Perspectives in Cardiology / January 2004 15

University of Ottawa Heart Institute

ECGof the Month

By Martin S. Green, MD, FRCPC

Too Fast or Too Slow?This is the ECG of an 85-year-old woman, with a history of syncope, who frequentlypasses out.

What is the diagnosis?

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Perspectives in Cardiology / January 200416

The ECG shows a regular, narrow complex ventric-ular rhythm, approximating 25 beats per minute(bpm). The morphology is consistent with an incom-plete right bundle branch block (RBBB).Superimposed upon this regular ventricular activityare P waves in a regular sinus rhythm approximating75 bpm. There appears to be no association betweenthe atria and ventricle rhythm. This electrocardio-graphic picture is consistent withcomplete heart block. This diag-nosis is made based on the disso-ciation of atrioventricular activi-ty, and with a regular ventricularescape (usually less than 40bpm). If the ventricular rhythm isnot regular in the presence ofmultiple atrial stimuli, one maysuppose that a high level of sec-ond-degree block exists, ratherthan complete heart block.

Provided the patient has anadequate ventricular escape, this rhythm is normallywell-tolerated in elderly patients. The prolongeddiastolic filling results in supra-normal preload and,consequently, large stroke volumes. Indeed, thiswoman’s blood pressure was 180/70 mmHg whenthe 12-lead ECG was obtained. So, why is thispatient passing out?

While waiting in the emergency department, thewoman passed out briefly on telemetry. The teleme-try strip (Figure 1) shows complete heart block at theoutset of the strip. The second and third beats repre-sent premature ventricular contractions with differ-ing morphologies. A compensatory pause ensues,

followed by a typical ventricular escape beat, andthen a third premature ventricular contraction. Thisshort-long-short activation sequence precedes apolymorphic wide complex rhythm that self-termi-nates after 15 seconds (not shown). This rhythm dis-turbance, in the setting of QT prolongation and apause-dependent initiation, is certainly suspiciousfor torsades des pointes. The QTc intervals of the

ECG and the beat preceding thisarrhythmia are 535 ms, and609 ms, respectively.

Torsades des pointes is apolymorphic ventricular tachy-arrhythmia that occurs in the set-ting of a characteristic initiation(short-long-short) and QTc pro-longation. This arrhythmia isusually non-sustained, but may,in rare cases, degenerate intoventricular fibrillation. In fact,one of the most common causes

of torsades des pointes is complete heart block. Thebradycardia results in a long QT and torsades, as inthis case.

The differential of QTc prolongation includesmedications (antiarrhythmics, antibiotics, antihista-mines and antidepressants), electrolyte abnormali-ties (hypokalemia, hypomagnesaemia), subarach-noid hemorrhage, ischemic heart disease, andbradyarrhythmias. In this case, the cause of torsadeswas, undoubtedly, extreme bradycardia. The patientreceived a temporary transvenous pacemaker, then apermanent pacemaker, and subsequently did notexperience any further tachyarrhythmias.

University of Ottawa Heart Institute

ECGof the Month

This Month’s ECG Diagnosis

Figure 1: Torsades des pointes.

For a good move see page 28

For a good move see page 28

PCard

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