Inferior infarction with right ventricular extension
This patient underwent a coronary angiography, which revealed a right proximal coronary thrombosis. Several electrocardiographic signs found in this patient point to a proximal right coronary artery disease: a taller elevation in lead III than in lead II (suggestive of a right coronary involvement), deep depression in leads I, AVL, right ventricular extension with sinus node dysfunction (suggestive of a proximal disease).
A right ventricular infarction is rarely isolated, most often associated with an inferior left ventricular infarction and is most often, as in this patient, the result of a proximal occlusion of the right coronary artery upstream of the marginal branch. Indeed, in a majority of patients, the right ventricle is predominantly supplied by collateral branches of the right coronary artery, as are the atrioventricular node, the sinus node, the posterior walls of both ventricles as well as the posterior third of the septum. The anterior interventricular artery is responsible for supplying a more restricted area of the right ventricle (tip and anterior aspect), a thrombosis of this artery being accompanied by clinical signs that are most often absent or very discrete of right ventricular disease. Similarly, the occlusion of the circumflex artery only leads to an infarction of the right ventricle in exceptional instances (in the case of a dominant left network).
It is important not to miss the diagnosis of right ventricular extension in the initial phase of an inferior infarction for which the electrocardiogram plays a central role in this setting. Indeed, the presence of a right ventricular infarction considerably worsens the short-term prognosis of an inferior infarction, increases the risk of complications and implies specific therapeutic management. Contrary to cardiogenic shock in conjunction with extensive anterior necrosis, shock secondary to an inferior infarction with right ventricular extension is most often associated with reduced long-term mortality if appropriately identified and treated, the right ventricle being considerably more resistant to ischemic lesions than the left ventricle and capable of recovering a normal contractile function.
The standard 12-lead electrocardiogram is centered on left ventricular analysis and is not sufficient to detect a possible right ventricular disease; the recording of right and posterior precordial leads is therefore essential in a patient with an inferior infarction to define the degree and extent of the expansion of the zone of necrosis.
Various electrocardiographic signs can be observed during an inferior infarction:
- as explained above, right ventricular infarction is exceptionally isolated and most often occurs in the context of an inferior infarction with elevation in the inferior leads;
- it is common to observe a ST-segment elevation in V1 (the lead closest to the right ventricle) on the 12-lead electrocardiogram; it is a sign of poor prognosis which sometimes represents the only evocative sign (absence of changes in the inferior territory);
- the electrocardiographic abnormality characterizing a right ventricular extension is the presence of an elevation > 1 mm in the right precordial leads; the V4R lead appears to have the highest sensitivity in detecting right ventricular extension, although the specificity of a V3R elevation appears higher; a reciprocity with depression can be observed in the opposite left leads (from V3 to V4); the elevation in the right leads is often fleeting, usually disappearing within 10 to 12 hours, thus justifying a systematic and early recording of the right leads upon the patient's arrival in the intensive care unit;
- a ST-segment elevation in right precordial leads can also be observed (differential diagnoses) in patients with pericarditis, pulmonary embolism, left bundle branch block or left ventricular hypertrophy;
- after the acute phase, the presence of Q-waves can be observed with a low specificity;
- in the case of an extensive inferior infarction, a posterior wall involvement can be observed with the presence of an elevation in V7-V8-V9;
- the association with an atrial infarction is possible and revealed by an elevation or depression of the PR segment in the inferior leads;
- the inferior infarction with right ventricular extension is frequently complicated by the occurrence of conduction disorders (nodal atrioventricular block or sinus node dysfunction) and atrial or ventricular rhythm disorders.