A 31-year-old woman with no significant medical history presents to her primary care provider with complaints of intermittent heart palpitations along with dizziness, shortness of breath, and fatigue provoked by exercise. She describes her palpitations as sporadic increases in heart rate and skipped beats that only last for a few seconds at a time. She denies any pain, nausea and/or vomiting, focal weakness, syncope, or other complaints.

Vital Signs and Physical Examination

Her initial pulse rate is 255 beats per minute while at rest. A manual pulse rate confirms tachycardia and an uneven rhythm is felt. A minute later, her pulse rate falls to 55 beats per minute. All other vital signs are unremarkable. During physical examination, intermittent heart palpitations are heard during auscultation; the rest of the examination is otherwise normal. Electrocardiography (ECG) and blood work are ordered. The ECG findings show signs of sinus arrhythmia with premature ventricular contractions (PVCs; Figure 1). Laboratory results are within normal range and not indicative of any acute disease.

Figure 1. Electrocardiography findings show sinus arrhythmia with premature ventricular contractions. Credit: Adrienne Germond, PA-S; Amanda Breeden, PA-C

Making the Diagnosis

After the initial ECG, the patient is referred from primary care to cardiology. The cardiologist evaluates the palpitations using different modalities because of her young age and symptomatic state. A 24-hour Holter monitor is ordered and shows sinus rhythm with PVCs and short runs of supraventricular tachycardia (SVT). An exercise stress test shows PVCs and short runs of SVT before and after exertion. After 5 minutes of exertion, she experiences symptoms of dizziness, fatigue, and dyspnea but occasional paired PVCs are noted. The patient is able to complete the stress test at a maximal heart rate.

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A sleep test is performed that reveals PVCs and runs of SVT during sleep but no sleep apnea or other sleep-related conditions. Transthoracic echocardiography is performed and shows only mild mitral regurgitation with no evidence of mitral valve prolapse or stenosis. The rest of the echocardiography findings are unremarkable. Cardiac magnetic resonance imaging (MRI) is performed and no structural issues are observed.

The 48-hour Holter monitor shows sinus rhythm with PVCs, short runs of SVT, and a junctional rhythm. The patient is started on digoxin for rate control, which is not successful in controlling her symptoms.

The patient is then referred for a cardiac electrophysiology (EP) study and possible cardiac ablation to resolve her symptoms. The EP study reveals competing electrical signals between the bundle of His and sinus node, which causes junctional beats. No evidence of a bundle branch block is found. Cardiac ablation is not performed because of the increased risk for iatrogenic heart block secondary to competing electrical signals. The patient is kept on digoxin and verapamil is added for rate control. The combination of medications lessens her symptoms initially; however, the palpitations and exertional symptoms continue to occur and limit her daily activities.

Because of the continued daily symptoms and the patient moving to a new location, she is referred to a second cardiac electrophysiologist. A 14-day continuous ambulatory ECG monitor is placed and reveals the predominant rhythm as sinus with occasional PVCs, many runs of SVT, second-degree atrioventricular (AV) block type I, and second-degree AV block type II. 

Based on these results and the patient’s symptomatic palpitations, a permanent pacemaker placement is considered. To properly assess for placement of the pacemaker, the patient’s cardiac electrophysiology needs to be mapped. During the study, the presence of concealed His extrasystoles, which manifests as what appears to be a second-degree AV block type II, is observed (Figure 2). She is diagnosed with pseudo AV block, also known as concealed junctional extrasystole. Following completion of the EP study, the patient is taken off digoxin and verapamil and is started on metoprolol, a β-blocker, which provides better control of her symptoms. A permanent pacemaker is not indicated.

Figure 2. Electrophysiology shows concealed His extrasystoles. Credit: Adrienne Germond, PA-S; Amanda Breeden, PA-C

A 7-day continuous ambulatory ECG monitor is placed after starting metoprolol and reveals resolution of all second-degree AV block type I and second- degree AV block type II arrhythmias but a continuation of SVT. Currently, the patient remains symptomatic. Other antiarrhythmics such as sotalol and flecainide are being considered for future treatment.


The patient in this case had an atypical presentation of arrhythmia. She is a young woman with no medical history or concerning family history but experienced rapid, symptomatic palpitations. The initial workup revealed rhythm abnormalities that were concerning to the clinician. The patient was referred to several specialists and had a thorough workup before being diagnosed with the rarely reported condition known as pseudo AV block.

Initial evaluation of a patient with new-onset palpitations should always include ECG and laboratory workup. After the initial assessment, further testing with Holter monitors, continuous ambulatory ECG monitors, and exercise stress tests can be used for further investigation.1 The clinician should also consider evaluation of the patient’s cardiac structure and function to determine the potential cause of a patient’s arrhythmia. Transthoracic ECG, sleep studies, and cardiac MRI can be useful to assess for structural changes.1 Most arrhythmias can be successfully diagnosed using these diagnostic tests.

Referral to a cardiac electrophysiologist for further evaluation of the electrical conduction should also be considered.1 Cardiac electrophysiology can provide valuable insight into recognizing rare or challenging arrhythmias. Treatment often can be provided during the procedures, including cardiac ablation, pacemaker placement, and defibrillator implant.1

Pseudo AV block is a rare type of cardiac arrhythmia that can present similar to a true AV block.2 The prevalence of pseudo AV block in the general population is currently unknown and must be studied further. It typically presents with a narrow QRS, junctional rhythm.2 True AV blocks typically present with a widened QRS and will have an associated bundle branch block.3 Patients with pseudo AV block often have a positive treatment response to β-blockers.2 However, in true AV block, the arrhythmia worsens when a β-blocker is given.3 Treatment of a true AV block will often involve pacemaker placement.3 Although pseudo AV block is an uncommon type of arrhythmia, this case serves as a reminder that some conditions are not always as they appear. 

Adrienne Germond, PA-C, is a licensed physician assistant in South Carolina; Amanda Breeden, MPA, PA-C, is assistant professor at Augusta University Physician Assistant Program.


1. Wexler RK, Pleister A, Raman SV. Palpitations: evaluation in the primary care setting. Am Fam Physician. 2017;96(12):784-789.

2. Hollanda L, Sobral R, Luize C, Carvalho M, Andrade J, Dietrich C. Pseudo atrioventricular block most likely caused by junctional extrasystoles mimicking Mobitz II second degree atrioventricular block: a case report. HeartRhythm Case Rep. 2020;6(8):507-510. doi:10.1016/j.hrcr.2020.05.002

3. Mangi MA, Jones WM, Mansour MK, et al. Atrioventricular block second-degree. In: StatPearls [Internet]. StatPearls Publishing; 2022. Updated May 22, 2022. Accessed September 22, 2022. https://www.ncbi.nlm.nih.gov/books/NBK482359/