patient (pulse, pressure, mentation), the monitor with pacer detection on (bipolar spikes are small), the generator lights, then the cable to the wire. Most failures are mechanical: a loose connection, a low battery, a dial moved by accident.

Call the team now for loss of capture not restored by maximum output in a dependent patient, thresholds that have doubled, spikes on T waves, a new wide-complex tachycardia, PMT that a mode change does not stop, suspected perforation or tamponade or a fractured or exposed wire. R-on-T VT or VF: pause the pacer, defibrillate, then find out why it undersensed (BJA Educ 2023).

Electrical safety, battery, cautery and defibrillation

A pacing wire is a low-resistance path to the myocardium, so a current too small to feel at the skin can fibrillate the ventricle (microshock). Gloves for every contact with wire ends or pins, ends capped and dry, no patient contact with pins or electrical devices while a wire is uncapped, only grounded three-prong equipment near the bed, wires kept dry (Medtronic, PCICS).

• Battery: new for every patient, replaced at the low-battery indicator and at least weekly in continuous use. Lock the unit first; the 5392 keeps pacing for at least 30 seconds at nominal settings while the battery is out (Medtronic).
• Electrocautery is oversensed and inhibits a demand pacer: dependent patient in DOO or VOO above the intrinsic rate, return pad far from the heart, bipolar cautery or short bursts, watch the arterial waveform, recheck thresholds afterwards (Medtronic, BJA Educ 2023).
• Defibrillation: Medtronic advises disconnecting the generator whenever possible; most units keep a dependent patient connected. Pads away from wires and generator; recheck capture and thresholds after the shock. Generator and connected wires are MR unsafe.
• Transport: generator clipped in its pouch, spare battery and generator, pads on a dependent patient, capture checked after every lift.

Weaning, wire removal and the evidence

Assess dependence each shift, pads on: lower the rate 10/min at a time to about 40 to 50/min. An escape within seconds at a tolerable rate means not dependent, and the generator can sit at a backup rate below the intrinsic rate; no escape, or one under 30 to 40/min, means dependence, so leave the rate alone and bring the permanent-device decision forward. The 2018 guideline asks for a waiting period after MI and after surgery; most centers wait 5 to 7 days for surgical block.

Epicardial wires come out after 24 to 48 hours without pacing, usually after postoperative day 2 and at least 24 hours before discharge (BJA Educ 2023). Anticoagulation rules differ: BJA wants heparin prophylaxis held, platelets above 100 × 10⁹/L, INR under 3.0 and removal before any DOAC; the PA Patient Safety Advisory 2006 lets the INR drift under 1.5 and holds IV heparin while aspirin and clopidogrel continue. Pull each wire with gentle steady traction with the patient on a monitor; resistance means stop, cut the wire flush with the skin if it will not come, and tell the surgeon. Then bed rest 1 hour and telemetry for 24 hours (PA 2006).

The evidence is thin. Prehospital trials of transcutaneous pacing in asystolic arrest (Cummins 1993 among them) showed no survival benefit, so the 2018 guideline grades it B-R only as a bridge and AHA 2025 keeps it out of the arrest algorithm. Transvenous pacing has had no large randomized trial in 60 years; its 14% to 40% complication rate comes from observational series. Unsettled: the bradycardia cutoff (50 in AHA 2025 versus 60 in older ACLS), the transcutaneous margin (2 mA, 5 to 10 mA or 10%), the INR limit for wire removal (3.0 versus 1.5), and disconnecting the generator for defibrillation.

• Sensitivity is in mV and runs backward: lower is more sensitive. Undersensing: lower the number. Oversensing: raise it.
• Output two to three times the capture threshold; sensitivity half the sensing threshold.
• Wide-QRS escape or Mobitz II is infranodal: atropine unlikely to help, pace. Atropine after heart transplant: Class III Harm.
• DDD at the upper rate with abrupt onset is pacemaker-mediated tachycardia: lengthen the PVARP or switch to DDI or VVI.
• Asynchronous modes (VOO, DOO) only for emergencies and cautery; spikes on T waves can cause VF.
• Arrest after cardiac surgery with wires in: pace at once (DDD 80 to 100 at maximum output or the emergency key), CPR within 1 minute if it fails (STS 2017).