Chapter 103: Temporary Pacemaker Insertion and Management of CV Implantable Electrical Devices in the ICU

Bradyarrhythmias occur commonly in the ICU, and most events do not necessitate temporary pacing. Transient bradycardia often occurs in the setting of enhanced vagal tone due to tracheal irritation, suction, or intubation; abdominal distention; or severe vomiting. Reversible causes such as severe electrolyte or acid-base imbalances should be corrected first whenever possible, as this may obviate the need for pacing or enhance the likelihood that a temporary lead will function appropriately when placed. Isolated sinus pauses, transient extended pauses in atrial fibrillation (AF), and nocturnal bradycardia in patients with obstructive sleep apnea are all common, and generally do not require temporary pacing. Pacing is considered when patients are having symptoms or have developed hemodynamic compromise thought to be secondary to a bradyarrhythmia, or if a rhythm is detected that is associated with a high risk of subsequent malignant bradyarrhythmia (Table 103–1). Recognizing circumstances that portend risk, for example, anterior wall or inferior wall myocardial infarction (MI), or preexisting infra-Hisian conduction disease, will help identify patients at high risk for need of temporary pacing.

Transcutaneous Pacing

There are multiple methods for temporary cardiac pacing, including transcutaneous, transvenous, and even transesophageal pacing. In the event of sustained hemodynamic compromise and/or ventricular asystole due to bradyarrhythmia, the most prompt and easiest pacing method is transcutaneous pacing. Current day external defibrillators allow for transcutaneous pacing via the defibrillation pads (Figure 103–1). One should ensure that the pads are applied to dry and intact skin. Ideally, the pads should be positioned in a relative anterior-posterior (AP) location, with the anterior pad placed to the left of the sternum near the point of maximal impulse, and the posterior pad to the left of the spine and just beneath the scapula. The external generator is set to “pacer” and the rate set based on the acute need. The output is ramped up until reliable capture is obtained, which is usually greater than 40 mA. Due to saturation of the electrocardiogram (ECG) signal from the pacing artifact, myocardial capture may not be clearly evident on the telemetry or ECG. The peripheral pulse can be checked to verify consistent capture. External pacing, despite appropriate technique and multiple adequate pad orientations, achieves consistent capture in only a small majority of patients at best. In addition, it is quite painful to the conscious patient. Hence, it should only be used as a temporizing measure in anticipation of urgent transvenous pacing unless capture is reliable, the patient is deeply sedated or unconscious, and/or when temporary pacing is required for a brief period of time.

Temporary Transvenous Pacing

Like all interventions, the benefits of a temporary transvenous pacemaker (TVP) must be weighed against its risks. Insertion of a temporary pacemaker puts patients at risk for complications related to central venous access, such as bleeding, pneumothorax (level of risk depending on venous access site), thrombosis, line-related sepsis, and cardiac tamponade. Additionally, an unstable temporary pacemaker lead or malfunctioning system has the potential to induce malignant ventricular tachyarrhythmias. Individuals who insert temporary pacemakers should be specifically trained in this area and this procedure should not be equated with other procedures that solely require obtaining central venous access.

Temporary pacemaker leads are most commonly placed via the internal jugular (IJ) or subclavian veins, but when needed, can be placed through the femoral, brachial, or even external jugular veins. When performed at bedside, the right IJ (best with ultrasound guidance) or left subclavian veins are most commonly used as they offer the most direct routes for the shaped balloon-tipped catheters. When fluoroscopy is available (either via portable C-arm or in the interventional laboratory), any of the earlier access sites can be used. In some institutions, the left subclavian is avoided so that this access site is kept available for potential permanent device implantation. Needless to say, strict sterile technique must be adhered to as a pacing wire is delivered into the endocardium, which places the patient at risk for bacteremia or endocarditis.

There are various types of temporary pacing leads commercially available. Balloon-tipped leads designed to enhance advancement to the right ventricle are probably the fastest, most accessible, and generally do not require fluoroscopy. These catheters are generally placed via 6-Fr sheaths. Standard multipole electrophysiology (EP) catheters (5 or 6 Fr) or active fixation leads that provide for increased stability can also be used but require fluoroscopy (Figure 103–2). In rare circumstances, when there is a need for very extended temporary pacing, individuals who implant permanent devices have inserted a permanent active fixation lead and connected them to an externalized permanent pacemaker device until the time for permanent implantation.

Methods of Placement

Lead placement can be performed via electrogram (EGM) or fluoroscopic guidance or both. The most practical way to insert a pacing wire is via EGM guidance. The patient is connected to a 12-lead ECG machine, with standard placement of the 4-limb leads (at least). A 12-lead ECG confirming the indication can be obtained (Figure 103–3A). Once the temporary lead is placed into the circulation, the “distal” end of the pacing lead (marked [–]) is passed to an assistant who connects the electrode to the V1 ECG clip. When connected in this manner, the “V1 lead” on the ECG actually displays the local unipolar intracardiac EGM at the tip of the pacing lead. Of note, care must be taken to cover this connection as this part of the pacemaker wire is no longer sterile. As one advances, the EGM pattern changes from a predominant atrial to a mixed atrial-ventricular signal at the level of the tricuspid valve, and finally when the valve is crossed, a large ventricular EGM is demonstrable. When good contact with the ventricular wall is made, a large localized ST elevation pattern referred to as the “current of injury” is typically seen (Figure 103–3B). The balloon is deflated at this point to allow the lead tip to oppose itself completely to the ventricular myocardium. The most reliable site for temporary pacing is the right ventricular apex. When the lead is positioned in the right ventricular (RV) apex, a paced QRS with a left bundle branch block (LBBB), interior axis pattern will be present (Figure 103–3C). Typically, the RV position is reached between 35 and 45 cm, and if the markers on the lead indicate that significantly more lead is intravascular, it is likely that a large loop is present, which may promote lead instability. When using fluoroscopy, visual guidance makes placement of the lead to the RV apex easier. The position can be confirmed by AP, right anterior oblique (RAO), and left anterior oblique (LAO) views.

Once the lead is placed in position with a good current of injury, careful assessment of pacing function is required. A normally functioning temporary pacemaker should have a low pacing threshold (typically 1 mA or less) and be capable of sensing spontaneous ventricular activity (preferably 5 mV signals or larger). If there is no underlying rhythm, or if the patient’s spontaneous rate is less than the minimal programmable rate of the temporary pacemaker, the sensing threshold cannot be measured.

Once lead stability and functionality is established, suturing the lead at the insertion site in a highly secure manner is critical, as even a minimal displacement of a perfectly placed lead may result in a totally nonfunctioning pacing system. Most operators choose to leave the sheath in place, especially if needed for central venous access (as a sidearm is usually present). In addition, many choose to place a sterile sleeve that is integrated with the introducer around the pacemaker wire, so as to allow for some degree of lead manipulation if a sudden need arises.

Note that the EGM-guided approach is practical only when there is spontaneous ventricular electrical activity. In rare circumstances when there is absolutely no ventricular activity, and fluoroscopy is not immediately available, the only practical option is to advance the lead blindly while pacing in the hope that the lead is advanced to a stable site in the RV and ventricular capture is achieved.

Pacemaker Generators

There are numerous types of temporary pacemaker generators. When a temporary transvenous lead is placed, it is typically connected to a single-chamber generator, though in certain circumstances a temporary transvenous atrial wire can also be placed creating a dual-chamber system. In the cardiothoracic surgical areas, patients may have temporary epicardial wires connected to single- or dual-chamber temporary pulse generators (Figure 103–4). Programming capabilities of these devices vary widely depending on the model type, but all allow for adjustments of pacing rates, outputs, and sensitivities. Most devices also have a capability to deliver rapid antitachycardia pacing, though such activities require the experience of a cardiologist or electrophysiologist.

A chest x-ray should be obtained soon after lead placement to rule out pneumothorax and establish initial radiographic location (Figure 103–5). Should unexplained hypotension or tachycardia ensue any time after placement, a transthoracic echo should be obtained to look for pericardial effusion and/or tamponade from a possible RV perforation. The insertion site should be monitored for bleeding/hematoma. Most importantly, the TVP should be checked at least once daily for both capture threshold and sensitivity, and also after any major movements or transfers. If any changes in device function are noted, a repeat chest x-ray (CXR) should be obtained for evaluation of lead position and a careful check of all connections should be made.

Even in the critical care setting, permanent pacemakers usually function normally and special modifications of programmed settings are very infrequently required. Fortunately, most complex mechanical and electrical devices in the critical care unit do not impact on pacemaker function. On occasion, attempts to increase cardiac output by pacing at more rapid rates are pursued, but this usually proves ineffective, as the higher pacing rate is often associated with a concomitant fall in stroke volume. Patients, who develop severe electrolyte or acid-base disturbances, may be at risk for developing pacemaker malfunction. In such circumstances, programming the device to higher pacing outputs and more sensitive settings may offset, at least temporarily, some of these pacing abnormalities.

A basic understanding of pacemaker codes and modes is essential for interpreting pacing patterns seen on ECGs and telemetry. It is important to appreciate that the pacing pattern manifested is a function of both the patient’s underlying rhythm and the programmed parameters of the pacemaker. Thus, the absence of any pacemaker activity during regular rhythms most often represents totally normal pacemaker function, and should not trigger any immediate concerns. In order to determine definitively whether function is normal, it is necessary to know the programmed settings of the device. Suspected discrepancies between the programmed settings and pacemaker function should trigger cardiology consultation.

Special Considerations

• Cardioversion—In patients with pacemakers or ICDs who are to undergo urgent or planned cardioversion in the ICU setting via external pads, the delivery of direct current energy poses a small risk to both the integrity of the pulse generator and to the lead tip-myocardial interface. The preferred manner is to place the defibrillator pads in an AP orientation near the midline and not overlying the device. In addition, if the device is an ICD, cardiology consultation can be requested to evaluate if cardioversion via the implanted device is appropriate.

• Newly implanted cardiac devices—If a hemodynamic monitoring catheter needs to be placed in a patient who has undergone pacemaker or ICD implantation in the previous 6 months, it poses a potential risk for dislodgement. Fluoroscopic guidance is preferred in this setting so as to decrease the risk of unintended lead displacement.

• Rate modulation—Many pacemakers are programmed with the rate modulation feature activated. This refers to the ability of the pacemaker to detect the need for an increased heart rate based on the information provided by specialized sensors. The 2 most common forms of rate modulation sensors and associated algorithms are piezoelectric crystal-based accelerometers (ie, equate movement with exertion) or calculated minute ventilation, which is based on transthoracic impedance changes. Infrequently, excessive shaking of the patient or high tidal volume–assisted ventilation may trigger inappropriately elevated pacing rates based on these sensors. In this uncommon circumstance, the rate modulation parameter should be programmed to off.

Most of the comments described in the pacing section are equally relevant to implantable ICDs, which have analogous pacing capabilities. There are additional considerations that should be kept in mind when dealing with a patient with an active ICD in the ICU setting.

Perhaps the most important consideration is that critically ill patients are frequently tachycardic, either as a physiologic response to their underlying circumstances or resulting from the pharmacologic agents that are being used to support their hemodynamics. This increases the possibility that the ICD patient may receive inappropriate ICD therapies if the heart rate exceeds the detection rate threshold of the device. While many devices have algorithms programmed to try to distinguish ventricular tachycardia (VT) from supraventricular tachycardia (SVT), AF, and sinus tachycardia, none is perfect. The best way to avoid inappropriate shocks is to assure that the tachycardia detection rate is above the patient’s heart rate. Since settings vary widely between patients, it is valuable to know the programmed parameters of these devices, so as to avoid the possibility of inappropriate ICD therapies. On occasion, temporary reprogramming to allow for delivery of antitachycadia pacing therapies under the guidance of an electrophysiologist may facilitate minimally invasive and better-controlled treatment of arrhythmias in the critical care setting.