EKG, electrocardiogram; N/A, not applicable; PSVT, paroxysmal supraventricular tachycardia.
CASE 3 › A 21-year-old man with no medical history presents with sudden onset of lightheadedness followed by syncope. He denies any chest pain or other associated symptoms. At the time of evaluation, he is asymptomatic. His EKG (FIGURE 3) is diagnostic of what syndrome?
The EKG abnormality and diagnosis. The patient had a classic presentation for Wolff-Parkinson-White (WPW) syndrome, a common congenital disorder that alters normal cardiac conduction. He described 2 past instances of unexplained light-headedness and palpitations. Subsequent EP studies demonstrated that the patient had an accessory atrioventricular (AV) tract, causing electrical activity in the heart to bypass the AV node, resulting in a delta wave on EKG (FIGURE 3, GREEN ARROWS).
The patient opted for ablation therapy, which successfully eliminated the delta wave on EKG. Five years later he has had no recurrences.
Epidemiology. The prevalence of WPW syndrome is .1% to 3%.23 Accessory AV tracts are found in men twice as often as in women. Only half of individuals with confirmed tracts develop a tachyarrhythmia. The estimated risk of sudden death due to WPW syndrome is .5% to 4%.24
Pathophysiology. Normally cardiac conduction originates from the sinus node and travels to the AV node, where conduction is slowed, and then proceeds to the His-Purkinje system, and finally to the rest of the ventricular myocardium. In WPW syndrome, ventricular depolarization occurs first by an accessory AV tract called the bundle of Kent, followed shortly thereafter by the His-Purkinje system. This sequence of depolarization is what leads to the EKG findings characteristic of WPW syndrome: a PR interval <.12 seconds, presence of a delta wave, widened QRS complex (>.12 seconds), and repolarization changes seen as ST segment and T-wave changes discordant to (opposite direction) the delta wave and QRS complex (FIGURE 3, RED ARROW).
Factors that influence electrical conduction through the bundle of Kent include cardioactive medications, physiological stress, circulating catecholamines, coronary ischemia, and aging. The end result is a propensity for the heart to convert to one of 4 arrhythmias: paroxysmal supraventricular tachycardia (PSVT), AF, atrial flutter, or ventricular fibrillation (TABLE 2).23
The most common arrhythmia in WPW syndrome is PSVT.23 This rhythm is induced by the formation of a reentry circuit—a pattern in which the heart’s electrical signal loops back on itself—involving the normal conduction pathway and the bundle of Kent. Reentry progressing down the His-Purkinje system and traveling up the bundle of Kent is referred to as orthodromic (anterograde) PSVT. Antidromic (retrograde) PSVT is due to a reentry circuit conducting from the bundle of Kent to the ventricles, and then retrograde through the His-Purkinje system and AV node to the atria.
Clinical features. Under normal circumstances, patients with WPW syndrome are asymptomatic. As was the case with our patient, individuals who develop one of the 4 characteristic arrhythmias can experience light-headedness and syncope.
Treatment. An unstable patient who is experiencing PSVT, AF, or atrial flutter should receive synchronized cardioversion; those experiencing ventricular fibrillation should receive defibrillation (TABLE 2).23 For stable patients, therapy is tailored to the type of arrhythmia. Calcium channel blockers, beta-blockers, and adenosine might be appropriate for patients with orthodromic PSVT but should be avoided in patients with antidromic PSVT, AF, or atrial flutter because these medications block AV node conduction and thus facilitate conduction down the bundle of Kent, which can result in potentially unstable arrhythmias. In general, the longer an arrhythmia has been present, the less effective the pharmacologic intervention because of the increasing sympathetic tone.
Preventive long-term therapies for WPW patients who have experienced arrhythmia include antiarrhythmic medications or ablative procedures. Long-term antiarrhythmic therapy often is reserved for older, more sedentary individuals with less frequent arrhythmias that are not life-threatening. Radiofrequency ablation is a popular option, with long-term success rates as high as 95% and complication rates <1%.23 Patients in whom a WPW pattern is identified incidentally on EKG should be referred to cardiology for EP studies and risk stratification.25
CASE 4 › A 61-year-old woman has an episode of substernal exertional chest pressure that lasted approximately 2 hours but resolved before she arrived at her physician’s office. She also experienced mild nausea. She has no history of coronary artery disease but says that she has experienced similar episodes of chest pressure. What abnormality is seen on her EKG (FIGURE 4)? What is the most likely cause of her symptoms?
The EKG abnormality and diagnosis. Although classically associated with syncope, hypertrophic cardiomyopathy (HCM) often presents similarly to acute coronary syndromes, with chest pain and dyspnea on exertion.26 This patient had no history of cardiac disease or family history of SCD or cardiomyopathy; however, her EKG showed changes indicating left ventricular hypertrophy (LVH), which is consistent with HCM (FIGURE 4, ARROWS). Echocardiography identified myocardial hypertrophy, normal left ventricular ejection fraction, but severe left ventricular outflow obstruction and mild diastolic dysfunction. She was treated with metoprolol and verapamil.