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Alternating left bundle branch block and right bundle branch block during tachycardia: What is the mechanism?
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Alternating left bundle branch block and right bundle branch block during tachycardia: What is the mechanism? Daniel R. Frisch, MD, Peter J. Zimetbaum, MD, Mark E. Josephson, MD From Beth Israel Deaconess Medical Center, Boston, Massachusetts.
Case presentation A 68-year-old woman with a history of paroxysmal atrial fibrillation was referred for pulmonary vein isolation. After the pulmonary veins were isolated, burst atrial pacing during infusion of intravenous isoproterenol induced atrial flutter at a cycle length of 230 ms, with variable but rapid AV conduction. An alternating pattern of left bundle branch block (LBBB) and right bundle branch block (RBBB) was observed during the tachycardia (Figure 1). What is the mechanism of the alternating bundle branch block?
Commentary LBBB was observed soon after initiation of the tachycardia, most likely due to phase 3 block in the left bundle, as some cycle length variation in the tachycardia initially created long–short intervals (not shown). Once LBBB developed, it was perpetuated by continuous retrograde invasion of the left bundle from the impulse conducted anterograde down the right bundle (Figure 2).1 AV Wenckebach block then occurred (Figure 2). Block proximal to the bundle branches terminated retrograde invasion of the left bundle branch and produced a pause that allowed conduction down both bundle branches during the subsequent atrial impulse, resulting in a narrow QRS. Development of RBBB was observed after a single narrow-complex QRS. The mechanism of RBBB required the previously present LBBB. Prior to AV Wenckebach block during LBBB, the right bundle branch was activated in an anterograde fashion before retrograde activation of the left bundle branch. Sequential activation of the bundle branches thus produced differential diastolic intervals (DI) of the bundle branches such that RBDI exceeded LBDI. Because action potential duration (APD) relies on the preceding diastolic interval, the incremental increase in RBDI relative to that of LBDI creates a comparatively prolonged RBAPD KEYWORDS Bundle branch block; Retrograde invasion; Phase 3 block; Aberrency (Heart Rhythm 2007;4:679 – 680) Address reprint requests and correspondence: Dr. Daniel R. Frisch, Beth Israel Deaconess Medical Center, Department of Medicine, Cardiology Division, Electrophysiology Section, 1 Deaconess Road, Baker 4, Boston, Massachusetts 02215. E-mail address: [email protected].
Figure 1 ECG leads V1–V3 showing alternating left bundle branch block with right bundle branch block during atrial flutter with rapid AV conduction.
and consequently a greater increase in the right bundle effective refractory period relative to the left bundle effective refractory period.2 Right bundle branch aberration results from phase 3 block in the right bundle, which in turn is perpetuated by retrograde invasion. The patient was symptomatic because of rapid heart rate, and isoproterenol was discontinued. Direct-current cardio-
1547-5271/$ -see front matter © 2007 Heart Rhythm Society. All rights reserved.
doi:10.1016/j.hrthm.2006.10.005
680
Heart Rhythm, Vol 4, No 5, May 2007
Figure 2 Ladder diagram of the mechanism of alternating bundle branch block. Surface leads V1 and V6 are shown with the intracardiac electrogram tracing from the proximal anterolateral right atrial bipole (ALRA5). Because of a long diastolic interval, the subsequent action potential duration of right bundle branch Purkinje cells is prolonged, which is responsible for phase 3 block in the right bundle branch (see text for details). A ⫽ atrium; AVJ ⫽ atrioventricular junction; ERP ⫽ effective refractory period; LB ⫽ left bundle branch; RB ⫽ right bundle branch; V ⫽ ventricle.
version was performed to restore sinus rhythm. Further ablation in the cavotricuspid isthmus rendered the patient uninducible for any supraventricular arrhythmias. The HV interval was measured and found to be within normal limits at 42 ms. Whereas alternating bundle branch block at slow heart rates without an intervening normal QRS is pathologic and requires a pacemaker, alternating bundle branch block dur-
ing rapid heart rates interrupted by a single normal QRS is not uncommon and is physiologic.
References 1.
2.
Wellens HJJ, Durrer D. Supraventricular tachycardia with left aberrant conduction due to retrograde invasion into the left bundle branch. Circulation 1968; 38:474 – 479. Josephson ME. Clinical Cardiac Electrophysiology. Third Edition. Philadelphia: Lippincott, Williams, & Wilkins, 2002.
Alternating left bundle branch block and right bundle branch block during tachycardia: What is the mechanism? Daniel R. Frisch, MD, Peter J. Zimetbaum, MD, Mark E. Josephson, MD From Beth Israel Deaconess Medical Center, Boston, Massachusetts.
Case presentation A 68-year-old woman with a history of paroxysmal atrial fibrillation was referred for pulmonary vein isolation. After the pulmonary veins were isolated, burst atrial pacing during infusion of intravenous isoproterenol induced atrial flutter at a cycle length of 230 ms, with variable but rapid AV conduction. An alternating pattern of left bundle branch block (LBBB) and right bundle branch block (RBBB) was observed during the tachycardia (Figure 1). What is the mechanism of the alternating bundle branch block?
Commentary LBBB was observed soon after initiation of the tachycardia, most likely due to phase 3 block in the left bundle, as some cycle length variation in the tachycardia initially created long–short intervals (not shown). Once LBBB developed, it was perpetuated by continuous retrograde invasion of the left bundle from the impulse conducted anterograde down the right bundle (Figure 2).1 AV Wenckebach block then occurred (Figure 2). Block proximal to the bundle branches terminated retrograde invasion of the left bundle branch and produced a pause that allowed conduction down both bundle branches during the subsequent atrial impulse, resulting in a narrow QRS. Development of RBBB was observed after a single narrow-complex QRS. The mechanism of RBBB required the previously present LBBB. Prior to AV Wenckebach block during LBBB, the right bundle branch was activated in an anterograde fashion before retrograde activation of the left bundle branch. Sequential activation of the bundle branches thus produced differential diastolic intervals (DI) of the bundle branches such that RBDI exceeded LBDI. Because action potential duration (APD) relies on the preceding diastolic interval, the incremental increase in RBDI relative to that of LBDI creates a comparatively prolonged RBAPD KEYWORDS Bundle branch block; Retrograde invasion; Phase 3 block; Aberrency (Heart Rhythm 2007;4:679 – 680) Address reprint requests and correspondence: Dr. Daniel R. Frisch, Beth Israel Deaconess Medical Center, Department of Medicine, Cardiology Division, Electrophysiology Section, 1 Deaconess Road, Baker 4, Boston, Massachusetts 02215. E-mail address: [email protected].
Figure 1 ECG leads V1–V3 showing alternating left bundle branch block with right bundle branch block during atrial flutter with rapid AV conduction.
and consequently a greater increase in the right bundle effective refractory period relative to the left bundle effective refractory period.2 Right bundle branch aberration results from phase 3 block in the right bundle, which in turn is perpetuated by retrograde invasion. The patient was symptomatic because of rapid heart rate, and isoproterenol was discontinued. Direct-current cardio-
1547-5271/$ -see front matter © 2007 Heart Rhythm Society. All rights reserved.
doi:10.1016/j.hrthm.2006.10.005
680
Heart Rhythm, Vol 4, No 5, May 2007
Figure 2 Ladder diagram of the mechanism of alternating bundle branch block. Surface leads V1 and V6 are shown with the intracardiac electrogram tracing from the proximal anterolateral right atrial bipole (ALRA5). Because of a long diastolic interval, the subsequent action potential duration of right bundle branch Purkinje cells is prolonged, which is responsible for phase 3 block in the right bundle branch (see text for details). A ⫽ atrium; AVJ ⫽ atrioventricular junction; ERP ⫽ effective refractory period; LB ⫽ left bundle branch; RB ⫽ right bundle branch; V ⫽ ventricle.
version was performed to restore sinus rhythm. Further ablation in the cavotricuspid isthmus rendered the patient uninducible for any supraventricular arrhythmias. The HV interval was measured and found to be within normal limits at 42 ms. Whereas alternating bundle branch block at slow heart rates without an intervening normal QRS is pathologic and requires a pacemaker, alternating bundle branch block dur-
ing rapid heart rates interrupted by a single normal QRS is not uncommon and is physiologic.
References 1.
2.
Wellens HJJ, Durrer D. Supraventricular tachycardia with left aberrant conduction due to retrograde invasion into the left bundle branch. Circulation 1968; 38:474 – 479. Josephson ME. Clinical Cardiac Electrophysiology. Third Edition. Philadelphia: Lippincott, Williams, & Wilkins, 2002.