Surgical repair for post-infarction papillary muscle rupture: where do we stand?

Mechanical complications following acute myocardial infarction (AMI) are associated with significant morbidity and mortality. Fortunately, these complications are rare and have become even rarer following the advent of percutaneous coronary intervention. Nevertheless, case fatality rates for post-AMI mechanical complications have remained largely unchanged, even despite increased use of mechanical circulatory support and refined surgical techniques [1]. Papillary muscle rupture (PMR) with resultant acute mitral regurgitation is one of the mechanical complications following AMI, with an in-hospital mortality rate reported to be between 10% and 40% [2]. Most of the literature on this topic has been in the form of small single-centre retrospective studies. As such, several questions remain to be answered, such as timing of surgical intervention, role of temporary mechanical circulatory support, optimal surgical technique, and impact of concomitant CABG. In this issue of the Journal, Massimi et al. [3] investigate patient characteristics and early outcomes of surgery for 214 patients with post-AMI PMR and severe mitral regurgitation. Their study included patients from 2001 to 2019 across 18 centres, using a database from a previous retrospective international multicentre study. The primary outcome was in-hospital mortality. Of the 214 patients, 67.3% had complete PMR and 15% had concomitant ventricular free wall or septal rupture. Sixty percentage were supported with an intra-aortic balloon pump preoperatively, while extracorporeal membrane oxygenation was utilized in <5%. A total of 82.7% of patients underwent mitral valve replacement (58.4% bioprosthetic, 41.6% mechanical), and 57% underwent concomitant CABG. A total of 64.5% of patients were operated on an emergent/salvage status, with <10% undergoing surgery after 1 week from diagnosis. In-hospital mortality was 24.8% and did not improve over time in the 18-year study period. On multivariable analysis, cardiac arrest and cardiopulmonary bypass (CPB) time were independent predictors of in-hospital mortality, while concomitant CABG was an independent predictor of early survival. This multicentre study, with its relatively large sample size, contributes significantly to the existing literature on surgical outcomes of post-AMI PMR. The analytic methods applied are rigorous, with an internally validated multivariable regression model, which incorporates clinically important variables and accounts for multicollinearity. The authors address many of the unanswered questions regarding surgical technique, temporary mechanical circulatory support and concomitant CABG. They also review the previous literature on this topic, putting their work into the context of prior studies. Interestingly, this study found that the site (posteromedial versus anterolateral) and type (complete versus partial) of PMR did not impact the odds of early mortality, nor did the surgical technique (mitral valve replacement versus repair). Patients with complete rupture tend to have a rapid clinical deterioration while those with partial may have a more subacute, stable presentation. As the authors point out, there may have just been too few patients with partial rupture to detect a difference in mortality. As far as technique, chordal sparing mitral valve replacement remains the standard, but there is a paucity of comparative data for valve replacement versus repair strategies. CPB time should be taken into consideration when choosing a technique, especially given its association with increased mortality demonstrated in this study. As for other mechanical complications of AMI, the optimal timing from diagnosis to surgery has not been fully determined, though urgent repair for PMR is typically indicated. TMCS, particularly in the form of intra-aortic balloon pump, can help bridge these patients to surgery by providing preload and afterload reduction. Concomitant CABG during surgery for PMR and for other mechanical complications of AMI may be associated with improved outcomes; however, this remains to be fully understood. In this study, CABG was associated with improved early survival. Prior series have reported similar or improved operative mortality when concomitant CABG is performed, while other studies have not found it to be a significant predictor of overall survival. Studies on post-AMI ventricular septal defect repair have suggested that complete revascularization at the time of surgical repair may be associated with improved survival, while incomplete revascularization may be associated with increased mortality [4–6]. The latter may prolong operative and CPB times while under-treating coronary artery disease, thus potentially decreasing the likelihood of cardiac recovery. Altogether, this study contributes significantly to the understanding of short-term surgical outcomes of post-AMI PMR. Additional investigation regarding long-term outcomes is warranted, as there have only been a handful of small studies [7].