The patient was diagnosed with an ST-segment elevation myocardial infarction (STEMI) and the cardiac catheterization laboratory and team were activated. She was placed on a cardiac monitor and provided supplemental oxygen by nasal cannula with a goal to maintain oxygen saturation above 92%. The patient had self-administered aspirin 325 mg by mouth before ED arrival, so this medication was held. Given concerns about cardiac preload dependence, she was cautiously given sublingual nitroglycerin 0.4 mg three times with some pain relief and started on maintenance IV 0.9% sodium chloride solution while her BP was monitored. She was given oral clopidogrel bisulfate 600 mg and IV heparin 4,000 units as a bolus.
The patient was then transported to the cardiac catheterization laboratory, where emergent coronary angiography revealed a 90% thrombotic stenosis of the mid-right coronary artery (RCA) and 80% stenosis of the proximal left anterior descending (LAD) artery. Percutaneous coronary intervention (PCI) was performed with placement of two drug-eluting stents in the mid-RCA and one drug-eluting stent in the proximal LAD.
Postprocedurally, the patient was admitted to the coronary care unit. Her chest pain completely resolved. A repeat right-sided ECG following the PCI revealed resolution of the ST-segment elevation in leads I, II, and aVF; resolution of the T-wave inversion in leads V1 and V2; and resolution of the ST-segment depression in lead V2 (Figure 4). A technically difficult transthoracic echocardiogram was performed after the PCI and exhibited a wall motion abnormality of the proximal LAD territory with an estimated ejection fraction of 45% to 50%. Her medical management was optimized by dual antiplatelet therapy with aspirin and clopidogrel bisulfate, a beta-blocker, high-intensity statin therapy, and an angiotensin-converting enzyme inhibitor. From a cardiac standpoint, she recovered without chest pain recurrence or cardiac complications such as dysrhythmias. She was discharged with plans to complete cardiac rehabilitation.
STEMI is a potentially life-threatening diagnosis that cannot be missed on ECG interpretation. However, evaluation for ST-segment elevation can be challenging in patients with mirror-image dextrocardia. Despite advances in imaging technology, patients with mirror-image dextrocardia may not be aware of their condition. This uncommon congenital heart anomaly occurs in about 1 in 10,000 people and may be associated with other medical comorbidities such as chronic sinusitis and bronchiectasis in Kartagener syndrome.1 Although mirror-image dextrocardia is an infrequent finding, it is the most common cardiac positioning abnormality and is primarily associated with situs inversus, in which all major visceral organs have a mirror-image orientation.2 In mirror-image dextrocardia, the heart develops in the right thoracic cavity with the apex pointing toward the right hemidiaphragm with a reversal of the traditional right-left orientation. Dextrocardia differs from dextroposition, where extracardiac factors displace the heart into the right hemithorax, and dextroversion, which has a rotational component to the cardiac anomaly. Embryologically, situs inversus with dextrocardia develops in the fetal heart when the primitive cardiac tube loops in a leftward fashion instead of rightward as seen in situs solitus (normal cardiac position).3,4 The cause of dextrocardia with situs inversus is largely unknown; however, patients with dextrocardia do not appear to be at an increased risk for intracardiac abnormality or coronary atherosclerotic disease despite the abnormal cardiac positioning.2,5,6 In dextrocardia, the left and right orientation of the heart is inverted; however, the anterior-posterior relationship of the heart is unchanged.
This abnormal cardiac positioning can result in atypical clinical presentations, which may delay the diagnosis of emergency conditions and points to the importance of obtaining a thorough medical history and maintaining a healthy level of clinical suspicion.
The clinical approach to evaluating patients with dextrocardia should include awareness that the patient's inverted anatomy will affect symptom location and physical examination findings. Because the heart is located in the right thoracic cavity, chest pain is likely to originate on the right. The pain radiation pattern is variable and has been described as radiating to both upper extremities and the jaw similar to typical angina.7 Right-sided chest pain may be attributed to pleural, musculoskeletal, neurologic, or gastrointestinal pathology instead of angina.
An ECG to evaluate right-sided chest pain in a patient with dextrocardia may be challenging to perform and interpret. For example, standard lead placement will result in a right axis deviation, polarity reversal in leads I and aVL, positive P-wave and QRS complex in aVR, and reversed R-wave progression. Appropriate lead placement in patients with dextrocardia is unclear. Multiple case reports recommend performing a right-sided ECG by reversing all precordial and limb leads to normalize the ECG.6-8 The Society for Cardiological Science and Technology, however, recommends performing a standard left-sided ECG followed by a modified right-sided ECG in which the limb leads and precordial leads V1 and V2 remain unchanged and only the precordial leads V3 through V6 are reversed.9 Mitchell and colleagues suggest that maintaining limb lead inversion in the modified right-sided ECG reminds the interpreter of the abnormal cardiac positioning.8 Despite these opposing thoughts, proper documentation of lead placement on the ECG is essential for patients with dextrocardia, to prevent potential errors in ECG interpretation. Clinicians may confuse ECG findings consistent with dextrocardia with limb lead placement errors in which the main difference is the precordial R-wave progression. In limb lead reversal, the precordial leads should have a typical R-wave progression; in patients with dextrocardia, the progression is reversed. Precordial lead reversal is critical in dextrocardia as this may expose hidden ST-segment elevation in the anterior, septal, and lateral leads. A case report by Richter and colleagues describes a patient with an acute anterior MI that was only identified after precordial lead reversal on ECG.10 He and colleagues described a patient with an acute lateral MI that was not apparent on a standard left-sided ECG and seen only on a right-sided ECG.7 Inferior STEMIs should be identifiable on standard left-sided ECGs because leads II, III, and aVF are unaffected in dextrocardia.
Clinical acumen about dextrocardia may prompt clinicians to place automated external defibrillator (AED) pads in a mirrored fashion similar to ECG leads; however, no studies have evaluated appropriate placement of AED pads in patients with dextrocardia. In fact, Cattermole and colleagues described a successful defibrillation with traditional anterolateral paddle positioning in a patient with unknown dextrocardia who was in ventricular fibrillation arrest.11 Gorenek and colleagues also described a successful cardioversion in a patient with dextrocardia by placing the paddles on the conventional right parasternum and atypical right lateral chest at the heart apex.12 These case reports suggest that AED pad placement may be less important than the energy that they deliver, though further studies are needed to further evaluate this. Fortunately, STEMI management in patients with dextrocardia is the same as in patients with normal heart position, although coronary angiography and percutaneous coronary intervention may be more technically challenging due to mirrored anatomy.
This case presents a common chief complaint in a patient with an unusual medical condition. Dextrocardia is rarely seen in the ED but clinicians must understand it. Recognizing the atypical clinical presentation, unusual ECG findings, and necessity of a right-sided ECG in patients with dextrocardia complaining of chest pain can prevent delayed or missed STEMI diagnoses.
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Keywords:Copyright © 2019 American Academy of Physician Assistants
situs inversus; dextrocardia; myocardial infarction; STEMI; ECG; chest pain