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Challenges in Clinical Electrocardiography |

Wenckebach—Second-Degree Heart Block and the Company It Keeps

Isaac R. Whitman, MD1; Nitish Badhwar, MD1
[+] Author Affiliations
1Electrophysiology Section, Division of Cardiology, University of California, San Francisco
JAMA Intern Med. 2016;176(3):382-385. doi:10.1001/jamainternmed.2015.7592.
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A man in his 70s with hypertension, coronary artery disease (CAD), and right coronary (RCA) stent placement 2 months prior for unstable angina presented to the emergency department after an episode of presyncope, a sense of chest tightness, and palpitations. He had a history of left bundle branch block (LBBB) on electrocardiography (ECG). His medications included carvedilol, aspirin, clopidogrel, and lovastatin. In the emergency department, his ECG showed first-degree heart block and LBBB, and telemetry showed atrioventricular (AV) Wenckebach (ie, Mobitz type 1) heart block (Figure 1). Periods of 2:1 AV block were also captured (Figure 2). A subsequent echocardiogram showed left ventricular hypertrophy but was otherwise normal. Cardiac catheterization demonstrated the recent RCA stent and a chronic left anterior descending (LAD) stent to be patent. Without an ischemic etiology for his symptoms, and noting his cardiac conduction disease, the emergency department referred the patient for electrophysiology study (EPS) (Figure 3).

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Figure 1.
Initial Surface Electrocardiogram Showing Abnormalities in Cardiac Electrical Conduction

A, First-degree heart block (with PR interval of 230 milliseconds, in brackets; normal interval, <200 milliseconds), left bundle branch block (LBBB) (which shows the typical morphologic characteristics in lead V1, circled), and a sinus rate of approximately 60 bpm (arrowheads). B, Typical AV Wenckebach electrocardiographic pattern of prolonging PR intervals with successive beats (brackets) prior to a dropped beat (circled). Note that the prolongation in PR interval from one beat to the next is subtle—only 40 milliseconds.

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Figure 2.
Surface Electrocardiogram Showing 2:1 Atrioventricular Conduction

There are 2 P waves (black arrowheads) for every QRS complex (red arrowheads). The sinus rate (approximately 80 bpm) is therefore twice the ventricular rate (approximately 40 bpm).

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Figure 3.
Electrophysiology Study Intraprocedural Surface and Intracardiac Tracings Showing Wenckebach Conduction Abnormality

HIS indicates catheter across the bundle of His (proximal, middle, and distal); HRA, catheter placed in the high right atrium; RVA, catheter placed in the right ventricular apex. The PR interval (black brackets) represents conduction from the sinus node, across the atrial muscle, to the onset of ventricular depolarization. With a multielectrode intracardiac catheter across the AV node (HIS), this interval can be subdivided into the AH interval (blue brackets, representing atrial conduction time through the AV node) and the HV interval (red brackets, representing conduction time from just beneath the AV node through ventricular depolarization). These tracings show a prolonging PR interval, comprising a fixed AH conduction time across the AV node (160 milliseconds [ms]), and a prolonging infranodal HV conduction time (100 ms increasing to 215 ms).

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