Transvenous pacing utilizes a central venous catheter (CVC), usually placed into the right internal jugular or left subclavian vein, which serves as an introducer to “float” a pacing wire through the venous system utilizing a small balloon, terminating into the apex of right ventricle. Transvenous pacers (TVPs) typically have both atrial and ventricular electrodes which permit pacing in a physiological, dual chamber manner to promote AV synchrony, optimizing cardiac output. Transvenous pacing is very well tolerated and comfortable for the patient and does not require sedation, if secured well is less likely to fail or lose capture compared to transcutaneous pacing and has the added benefit of utilizing a pacer box to control pacing output.
TVP placement complications is not without risk. Complications may be related to venous access (e.g. arterial puncture, pneumothorax, etc.), right heart catheterization (e.g. dysrhythmias, atrial or ventricular perforation, misplacement of the wire into the coronary sinus, valvular damage, etc.), the pacing wire itself (e.g. wire fracture, displacement, fibrosis, infection), and the external generator.
Indications for prophylactic TVP placement
If a patient has required transcutaneous pacing and time and resources permit, a TVP should be placed urgently, ideally in the first 24 hours. Certain pathology also predisposes patients to arrythmias, and often a TVP should be place prophylactically prior to transport. Myocardial infarctions (MIs) affecting the inferior or posterior aspects of the myocardium can result in complete (3rd degree) heart block in up to 5% of patients. These patients may also have a high degree AV block (P wave to QRS complex ratio of ≥ 3:1), which is usually transient and less likely to be symptomatic. Right sided MIs often affect the SA node and conduction system, resulting in symptomatic bradycardia requiring pacing. An anterior-lateral MI may also result in high grade AV blocks, new bundle branch block, particularly the left bundle branch, or bi-fascicular blocks. Prior to transport a Cardiology consultation may be helpful to guide prophylactic TVP placement.
Epicardial wires are placed during cardiothoracic surgery and sutured directly into the epicardium and exit through the skin and are covered by a dressing. By surgical convention, atrial (A) wires emerge on the patient’s right, and ventricular (V) wire emerge on the patient’s left. These wires will connect to the pacemaker box using a special cable with a screw in connector that will accept the wires placed by the surgeon. Patients will always have V wires but will not uncommonly have A wires as well; a patient will never have only A wires. Pacer box usage is the same for both epicardial or transvenous pacing, with the exception being if the patient does not have atrial epicardial wires.
Transvenous Pacer Box nomenclature and modes
Ventricular demand pacing is the mode of choice during patient evacuations because attaining the correct electrode position when “floating” the transvenous pacemaker is relatively simple. Although the loss of AV synchrony can result in about a 20% decrease in cardiac output, it is generally tolerated by most patients, apart from those with significant myocardial depression. It is also the least sensitive to small changes in catheter positions.
Transvenous pacemaker modes to use for conduction pathologies are summarized in Table 1 below:
Troubleshooting transvenous pacing
1. Intermittent loss of capture must be addressed urgently, as sudden and complete loss of capture will likely result in hemodynamic instability or collapse. Consider in-flight diversion if possible or a communication patch to a Cardiologist.
2. Immediately prepare to transcutaneous pace while troubleshooting.
3. Check to ensure electrodes are properly inserted and attached to pacer box.
4. Ensure the pacer box has battery power.
5. Assess the patient for landmarks on the TVP catheter wire.
a. May also utilize point of care ultrasound to evaluate wire position.
6. Consider switching to asynchronous mode (e.g. DOO, VOO).
7. Evaluate systematically:
a. EMI from aircraft (pacemaker will be inhibited from firing and ECG will look like electrocautery or perhaps even VF)
i. Switch to asynchronous mode, but ensure rate is greater than the patient’s intrinsic rate to avoid R on T phenomenon.
1. DOO for 3rd degree heart block without atrial fibrillation
2. VOO for 3rd degree heart block with atrial fibrillation
b. Failure to pace due to output failure (pacing spikes absent or heart rate not reaching set value)
i. Increase mA (20mA atria and 25mA ventricle) and decrease sensitivity (if in VVI) while observing cardiac monitor to ensure there is electrical capture
ii. Switch to an asynchronous mode to prevent oversensing (DOO, VOO)
c. Failure to capture (visible pacing spikes on ECG but lack of mechanical capture – pulse, arterial line wave form pulsation)
i. Increase output
ii. Check connections, rule out mechanical issue
iii. May also be due to drug interaction (anti-arrhythmics) or post cardiac defibrillation
d. Failure to sense (producing pacing spikes inappropriately)
i. Decrease absolute value of sensing (therefore making it easier to inhibit)
e. Oversensing (inhibited pacing)
i. Large P or T waves may be sensed as intrinsic atrial activity
ii. Increase sensitivity (therefore making it hard to inhibit) or switch to asynchronous mode (DOO, VOO)
f. AV dyssynchrony – loss of atrial kick causing hypotension (SBP usually falls at least 20 points)
i. Ensure both leads are properly capturing and pacer is in dual chamber mode.
Transvenous pacing: Other points to consider