A physically fit 17-year-old male was referred by his internist for clearance prior to joining the fire department. The patient has a history of situs inversus totalis. An ECG was performed at Winthrop University Hospital using standard lead placement. Another ECG was then performed by reversing both the arm and leg leads as well as using right-sided chest leads. There was no complaint of chest pain, syncope, or shortness of breath, and no other abnormality was noted.
Situs inversus totalis is a congenital condition in which all the major visceral organs are mirrored from their normal position.1,2 The condition occurs in less than 1 of 10,000 people (less than 0.01 percent), although its presence varies across populations.2 Situs inversus totalis is not a structural heart disease and is normally not associated with congenital heart disease.3 However, in malpositions of situs inversus with levocardia and situs solitus with dextrocardia, structural heart conditions tend to be more prevalent, such as double outlet right ventricle, endocardial cushion defect, pulmonary stenosis or atresia, single ventricle, transposition of the great vessels, atrial septal defect, and ventricular septal defect.2
Figure 1 shows a sinus rhythm with inverted P waves in leads II, III, and aVF. Importantly, the P wave, QRS complex, and T wave are inverted in lead I. Only two conditions will routinely have this pattern: limb lead reversal and dextrocardia. For limb lead reversal, precordial leads are typically normal. A simple rule of thumb is that the configuration in leads I, aVL, and V6 should be aligned with respect to their QRS polarity. However, in this case, leads I, aVL, and V6 are aligned opposite the normal configuration (i.e., inverted QRS configuration). In addition, precordial leads have significant QRS voltage in V1, but as the leads transition to V6, the voltage of the QRS complex decreases in amplitude. This is because the electrodes move further away from a right-sided myocardium/electrical generator. In dextrocardia, the P, QRS, and T waves are all inverted in lead I, but the precordium loses voltage as the electrodes move from V1 to V6.
The referring internist was astute enough to reverse the limb leads and place the precordial leads across the right chest. Interestingly, the QRS nearly normalizes (i.e., upright QRS in leads I and aVL and inferiorly [leads II, III, and aVF], and increasing QRS amplitude moving from the right-sided V1 to the more lateral right-sided V6). The only abnormalities appear to be the inverted P waves in the inferior leads.
Review by two cardiologists indicated the patient had a low atrial rhythm, a condition in which the electrical activity starts in the lower atrium instead of the sinoatrial (SA) node in the upper atrium due to a poorly or non-functioning SA node.4 This condition, in younger and healthier patients, is generally harmless and painless.4 Low atrial rhythm may be asymptomatic or accompanied by symptoms such as palpitations, fatigue, or poor exercise tolerance.4
The low atrial rhythm is not directly related to the situs inversus totalis. The patient did not appear to have any structural heart disease, which could have affected the upper atrium and, therefore, damaged the SA node. It is possible that the patient had a virus that damaged the SA node. This patient’s ectopic atrial rhythm appears to be benign since he lacks any of the symptoms listed above; therefore, treatment would not be recommended.
Disclosures: The authors have no conflicts of interest to report.
- Schumacher KR. Dextrocardia. MedlinePlus Medical Encyclopedia. Published June 5, 2012. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/007326.htm. Accessed August 26, 2013.
- Wilhelm A, et al. Situs Inversus Imaging. Medscape. Published May 25, 2011. Available online at emedicine.medscape.com/article/
- 413679-overview. Accessed August 26, 2013.
- Perloff JK, Marelli AJ. Perloff’s Clinical Recognition of Congenital Heart Disease, 6th Edition. Philadelphia, PA: Elsevier Inc. 2012.
- Singh V, Vidhani Y. Electrocardiographic abnormality in aircrew: low atrial rhythm. Ind J Aerospace Med. 2009;53:65-67.