A 46-year-old male with a history of a right upper lobe carcinoid tumor and hypertension was admitted for lung tumor resection. He underwent a successful robotic-assisted thoracoscopic total pleural decortication, right middle lobectomy with bronchoplasty, and mediastinal lymphadenectomy without complication.

On postoperative day 3, while preparing for discharge, telemetry revealed the abrupt onset of a wide complex tachycardia with ventricular rates up to 280 beats/min. An electrocardiogram was obtained, and the cardiology service was consulted for further evaluation.

During this episode, he experienced no sudden-onset palpitations, lightheadedness, dizziness, or shortness of breath. At the time of assessment, his vital signs demonstrated a blood pressure of 119/76 mm Hg, a heart rate of 170 beats/min, a respiratory rate of 20 breaths/minute, and an oxygen saturation of 98% on room air.

Physical examination revealed an alert and oriented patient in no acute distress. Pulmonary examination was notable for clear breath sounds bilaterally with unlabored respirations. Cardiovascular examination demonstrated an irregular rhythm without murmurs, rubs, or gallops.

An electrocardiogram obtained during the tachycardia is shown in Figure 1 .

Electrocardiogram during tachycardia demonstrating irregular wide-complex rhythm consistent with pre-excited atrial fibrillation. AF = atrial fibrillation; ECG = electrocardiogram.

A preoperative ECG performed prior to thoracic surgery is shown in Figure 2 .

Baseline electrocardiogram demonstrating a short PR interval and delta wave consistent with ventricular pre-excitation. ECG = electrocardiogram.

Question 1:

What is this patient’s underlying rhythm for this tachyarrhythmia?

• A.

  Polymorphic Ventricular Tachycardia (PMVT)

• B.

  Monomorphic Ventricular Tachycardia (MMVT)

• C.

  Atrial Fibrillation with RBBB Aberrancy

• D.

  Atrial Fibrillation with Pre-excitation via Accessory Pathway (Wolff–Parkinson–White)

• E.

  Antidromic AVRT

Answer 1: D: Atrial Fibrillation with Accessory Pathway (Wolff–Parkinson–White)

Explanation:

The underlying rhythm is atrial fibrillation with pre-excitation through an accessory pathway. This diagnosis is supported by an irregularly irregular ventricular rhythm without discernible P waves, consistent with atrial fibrillation, in combination with a wide complex tachycardia demonstrating marked beat-to-beat variability in QRS morphology and axis. This variability reflects changing degrees of ventricular activation through both the atrioventricular node and the accessory pathway, producing fusion complexes with differing morphologies. In addition, several RR intervals approach or fall below 250 ms—a ventricular response that is rarely achievable through AV nodal conduction alone, given its typical effective refractory period. These findings indicate rapid, variable antegrade conduction over an accessory pathway during atrial fibrillation.

Polymorphic ventricular tachycardia is unlikely, as although PMVT may appear irregular, it is ventricular in origin and typically demonstrates evolving or repeating QRS patterns, such as the gradual axis rotation seen in torsades de pointes, rather than abrupt beat-to-beat variability. Monomorphic ventricular tachycardia is excluded by the absence of a regular ventricular rhythm and fixed QRS morphology. Atrial fibrillation with right bundle branch block aberrancy would produce a consistent QRS morphology across beats and does not account for the continuously varying complexes observed. Ashman phenomenon results in isolated aberrantly conducted beats following long–short RR intervals and does not explain sustained wide complex tachycardia with continuously changing morphology. Antidromic atrioventricular reentrant tachycardia is also excluded, as it is a regular tachycardia with fixed ventricular activation over a single accessory pathway.

Retrospective review of the preoperative ECG ( Figure 2 ) demonstrates a shortened PR interval with subtle slurring of the initial QRS upstroke consistent with a delta wave, confirming manifest ventricular pre-excitation. The degree of pre-excitation was modest, which may explain why it was not recognized preoperatively. Although identification of a Wolff–Parkinson–White (WPW) pattern would not necessarily have altered the planned surgical procedure in this asymptomatic patient, documentation of ventricular pre-excitation would have heightened awareness of the risk of rapid antegrade conduction during atrial fibrillation and reinforced avoidance of AV nodal blocking agents in the postoperative setting.

Taken together, the presence of atrial fibrillation, an extremely rapid and irregular ventricular response, very short RR intervals, and beat-to-beat QRS variability is diagnostic of atrial fibrillation with variable pre-excitation over an accessory pathway.

Question 2:

The patient’s blood pressure was 119/76 mm Hg, heart rate was 170/min, mental status was normal, no evidence of acute heart failure, and no ischemic chest pain. What is the most appropriate management of this patient’s tachycardia?

• A.

  Defibrillation

• B.

  DC Cardioversion

• C.

  Administer IV Metoprolol

• D.

  Administer IV Ibutilide

• E.

  Administer IV Adenosine

Answer 2: D: Administer IV Ibutilide

Explanation :

This patient is experiencing pre-excited atrial fibrillation and remains hemodynamically stable, as evidenced by preserved blood pressure, normal mental status, absence of ischemic symptoms, and no signs of acute heart failure. In this clinical context, pharmacologic rhythm control is appropriate. Intravenous procainamide, a class IA antiarrhythmic agent, and intravenous ibutilide, a class III antiarrhythmic agent, are recommended therapies for the management of hemodynamically stable pre-excited atrial fibrillation, as they slow conduction over the accessory pathway and promote termination of atrial fibrillation without enhancing accessory pathway conduction. ^,

If the patient was hemodynamically unstable or had evidence of ischemic chest pain, altered mental status, or acute heart failure, DC cardioversion would be appropriate. Defibrillation will be appropriate if the patient develops ventricular fibrillation or pulseless ventricular tachycardia. ^, AV nodal blocking agents like metoprolol, diltiazem, adenosine, and digoxin are contraindicated in pre-excited atrial fibrillation because suppression of AV nodal conduction may promote preferential conduction over the accessory pathway and precipitate ventricular fibrillation.

Question 3:

A significant proportion of patients with ventricular preexcitation remain asymptomatic but are still at risk for life-threatening arrhythmias. Which of the following most identifies patients with WPW syndrome at high risk for rapid ventricular pre-excitation (VPE) precipitating ventricular fibrillation (VF)?

• A.

  Gradual loss of VPE during treadmill exercise testing

• B.

  Shortest pre-excited RR interval (SPERRI) during atrial fibrillation <250 ms

• C.

  Accessory pathway effective refractory period <300 ms

• D.

  WPW ECG pattern detected after 65 years of age

• E.

  Pre-excited tachyarrhythmias occurring at rest

Answer 3: B: Shortest pre-excited RR interval (SPERRI) during atrial fibrillation <250 ms

Explanation :

The risk of sudden cardiac death in patients with WPW syndrome is primarily determined by the ability of the accessory pathway to conduct atrial impulses rapidly to the ventricles during atrial fibrillation. ^,,

The most powerful predictor of this risk is the shortest pre-excited RR interval (SPERRI) measured during atrial fibrillation. Historically, in the 1970s and 1980s, atrial fibrillation was intentionally induced during electrophysiology studies in patients with WPW to directly assess accessory pathway conduction. Patients who experienced ventricular fibrillation or cardiac arrest were found to have extremely short RR intervals during pre-excited atrial fibrillation, typically <250 ms. ^, As a result, a SPERRI below 250 ms became recognized as a marker of a high-risk accessory pathway that would benefit from definitive treatment. ^,

Induction of atrial fibrillation in the electrophysiology laboratory, however, was not without risk, as it could unpredictably degenerate into ventricular fibrillation and require defibrillation. Consequently, during the 1980s and 1990s, safer surrogate measures were developed. The accessory pathway effective refractory period (APERP) was determined using atrial extrastimuli to identify the shortest coupling interval that still conducted antegrade over the accessory pathway. ^, An APERP approximately <240 to 250 ms was found to correlate closely with a SPERRI <250 ms and similarly indicated a high-risk pathway. ^,

Noninvasive testing plays an important role in the initial evaluation of asymptomatic patients with ventricular pre-excitation. ^, A standard 12-lead ECG, ambulatory monitoring, and exercise treadmill testing are safe and recommended with Level 1 evidence. During exercise testing, abrupt and complete loss of ventricular pre-excitation, manifested by disappearance of the delta wave with normalization of the PR interval and QRS duration, suggests block in the accessory pathway and a prolonged anterograde APERP, indicating a low-risk pathway. In contrast, gradual loss of pre-excitation during exercise is common and has unclear clinical significance and therefore does not reliably identify low-risk patients. ^,

Clinical features that further increase arrhythmic risk in WPW include male sex, detection of the WPW pattern during childhood or adolescence, a history of atrial fibrillation, arrhythmic symptoms such as syncope, congenital heart disease, including Ebstein anomaly, and familial WPW syndrome. ^, In asymptomatic patients with pre-excitation, an invasive electrophysiology study is considered reasonable for further risk stratification, consistent with Level 2a evidence (Class IIa, Level B) per the 2015 AHA/ACC guidelines. During invasive testing, key parameters include the accessory pathway effective refractory period and the shortest pre-excited RR interval during atrial fibrillation. ^, Short APERP values and short SPERRI reflect rapid anterograde conduction and are associated with a heightened risk of malignant arrhythmias, whereas longer refractory periods suggest lower risk. ^,

Adjunctive maneuvers such as isoproterenol infusion may be used during electrophysiology testing to simulate adrenergic stimulation and potentially unmask high-risk pathways, although autonomic effects on both the accessory pathway and AV node may limit reliability. Incremental atrial pacing can also assess accessory pathway conduction by determining the fastest rate at which 1:1 antegrade conduction occurs. If atrial fibrillation cannot be induced, assessment must rely on APERP or rapid atrial pacing parameters. The induction of atrioventricular reentrant tachycardia, particularly when it spontaneously degenerates into pre-excited atrial fibrillation, as well as the presence of multiple or septally located accessory pathways, further increases the risk of serious arrhythmic events, including sudden cardiac death. ^,