Symptoms

A 44-year-old male with a history of obstructive sleep apnea presents to the ED with extreme dyspnea accompanied by somewhat pleuritic, diffuse, nonradiating chest pain. These symptoms had increased over the previous two weeks, and were accompanied by a dry cough. He recently had received a fluoroquinolone from his primary care physician for presumed bronchitis, without improvement. He denied a history of cardiac disease, pneumonia, pulmonary embolism, and pneumothorax. Physical examination revealed a morbidly obese male, in extremis. His vital signs were temperature 98.3(F, heart rate 140 beats per minute, respiratory rate 40 breaths per minute, and blood pressure 142/63 mm Hg. Pulse oximetry was 100% on 100% non-rebreather face mask. His neck could not be assessed for jugular venous distension due to his size, but the trachea was midline. Lungs featured course rhonchi bilaterally. Heart sounds were without murmurs, gallops, or rubs. Extremities showed bilaterally symmetric edema. Below is the initial 12-lead ECG. What diagnosis do you suspect? Continued on p. 26.Figure: Initial ECG in a 44-year-old obese male with extreme dyspnea and chest pain. What is the most likely cause of his symptoms?This patient had a large pericardial effusion, confirmed by bedside echocardiogram. His chest radiograph demonstrated cardiomegaly with a “water-bottle” configuration. He received emergent pericardial drain placement, and also was found to have severe pulmonary hypertension, not surprisingly due to his obstructive sleep apnea. His work-up was negative for rheumatologic, endocrinologic, neoplastic, or infectious etiologies of the effusion. The initial ECG is suggestive of the ultimate diagnosis of pericardial tamponade, featuring both sinus tachycardia and electrical alternans, nicely demonstrated in all leads, particularly the lead II rhythm strip. His borderline low voltage also is suggestive of this diagnosis, although it too is nonspecific. These findings will be discussed along with other causes of electrical alternans on the ECG. Electrical alternans, although classically associated with pericardial effusion and tamponade, is not pathognomonic of that entity. Its classification goes beyond that due to pericardial effusion (see table 1).1 The emergency physician should not assume that electrical alternans automatically implies impending tamponade. For the purposes of this discussion, electrical alternans in association with pericardial tamponade will be considered initially, followed by a brief discussion of a variety of other entities responsible for this electrocardiographic phenomenon. Electrical Alternans In the 1940s and 1950s, case reports of electrical alternation involving the P, QRS, and T components of the electrocardiogram began appearing in the literature, almost always associated with malignant or tuberculous pericardial effusions.2,3 This phenomenon included the periodic change in amplitude and morphology of complexes on the ECG. Then, as now, the leading putative explanation is that the heart, surrounded with a significant effusion and thus released from the tethering forces of surrounding structures (e.g., lungs and mediastinal contents) is allowed to rotate slightly with contraction. This tendency to rotate is due to the coiled structure of the great vessels, along with the spiral arrangement of myocardial fibers, causing the heart to swivel slightly with systole.3 The result is an oscillating, pendular motion of the heart.1-4 When all waveform components on the ECG are involved, it is termed total electrical alternans, and can be differentiated from those versions where isolated components are involved. In cases where total electrical alternans is present, it is much more specific for large pericardial effusion with impending tamponade; alternation of the QRS complex alone (ventricular alternans) is less specific.3-5 Electrical alternans, however, is a highly insensitive predictor of tamponade. In a case series of 56 patients with cardiac tamponade, total alternans was present in only four (7%), and QRS alternans alone was found in an additional seven patients (13%), thus some manifestation of electrical alternans was seen in only one-fifth of patients with pericardial tamponade.6 Precise alternation (i.e., every other beat) is not necessary to have electrical alternans, as is illustrated in the rhythm strip seen in Figure 2. In cases such as this, the variations in amplitude may occur gradually rather than in a true alternating fashion.1,4 A corroborative electrocardiographic finding suggestive of pericardial effusion as the cause of electrical alternans is low voltage of the QRS complexes. A generally accepted amplitude criterion for low voltage includes limb lead QRS complexes <0.5mV and precordial lead QRS size <1.0mV.4 The amount of fluid is not directly proportional to the degree of voltage reduction, however. Moreover, P wave size may be unchanged, due to the lack of fluid insulating the posterior portion of the atria.4 Failure of the QRS complexes to increase in size after pericardiocentesis should raise clinical suspicion for underlying hypothyroidism, amyloidosis, scleroderma, neoplasm, or chronic constrictive pericarditis.4,5 ST segment elevation also has been described with pericardial effusion; it is attributed to compression of the coronary vessels resulting in ischemia, and is not a characteristic of slowly developing effusions. ST segment changes should disappear with pericardiocentesis if they are due to the compressive effects of the effusion.5 Types of Electrical Alternans Alternans involving the QT interval, T wave, or U wave is termed ventricular repolarization alternans, and is not associated with pericardial tamponade when it occurs in isolation. In such cases, the appearance of the QT interval, the T wave, and the U wave (if evident) will vary from beat to beat. Prolongation of the QT interval predisposes the individual to T wave alternans and torsade de pointes.1,4 Alternans of conduction is a more diffuse phenomenon, and may involve the atria, the atrioventricular junction, the bundle branches, the Purkinje fibers, the myocardium, or an accessory pathway, in short, any portion of the cardiac conduction system.1,4 Thus, the electrocardiographic manifestations of conduction alternans are dependent upon the site involved. Isolated P wave alternans is extremely rare, especially if rigid diagnostic criteria are adhered to; it has been described with pulmonary embolism.7 Subtle changes in QRS length or amplitude in the absence of definitive changes in the axis or morphology of the complex are frequently seen in supraventricular tachycardias.1,4 Finally, ST segment alternans has been associated with myocardial ischemia, and manifests with alternating degrees of ST segment elevation from beat-to-beat within the same lead(s). This ST alternans is classically linked to vasospastic angina pectoris, but has also been described with acute myocardial infarction, exercise testing, and following subarachnoid hemorrhage.1,4 Electrical alternans is an insensitive finding in cardiac tamponade. The finding of QRS alternans in the proper clinical situation — or the finding of total electrical alternans — is an electrocardiographic harbinger of tamponade. Electrical alternans may involve any and all electrocardiographic components of the cardiac cycle, or be restricted to isolated intervals, segments, or complexes. Interpretation of the significance of electrical alternans requires clinical correlation and an awareness of the different entities that may cause alternation in the components of the ECG. Electrocardiographic Manifestations of Electrical Alternans Alternans of repolarization and refractoriness Alternans of conduction Alternans in association with myocardial ischemia Alternans in association with cardiac motion (tamponade) Source: J Am Coll Cardiol 1992;20:483.Figure: ECG tracing of patient with pericardial tamponade confirmed by echocardiogram. Note the rhythm: 2:1 atrial flutter as well as the electrical alternans.Figure: The electrical alternans shown in this tracing does not demonstrate “true” alternans because the periodicity is not every other beat. This rhythm strip is from the same patient prior to pericardiocentesis.