- Email: [email protected]
What is the cause of the apparent pacemaker malfunction?
108
Editorial / Journal of Electrocardiology 46 (2013) 107–108
College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2009;120:2271. 3. Fox KA, Goodman SG, Klein W, et al. Management of acute coronary syndromes. Variations in practice and outcome; findings from the Global Registry of Acute Coronary Events (GRACE). Eur Heart J 2002;23:1177. 4. Hombach V, Merkle N, Kestler HA, et al. Characterization of patients with acute chest pain using cardiac magnetic resonance imaging. Clin Res Cardiol 2008;97:760.
5. Plein S, Younger JF, Sparrow P, Ridgway JP, Ball SG, Greenwood JP. Cardiovascular magnetic resonance of scar and ischemia burden early after acute ST elevation and non-ST elevation myocardial infarction. J Cardiovasc Magn Reson 2008;10:47. 6. Lamfers EJ, Hooghoudt TE, Hertzberger DP, Schut A, Stolwijk PW, Verheugt FW. Abortion of acute ST segment elevation myocardial infarction after reperfusion: incidence, patients' characteristics, and prognosis. Heart 2003;89:496.
ECG Quiz
What is the cause of the apparent pacemaker malfunction? Quiz A 90-year-old woman with history of sick sinus syndrome, atrial fibrillation and a single-chamber right ventricular rate responsive pacemaker placement several years ago was hospitalized for atypical chest pain. She had negative cardiac serum markers and a negative chest computerized tomogram for pulmonary embolism. The electrocardiogram (ECG) on presentation (Fig. 1) was concerning for possible pacemaker malfunction. Note the large, 1-mV pacemaker spikes in front of four QRS complexes but no pacer spikes in front of the others. What was the cause of this apparent pacemaker malfunction?
Fig. 1. ECG of a patient with apparent pacemaker malfunction. The ECG was recorded with a GE Marquette MAC 5000 electrocardiograph. Ross Butschek, MD Carolinas Medical Center, Charlotte, NC 28232, USA Robert M. Farrell, PhD GE Healthcare, Diagnostic Cardiology Engineering Wauwatosa, WI 53226, USA Laszlo Littmann, MD, PhD Carolinas Medical Center, Charlotte, NC 28232, USA E-mail address: [email protected]
http://dx.doi.org/10.1016/j.jelectrocard.2012.11.009
(Solution on page 109)
ECG Quiz / Journal of Electrocardiology 46 (2013) 108–109
109
continued from page 108
Solution In reality, there was no pacemaker malfunction present. The occasional absence of ventricular pacer spikes was the result of the digitized sampling mode of the GE Marquette MAC 5000 electrocardiograph as will be discussed below. The clue to a normal pacemaker function lies in the fact that the QRS complexes are precisely regular and all complexes, paced and apparently not paced, have identical morphologies. This was confirmed by simultaneous recording of all limb leads and all chest leads. In addition, chest x-ray and chest CT did not indicate pacemaker lead fracture, and pacemaker interrogation confirmed normal pacemaker function including normal lead impedance. Pacemaker setting of the St. Jude Model 5610 Victory device included a pacemaker pulse width of 1 ms and amplitude of 2.5 V. Another way to define the paced QRS morphology is magnet application. This usually results in ventricular capture at about 100/min allowing confirmation of the paced QRS morphology. Three factors conspire to reduce the amplitude of the pacemaker spikes on the stored or printed ECG. First, although the GE Marquette MAC 5000 electrocardiograph digitizes the signals at 4000 samples per second (sps), they are downsampled to 500 sps by the time they are analyzed, printed, and stored. At 500 sps, each sample represents a duration of 2 ms. The 500-sps signal has a bandwidth of 150 Hz, meaning that higher-frequency components of the waveforms such as pacer spikes and sharp, narrow QRS complexes are attenuated. Second, the signals may be printed with a lower-frequency filter depending on the settings at which the recording equipment is programmed to record. Common settings are 150-, 100-, or 40-Hz filtering. As the filter setting is reduced below 150 Hz, highfrequency aspects of the ECG are further diminished. The ECG in Fig. 1 is printed with a 100-Hz filter applied, as is commonly done in clinical practice in order to reduce noise from sources such as motion, muscle tremor, or poor electrode contact with the skin. Third, ECGs are stored and transmitted with a user-configurable compression method that reduces record size and transmission time. In the compression method used in this case, the QRS complexes are stored with no loss of signal fidelity, but the intervals between QRS complexes (often including pacer spikes) are further downsampled to 125 sps.1 So why are prominent pacer spike visible in front of some QRS complexes but not in front of others? The answer is that the +1-mV pacer spikes in front of complexes 2, 7, 8, and 9 are artificially generated specifically to compensate for the diminished amplitude caused by the three aforementioned factors. The pacer spikes in front of those complexes were detected and subsequently enhanced by the electrocardiograph, while the rest were not. Another way newer ECG equipments can help providers recognize small pacemaker spikes is by placing arrowheads or “flags” under the detected atrial and ventricular pacer spikes (Fig. 2). Because of the described sampling and transmitting limitations, detection of narrow pacemaker spikes, especially in thin individuals, may become unreliable and can result in intermittent absence of the pacer spikes in the surface recording,2 as in our case, and in varying amplitude and polarity of the pacer spikes.3,4 Both of these can be easily misinterpreted as signs of pacemaker lead fracture or pacemaker generator failure. The issues described here extend to bedside and telemetry monitoring as well, where pacemaker stimulus artifacts are frequently not visible in the leads being monitored. This can result in medical personnel misinterpreting the QRS complexes as bundle branch block. More importantly when A-V sequential pacemaker is present, an atrial tachycardia that is tracked by the ventricular pacer can easily be misinterpreted as ventricular tachycardia.
Fig. 2. Arrowheads or “flags” denoting atrial (top panel), ventricular (middle panel) and both atrial and ventricular pacer spikes (bottom panel). Note that in the top 2 panels, recognition of the pacemaker spikes without the electrocardiograph-generated arrowheads would be difficult.
References 1. Reddy BR, Christenson DW, Rowlandson GI, et al. Data compression for storage of resting ECGs digitized at 500 samples/second. Biomed Instrum Technol 1992;26:133. 2. Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the standardization and interpretation of the electrocardiogram. Part I: the electrocardiogram and its technology. A scientific statement from the American Heart Association
Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation 2007;115:1306. 3. Engler RL, Goldberger AL, Bhargava V, Kapelusznik D. Pacemaker spike alternans: an artifact of digital signal processing. Pacing Clin Electrophysiol 1982;5:748. 4. Tomcsányi J, Bezzeg P, Bózsik B. Pacemaker spike alternans. J Electrocardiol 2011;44:221.
Editorial / Journal of Electrocardiology 46 (2013) 107–108
College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2009;120:2271. 3. Fox KA, Goodman SG, Klein W, et al. Management of acute coronary syndromes. Variations in practice and outcome; findings from the Global Registry of Acute Coronary Events (GRACE). Eur Heart J 2002;23:1177. 4. Hombach V, Merkle N, Kestler HA, et al. Characterization of patients with acute chest pain using cardiac magnetic resonance imaging. Clin Res Cardiol 2008;97:760.
5. Plein S, Younger JF, Sparrow P, Ridgway JP, Ball SG, Greenwood JP. Cardiovascular magnetic resonance of scar and ischemia burden early after acute ST elevation and non-ST elevation myocardial infarction. J Cardiovasc Magn Reson 2008;10:47. 6. Lamfers EJ, Hooghoudt TE, Hertzberger DP, Schut A, Stolwijk PW, Verheugt FW. Abortion of acute ST segment elevation myocardial infarction after reperfusion: incidence, patients' characteristics, and prognosis. Heart 2003;89:496.
ECG Quiz
What is the cause of the apparent pacemaker malfunction? Quiz A 90-year-old woman with history of sick sinus syndrome, atrial fibrillation and a single-chamber right ventricular rate responsive pacemaker placement several years ago was hospitalized for atypical chest pain. She had negative cardiac serum markers and a negative chest computerized tomogram for pulmonary embolism. The electrocardiogram (ECG) on presentation (Fig. 1) was concerning for possible pacemaker malfunction. Note the large, 1-mV pacemaker spikes in front of four QRS complexes but no pacer spikes in front of the others. What was the cause of this apparent pacemaker malfunction?
Fig. 1. ECG of a patient with apparent pacemaker malfunction. The ECG was recorded with a GE Marquette MAC 5000 electrocardiograph. Ross Butschek, MD Carolinas Medical Center, Charlotte, NC 28232, USA Robert M. Farrell, PhD GE Healthcare, Diagnostic Cardiology Engineering Wauwatosa, WI 53226, USA Laszlo Littmann, MD, PhD Carolinas Medical Center, Charlotte, NC 28232, USA E-mail address: [email protected]
http://dx.doi.org/10.1016/j.jelectrocard.2012.11.009
(Solution on page 109)
ECG Quiz / Journal of Electrocardiology 46 (2013) 108–109
109
continued from page 108
Solution In reality, there was no pacemaker malfunction present. The occasional absence of ventricular pacer spikes was the result of the digitized sampling mode of the GE Marquette MAC 5000 electrocardiograph as will be discussed below. The clue to a normal pacemaker function lies in the fact that the QRS complexes are precisely regular and all complexes, paced and apparently not paced, have identical morphologies. This was confirmed by simultaneous recording of all limb leads and all chest leads. In addition, chest x-ray and chest CT did not indicate pacemaker lead fracture, and pacemaker interrogation confirmed normal pacemaker function including normal lead impedance. Pacemaker setting of the St. Jude Model 5610 Victory device included a pacemaker pulse width of 1 ms and amplitude of 2.5 V. Another way to define the paced QRS morphology is magnet application. This usually results in ventricular capture at about 100/min allowing confirmation of the paced QRS morphology. Three factors conspire to reduce the amplitude of the pacemaker spikes on the stored or printed ECG. First, although the GE Marquette MAC 5000 electrocardiograph digitizes the signals at 4000 samples per second (sps), they are downsampled to 500 sps by the time they are analyzed, printed, and stored. At 500 sps, each sample represents a duration of 2 ms. The 500-sps signal has a bandwidth of 150 Hz, meaning that higher-frequency components of the waveforms such as pacer spikes and sharp, narrow QRS complexes are attenuated. Second, the signals may be printed with a lower-frequency filter depending on the settings at which the recording equipment is programmed to record. Common settings are 150-, 100-, or 40-Hz filtering. As the filter setting is reduced below 150 Hz, highfrequency aspects of the ECG are further diminished. The ECG in Fig. 1 is printed with a 100-Hz filter applied, as is commonly done in clinical practice in order to reduce noise from sources such as motion, muscle tremor, or poor electrode contact with the skin. Third, ECGs are stored and transmitted with a user-configurable compression method that reduces record size and transmission time. In the compression method used in this case, the QRS complexes are stored with no loss of signal fidelity, but the intervals between QRS complexes (often including pacer spikes) are further downsampled to 125 sps.1 So why are prominent pacer spike visible in front of some QRS complexes but not in front of others? The answer is that the +1-mV pacer spikes in front of complexes 2, 7, 8, and 9 are artificially generated specifically to compensate for the diminished amplitude caused by the three aforementioned factors. The pacer spikes in front of those complexes were detected and subsequently enhanced by the electrocardiograph, while the rest were not. Another way newer ECG equipments can help providers recognize small pacemaker spikes is by placing arrowheads or “flags” under the detected atrial and ventricular pacer spikes (Fig. 2). Because of the described sampling and transmitting limitations, detection of narrow pacemaker spikes, especially in thin individuals, may become unreliable and can result in intermittent absence of the pacer spikes in the surface recording,2 as in our case, and in varying amplitude and polarity of the pacer spikes.3,4 Both of these can be easily misinterpreted as signs of pacemaker lead fracture or pacemaker generator failure. The issues described here extend to bedside and telemetry monitoring as well, where pacemaker stimulus artifacts are frequently not visible in the leads being monitored. This can result in medical personnel misinterpreting the QRS complexes as bundle branch block. More importantly when A-V sequential pacemaker is present, an atrial tachycardia that is tracked by the ventricular pacer can easily be misinterpreted as ventricular tachycardia.
Fig. 2. Arrowheads or “flags” denoting atrial (top panel), ventricular (middle panel) and both atrial and ventricular pacer spikes (bottom panel). Note that in the top 2 panels, recognition of the pacemaker spikes without the electrocardiograph-generated arrowheads would be difficult.
References 1. Reddy BR, Christenson DW, Rowlandson GI, et al. Data compression for storage of resting ECGs digitized at 500 samples/second. Biomed Instrum Technol 1992;26:133. 2. Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the standardization and interpretation of the electrocardiogram. Part I: the electrocardiogram and its technology. A scientific statement from the American Heart Association
Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation 2007;115:1306. 3. Engler RL, Goldberger AL, Bhargava V, Kapelusznik D. Pacemaker spike alternans: an artifact of digital signal processing. Pacing Clin Electrophysiol 1982;5:748. 4. Tomcsányi J, Bezzeg P, Bózsik B. Pacemaker spike alternans. J Electrocardiol 2011;44:221.