Chest pain, ST-segment elevation and acute pericarditis
The clinical history and the electrocardiogram of this patient are highly evocative of the diagnosis of viral acute pericarditis. Treatment including rest and high-dose anti-inflammatory medication quickly relieved symptoms and normalized the electrical appearance within a few weeks. The pericardium is a serous membrane surrounding the heart, comprised of a thin internal visceral layer and a thicker outer parietal layer. Between these two sheets, there is a virtual cavity containing 15 to 50 ml of liquid. Pericarditis corresponds to an acute inflammation of this serosa which may or may not be accompanied by a more or less abundant pericardial effusion. The clinical presentation of acute pericarditis varies according to the abundance of effusion and etiology (infectious, autoimmune, neoplastic, post-infarction, traumatic, uremic, irradiation, etc).
Since the pericardium is devoid of electrical activity, the changes observed on the electrocardiogram are indirect. Most diseases of the pericardium are accompanied by electrical abnormalities which can vary according to different parameters. An associated alteration of the superficial layers of the myocardium is frequent (myopericarditis) and may render the differential diagnosis with a coronary syndrome difficult; the position of the cardiac cavities may be modified by the presence of an abundant effusion; the structural changes observed in chronic pericarditis indicate a constriction, a reduction in compliance and an overload of the right cavities; an effusion or a pericardial fibrous shell modifies the transmission of electrical impulses.
While the description of a characteristic pattern of the electrocardiogram is rendered difficult by these interindividual variations, electrical changes are observed in a majority of patients with acute pericarditis and allow good diagnostic performance when they occur in an evocative clinical and ultrasound setting.
The electrical signs of pericarditis are induced by the widespread alteration of the superficial epicardial layers of the myocardium. They are characterized by aspecific and evolving repolarization disorders on successive tracings:
- involvement of the atrial myocardium is frequent although pericarditis usually does not alter the amplitude or morphology of the P-wave, although an alternating P-wave can be observed in the presence of abundant pericardial effusion. On the other hand, atrial repolarization abnormalities are frequent and related to an atrial epicardial lesion current; they are reflected by the presence of an inconsistent PQ segment depression, of the discordant type (in the opposite direction of the P-wave), often discrete (< 1 mm), more common in limb leads than in precordial leads and generally absent in aVR or V1 (where, on the contrary, an elevation is observed). This sign is often precocious, relatively specific (although a PQ depression can also be observed for example in a sinus tachycardia), and may constitute the only abnormality found in acute pericarditis;
- the QRS-complexes are generally not modified with absence of necrosis Q-waves except in the case of associated myocardial disease (myopericarditis). A reduction in the amplitude of the QRS-complexes (low voltage) with possible electrical alternans can be observed in the presence of a pericardial effusion;
- alterations of the ST-segment and T-wave of subepicardial localization are the most consistent and most significant. The ST-segment elevation is relatively characteristic since diffuse, most often maximal in leads I, II and from V4 to V6 with possible depression in aVR and V1. This elevation is transient, generally small (≤ 5 mm), ascending and concave upwards in its initial portion. A few days after the onset of symptoms, T-waves can become negative in the leads where the elevation was observed.