Circulation Skills 9:
Transvenous Cardiac Pacing
Not all cases of heart block with shock respond to external pacing. When this occurs, transvenous pacing is indicated.
A pacer lead can penetrate the right ventricle; consider the possibility of cardiac tamponade as a complication.
- Prepare. Assure that ECG leads are attached. Try the sensing method first. Place an external defibrillator nearby. An O2 sat monitor is useful for detecting capture. An Arrow Transvenous Pacing Kit contains all of the necessary supplies, except the pacing box.
The supplies needed for transvenous pacing lead insertion. From the left, a 6 French side port introducer with a Touhy-Borst valve attached, the guidewire for the introducer, a # 11 scalpel, a 5 French bipolar pacing catheter with a balloon, a catheter contamination shield, and a Medtronic transvenous pacer.
- Obtain central access. Perform central venous cannulation as in Vol II—Circ Skills 2 Central Venous Access. Wear a mask while performing this procedure. Insert the 6 French side port introducer contained in the Arrow Catheter kit. The left or right supraclavicular routes, the left subclavicular route, and the femoral route are better than the right subclavicular route. The Touhy-Borst adaptor on the 6 French introducer has a valve that can be tightened down, eliminating blood loss and restricting movement of the pacing lead. Lay sterile towels down over the field.
- Insert the pacing lead. Place the 5 French bipolar pacing wire on the chest. The distal metal lead on this wire is the negative pole; the more proximal metal lead is the positive pole. Obtain the CathGard protector and put the pacing lead through it. This consists of an accordioned length of soft plastic tubing that stretches out to cover the wire. Lay the wire on the drape covering the patient's chest. Position the wire so that its natural curvature points the tip to the left (toward the heart). Start the wire through the Touhy-Borst valve. Hand off the proximal end of the wire to a fellow team member who will insert its leads into the appropriate lead holes in the pacing box. Turn the mA knob and the pacing rate knob as low as they go. Turn the sensing knob to DEMAND. Turn to ON. Press the battery check button to ensure the battery is functioning.
- Advance the wire to the right ventricle. Advance the pacing wire down the superior vena cava while watching for the sensing light on the box to flash when the patient's native beat is sensed. When every native beat is sensed, the wire is in a position to pace the heart. It may be in the right atrium, floating in the right ventricle, or lodged against the right ventricular wall. Turn down the sensitivity of the box by turning the async-demand knob counterclockwise until sensing is lost. Now advance or retract the wire to regain sensing. This improves the wire's position. If you can turn down the sensitivity half way, the wire is well placed.
- Obtain capture. Turn the rate knob of the pacemaker box to the desired rate and the pacing mode knob to ASYNCHRONOUS. Now turn up the mA knob to 4. Capture is obtained. The pulse rate sensed by the O2 sat monitor should equal the pacing rate. On ECG, the pacer spike should be evident followed immediately by a QRS complex. Now turn down the amperage until capture is lost (usually less than 1.0 mA). Turn up the amperage again until capture is regained. This is the threshold. Double it for safety and leave it at that setting. If the pacing wire is in the atrium and the patient has a third-degree heart block, the pulse rate would not improve. The pacing spike will be seen to precede the P wave. Advance the pacing wire into the ventricle by temporarily inflating its balloon to the volume specified on the kit's container. If capture does not result, start over.
- Secure it. Tighten down the Touhy-Borst adaptor to limit any motion of the wire. Extend the CathGard and carefully coil the pacing wire on the patient's chest and secure it with tape, always leaving the leads connected to the pacer box. Place the box in a plastic bag to assure that the knobs are not turned. Caution the patient about the importance of the wire and the pacer and why they must not be moved.
Diagram of a transvenous pacing module (Medtronic Demand Pulse Generator)
If the sensing method fails, use a continuous ECG monitor trace to aid in placement.
- Connect to the ECG V lead. Connect the V lead of the ECG to the negative lead of the pacing wire. Set the ECG monitor to read the V lead.
- Detect intraventricular placement. As the pacing wire advances down the superior vena cava, it enters the right atrium. When it does, the P wave becomes prominent. It might have either a positive or negative deflection. When the pacing wire enters the right ventricle, a large QRS deflection is seen. If the wire touches the myocardium, a large ST elevation will be seen, signifying an injury current. It is possible to pace the heart, even if the wire is not actually touching the myocardium.
- Pace. As before, connect the leads to the pacer box. Set the knobs to 4 mA and ASYNC. Set the rate knob to the desired rate. Turn it on. Capture should be obtained. Determine the threshold as above and double it for safety. The threshold is usually less than 1 mA but may be higher with myocardial ischemia. A balloon catheter may be used. Test the balloon before insertion with air using the volume recommended by the manufacturer. Deflate the balloon. When the catheter is in the atrium, inflate the balloon so that the catheter is swept into the ventricle with the flow of blood. Deflate the balloon when ventricular placement is achieved.
Complications: Check for the presence of blood in the pericardium resulting from penetration of the right ventricle by the pacing wire. Use ultrasound. Beware of the complications of central venous cannulation, such as air embolism, etc.
Reference
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Morelli RL, Goldschlager N. Temporary transvenous pacing. Part 1 and Part 2. J Crit Illness. 1987;14(3,4):63-80.