Amita Sudhir1 and William J. Brady2 1Department of Emergency Medicine, University of Virginia School of Medicine, Charlottesville, VA, USA 2Departments of Emergency Medicine and Medicine, University of Virginia School of Medicine, Charlottesville, VA, USA Permanent cardiac pacemakers are increasingly encountered in clinical medicine. A basic familiarity with the devices and their electrocardiographic (ECG) findings is essential for clinicians treating both hospitalized patients and patients in the clinic or outpatient setting. The “modern” pacemaker infrequently malfunctions yet a review of the types of pacemaker dysfunction is still appropriate. There are several types of pacemakers, and they are identified according to a universally accepted 3, 4, or 5 designation alphabetical position code. The pacemaker’s abilities are described with this coding sequence using various letter designations as described in Table 18.1 and Boxes 18.1 and 18.2. A pacer spike is a narrow‐appearing electrical discharge on the ECG (Figure 18.1). It can be very large with high amplitude or very small with minimal amplitude. In certain leads, a pacer spike may not be evident. With atrial pacing, a pacer spike can be seen just before the P wave, and both the P wave and the QRS complex appear normal. The ECG appears to be in normal sinus rhythm with the exception of a pacing spike preceding the P wave. With ventricular pacing, a pacer spike can be seen just before the QRS complex, and the QRS complex appears wide. The overall ECG looks similar to a left bundle branch block (LBBB) with the presence of pacer spikes before the QRS complexes. Figure 18.1 demonstrates atrial, ventricular, and atrioventricular pacing. Pacer spikes may not be visible on a rhythm strip, nor may they be seen on all leads on an ECG. To differentiate between a ventricular paced rhythm (VPR) and LBBB (or other ventricular rhythm), one should consider lead V6. The QRS complex in lead V6 is usually upright with an LBBB, but negative with a VPR. Pacemaker malfunction can be classified in a number of categories. The issues most often producing ECG abnormality include the following: pacemaker unit malfunction (i.e. battery depletion or component failure), transvenous lead problems, and pacemaker lead–myocardial interface problems. The following pacemaker malfunctions can be seen via the ECG in the clinical setting. The pacemaker does not fire when it should; thus the pacemaker fails to pace (Figure 18.2). On the ECG, pacer spikes are absent. The cardiac rhythm is dependent on the patient’s native, or underlying, cardiac rhythm. The pacemaker is firing (i.e. a pacer spike is seen), but no myocardial depolarization occurs (Figure 18.3). Pacer spikes can be seen on the ECG, but without an associated P wave or QRS complex. Again, the cardiac rhythm is dependent on the patient’s underlying cardiac rhythm. Table 18.1 Pacemaker coding sequence and letter designations.
18
The Electrocardiogram in Patients with Implanted Devices
The Paced Electrocardiogram
Pacemaker Malfunction
Failure to Pace
Failure to Capture
I – Chamber paced
II – Chamber sensed
III – Sensing response
IV – Programmability
V – Antidysrhythmic functions
A = atrium
A = atrium
T = triggered
P = simple
P = pacing
V = ventricle
V = ventricle
I = inhibited
M = multiprogrammable
S = shock
D = dual
D = dual
D = dual (A and V inhibited)
R = rate adaptive
D = dual (shock and pace)
O = none
O = none
O = none
C = communicating
O = none
Full access? Get Clinical Tree
