Acute total occlusion of the unprotected left main coronary artery (LMCA) is usually a catastrophic event with a dismal presentation. Owing to the amount of affected myocardium, it often leads to abrupt severe circulatory failure, malignant arrhythmias and sudden cardiac death. As such, these patients represent a group with very high risk of mortality.

There are limited and inconsistent data regarding this population, mostly confined to small observational studies, most of which also include patients with subtotal occlusion of the LMCA.1–7 Thus, clinical management of these patients represents a particular challenge.

The objectives of our study are to describe the clinical presentation and outcomes of patients with acute total occlusion of the LMCA and to determine predictors of in-hospital mortality in these patients.

We performed a retrospective multicenter study that identified patients with ST-elevation myocardial infarction (STEMI) or high-risk non-ST-elevation myocardial infarction who underwent emergent coronary angiography between January 2008 and December 2020 in three tertiary hospitals. Among this cohort, patients with acute total occlusion of the LMCA (thrombolysis in myocardial infarction [TIMI] flow 0) were included in the study.

We excluded patients with subacute (>12 h) presentation, subtotal LMCA occlusion, previous LMCA angioplasty, previous coronary artery bypass grafting, or iatrogenic LMCA occlusion. Patients with acute aortic or coronary dissection or infective endocarditis were also excluded.

Data on demography, clinical features and outcome were collected from all in-hospital and clinical records.

In each center an interventional cardiologist was responsible for reviewing the coronary angiograms performed in their respective center. These investigators were blinded to all other patient data.

Variables assessed included the presence of cardiogenic shock at admission, defined as the presence of sustained hypotension (systolic blood pressure <90 mmHg lasting ≥30 min) or the need for support to maintain systolic blood pressure >90 mmHg, associated with signs of end-organ hypoperfusion including cool extremities, oliguria (<30 ml/h) and altered level of consciousness.8

Coronary collateral circulation was graded according to Rentrop's classification: grade 0, no filling of the occluded vessel; grade 1, filling of the side branches; grade 2, partial filling of the epicardial vessel; or grade 3, complete filling of the epicardial vessel.9

Angiographic success was defined as residual stenosis <30% with TIMI flow 3.

The study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki as reflected in prior approval by the institution's human research committee.

There is a paucity of data regarding patients with true acute total occlusion of the LMCA. Most of the existing literature includes patients with subocclusion or severe stenosis of the LMCA. To our knowledge, there are only two retrospective studies that exclusively included patients with true occlusion of the LMCA (TIMI flow 0).2,3

In our study, acute total occlusion of the LMCA was an uncommon event, accounting for less than 1% of acute coronary syndromes undergoing emergent coronary angiography. This is lower than reported in most studies, as patients with LMCA subocclusion or severe stenosis were often included.1,5,10–12 Although rare, this figure is likely to be underestimated, as only patients undergoing angiography were included in our study.

We observed that acute total occlusion of the LMCA occurred in a relatively young population of patients. Importantly, only a few had known ischemic heart disease, and the prevalence of known cardiovascular risk factors was relatively low. This may indicate difficulty in identifying patients at risk of suffering such dramatic events and the need to develop tools to improve individual cardiovascular risk stratification among the general population. The ominous nature of true acute LMCA occlusion makes this particularly relevant: our study showed that most patients present with cardiogenic shock and frequently suffer cardiac arrest during the acute phase of the event. A high degree of suspicion for acute total occlusion of the LMCA is needed in this clinical scenario, as prompt management may be critical for patient outcomes.

Regarding angiographic and procedural data, we observed that a significant proportion of patients with acute total LMCA occlusion did not achieve angiographic criteria of success. These results are in line with previous reports3 and are significantly worse than those reported in patients with STEMI13 and among patients who undergo elective angioplasty of the LMCA.14,15 This may be partly explained by functional and structural microvascular obstruction, which is demonstrated to occur frequently in STEMI patients despite epicardial recanalization of the culprit vessel, and may be particularly prominent in the setting of acute LMCA occlusion.16 However, evidence-based strategies targeting microvascular dysfunction are lacking.17 A randomized trial comparing the effect of deferred versus conventional immediate stenting on clinical outcomes of patients with acute occlusion of the LMCA is underway.18 This is relevant, as stenting of the LMCA was associated with a non-significant increase in in-hospital mortality in our study. As angiographic success appears to be one of the main determinants of in-hospital mortality in patients with acute total occlusion of the LMCA, every effort should be made to achieve this goal. Consistent with the reported literature, we did not observe any case with left dominance, which supports previous suggestions that this presentation may be incompatible with life.19

Our study revealed high in-hospital mortality, with most deaths occurring very early during hospitalization. This is consistent with recent2,3,12 as well as older reports.1,7,20 As in these studies, this mortality may be underestimated, as patients who died before reaching the catheterization laboratory were not included in our analysis. Despite clinical and technological advances in recent decades that have led to significant prognostic improvement in patients with STEMI,21 acute LMCA occlusion remains associated with poor prognosis. On the other hand, as in previous reports,1–4,6,19,22–24 patients surviving the index hospitalization had a favorable prognosis, with a five-year survival of nearly 70%. Hospitalizations for heart failure or subsequent acute coronary event were low.

After adjusting for confounding variables, the independent predictors of in-hospital mortality were cardiogenic shock at presentation and achievement of angiographic success. These results highlight the poor prognosis associated with cardiogenic shock, reflecting the importance of balancing aggressive hemodynamic support with the need to promptly and adequately restore coronary blood flow.

Temporary MCS devices may be important for improving patient outcomes, but the lack of randomized data creates difficulties regarding patient selection and management. In our study, the use of MCS was not a predictor of in-hospital mortality, while implantation of MCS prior to PCI was associated with a non-significant increase in in-hospital mortality. The retrospective nature of our analysis and small sample size limit conclusions regarding this issue. Overall, acute management of patients with acute occlusion of the LMCA is still a challenge that needs to be overcome.

There remains some controversy regarding the impact of early recruitment of collateral circulation on outcomes in STEMI patients.25,26 Among patients with acute total occlusion of the LMCA, data are lacking on this subject. It has long been suggested that the presence of a well-developed collateral circulation may be an important predictor of survival in this clinical scenario.7,19,27 Our study found that patients with well-developed collateral circulation (Rentrop score ≥2) had a significantly lower prevalence of cardiogenic shock at presentation, highlighting its role in these patients. However, collateral circulation was not an independent predictor of in-hospital mortality after adjustment for confounding variables. Further studies are needed in order to elucidate the role of collateral circulation in patients with acute total occlusion of the LMCA.

There was no in-hospital mortality recorded among patients who underwent CABG. These results may reflect a subgroup of patients who were more stable and able to undergo this procedure, which is generally not an option in highly unstable patients.

Acute total occlusion of the LMCA is an uncommon event associated with a catastrophic presentation. Most patients present in cardiogenic shock and many suffer cardiac arrest. In-hospital mortality is high and often occurs during the first day of admission. Cardiogenic shock and achievement of angiographic success criteria play a major role in predicting the outcome of these patients. However, the latter is not achieved in almost half of procedures. There is a need to better define the role of MCS in this challenging clinical scenario.

None to declare.

The authors have no conflicts of interest to declare.