Pulmonary congestion is a powerful prognostic factor for the detection of adverse cardiovascular events, including death, in patients with STEMI (Killip and Kimball, 1967). In addition, the presence of pulmonary congestion increases the discriminatory capacity of scoring classifications such as Thrombolysis in Myocardial Infarction (TIMI) and Global Registry on Adverse Cardiovascular Events (GRACE) (Bedetti et al., 2010).

Lung ultrasound is a non-invasive, risk-free tool that has demonstrated to be superior when compared with physical examination for the detection of pulmonary congestion due to a higher sensitivity (Gopar -Nieto et al., 2019). However, the association between the degree of pulmonary congestion detected by LUS and cardiovascular outcomes in patients with STEMI has not been completely elucidated.

The objective of our study was to evaluate the association of pulmonary congestion assessed by LUS with cardiovascular outcomes in patients with STEMI.

From the total population included in the PHASE-Mx study, LUS was performed only in 329 of which 103 were excluded due to the following specific causes: 91 patients due to failed thrombolysis, six patients due to first contact time greater that 12 h, three patients due to previous heart failure, and three patients due to previous revascularization surgery. Therefore, the final analytic sample consisted of 226 patients. Baseline laboratory characteristics were taken at hospital admission, while lung ultrasound was performed at any time after revascularization and within 24 h from the symptom onset. There were 49 (21.6%) patients classified within the “LUS-congestion” group and 177 (78.3%) within the “non-LUS-congestion” group (Figure 2). Baseline characteristics of the study population stratified by presence or absence of LUS congestion are summarized in Table 1. Compared with patients in the “non-LUS-congestion” group, patients in the “LUS-congestion” group were older (61.51 vs. 57.23 years, p = 0.015) and had higher levels of blood urea nitrogen (21.22 vs. 17.75 mg/dl, p = 0.023) and NT-proBNP (3,488.01 vs.1377.04 pg/ml, p < 0.001).

Patients in the LUS-congestion group had higher TIMI, GRACE and CRUSADE scores compared to patients in the non-LUS-congestion group. The total ischemic time was not different between patients with and without pulmonary congestion (median time: 316 vs. 282 min, respectively, p = 0.169). A higher proportion of patients with LUS congestion (55.3%) were classified as Killip-Kimball class (KKC) >I compared with patients in the non-LUS- congestion group (30.4%) (p < 0.001).

In the present study, pulmonary congestion assessed by LUS in patients with STEMI was associated with a higher frequency of adverse cardiovascular events, particularly acute HF and cardiogenic shock.

The interest in the use of LUS as a non-invasive tool for semi-quantification of pulmonary congestion has grown in recent years (Platz et al., 2017; Picano et al., 2018). LUS has demonstrated to be superior in the detection of pulmonary congestion in patients with HF, showing a higher sensitivity when compared with physical examination or chest X-ray (Pivetta et al., 2019; Araiza-Garaygordobil et al., 2021b). Furthermore, studies including patients with chronic or acute decompensated HF have demonstrated that LUS derived B- lines have an important prognostic role for the detection of HF-derived events, such as rehospitalizations or cardiovascular mortality (Miglioranza et al., 2017; Rivas-Lasarte et al., 2019; Araiza-Garaygordobil et al., 2020). This prognostic role exceeds that of other commonly used congestion evaluation parameters such as clinical examination or concentrations of natriuretic peptides (Miglioranza et al., 2013).

Acute HF after MI is a potentially serious complication that increases mortality. Detection of signs of HF after MI allows the identification of a subgroup of patients with worse prognosis. Reduced left ventricular ejection fraction, increased concentrations of natriuretic peptides, increased pulmonary capillary wedge pressure (using a pulmonary flotation catheter), and physical examination showing signs of HF (lung crackles, presence of a third heart sound, jugular vein distention or peripheral oedema) have all been associated with increased hospital mortality after MI (Platz et al., 2017; Öhman et al., 2018; Ye et al., 2019). LUS may complement the findings of the aforementioned techniques with additional advantages such as low cost, bedside availability and no associated risks. Recently, a prospective observational study (Araujo et al., 2020) documented the prognostic ability of admission LUS in 215 patients with STEMI. The investigators reported an area under the ROC curve of 0.89 for in-hospital mortality and a 0.18 net reclassification improvement over the KKC. It is worth mentioning that absence of pulmonary congestion detected by LUS implied a negative predictive value for in-hospital mortality of 98.1%. Likewise, our study shows consistent results, with an increased risk of adverse outcomes seen in those patients showing LUS congestion.

There are some limitations in our study. One of the most important limitations is that our study may be influenced by selection bias. As our Institute is a reference center, it is possible that some patients, who were unable to be transferred because of instability or who could have died before reaching our center, were not registered in our study. This would explain a relatively low frequency of some risk factors of adverse events, manifested by the low frequency of stage III or IV of the KKC, and lower TIMI score values. There is a small difference, with no statistical significance, in the pulmonary congestion group, as more received primary PCI. This could be related to the administration of contrast; unfortunately, we do not have the amount of contrast administered in each study. Although there is a difference mortality, it is not statistically significant, which may be determined by the relatively small sample size.

Lung ultrasound was performed after reperfusion therapy, and although the type of reperfusion strategy is balanced between both groups, we believe it may be one of the factors that influenced the limitation to predict mortality. To date, we do not know the influence of timely reperfusion on the presence and variation of the number of B-lines in STEMI patients. Nonetheless, a statistically significant association between the presence of B-lines in STEMI and major adverse endpoints during hospital stay was found, which strengthens the importance of pulmonary congestion among patients with STEMI, even after adequate reperfusion therapy was received.

LUS is a readily available, risk-free diagnostic tool that predicts adverse cardiovascular events in patients with STEMI. The application of this technique should be integrated as part of the initial risk stratification protocol for all patients with suspected STEMI as it conveys important prognostic information.