The Electrocardiogram in Nonsystemic Ventricular Pacing in a Patient with Congenitally Corrected Transposition of the Great Arteries and Dextrocardia

Authors: Robert Hull, M.D. (robert.a.hull26.mil@mail.mil) 1

Roy Norris, M.D. (roy.s.norris2.mil@mail.mil) 1

Jonathan Schuenemeyer, M.D. (jonathan.w.schuenemeyer.mil@mail.mil)1

Pankaj Madan, M.D. (pankaj.madan@hcahealthcare.com) 2 Linda Huffer, M.D. (linda.l.huffer2.mil@mail.mil) 1

Corresponding Author:Roy Norris, M.D.Division of CardiologySan Antonio Military Medical Center3551 Roger Brooke Drive, Fort Sam Houston, TX 78234Email: roy.s.norris2.mil@mail.mil

1 Division of Cardiology, San Antonio Military Medical Center, 3551 Roger Brooke Drive, Fort Sam Houston, TX 78234.2 Methodist Physician Practices, 4801 NW Loop 410, San Antonio, TX 78229.

Total Word Count: 1154

Subject Terms List:Dextrocardia, Electrocardiogram, Pacemaker, Transposition of the Great Arteries

Disclaimer: The view(s) expressed herein are those of the author(s) and do not reflect the official policy or position of Brooke Army Medical Center, the U.S. Army Medical Department, the U.S. Army Office of the Surgeon General, the Department of the Army or the Department of Defense or the U.S. Government.

Introduction:

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Congenitally corrected transposition of the great arteries (CCTGA) or L-transposition of the great arteries is a rare congenital condition estimated to account for less than 0.5% of clinically apparent congenital heart disease. In CCTGA there is both atrioventricular and ventriculo-arterial discordance with “reversal” of ventricular morphologies such that the morphologic left ventricle (LV) now serves as the pump for the pulmonary circuit and the right ventricle (RV) serves as the systemic ventricle. Dextrocardia may be present in as many as 20% of such patients (1,2).

When describing atrial location, if the morphologic right and left atrium maintain their respective right- and left-sidedness, the term situs solitus is used. When the morphologic right and left atrium are reversed such that the morphologic left atrium now occupies the right sided position, the term situs inversus is used. In approaching dextrocardia, three subtly different terms describe different forms of reversal: mirror-image dextrocardia, dextroposition, and dextroversion. These forms differ in the anterior-posterior and right-left relationships of the atria and ventricles. Mirror-image dextrocardia, or dextrocardia with situs inversus, maintains the normal anterior-posterior relationship of the cardiac chambers with complete right-left reversal of both the atria and ventricles. Dextroposition occurs when a normal heart is shifted rightward by extracardiac factors. Dextroversion, or dextrocardia with situs solitus, occurs when the morphologic left and right atria preserve their normal right-left relationship, but there is rightward rotation of the ventricles (3,4). Thus, when CCTGA and dextrocardia co-exist, there is reversal of the ventricular positions from what would be normally expected in addition to rightward rotation of the ventricles. This anatomy is easily depicted on coronary CT angiography (Figure 1) (4).

The pattern of ventricular activation seen electrocardiographically will vary depending on the form of dextrocardia in addition to whether morphologic reversal of the ventricles is present (5). The challenges of pacemaker implantation in the setting of dextrocardia and transposition have been described, but the electrocardiographic pattern that occurs with ventricular pacing of the nonsystemic ventricle in a patient with CCTGA and dextrocardia warrants further discussion. We describe the electrocardiographic changes observed in a patient with dextrocardia, situs solitus, and CCTGA complicated by complete heart block requiring non-systemic ventricular pacing.

Case Report:

The patient is a 34 year-old male with a history of dextrocardia, situs solitus, and CCTGA complicated by third degree atrioventricular block status-post dual chamber pacemaker implantation programmed DDDR. He presented with three weeks of orthopnea and paroxysmal nocturnal dyspnea with diffuse groundglass opacities and bilateral pleural effusions on computed tomography (CT) consistent with acute decompensated heart failure syndrome. He also reported one day of new-onset atypical chest pain. Given his known history of dextrocardia, both right-sided and standard left-sided electrocardiograms (ECG) were performed (Figures 2 and 3). The right-sided ECG demonstrated sinus rhythm with right bundle branch block pattern without changes diagnostic of ischemia in the setting of a paced rhythm. He was admitted to the Cardiology service with serial trending of troponins which were negative. The patient was started

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on intravenous diuresis and coronary CT angiography was performed which confirmed CCTGA with dextrocardia and situs solitus. No evidence of epicardial coronary artery disease was detected (Figure 4). Echocardiography did not demonstrate significant valvular heart disease. Device interrogation demonstrated normal pacemaker function. His chest pain was determined to be noncardiac in nature and responded to acetaminophen. The patient responded well to intravenous diuresis which was transitioned to an oral regimen. He was scheduled for follow-up with his adult congenital heart disease (ACHD) cardiologist.

Discussion:

It is important to be aware that there are multiple forms of dextrocardia with subtle electrocardiographic distinctions. Both left- and right-sided ECGs are required for complete evaluation. Thorough electrocardiographic evaluation can raise suspicion for significant adult congenital heart disease, including complex congenital disease such as CCTGA.

The P wave axis in sinus rhythm on standard left-sided leads in dextrocardia varies based on the location of the dominant pacemaker and whether situs solitus (normal relationship of the atria), situs inversus (left-to-right reversal of the atria), or situs ambiguus is present. A comparatively large retrospective study of dextrocardia showed situs solitus in 43%, situs inversus in 38%, and situs ambiguus in 19% of dextrocardia patients. Situs solitus is suggested by a normal P wave axis on standard left-sided ECG leads whereas a P wave vector of +135 degrees (negative in I and avL and positive in aVR) on standard leads suggests situs inversus (5,6). Our patient’s normal P wave axis on standard leads is consistent with sinus rhythm in the setting of situs solitus.

Dextrocardia, regardless of the relative orientation of the morphologic left and right ventricles, will demonstrate anteriorly-directed ventricular forces with no q waves in V1 and V2. Normal depolarization, in the absence of significant conduction system disease, begins in the interventricular septum and proceeds from the morphologic LV to the morphologic RV, thus analysis of the initial QRS forces can aid in identifying the relative positions of the morphologic LV and RV. If the initial QRS vector is directed rightward, with q waves in V5 and V6 and no Q waves in V5R and V6R, it suggests the morphologic LV remains the leftmost ventricle. If the initial QRS vector is directed leftward, with q waves in V5R and V6R and no Q waves in V1 and V2, it suggests the morphologic LV is the more right-sided ventricle (5). In non-dextroposition dextrocardia the standard left-sided lateral precordial leads represent the high and mid-portions of the right-sided ventricle with progressive decrease in QRS amplitude in V1-V6, a feature seen in our patient (6). Our patient’s ECG demonstrated a leftward directed QRS axis in the standard lead frontal plane with monophasic R waves in the left-sided precordial leads and QS precordial complexes on right-sided precordial leads, consistent with apical pacing of the more right-sided of two ventricles located in the right thoracic cavity as demonstrated on his chest X-ray (Figure 5). V1 and V1R, which are located on the opposite side of the ventricular septum in their respective precordial lead sets, show discordance with the other precordial leads consistent with the vector of the wavefront of electrical activation of the ventricles. Important limitations include the effect of right ventricular hypertrophy on electrocardiographic balancing of forces and the effect of spatial changes in septal or cardiac orientation on electrocardiographic vectors with respect to lead placement (5).

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In this case, the presence of dextrocardia with morphologic reversal of the ventricles secondary to CCTGA combined with pacing of the non-systemic morphologic LV results in a right bundle branch block pattern on right-sided ECG and a left bundle branch block pattern on left-sided ECG. This represents normal ventricular pacing and is an electrocardiographic representation of the altered cardiac anatomy. Although such patients are rare, given the increased survival of AHCD patients and high prevalence of both complete heart block and dextrocardia in CCTGA, it is important to be familiar with the expected electrocardiographic findings in these patients with nonsystemic ventricular pacing (7).

Acknowledgments: None

Sources of Funding: None

Disclosures: None

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as a bridge to heart transplantation in a patient with congenitally corrected transposition of the great arteries and dextrocardia. Interactive cardiovascular and thoracic surgery 2016;23:988-990.

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international journal of cardiovascular imaging 2006;22:731-3.5. Rao PS. Dextrocardia: systematic approach to differential diagnosis. American heart

journal 1981;102:389-403.6. Portillo B, Anselmi G, Sodi-Pallares D, Medrano GA. Importance of the unipolar leads in

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7. Stout KK, Daniels CJ, Aboulhosn JA et al. 2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Journal of the American College of Cardiology 2018.

Figure legends

Figure 1 – A: Dextrocardia with situs solitus and CCTGA, B: Normal anatomy

Figure 2 – Standard frontal limb leads with right-sided precordial leads demonstrating normal sinus rhythm with P synchronous ventricular pacing. The normal P wave axis is consistent with situs solitus. The QS complexes in the precordial leads are consistent with nonsystemic ventricular pacing analogous to that seen in RV apical pacing in patients with normal anatomy.

Figure 3– Standard left-sided 12-lead EKG demonstrating normal sinus rhythm with P synchronous ventricular pacing. The R complexes in the precordial leads occur as the wavefront

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of activation proceeds from the nonsystemic and morphologic left ventricle, which is the more rightward located of his two ventricles, towards the patient’s left where the systemic and morphologic right ventricle is located.

Figure 4 – CCTA image demonstrating parallel great vessels consistent with CCTGA and the ventricular lead placed near the apical septum in the nonsystemic and morphologic left ventricle.

Figure 5 – CXR with chambers delineated

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