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What caused a patient in their 60s to develop intermittent heart palpitations and periodic weakness?

At presentation to the emergency department, the patient said they had not had any significant medical issues prior to this, and they had no family history of significant health problems, noted Zhibing Lu, MD, PhD, of Zhongnan Hospital of Wuhan University in China, and colleagues in .

A physical examination revealed an irregular cardiac rhythm and a blood pressure of 92/58 mm Hg. The medical team performed an initial 12-lead ECG, which showed a wide complex tachycardia following a brief sinus rhythm.

Lu and team described the most important findings of the ECG as a wide complex tachycardia "characterized by an initial right bundle branch block (RBBB)-like pattern in the first two wide QRS complexes, followed by stabilization into a left bundle branch (LBBB)-like pattern from the fourth to seventh complexes."

They identified the third beat as a fusion beat. They also noted evidence of atrioventricular dissociation, combined with initial dominant R waves in the lead aVR and QS/rS pattern in leads V₃ to V₆. These findings pointed to a diagnosis of ventricular tachycardia, they said.

When the team examined the inferior and precordial leads during the episode of ventricular tachycardia, they observed a small deflection after the QRS complexes, which was only evident in the RBBB-like beats. The short sinus rhythm demonstrated RBBB, low voltage, QRS complexes, and T-wave inversion in leads II and V₂ to V₄.

In addition, the QRS complex revealed terminal deflections that became more evident in the corresponding leads during sinus rhythm; these were considered to be epsilon waves.

The patient underwent an echocardiogram, which showed diminished activity in the right ventricle (RV), dilation of the right atrium and ventricle, and severe tricuspid regurgitation. Cardiac MRI "confirmed global RV hypokinesia with fibrofatty infiltration, especially within the interventricular septum, and anterior and inferior myocardium of RV on postcontrast hyperenhancement images," Lu and colleagues wrote.

Still, neither the ECG nor the cardiac MRI findings indicated abnormal functioning of the left ventricle (LV). The patient underwent genetic testing, which did not show any relevant gene variants. It was suggested that the patient undergo an electrophysiological study, but this was declined.

Lu and colleagues noted that the available results met two major and two minor criteria of Padua. Therefore, they made a provisional diagnosis of arrhythmogenic right ventricular cardiomyopathy (ARVC).

The team considered their patient's level of risk of ventricular arrhythmia as intermediate, based on evidence of moderate RV dysfunction, intermittent ventricular tachycardia episodes, and the absence of syncope or sudden cardiac death history. The patient subsequently received a cardioverter defibrillator implant, along with medical therapy.

Discussion

ARVC is a hereditary disease affecting the RV or both ventricles. It is characterized by fibrofatty tissue infiltration or substitution of myocardium. ARVC may result in ventricular arrhythmias that can be fatal, the authors noted. Patients -- particularly young athletes -- may present with fainting episodes or sudden cardiac death.

A requires findings of a comprehensive evaluation that includes myocardial structure, function, family history, and genetic testing, Lu and team said. However, an ECG can be helpful in assessing the presence of ventricular arrhythmia, depolarization, and repolarization abnormalities.

Notably, a pathogenic mutation can be identified in more than 60% of patients with ARVC, according to one review of . "Consistent with this, genetic testing has emerged as an important diagnostic tool and is important for cascade family screening," wrote the authors of that review.

Traditionally, ECG evidence of the epsilon wave has been considered a characteristic feature of ARVC, noted Lu and co-authors. However, recent reports have identified the epsilon wave in several conditions that involve RV enlargement, injury, or necrosis, including coronary artery disease, congenital heart disease, and .

In addition, "the epsilon wave is not limited to supraventricular rhythm, but can also be observed in RBBB-like ventricular tachycardia," Lu and team wrote. In this patient, the disappearance of the epsilon wave in LBBB-like beats indicated a different origin of ventricular tachycardia.

Generally, an RBBB-like pattern of ventricular activation originates in the LV, creating ventricular dyssynchrony, which reveals the epsilon wave in the RV, they explained. In contrast, ventricular activation that originates from the RV delays depolarization of the LV, thus obscuring the epsilon wave.

"Deflection following a wide complex should be differentiated from a retrograde P wave in ventricular rhythm and intrinsic conduction delay of RBBB," the authors noted. "In this case, the PP interval can be measured by the first two sinus beats, and the position of the following potential sinus P waves during ventricular tachycardia can be inferred."

This led the clinicians to identify the deflection they observed in RBBB-like rhythm as an epsilon wave rather than a retrograde P wave.

"Furthermore, the terminal delay vector in RBBB indicates a right frontal orientation, enabling observation of S waves in leads I, aVL, V₅, and V₆ as well as R waves in right precordial leads," Lu and colleagues wrote. "By contrast, the polarity and orientation of epsilon wave cannot be determined due to its wiggly small spike pattern, and the distribution in ECG depends on the specific ventricular region involved. However, it is not uncommon for the epsilon wave and RBBB to coexist in one patient."

While it is possible to detect an epsilon wave in ventricular tachycardia, it's important to consider retrograde P waves when a deflection repeatedly follows a wide complex, they added. "Careful recognition of a concealed sinus P wave in ventricular tachycardia may be attributed to differential diagnosis."

Immediate placement of an implantable cardioverter defibrillator is not necessary for all patients. "Appropriate risk evaluation and medicine strategy is associated with substantially improved patient outcomes," Lu and colleagues concluded.

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