CHAPTER 49: ISCHEMIC MITRAL REGURGITATION

INTRODUCTION

Mitral regurgitation (MR) can be classified into two major etiologic categories: primary (degenerative) and secondary (functional). Primary MR is a consequence of disease affecting the leaflets or chordae tendineae, such as in mitral valve (MV) prolapse, myxomatous degeneration, infective endocarditis, or rheumatic disease. These disease processes are discussed in Chap. 48. In secondary MR, leaflet structure is normal and the valve is more of an “innocent bystander.” Regurgitation results from a distortion of the normal spatial and functional relationships of the left ventricle (LV) and valve apparatus, usually as a consequence of adverse LV remodeling. The trigger for LV remodeling can be ischemic (following myocardial infarction [MI]) or nonischemic (as with dilated cardiomyopathy) (Fig. 49–1). This chapter will focus on chronic ischemic MR (IMR) and will not discuss acute severe MR caused by papillary muscle rupture in the acute/subacute phase of MI.

INCIDENCE

The reported incidence of IMR following MI has ranged from 19% to 50%.^1,2,3,4 Estimates vary in relation to the nature of the screening techniques utilized. Of 1209 patients with coronary artery disease (CAD) amenable to coronary artery bypass grafting (CABG) and LV ejection fraction (LVEF) ≤ 35% enrolled in the Surgical Treatment for Ischemic Heart Failure (STICH) trial, mild, moderate, and severe MR were present in 46%, 15%, and 3% of patients, respectively.⁵ It is estimated that IMR affects 1.6 million to 2.8 million patients in the United States.⁶

STAGES

Analogous to, but somewhat different than, other types of valvular heart disease, the natural history of IMR can be considered across four overlapping stages:

• Stage A: “At-risk” stage (eg, early following MI).

• Stage B: Symptomatic progressive stage (eg, during the phase of active LV remodeling).

• Stage C: Asymptomatic severe stage (prior to onset of heart failure [HF] symptoms).

• Stage D: Symptomatic severe stage (following onset of HF symptoms).

Descriptions of valve anatomy, valve hemodynamics, associated cardiac findings, and symptoms for each stage are presented in Table 49–1. Boundaries between these stages are not rigid and patients with moderate IMR may also develop HF symptoms (see below and Table 49–1 and Table 49–2 for definitions of moderate and severe ischemic MR). Angina may also be a feature of the disease process.