Two Cases of Rhythm Disturbance

December 31, 2006

For 2 days, a 49-year-old man with hypertension and hypercholesterolemiahas experienced light-headedness and fatigue.Based on the presenting ECG, what is the most likely cause of hissymptoms?A. Accelerated junctional rhythm.B. First-degree atrioventricular (AV) block.C. Mobitz type I (Wenckebach) second-degree AV block.D. Mobitz type II second-degree AV block.E. Third-degree AV block (complete heart block).

Case 1:


Middle-aged Man With Exertional Fatigue and Light-headedness


For 2 days, a 49-year-old man with hypertension and hypercholesterolemiahas experienced light-headedness and fatigue.Based on the presenting ECG, what is the most likely cause of hissymptoms?

A.

Accelerated junctional rhythm.

B.

First-degree atrioventricular (AV) block.

C.

Mobitz type I (Wenckebach) second-degree AV block.

D.

Mobitz type II second-degree AV block.

E.

Third-degree AV block (complete heart block).

Case 1 :Middle-aged man with exertional fatigue and light-headedness.

The ECG tracing shows

Mobitz type I (Wenckebach) second-degree AV block,

C.

In patients with this abnormality, there is often progressive lengtheningof the PR interval (brackets), which leads to a dropped beat (on-time, nonconductedP wave). In this ECG, the blocked P wave (arrowheads) is superimposedon the ST segment of the last beat before the pause. Of note, thePR interval following the dropped beat is shorter than the PR interval beforethe pause. Progressive lengthening of the PR interval with each beat isnot always apparent in Wenckebach block.In contrast, an accelerated junctional rhythm would not produce distinctiveP waves. First-degree AV block requires a constant PR interval (more than0.21 second) with 1:1 AV conduction. First-degree AV block usually representsAV nodal conduction delay rather than a true "block."Mobitz type II second-degree AV block is characterized by a suddenfailure of conduction of a P wave during a period of regular PP intervals. Incontrast to the pattern seen in Wenckebach block, PR intervals remain constantbefore and after the nonconducted P wave. In third-degree AV block(complete heart block), there is complete failure of conduction of all atrialimpulses to the ventricles, which manifests as AV dissociation. The escaperhythm may originate in the AV junction (narrow QRS complex) or belowthe bundle of His (wide QRS complex).In this case, the patient underwent implantation of a dual-chamber pacemakerand is now asymptomatic.

Case 2:

Middle-aged Woman With Episodes of Syncope.

A 57-year-old woman with congestive heart failure presents with a 3-weekhistory of episodic light-headedness and syncope.
Based on the ECG tracing, what is the most likely diagnosis?

A.

Accelerated junctional rhythm.

B.

First-degree atrioventricular (AV) block.

C.

Mobitz type I (Wenckebach) second-degree AV block.

D.

Mobitz type II second-degree AV block.

E.

Third-degree AV block (complete heart block) with ventricular asystole.

F.

Baseline artifact.

Case 2: Middle-aged woman with episodes of syncope.

The patient hasthird-degree AV block (complete heart block) with ventricular asystole, E.The ECG tracing shows a normal PR interval with an underlying left bundle-branch block, followed by a complete failure of conduction of all atrialimpulses (arrowheads) with ventricular asystole because of the absence ofan escape rhythm. The patient underwent emergent placement of a temporarytransvenous pacemaker; a permanent pacemaker was subsequentlyimplanted.