Whats Wrong With This Picture?: Middle-aged Woman With Chest Pain and Dyspnea

A 48-year-old woman with a historyof hypertension and mildasthma has been transferred to themedical service because of an abnormalpostoperative ECG. She hadbeen admitted 2 weeks earlier to thegynecology-oncology service for localrecurrence of a previously resecteduterine sarcoma and underwent laparotomyfor debulking of the pelvicmass and resection of the rectosigmoidcolon. She did well until postoperativeday 14, when sudden chestpain and dyspnea developed.

Blood pressure is now 150/88mm Hg, heart sounds are normal,lungs are clear, and abdominalfindings are normal. Serum potassiumlevel is 3.8 mEq/L; magnesium,1.7 mEq/L. An arterial blood gasmeasurement on room air reveals apH of 7.4; partial pressure of oxygen,57 mm Hg; partial pressure of carbondioxide, 39 mm Hg; and serumbicarbonate, 25 mEq/L. White bloodcell count is 19,400/μL with a leftshift.

Her postoperative (A) and preoperative(B) ECGs are shown here.1. What abnormality is evident onthe postoperative ECG?2. Is the preoperative ECG normal?3. Are the postoperative ECGfindings related to the patient'srecent chest pain and dyspnea?WHAT'S WRONG:1. What abnormality is evident on the postoperativeECG?

The patient's ECG shows normal sinus rhythm witha prolonged corrected QT interval (QTc) of 625 milliseconds(normal QTc, less than 440 milliseconds) and inferiorand anterolateral T-wave abnormalities.

The QT interval, which varies inversely with theheart rate, is measured from the start of the QRS complexto the end of the T wave. It includes the total durationof ventricular activation and recovery. The QTc isdefined as the QT interval divided by the square rootof the R-R interval (measured in seconds); it is the bestreflection of the ventricular repolarization time.2. Is the preoperative ECG normal?

No. The preoperative ECG also shows a prolongedQTc of 516 milliseconds and similar inferolateral T-waveabnormalities.3. Are the postoperative ECG findings related to thepatient's recent chest pain and dyspnea?

Although a long QT interval may indicate myocardialischemia--which was a concern in this patient--it has many possible causes. The long QT syndrome(LQTS) is the phenotypic description of a heterogeneousgroup of disorders characterized by a prolonged QTinterval. The syndrome can be inherited or acquired.Causes of acquired LQTS include medications (ie, classI or III antiarrhythmics and some antibiotics and psychotropicdrugs), electrolyte abnormalities, and bradycardia.Because a prolonged QT interval was evidenton all of our patient's ECGs, the etiology is most likelyto be congenital and unrelated to her recent chest painand dyspnea.

Recognition of a prolonged QT interval is important,because this seemingly benign ECG findingplaces a patient at risk for torsades de pointes, or "twistingof the points," a potentially fatal form of ventriculartachycardia. Once a prolonged QT interval is identified,correct all electrolyte abnormalities, especially hypokalemia,hypomagnesemia, and hypocalcemia; discontinueall potentially offending medications; and monitorthe patient closely via telemetry. If all secondarycauses have been ruled out, consider congenitalLQTS.

Congenital LQTS is caused by genetic mutationsthat encode for abnormal cardiac ion channels. In thesesituations, it is important to obtain a detailed family history,because LQTS puts patients at risk for suddendeath. Our patient had no family history of cardiac diseaseor sudden death, which suggests a sporadic orrecessive mutation. In patients in whom congenitalLQTS is suspected, genetic testing can confirm one ofthe 7 identified forms of this syndrome.FURTHER WORKUP--AND A NEW TWIST

The patient is transferred to the coronary care unit. A contrast CT angiogramof the chest shows no evidence of pulmonary embolism, but Dopplerstudies reveal a left lower extremity deep venous thrombosis. Low molecularweight heparin is started, and a Greenfield filter is placed in the inferior venacava.

Serial enzyme determinations rule out myocardial infarction. An echocardiogramreveals mildly decreased left ventricular systolic function and mild tomoderate mitral regurgitation. A stress test, performed 23 months before admission,had found only mild anteroseptal ischemia and normal left ventricularfunction. Thus, no specific cause of the patient's chest pain is found.

Her condition improves, and she is transferred back to the gynecologyoncologyservice. Two days after the transfer, the patient has a cardiac arrest,and the following rhythm is recorded.1. What is this rhythm?2. What should be done next to treat the patient?WHAT'S WRONG:1. What is this rhythm?

The rhythm shown is torsades de pointes. This specifictype of polymorphic ventricular tachycardia occursin the setting of a prolonged QT interval. In patientswith this arrhythmia, the QRS axis swings from a positiveto a negative direction in a single lead.2. What should be done next to treat the patient?

Emergent treatment of torsades de pointes is critical,because the rhythm can quickly degenerate intoventricular fibrillation. Magnesium sulfate, 2 g, given asan intravenous bolus, followed by 1 to 3 g/h, is an effectiveintervention. Other therapies that accelerate the patient'sheart rate shorten the QT interval and can terminatetorsades de pointes. Isoproterenol, 2 to 8 μg/min,can also be used. However, the safest and most effectivetreatment is placement of a temporary pacemaker,which "overdrive paces" the ventricle and shortensrepolarization time.

Secondary causes of LQTS can induce torsadesde pointes when the baseline QT interval is already prolonged.At the time of the arrhythmia, our patient'spotassium and magnesium levels were low, which probablyreduced the threshold for torsades de pointes.OUTCOME AND FOLLOW-UP

During her episode of torsades de pointes, the patient receives 2 shocksof 360 joules and 2 g of intravenous magnesium sulfate. Her ECG shows normalsinus rhythm (Figure); however, the pattern is T-wave alternans, which ischaracterized by changes in contour, amplitude, or polarity of the T wave thatappear regularly--usually every other beat--without changes in the cyclelength. Recently, T-wave alternans has been implicated as a predictor of susceptibilityto malignant ventricular arrhythmias in patients with cardiomyopathy,previous myocardial infarction, or LQTS. The prognostic value of T-wavealternans has not been assessed in patients with congenital or acquired LQTS.

The patient is transferred to the coronary care unit. Her electrolytes areaggressively replenished, and she is monitored by telemetry for the next 48hours with no further events.

Subsequent ECGs continue to show intermittent T-wave alternans anda prolonged QT interval. An automatic cardioverter-defibrillator is implanted.Noninvasive testing indicates that the device is functioning well, andthe patient is discharged with prescriptions for metoprolol, furosemide, anddalteparin. Routine follow-up with her gynecologist and cardiologist isscheduled.