4.4 Temporary Pacing: Transcutaneous, Transvenous and Epicardial

Why Temporary Pacing Is Tested on the CMC

Test-plan item III.D.1 sits inside Therapeutic Interventions, the 39% domain. Temporary pacing is the one electrophysiologic intervention a bedside cardiac nurse may have to initiate, titrate and troubleshoot alone, at 0300, before an electrophysiologist arrives. CMC items therefore rarely ask who implants the wire; they ask what the nurse does when the monitor shows spikes without QRS complexes, or when a post-op patient with epicardial wires drops into complete heart block.

Indications for Temporary Pacing

Temporary pacing is any short-term electrical support of rate or rhythm delivered through transcutaneous pads, a transvenous endocardial lead, or surgically placed epicardial wires.

Two traps recur. First, in inferior MI the block is usually at the AV node, produces a narrow junctional escape at 40–60 bpm, and often responds to atropine; in anterior MI the block is infranodal, produces a wide escape at 20–40 bpm, is atropine-refractory, and predicts asystole — that patient needs pacing readiness immediately. Second, for torsades the nurse does not simply pace faster and stop there: magnesium sulfate 2 g IV, potassium repletion to 4.5–5.0 mEq/L, and withdrawal of every QT-prolonging drug run in parallel with overdrive pacing at a rate that shortens the QT and abolishes the pauses.

Transcutaneous Pacing

Transcutaneous pacing (TCP) is the emergency, non-invasive bridge. It is fast to apply and painful to receive.

• Pad placement. Anteroposterior is preferred: anterior pad over the left precordium at the apex (V2–V5 area, avoiding breast tissue and any implanted generator), posterior pad between the spine and the left scapula. Anterolateral is acceptable when the patient cannot be turned. Clip, do not shave, excess hair; skin must be dry.
• Settings. Select demand mode when a native rhythm exists, rate 60–80 ppm. Start milliamperes low and increase in 5–10 mA steps until capture; in a peri-arrest patient, start at maximum output and titrate down to the lowest capturing value. Typical capture thresholds are 40–90 mA. Once capture is achieved, add roughly 10% or 5–10 mA as a safety margin.
• Electrical capture is a wide QRS with a broad T wave following each spike. Do not accept the pacer's own rate display or the pulse oximeter waveform artifact as proof.
• Mechanical capture must be verified at the femoral pulse, the right radial/brachial pulse, or the arterial line waveform. Never assess capture at the carotid: pacing stimulates pectoral, neck and shoulder muscle, and that twitch is easily mistaken for a pulse. This is a favorite CMC distractor.
• Analgesia and sedation. Capture-level output causes severe skeletal muscle contraction. Give IV analgesia and sedation (for example fentanyl 25–50 mcg IV with midazolam 0.5–1 mg IV, titrated) unless the patient is unresponsive, and monitor airway and blood pressure.
• Failure modes. Loss of capture from pad displacement, diaphoresis or dried gel; failure to sense causing spikes on native T waves; and the false reassurance of electrical capture without a pulse (pulseless electrical activity is still PEA — start CPR). TCP is a bridge only; efficacy falls over hours and burns develop, so transvenous or permanent pacing should follow promptly.

Transvenous Pacing

A temporary transvenous pacemaker (TVP) places a bipolar or balloon-tipped semi-floating catheter into the right ventricular apex, usually through the right internal jugular (straightest path to the RV, preserves the left subclavian for a future permanent device) or the left subclavian vein; femoral access is used when the chest is occupied but carries higher infection and thrombosis risk. Position is confirmed by fluoroscopy, intracardiac electrogram, bedside echocardiography, or the paced 12-lead pattern — RV apical pacing gives a left bundle branch block morphology with a leftward/superior axis. A post-insertion chest radiograph documents lead tip position and excludes pneumothorax.

Threshold Testing and the Safety Margin

Capture threshold is measured at least once per shift and after any position change:

1. With the patient paced at a rate 10–20 ppm above the intrinsic rate so every beat is paced, slowly reduce output (mA) until capture is lost.
2. The lowest output that still captures every beat is the capture threshold. At insertion it should be ≤ 1.0 mA; a value that has climbed above 1.5–2.0 mA suggests lead migration, exit block from tissue edema or fibrosis, ischemia at the lead tip, hyperkalemia, acidosis, or antiarrhythmic effect.
3. Set the maintenance output at 2–3 times threshold (for example, threshold 0.8 mA, set 2.0–2.4 mA). Never leave a pacemaker-dependent patient running at threshold.

Sensitivity is tested by reducing the pacing rate below the intrinsic rate and lowering the mV number until sense markers appear with every native beat; the maintenance setting is typically half that value (more sensitive). Demand (VVI) mode is the default because it prevents competitive pacing. Asynchronous (VOO) mode is used deliberately when electromagnetic interference could inhibit output — during electrocautery, for example — but never in a patient with an underlying organized rhythm outside that setting, because a spike landing on the T wave can trigger R-on-T ventricular fibrillation.

Secure the catheter with a suture and a sterile occlusive dressing, loop and tape the external lead to prevent traction, label the generator, tape the dials or apply the key-lock, and never let the generator hang unsupported from the wires.

Complications

• Right ventricular perforation and tamponade — the emergency. Suspect it with a sudden rise in capture threshold or loss of capture, a change in the paced QRS from left to right bundle branch morphology, new pleuritic or pericardial chest pain, hiccups or diaphragmatic pacing, hypotension with a narrowing pulse pressure, rising CVP, pulsus paradoxus and muffled tones. Call for echocardiography and prepare for pericardiocentesis.
• Lead dislodgement — intermittent or complete failure to capture, often positional. Placing the patient in the left lateral decubitus position may restore contact temporarily; increase output and reapply transcutaneous pads while awaiting repositioning.
• Infection and bacteremia — risk climbs after 48–72 hours; maintain a sterile dressing, monitor the site, and escalate for fever or purulence.
• Ventricular arrhythmias during insertion from catheter irritation of the RV; keep a defibrillator at the bedside.
• Access complications: pneumothorax, arterial puncture, air embolism, and venous thrombosis.

Epicardial Pacing After Cardiac Surgery

Temporary epicardial wires are sutured to the atrial and ventricular epicardium before the chest is closed and brought out through the skin below the sternotomy.

• Wire identification. The standard US convention is that atrial wires exit to the patient's right of the sternal incision and ventricular wires to the left. Color coding (commonly blue for atrial, white for ventricular) is institution-specific and must be confirmed against the operative note and handoff — never assume. If chamber identity is uncertain, pacing the wire and reading the resulting complex settles it: a spike followed by a P wave is atrial, a spike followed by a wide QRS is ventricular.
• Mode selection. AAI for sinus node dysfunction with intact AV conduction — it preserves the atrial kick, which supplies 20–30% of cardiac output and matters most in the stiff, hypertrophied or diastolic-dysfunction ventricle. VVI when the patient is in atrial fibrillation with a slow ventricular response or only ventricular wires function. DDD for AV block with sinus rhythm, restoring AV synchrony; AV delay is often optimized around 150–200 ms.
• Atrial overdrive pacing. Continuous atrial pacing at 80–100 ppm is used to suppress the bradycardia- and pause-triggered ectopy that initiates postoperative atrial fibrillation, which affects roughly 30% of CABG and up to 50% of valve patients, peaking on postoperative days 2–3. Rapid atrial burst pacing (short bursts 10–20 ppm faster than the flutter rate, often 300–400 ppm) can terminate atrial flutter through the atrial wires. It cannot convert established atrial fibrillation — a classic exam trap — and burst pacing can convert flutter into fibrillation, so the patient must be monitored and rate-controlled.
• Wire removal. Wires are typically removed on postoperative day 3–5, before discharge, and before full anticoagulation is resumed. Confirm the institution's parameters (many require INR below about 2.0–2.5, hold IV heparin 4–6 hours before and resume 4–6 hours after, hold prophylactic anticoagulation per protocol, and check platelets). Pull gently and steadily; never pull against resistance — a retained wire is cut at the skin and left, and this is documented. Keep the patient supine on bedrest with continuous ECG and blood pressure monitoring for at least 1 hour afterward, and assess for the delayed but real risk of bleeding into the pericardium and tamponade: new hypotension, tachycardia, dyspnea, chest pain, rising CVP or falling urine output demands immediate echocardiography.

Bedside Troubleshooting

Every temporary pacing malfunction reduces to four patterns. Identify the pattern on the rhythm strip first, then act.

Memory hook for the two sensing problems: sensitivity is an inverse number. A lower mV setting means the generator "listens harder" and senses more. Undersensing is fixed by listening harder (lower the number); oversensing by listening less (raise the number).

Electrical Safety and Micro-Shock

Any exposed pacing wire or transvenous lead is a direct low-resistance conductor to myocardium and bypasses the skin's normal protection. Leak currents that a patient would never feel through intact skin become lethal when delivered intracardiac: as little as roughly 20 microamperes (0.02 mA) applied directly to the ventricle can induce ventricular fibrillation. Standing precautions:

• Insulate all exposed wire tips and terminal pins in a nonconductive cap, finger cot or rubber glove, and secure them to the chest wall.
• Wear gloves whenever handling wires, terminals, or the generator, and keep hands, dressings, wires and bedding dry.
• Use only grounded, biomedical-inspected equipment; keep unnecessary electrical devices (personal chargers, non-hospital electronics) away from the bed.
• Use bipolar rather than monopolar electrocautery when possible, and place the electrosurgical return pad so that the current path does not cross the heart.
• Do not disconnect the generator from a dependent patient to "test" anything; verify a backup generator and battery are at the bedside every shift and after every generator change.
• Document rate, output, sensitivity, mode, underlying rhythm, capture and sensing thresholds, dependence status, and site condition at least every shift.