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What is the real rhythm?
The American Journal of Medicine (2005) 118, 838 – 839
ECG IMAGE OF THE MONTH
What is the real rhythm? Julia H. Indik, MD, PhD ECG Image of the Month Editor Sarver Heart Center, University of Arizona, Tucson.
Presentation A 70-year-old man was referred for replacement of his dual-chamber implantable cardioverter defibrillator (ICD) generator. He has a history of nonischemic cardiomyopathy with a left ventricular ejection fraction of 20%, ventricular tachycardia, and complete heart block. He had no specific complaints and was able to do minimal to moderate exertion consistent with a New York Heart Association functional class I-II. About 3 months earlier, he had received an appropriate shock from his device for ventricular tachycardia at a rate of 200 bpm. He had no underlying escape rhythm and was thus entirely dependent on the pacing functions of his ICD. His device was set to pace in a DDD mode (dual-chamber stimulation; dual-chamber sensing, and dual modes of response) at a low rate of 60 bpm. His ECG clearly displays the atrial and ventricular pacing spikes (see Figure 1a). However, the device is not functioning appropriately.
the baseline, evidence that atrial capture is not occurring. Now look at the segments in between the T waves and atrial pacing spikes. These segments undulate with a low amplitude electrical activity. What is the rhythm?
Diagnosis The rhythm is atrial fibrillation, but the voltage and associated amplitude of the waves seen on ECG are so low that the device is not consistently sensing the presence of the abnormal rhythm. Occasionally, the ICD does sense some atrial activity, and it responds with a ventricular paced beat. Since there is complete heart block, the ventricular rate is slow and mostly regular. There is no atrial capture in response to atrial pacing since a fibrillating chamber cannot be paced and captured. Yet, the patient’s device reported over 58 000 mode switch events, corresponding to when it had successfully detected atrial fibrillation in the past.
Management Assessment A close look at the rhythm strip from lead II indicates that some ventricular paced beats occur earlier than the lower rate of 60 bpm (see Figure 1b). These earlier beats are not preceded by an atrial pacing spike. This means that the device must be sensing atrial activity and responding with a ventricular paced beat, which would be normal behavior if, for instance, a premature atrial complex was sensed. Now look at the segment just after the atrial pacing spikes. In lead II, P waves should form after the atrial pacing spikes, indicating capture of the atria. Instead, there is no change in
0002-9343/$ -see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.amjmed.2005.04.035
Following generator replacement, the new device was programmed to a VVI mode (ventricular stimulation, ventricular sensing, and inhibition by a sensed impulse) with rate response. Most importantly, the patient was started on warfarin to prevent stroke. The option of attempting to restore sinus rhythm with antiarrhythmic medications and cardioversion was discussed with the patient. He declined this treatment route since he considered himself to be asymptomatic. This case demonstrates that one cannot always trust what a high-technology device reports; sometimes the diagnosis is made by the ever-dependable ECG.
Indik
What is the real rhythm?
839
Figure 1a: Atrial and ventricular pacing spikes are evident in a rhythm strip from the 12-lead ECG. What is amiss? Figure 1b: This is the rhythm strip from leads V1 and II. Notice that both atrial and ventricular pacing spikes occur in this patient with complete heart block. The asterisks denote beats that occur early. What is the underlying rhythm here?
ECG IMAGE OF THE MONTH
What is the real rhythm? Julia H. Indik, MD, PhD ECG Image of the Month Editor Sarver Heart Center, University of Arizona, Tucson.
Presentation A 70-year-old man was referred for replacement of his dual-chamber implantable cardioverter defibrillator (ICD) generator. He has a history of nonischemic cardiomyopathy with a left ventricular ejection fraction of 20%, ventricular tachycardia, and complete heart block. He had no specific complaints and was able to do minimal to moderate exertion consistent with a New York Heart Association functional class I-II. About 3 months earlier, he had received an appropriate shock from his device for ventricular tachycardia at a rate of 200 bpm. He had no underlying escape rhythm and was thus entirely dependent on the pacing functions of his ICD. His device was set to pace in a DDD mode (dual-chamber stimulation; dual-chamber sensing, and dual modes of response) at a low rate of 60 bpm. His ECG clearly displays the atrial and ventricular pacing spikes (see Figure 1a). However, the device is not functioning appropriately.
the baseline, evidence that atrial capture is not occurring. Now look at the segments in between the T waves and atrial pacing spikes. These segments undulate with a low amplitude electrical activity. What is the rhythm?
Diagnosis The rhythm is atrial fibrillation, but the voltage and associated amplitude of the waves seen on ECG are so low that the device is not consistently sensing the presence of the abnormal rhythm. Occasionally, the ICD does sense some atrial activity, and it responds with a ventricular paced beat. Since there is complete heart block, the ventricular rate is slow and mostly regular. There is no atrial capture in response to atrial pacing since a fibrillating chamber cannot be paced and captured. Yet, the patient’s device reported over 58 000 mode switch events, corresponding to when it had successfully detected atrial fibrillation in the past.
Management Assessment A close look at the rhythm strip from lead II indicates that some ventricular paced beats occur earlier than the lower rate of 60 bpm (see Figure 1b). These earlier beats are not preceded by an atrial pacing spike. This means that the device must be sensing atrial activity and responding with a ventricular paced beat, which would be normal behavior if, for instance, a premature atrial complex was sensed. Now look at the segment just after the atrial pacing spikes. In lead II, P waves should form after the atrial pacing spikes, indicating capture of the atria. Instead, there is no change in
0002-9343/$ -see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.amjmed.2005.04.035
Following generator replacement, the new device was programmed to a VVI mode (ventricular stimulation, ventricular sensing, and inhibition by a sensed impulse) with rate response. Most importantly, the patient was started on warfarin to prevent stroke. The option of attempting to restore sinus rhythm with antiarrhythmic medications and cardioversion was discussed with the patient. He declined this treatment route since he considered himself to be asymptomatic. This case demonstrates that one cannot always trust what a high-technology device reports; sometimes the diagnosis is made by the ever-dependable ECG.
Indik
What is the real rhythm?
839
Figure 1a: Atrial and ventricular pacing spikes are evident in a rhythm strip from the 12-lead ECG. What is amiss? Figure 1b: This is the rhythm strip from leads V1 and II. Notice that both atrial and ventricular pacing spikes occur in this patient with complete heart block. The asterisks denote beats that occur early. What is the underlying rhythm here?