Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 127

 Posterior leaflet tethering – A degree of ischemic MR is seen in ~30% of acute MI. Inferior MI with localized inferior/posterior akinesis pulls the posterior papillary muscle posterolaterally, with subsequent tethering of the posterior mitral leaflet (predominantly). This tether- ing may lead to severe MR, a dynamic form of MR that may be mild at rest and severe with increased ventricular loading. Tethering may also occur with anterior MI and is usually a posterior tethering as well. In anterior MI, posterior tethering is secondary to global LV dilatation.

 Papillary muscle rupture – Severe MR may result from rupture of a papillary muscle head, usually the posterior papillary muscle in the context of an inferior or posterior MI (two-thirds of severe MR cases in the SHOCK registry).¹²¹ The posterior papillary muscle is supplied by one artery, the PDA (from a dominant RCA or LCx), whereas the anterolateral muscle has a dual blood supply from the LAD (usuallyfirst diagonal) and the LCx. Papillary muscle rupture occurs in ~1% of MIs, and, unlike ventricular septal rupture, the infarct is relatively small in 50% of the cases. Each papillary muscle extends chordae to both leaflets, and therefore flailing of either or both leaflets may occur with rupture of either papillary muscle.Echo distinguishes papillary muscle rupture (treated surgically) from leaflet tethering (initially treated with revascularization and supportive measures). In the former, the leaflet(s) are flail, prolapsed, with flailing of chordae and flailing of an echogenic piece of papillary muscle; in the latter, the posterior leaflet is restricted and the jet is usually posterior.

 B.Ventricular septal rupture (VSR) occurs in ~1% of MIs (only 0.2% of reperfused MIs). Anterior MI (LAD) and inferior MI (mainly RCA) were equally common causes of VSR in the SHOCK registry, while other registries suggest that anterior MI is slightly more common.¹²² Patients with a wrap-around LAD have less septal collaterals and are at a higher risk of septal rupture with anterior MI. The location is apical septal in anterior MI and basal inferior in inferior MI. VSR leads to a severe left-to-right shunting with severe hypotension and LV volume overload.

 C.Free wall rupture occurs in ~2% of MIs and is the most common and most underdiagnosed mechanical complication (≤1.5% of patients treated with PCI, 3% of patients treated with thrombolysis, 6% of patients not reperfused).123,124 The most common location is anterior MI (LAD culprit); the second most common location is lateral MI (LCx culprit).¹²⁵

Free wall rupture often leads to tamponade and a bradycardic pulseless electrical activity. It commonly has one of the following pro- dromes: chest pain, re-elevation of ST segments, bradycardia, or syncope from a vagal shock.¹²⁴ In ~30% of the cases, it is preceded by a concealed rupture and a moderate pericardial effusion, where the pericardium temporarily seals the rupture.¹²⁴

Risk factors for VSR and free wall rupture: female sex, older age, first MI, absence of collaterals, history of HTN, anterior MI. Also, the use of NSAIDs or steroids increases the risk of rupture. Anticoagulants do not clearly increase the risk of rupture.

Reperfusion with thrombolysis or PCI reduces the incidence of all mechanical complications. While early thrombolysis reduces the risk of free wall rupture, late thrombolysis >12 hours, particularly in elderly patients, may increase the risk of free wall rupture according to a meta-analysis of thrombolytic trials.^126,127

The majority of patients with VSR have multivessel disease, while patients with papillary muscle or free wall rupture usually have a single-vessel disease with good LV function.