Advantages of Ultrasound Guidance

The use of bedside ultrasound will provide benefits during various stages of placing a transvenous pacemaker. It should be noted that the first step in placing a transvenous pacemaker is obtaining central venous access in order to facilitate advancement of a pacemaker catheter into the right ventricle. As noted in the central venous access chapter, utilizing ultrasound guidance for placing central venous catheters significantly decreases complications and increases success rates.

For the placement of a transvenous pacemaker, continuous real-time ultrasound guidance can be utilized to visualize proper placement and propagation of a cardiac pacing catheter and avoid potential complications, which may include advancement into the pulmonary artery, damage to the myocardium, or coiling in the right atrium. Ultrasound visualization of the inferior vena cava (IVC) is also useful for evaluation of catheter malposition.

Bedside ultrasound can additionally be beneficial in assessing for capture in both transcutaneous [2] and transvenous pacing. The standard cardiac views will be used to evaluate for cardiac activity after each of these procedures has been performed. This may be a valuable adjunct in addition to the clinical signs which are typically used to evaluate the effectiveness of temporary pacing. Bedside echocardiographic evaluation before and after pacemaker implantation can demonstrate the effectiveness of the procedure. Additionally, ultrasound can be repeated to assess for continued effectiveness given any changes in the clinical picture.

Anatomy

The preferred sites for placement of a transvenous pacemaker are the right internal jugular vein and left subclavian vein. These sites provide the most direct course to the right atrium, via the superior vena cava, and limit the potential for malpositioning [1]. The right internal jugular vein is typically recommended as the site for temporary transvenous pacemaker placement, because the left subclavian vein is typically utilized for patients requiring permanent catheter placement.

Once a central venous catheter is placed, the pacing catheter will be directed through the central venous line, known as the introducer sheath. The introducer sheath will terminate in the SVC, and the transvenous pacing catheter will be advanced further with the goal of traversing the right atrium, through the tricuspid valve, and ultimately terminating in the right ventricle. The ultrasound views will include the standard subxiphoid, parasternal, and apical views with focus on obtaining views which will optimize visualization of the right atrium and ventricle (typically the subxiphoid and apical), allowing for advancement of the pacing catheter under dynamic ultrasound visualization.

Indications

Emergent cardiac pacing is indicated in multiple clinical scenarios which result in interruption or dysfunction of normal cardiac electrical activity. Common causes include SA node dysfunction, AV block, electrolyte or metabolic disorders, overdose or drug-associated dysrhythmias, and infection-related dysrhythmias. Cardiac pacing in an emergent setting is typically performed until a permanent pacemaker can be implanted or until the underlying etiology can be treated. Emergent pacing is generally provided via the transcutaneous or transvenous methods. A typical clinical scenario includes initiation of transcutaneous pacing with subsequent placement of a transvenous pacemaker. Transvenous pacing is generally better tolerated by the patient and more effective at obtaining capture, though it is more invasive and takes longer to initiate.

Contraindications

Placement of a transvenous pacemaker should be avoided when the cause of bradycardia can be corrected by immediate alternative measures. This is true in the case of hypothermia, in which the appropriate treatment would be active rewarming. Other examples included drug toxicity where an antidote is readily available or electrolyte abnormalities that can be easily corrected.

Emergent transvenous pacing is contraindicated when bradycardia is not associated with hypotension or signs of end-organ dysfunction. Many patients may have bradycardia of little to no clinical significance in whom pacemaker placement can safely be delayed. Having the equipment to perform this procedure at bedside is important for any patient in which the possibility of hemodynamic compromise is anticipated. In addition, contraindications to central venous access similarly apply to this procedure.

Equipment/Probe Selection

For initial central venous access, a high-frequency linear probe will be utilized to identify appropriate anatomy and visualize advancement of the needle tip as described in the central venous access chapter. During placement of the transvenous pacemaker, a phased array (or curvilinear) probe will be used to obtain cardiac and IVC views.

Equipment (Fig. 5.3)

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  Antiseptic (chlorhexidine gluconate, betadine, etc.)

  
  
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  Local anesthetic (1% lidocaine)

  
  
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  Gauze

  
  
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  25 gauge needle for anesthetic infiltration

  
  
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  18 gauge introducer needle

  
  
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  Syringes (3 cc, 10 cc)

  
  
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  Needles for anesthetic (18 gauge, 25 gauge)

  
  
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  Sterile drapes

  
  
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  Sterile gown, sterile gloves, mask

  
  
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  Sterile ultrasound probe cover

  
  
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  J-shaped guidewire

  
  
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  Dilator

  
  
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  11 blade scalpel

  
  
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  Introducer catheter (larger in diameter than pacemaker catheter). A critical point about the cordis introducer sheath diameter is that not only does it have to be larger than the diameter of the pacemaker catheter, but also it has to be just slightly larger. Most pacemaker catheters will have specific introducer sheaths for them or at least list what diameter/French the cordis should be. Placing the pacemaker catheter through even a slightly larger one, than indicated on the packaging, will result in persistent leakage of blood from the insertion point. The greater the diameter disparity, the greater the leak.

  
  
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  Sterile cap for introducer catheter

  
  
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  Large Tegaderm

  
  
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  Cardiac monitoring equipment

  
  
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  Pacemaker catheter with (+) and (−) leads

  
  
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  Sterile transparent sheath for pacing catheter

  
  
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  Pacer generator (Fig. 5.4)

  
  
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  Battery with backup, new battery

Preparation/Preprocedural Evaluation

As with any invasive procedure, the insertion of a transvenous pacemaker begins with patient consent and preparation. Informed consent should be obtained whenever possible. In the emergent setting, when the patient or a next of kin is unable to provide timely consent, implied consent may be necessary. The procedure should be performed under sterile conditions with proper skin preparation, local anesthesia at site of catheter insertion, full drape and gown, gloves, and mask for the provider performing the procedure. Generally, central venous access is to be obtained to facilitate placement of the pacing catheter. Often a kit containing the equipment both for central venous access and for pacing can be found in a single transvenous pacemaker kit. The additional equipment required for the pacemaker portion include sterile transparent sheath, the pacing catheter, pacing generator with battery, and backup battery.

Adequate preparation involves ensuring all the necessary equipment is available and working. Evaluate the patency of the pacer catheter balloon by filling balloon with 1.5 mL of sterile saline and inspecting for leaks. A nonsterile assistant will be necessary to connect the electrode connectors to the pacing generator, and operate the ultrasound during guidance of pacing catheter placement. Additionally, since advancement of the pacing catheter should be performed under and directed by real-time ultrasound visualization of the heart, a sterile assistant is important who can feed the sheath-covered pacing catheter into the cordis introducer sheath one to several centimeters at a time.

Procedure

The first step is insertion of the central venous catheter (introducing catheter), as described in the central venous access chapter. Once central venous access is obtained, connect the transparent catheter sheath to the introducing catheter hub, and insert the pacing catheter through the sheath and into the introducing catheter hub. Advance the pacing catheter about 10 cm to assure the distal tip lies beyond the length of the introducing catheter. At this time, 1.5 mL of sterile saline can be used to inflate the balloon to facilitate proper advancement. The proximal electrode tip can be connected to the positive (+) connector terminal of the pacer generator. While critical for blind placement of temporary transvenous pacemakers, alligator clips connected to distal electrodes will be of lesser value when using ultrasound guidance and may make the procedure more cumbersome. Real-time cardiac ultrasound will allow visualization and guidance of the pacing catheter tip into its ideal destination at the apex of the right ventricle. Traditionally, adequate positioning of the pacing wire would be confirmed by observing a left bundle branch block ECG pattern [1]. Relying on this method is not only time consuming, but also has the potential for inaccurate interpretation and is impossible to justify in the setting of real-time ultrasound guidance of pacing catheter placement directly into the right ventricle. Previous descriptions of this procedure have also indicated the use of fluoroscopy to visualize proper placement in real time. This has the obvious disadvantage of using large, bulky equipment (most of which is typically not available in clinical settings), taking the time necessary to obtain this equipment and the associated radiation for the patient and those performing and assisting with the procedure.

Using bedside ultrasound, the progression of the pacemaker catheter can be visualized in the right atrium and through to the right ventricle. The best views for visualizing the regions are the subxiphoid and apical four chamber and are typically the most useful for ultrasound-guided transvenous pacemaker placement (Figs. 5.5 and 5.6). However, it should be noted that a parasternal long-axis view with a tilt to visualize the right ventricular inflow tract and right atrium can provide an excellent vantage point for visualizing and guiding pacer balloon entry when other options are limited. As in many real clinical scenarios and settings, perfect images and an availability of three or more clear windows to the heart are unrealistic and rare. Thus, being aware of more than one option for pacer balloon guidance is critical. The preference for which view to obtain relies on which will provide the best image available to assure adequate placement. If the pacer tip is not visualized initially, fanning of the probe may be required for adequate visualization [3, 4]. Additionally, inflating and deflating the balloon will often make it more obvious. Finally, inflating the balloon with saline from a 10 ml syringe in which 9 ml of fluid and 1 ml of air are mixed through vigorous syringe agitation can create a hyperechoic spherical object that may stand out even in the most limited images.

Once the transvenous pacemaker is in appropriate position, the pacing generator can be turned on. In the setting of peri-arrest or hemodynamic compromise, the initial settings include a rate of 80–100 bpm, maximum output (typically 5 mA), and sensitivity of 3 mV. Observe for capture and for clinical improvement. Palpate for peripheral pulses once capture is noted. Bedside echocardiogram with ECG lead attachments can additionally be utilized at this time to evaluate for proper capture of pacing beats. The output can then be decreased until capture is no longer appreciated. This is known as the threshold output. Output should be set to 2–3× the threshold output. In nonemergent situations, the initial output can be set low and gradually increased until capture is appreciated. Following proper placement and appreciation of capture, the balloon should be deflated, the pacing catheter can be secured into place, the sterile sheath can be advanced over the external portion of the pacer wire, and a sterile dressing can be applied.

Complications

There are multiple complications which can occur throughout various stages of this procedure of which the provider should be aware. The intrinsic complications associated with obtaining venous access have the potential to occur during the initial step of inserting the introducer catheter. These include pneumothorax, vascular injury, cannulation of the associated artery, thrombus formation, and infection.

Failure to adequately obtain cardiac capture is another complication and one which may occur for various reasons. Malpositioning, such as in the pulmonary artery, right atrium, or IVC, of the pacing catheter may result in failure to capture, which can be determined by bedside ultrasound. If the pacing catheter cannot be identified in the right atrium or right ventricle despite appropriate advancement, the tip may lie in the IVC. Simply switching ultrasound views from a cardiac view to a view of the IVC (Fig. 5.7) will allow for possible identification of the pacing catheter [5]. If this is the case, the catheter should be withdrawn, and additional attempts of advancement with the inflated balloon should be made. The pacing catheter may lie in the right atrium and meet resistance at the level of the tricuspid valve, preventing proper placement in the right ventricle. This can be diagnosed by identifying the tip of the pacing catheter in the right atrium via ultrasound. The potential for placement of the pacing catheter in either the IVC or right atrium increases in the setting of hemodynamic compromise and poor forward blood flow [1]. In the case of a pacing catheter in the right atrium, advancement of the catheter during a visualized diastolic cycle may aid in appropriate placement. In some patients, guiding the balloon into the right atrium proves to be exceedingly difficult. Twisting the pacer catheter at the hub clockwise and then counterclockwise slowly while advancing the catheter may facilitate balloon entry into the right atrium. If the pacing catheter has been advanced into the pulmonary circulation, it will need to be retracted and the tip of the catheter properly situated in the right ventricle. Cases of catheter tip over advancement into the pulmonary circulation illustrate the importance of using ultrasound for direct visualization during the procedure.

Additional complications include ventricular arrhythmias and ventricular injury. The most serious of ventricular injuries would involve perforation of the right ventricle. The potential for this complication is reduced by proper direct visualization under ultrasound with the focus on appropriate placement and continued assessment of where the tip of the pacing catheter lies. More importantly, the operator should never force advancement of a catheter. If resistance is met, the operator can try to determine the cause with ultrasound or try withdrawing and re-manipulating the catheter before attempting further advancement. In the setting of ventricular perforation, close hemodynamic monitoring and repeat bedside echocardiograms will be important to evaluate for signs of hemopericardium and tamponade. A common ventricular arrhythmia encountered during this procedure is non-sustained ventricular tachycardia, though persistent ventricular tachycardia or ventricular fibrillation may be encountered. Patients requiring this procedure often have myocardium which is more sensitive to dysrhythmias. Therefore, continuous cardiac monitoring should be maintained throughout the procedure. Magnesium can help stabilize myocardial cell membranes, and 2 grams can be infused in as little as 20 minutes when needed. If significant myocardial irritability is noted or suspected and time allows, magnesium infusion may significantly decrease the risk of ventricular tachycardia or fibrillation without dropping heart rate or blood pressure further.

If proper placement of the catheter is visualized via ultrasound, failure to capture may occur for alternative reasons. The procedure itself may be successful, but electromechanical dissociation may persist. Ultrasound is useful in determining this [6]. The patient’s underlying medical condition may prevent appropriate capture or proper functioning of the myocardium despite pacing. It is always important to consider treatment of the underlying cause as the definitive therapy and frequent reassessments should be made to assure clinical improvement. This is especially true in the case of metabolic or toxicologic etiologies.

Reevaluation of the pacing equipment should be made as well if encountering problems in providing appropriate pacing. This includes checking functionality of the power source, changing to a new battery for the pacer generator, and checking for appropriate connectivity of all leads.

Pearls/Pitfalls

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  Cardiac images via bedside ultrasound may be limited by patient body habitus, bowel gas, positioning, or the clinical scenario which may require multiple simultaneous interventions.

  
  
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  Subxiphoid and apical four-chamber views tend to best visualize the right ventricle and transvenous wire.

  
  
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  Two providers are required to insert a transvenous pacemaker under direct ultrasound guidance. The provider operating the ultrasound should be proficient in obtaining and interpreting cardiac views. This can be difficult to achieve in a busy clinical setting but is important to optimize success of the procedure.

  
  
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  Failure to appreciate the pacemaker catheter in the right ventricle may simply be the result of the catheter lying out of plane of the ultrasound field of view. Fanning of the probe to allow full visualization of the right ventricle may reveal the tip of the catheter [3, 4].

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