Permanent pacing is not performed in the ED.1 Permanent pacemaker pulse generators (battery) are placed subcutaneously on the side of the patient's nondominant hand (thus, usually in the left prepectoral region below the left clavicle). The endocardial transvenous leads are positioned in the right ventricle at the apex, septum, or right ventricular outflow tract, and in the case of a dual-chamber device, also in the right atrium. A subclavian or cephalic vein approach is common. An epicardial lead may be implanted during concomitant open heart surgery.
Pacemaker leads are either bipolar or unipolar in configuration; unipolar leads are prone to oversensing myopotential and electromagnetic interference. The disadvantage of the bipolar configuration is that it is larger and more prone to lead fractures.
A five-letter code is used to describe the features of the pacemaker3 (Table 33-6). The first three code letters are used most commonly. The first letter refers to the chamber or chambers in which the pacing occurs: A = atrium, V = ventricle, and D = dual chamber or both A and V. The second letter refers to the chamber or chambers in which sensing occurs. The letters are the same as those for the first letter code. "I" indicates that a sense event inhibits the output pulse and causes the pacemaker to recycle the timing cycles, "T" means that an output pulse is triggered in response to a sensed event. "D" means that both "T" and "I" response can occur. The most common pacemakers are VVI and DDD. The fourth letter is used to indicate the presence or absence of an adaptive-rate mechanism (rate modulation). Pacemakers are then indicated as VVIR or DDDR. The fifth letter is used to indicate whether multisite pacing is present and is rarely used. See Figures 33-4 and 33-5 for examples of ECGs with pacemaker spikes.
TABLE 33-6The Five-Letter Code System for Implanted Cardiac Pacemakers: The NASPE/BPEG Generic Pacemaker Code ||Download (.pdf) TABLE 33-6 The Five-Letter Code System for Implanted Cardiac Pacemakers: The NASPE/BPEG Generic Pacemaker Code
|Letter Position ||1 ||II ||III ||IV ||V |
|Category ||Chamber(s) Paced ||Chamber(s) Sensed ||Response to Sensing ||Programmability, Rate ||Antitachyarrhythmic Function(s) |
| ||0, none ||0, none ||0, none ||0, none ||0, none |
| ||A, atrium ||A, atrium ||T, triggered ||P, simple programmable ||P, pacing |
| ||V, ventricle ||V, ventricle ||1, inhibited ||M, multiprogrammable ||S, shock |
| ||D, dual (A + V)* ||D, dual (A + V)* ||D, dual (D + l)† ||C, Communicating (telemetry) ||D, dual (P + S)‡ |
| ||S, single chamber ||S, single chamber ||— ||R, rate modulation ||— |
Single-lead pacemaker. Only the ventricle is paced.
Atrioventricular pacer spikes seen best in leads II and aVF.
RESUSCITATION IN PATIENTS WITH PERMANENT PACEMAKER
If a patient who has a permanent pacemaker requires countershock, place the pads or paddles at least 8 cm from the pulse generator. The current normal positioning of the paddles—below the right clavicle and apex of the heart—is safe because the majority of pulse generators are below the left clavicle. Alternatively, place adhesive electrodes in an anteroposterior configuration. After countershock, interrogate the pacemaker to ensure that it is still functioning normally.
Potential problems after defibrillation include:
Another reason that immediate return of pacing (capture) fails after defibrillation is that global myocardial ischemia increases pacing threshold. If this occurs, try transcutaneous pacing at higher delivered energy settings.
Complications for which a patient may seek care in the ED in the early period after pacemaker insertion are listed in Table 33-7. Two are discussed in detail.
TABLE 33-7Complications Seen after Pacemaker Insertion ||Download (.pdf) TABLE 33-7 Complications Seen after Pacemaker Insertion
|Complication ||Comment |
|Infection || |
Infection rate is <1%.
Infections are more common in patients after pacemaker replacement or prolonged procedure.
Early infections are most commonly caused by Staphylococcus aureus or Staphylococcus epidermidis.
Pacemaker infection presents as:
Local inflammation or abscess formation in the pacemaker pocket, as evidenced by pain, tenderness, or redness at the site. Skin adherence to the device, especially with discoloration of the skin over it, is highly indicative of localized infection. Do not aspirate the pocket because this can worsen the infection. If only a superficial infection is suspected, antibiotics and analgesics may be given with an early referral to the device implanter to review.
Erosion of the device or lead through the skin resulting in the leads or pulse generator being exposed. Complete device and lead removal is almost always required.
Cardiac device–related infective endocarditis involving the lead or valves. Patient may present with sepsis and positive blood culture without sign of local inflammation.
|Thrombophlebitis and venous obstruction || |
Symptomatic thrombosis of the upper extremities and central veins is uncommon, possibly because of extensive venous collaterals (0.3%–3.0% of patients).
Site of insertion does affect incidence.
Symptoms include edema, pain, or venous engorgement of the arm ipsilateral to lead insertion.
Treatment includes IV heparin therapy followed by long-term warfarin administration.
|Pneumothorax || |
1% of patients.
More common with subclavian introducer technique.
Hemothorax and pneumomediastinum are rare.
|Pacemaker syndrome || |
20% of patients.
New or worsening of symptoms such as syncope or near-syncope, orthostatic dizziness, exercise intolerance, dizziness, uncomfortable pulsation over the neck and abdomen, right upper quadrant pain, etc.
Atrioventricular synchrony and the presence of ventriculoatrial conduction are most common in the setting of VVI pacing but may occur with the DDI mode. With VVI pacing, the ventricle is electrically stimulated, resulting in ventricular contraction. If sinus node functions are intact, the atria can be depolarized by a sinus impulse and contract when the tricuspid and mitral valves are closed. This results in an increase in jugular and pulmonary venous pressures and may produce symptoms of congestive heart failure. Atrial distention can result in reflex vasodepressor effects mediated by the central nervous system. If the contribution of atrial contraction to late diastolic ventricular filling is important in maintaining an adequate cardiac output, orthostatic hypotension may occur. DDI pacing in a patient with atrioventricular block can result in pacemaker syndrome if the sinus node discharge rate exceeds the programmed rate of the pacemaker.
In most instances, symptoms are mild and patients adapt to them. In about one third of these patients, symptoms are severe. Treatment usually requires upgrading a VVI pacemaker to a dual-chamber pacemaker or lowering the pacing rate of the VVI unit, so that ventricular pacing does not occur but provided intrinsic conduction occurs. If symptoms occur in a patient paced in the DDI mode, optimizing the timing of atrial and ventricular pacing is usually required. Consult with a cardiologist.
Pacemaker malfunction is divided into four areas: failure to sense, failure to pace, failure to capture, or overpacing or pacemaker-associated tachycardia.4
Failure to Sense (Undersensing)
Undersensing occurs when the pacemaker cannot adequately detect the intrinsic electrical cardiac activity. This results from lead placement in an area of the heart with poor or variable conductivity, or if a lead is loose, dislodged, or physically broken. Sensing failure can occur if the programmed sensing threshold is set too high. With undersensing, if the pacer is set in an inhibit mode, it will fire at a set rate that is not coordinated with the patients underlying cardiac cycle (Figure 33-6A).
Various pacemaker malfunctions. A. Undersensing. B. Oversensing. C. Failure to capture.
Failure to Pace (Oversensing)
Oversensing occurs when the pacemaker experiences interference from electrical signals within the body (i.e., skeletal or smooth muscle myopotentials) that are not related to the normal cardiac cycle. Sources of interference may include skeletal muscle, the diaphragm, nerve stimulators, broken pacer leads, and uncommonly, coarse atrial fibrillation. When electrical activity is oversensed, the pacemaker erroneously inhibits the pulse generator and the patient may develop bradycardic rhythms (Figure 33-6B).
Failure to capture occurs when the pulse generator fires but the current delivered to the endocardium is too low to initiate depolarization and wavefront propagation. Dislodged leads, poor cardiac conductivity due to myocardial disease (e.g., ischemia, acidosis, fibrosis), and programming problems are the most common reasons for this malfunction. Failure to capture can be intermittent (Figure 33-6C).
Occasionally the patient with an implanted device may present with a rapid paced rhythm. This may be due to:
Unless preprogrammed to mode switch, pacemakers detect rapid atrial rhythms and track them, resulting in pacing at the upper rate limit. Pacemaker-mediated tachycardia can occur in a dual-chamber pacemaker when a premature ventricular ectopic beat triggers a retrogradely conducted atrial depolarization outside the atrial refractory period, which is then sensed by the pacemaker, initiating ventricular pacing. If this continues, it can cause an endless loop tachycardia. Rarely the pacemaker may malfunction with acceleration of pacing (runaway pacemaker). This occur when the pulse generator discharges at a rapid rate above its preset upper limit and is most commonly associated with a battery failure or damage from external interference. Placing a magnet over the pacemaker may help in the pacemaker-mediated tachycardia or runaway pacemaker. However, interrogation of the device is usually required, and the device must be replaced if programming is not successful.
PACEMAKER PROGRAMMING ERRORS
Pacemakers are computer-controlled devices with complex software that requires adjustment and maintenance. Reprogramming is accomplished noninvasively with devices that communicate to the pacemaker through radiofrequencies. Occasional settings can be inadvertently altered, and software, as with any computer, can fail. Software changes may occur in set rates, sensing thresholds, and current outputs.