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Intermittent atrioventricular block: What is the mechanism?
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Intermittent atrioventricular block: What is the mechanism? Rakesh K. Pai, MD, Marcos Daccarett, MD, Nathan M. Segerson, MD, Moeen Abedin, MD, T. Scott Wall, MD, Roger A. Freedman, MD, Mohamed H. Hamdan, MD From the University of Utah Health Sciences Center, Salt Lake City, Utah.
Figure 1 A and B are a near-continuous telemetry rhythm strip. Sinus activity is denoted by asterisks. Junctional escape is denoted by closed circles. The beginning of the tracing shows sinus rhythm with third-degree AV block and pacing stimuli that do not capture. The remainder of the tracing shows atrial flutter with 2:1 and variable AV conduction with right bundle branch block.
Case presentation A 48-year-old man with a history of bicuspid aortic valve disease underwent aortic valve replacement with a mechanical prosthesis in 1997. Subsequently, upon routine echocardiographic monitoring, he was discovered to have an ascending aortic aneurysm requiring operative intervention. In 2006, the patient underwent a repeat sternotomy with resection of the aortic aneurysm and reimplantation of a mechanical aortic valve with a Hemashield aortic graft. Preoperative ECG revealed sinus rhythm with normal baseline intervals. Postoperatively, while in normal sinus rhythm, the patient developed high-degree AV block with a wide escape QRS at rate of 58 bpm, requiring epicardial pacing (Figure 1A). Subsequently, the patient developed atrial flutter with a ventricular response of 150 bpm and right bundle branch block (Figures 1A and 1B). A permanent dualchamber pacemaker was implanted, and following the procedure the patient was cardioverted. Once again, immediately following restoration of normal sinus rhythm, the patient developed high-degree AV block. How do you explain the presence of intact AV conduction during atrial flutter when high-degree AV block prevailed during normal sinus rhythm?
escape rate of almost 60 bpm suggests that the site of block most likely is at the AV node or in the His-Purkinje system above the bifurcation of the bundle branches with aberrant conduction. Figure 1B shows atrial flutter with 2:1 and variable AV conduction associated with right bundle branch block. Resumption of AV conduction during atrial flutter when absent during normal sinus rhythm suggests that the previously seen AV block was bradycardia dependent. Because AV block occurred when the atrial rate was relatively slow, we believe this was due to phase 4 block, also referred to as bradycardia-dependent block. Phase 4 block usually occurs in the His-Purkinje system; therefore, in this case the most likely site of block is infranodal. Numerous authors have demonstrated the presence of phase 4 block in the His-Purkinje system1 and in accessory pathways.2,3 Similarly, phase 4 block has been reported following aortic valve surgery in a patient with bundle branch reentry.4 This case demonstrates another example of phase 4 block as a cause of intermittent AV block in a patient following valve surgery.
References 1.
Commentary
2.
The beginning of Figure 1A shows normal sinus rhythm with third-degree AV block and a wide escape rhythm. The
3.
Address reprint requests and correspondence: Dr. Rakesh K. Pai, Cardiology Division, University of Utah, Room 4A100, 30 North 1900 East, Salt Lake City, Utah 84132. E-mail address: [email protected].
4.
1547-5271/$ -see front matter © 2006 Heart Rhythm Society. All rights reserved.
Kretz A, Suarez LD, Alvarez JA, Leguizamon Palumbo JR, Martinez Martinez JA. Transient tachycardia- and bradycardia-dependent left anterior and posterior hemiblocks. Effects of isoproterenol. Int J Cardiol 1981;1:49 – 64. Fujiki A, Yoshida S, Tani M, Sasayama S. Intermittment Wolff-ParkinsonWhite syndrome due the phase 3 and phase 4 block: disappearance of rapid ventricular response during atrial fibrillation. J Electrocardiol 1988;1:77– 82. Fujiki A, Tani M, Mizumaki K, Yoshida S, Sasayama S. Rate-dependent accessory pathway conduction due to phase 3 and phase 4 block: antegrade and retrograde conduction properties. J Electrocardiol 1992;1:25–31. Fedgchin B, Pavri BB, Greenspon AJ, Ho RT. Unique self-perpetuating cycle of atrioventricular block and phase IV bundle branch block in a patient with bundle branch reentrant tachycardia. Heart Rhythm 2004;4:493– 496.
doi:10.1016/j.hrthm.2006.08.007
Intermittent atrioventricular block: What is the mechanism? Rakesh K. Pai, MD, Marcos Daccarett, MD, Nathan M. Segerson, MD, Moeen Abedin, MD, T. Scott Wall, MD, Roger A. Freedman, MD, Mohamed H. Hamdan, MD From the University of Utah Health Sciences Center, Salt Lake City, Utah.
Figure 1 A and B are a near-continuous telemetry rhythm strip. Sinus activity is denoted by asterisks. Junctional escape is denoted by closed circles. The beginning of the tracing shows sinus rhythm with third-degree AV block and pacing stimuli that do not capture. The remainder of the tracing shows atrial flutter with 2:1 and variable AV conduction with right bundle branch block.
Case presentation A 48-year-old man with a history of bicuspid aortic valve disease underwent aortic valve replacement with a mechanical prosthesis in 1997. Subsequently, upon routine echocardiographic monitoring, he was discovered to have an ascending aortic aneurysm requiring operative intervention. In 2006, the patient underwent a repeat sternotomy with resection of the aortic aneurysm and reimplantation of a mechanical aortic valve with a Hemashield aortic graft. Preoperative ECG revealed sinus rhythm with normal baseline intervals. Postoperatively, while in normal sinus rhythm, the patient developed high-degree AV block with a wide escape QRS at rate of 58 bpm, requiring epicardial pacing (Figure 1A). Subsequently, the patient developed atrial flutter with a ventricular response of 150 bpm and right bundle branch block (Figures 1A and 1B). A permanent dualchamber pacemaker was implanted, and following the procedure the patient was cardioverted. Once again, immediately following restoration of normal sinus rhythm, the patient developed high-degree AV block. How do you explain the presence of intact AV conduction during atrial flutter when high-degree AV block prevailed during normal sinus rhythm?
escape rate of almost 60 bpm suggests that the site of block most likely is at the AV node or in the His-Purkinje system above the bifurcation of the bundle branches with aberrant conduction. Figure 1B shows atrial flutter with 2:1 and variable AV conduction associated with right bundle branch block. Resumption of AV conduction during atrial flutter when absent during normal sinus rhythm suggests that the previously seen AV block was bradycardia dependent. Because AV block occurred when the atrial rate was relatively slow, we believe this was due to phase 4 block, also referred to as bradycardia-dependent block. Phase 4 block usually occurs in the His-Purkinje system; therefore, in this case the most likely site of block is infranodal. Numerous authors have demonstrated the presence of phase 4 block in the His-Purkinje system1 and in accessory pathways.2,3 Similarly, phase 4 block has been reported following aortic valve surgery in a patient with bundle branch reentry.4 This case demonstrates another example of phase 4 block as a cause of intermittent AV block in a patient following valve surgery.
References 1.
Commentary
2.
The beginning of Figure 1A shows normal sinus rhythm with third-degree AV block and a wide escape rhythm. The
3.
Address reprint requests and correspondence: Dr. Rakesh K. Pai, Cardiology Division, University of Utah, Room 4A100, 30 North 1900 East, Salt Lake City, Utah 84132. E-mail address: [email protected].
4.
1547-5271/$ -see front matter © 2006 Heart Rhythm Society. All rights reserved.
Kretz A, Suarez LD, Alvarez JA, Leguizamon Palumbo JR, Martinez Martinez JA. Transient tachycardia- and bradycardia-dependent left anterior and posterior hemiblocks. Effects of isoproterenol. Int J Cardiol 1981;1:49 – 64. Fujiki A, Yoshida S, Tani M, Sasayama S. Intermittment Wolff-ParkinsonWhite syndrome due the phase 3 and phase 4 block: disappearance of rapid ventricular response during atrial fibrillation. J Electrocardiol 1988;1:77– 82. Fujiki A, Tani M, Mizumaki K, Yoshida S, Sasayama S. Rate-dependent accessory pathway conduction due to phase 3 and phase 4 block: antegrade and retrograde conduction properties. J Electrocardiol 1992;1:25–31. Fedgchin B, Pavri BB, Greenspon AJ, Ho RT. Unique self-perpetuating cycle of atrioventricular block and phase IV bundle branch block in a patient with bundle branch reentrant tachycardia. Heart Rhythm 2004;4:493– 496.
doi:10.1016/j.hrthm.2006.08.007