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American Journal of Critical Care. 2006;15: 437-438
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ECG PUZZLER
A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses ECG interpretation for clinical practice. We welcome letters to the Editors regarding this feature.

Long QT Syndrome

By Michele M. Pelter, RN, PhD and Mary G. Carey, RN, PhD. From Washoe Health System and Orvis School of Nursing, University of Nevada, Reno, Nev (MMP), and the School of Nursing at the State University of New York at Buffalo (MGC).

Scenario: This ECG was obtained in a 79-year-old woman admitted to the intensive care unit for acute exacerbation of chronic obstructive pulmonary disease and pneumonia treated with erythromycin. The bedside monitor alarmed for "V Tach." The nurse could not assess the patient’s mental status because the patient was intubated and sedated with propofol. The patient’s blood pressure was 109/48 mm Hg and her pulse oximeter reading was 93%. The rhythm spontaneously returned to normal sinus rhythm after 30 seconds.


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Interpretation: The strip begins with a ventricular triplet. These complexes are further labeled as multiform because of the different QRS morphologies. The fourth beat is a normal sinus beat with a long QT interval (0.64 seconds). This beat is followed by an R-on-T premature ventricular contraction (PVC) inducing torsades de pointes (TdP).

Rationale

Torsades de pointes is a French term meaning "twisting of the points." TdP is a form of polymorphic ventricular tachycardia characterized by a continuously changing QRS morphology that appears to twist around the isoelectric baseline. TdP commonly occurs in patients with long QT syndrome (LQTS). LQTS can be acquired or congenital. Causes of acquired LQTS include drugs that prolong the QT interval, electrolyte disturbances, heart block, or cerebral disease or injury. The cause of congenital LQTS is a genetic mutation.

One drug that can cause TdP is erythromycin, a likely cause in this patient. Importantly, because the QTc interval is typically longer in women than in men, women may be more vulnerable to the effects of drugs that prolong the QT interval. The diagnosis of acquired LQTS is supported in this example by the long QT interval seen with the 1 recorded sinus beat. It is common to see a significant heart rate increase in the minute prior and a variable short-long-short cycle length of the R-to-R interval sequence before the onset of TdP. This example shows the characteristic onset of TdP immediately preceding the arrhythmia; ventricular ectopy (3 beats in this example), followed by a pause, then a sinus beat, and finally an R-on-T PVC.

Nursing Actions

Because TdP can quickly degenerate into ventricular fibrillation, the crash cart should be readily available for immediate defibrillation. Immediate treatment also includes withdrawal of any offending agent such as the erythromycin, infusion of magnesium sulfate, defibrillation per Advanced Cardiac Life Support, and administration of antiarrhythmic drugs to prevent return of the TdP. Maintain continuous ECG monitoring and carefully measure the QT interval as per the unit protocol.





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