Under physiological conditions, the pericardial cavity contains a small amount of liquid (approximately 50 ml). Pericardial effusion is excess liquid in the pericardial cavity [1]. Malignant tumor is a common cause of pericardial effusion, either during invasion or treatment of the tumor [2]. Pericardial effusion, as a serious complication in patients with advanced cancer, is significantly associated with reduced survival [3]. The diagnosis of malignant pericardial effusion (MPE) is often associated with a poor prognosis, but due to the complexity and unspecific nature of MPE patients' clinical manifestations, imaging often performs an essential role in diagnosis and prognosis [4].

Accordingly, in this study, we analyzed the clinical data of 216 patients diagnosed with MPE and explored the prognostic factors affecting MPE to provide a reference and guidance for the clinical diagnosis and management of MPE.

MPE is a serious complication of advanced malignant tumor patients and indicates a poor prognosis [7]. This report describes a study with a large number of patients with MPE. The primary cancers that cause MPE were mainly lung cancer, breast cancer and esophageal cancer, which were similar to reports from other studies [8]. This systematic summary and analysis of the basic clinical features, imaging findings, treatments and prognoses of MPE will help to enhance physicians’ comprehensive understanding of the disease.

The normal pericardial cavity contains up to 50 ml of liquid, and cancer cells can invade the pericardial cavity by direct invasion or by blood or lymphatic metastasis, resulting in a large amount of malignant liquid accumulation. The clinical manifestations of MPE patients are related to the rate of fluid accumulation. When pericardial fluid accumulates rapidly, only 200 ml of liquid will cause significant hemodynamic changes [9]. When pericardial fluid slowly increases, the pericardium slowly relaxes without significant changes in pericardial cavity pressure. Even if the pericardial cavity contains up to 2000 ml of fluid, the patient may have no obvious clinical symptoms [10]. Therefore, the clinical manifestations of MPE patients lack specificity. This study showed that the most common symptom of MPE was dyspnea (62.9%), which may be related to pericardial fluid accumulation and impaired ventricular filling. According to the physical examination results, 74.9% (131/175) of patients had signs of pericardial fluid, but only 21.7% (38/175) had a specific clinical manifestation of chest pain, further confirming the complexity and diversity of MPE clinical manifestations.

Abnormal ECG changes in patients with MPE are usually associated with myocardial injury and pericardial effusion under the pericardium. Common abnormal changes are ST-T segment abnormalities, sinus tachycardia, low QRS voltage and electrical alternation [11]. Abnormalities in the ST-T segment can reflect the extent of myocardial damage. This study showed that 28.2% (61/216) of patients had ST-T segment abnormalities, which we presumed to be related to direct tumor invasion and pericardial hydraulic compression. Regardless of the cause of effusion, effusion itself causes a conduction short circuit, resulting in a low voltage. This study showed that only 17.6% (38/216) of patients had low QRS voltage. Studies have shown that a low QRS voltage is not directly related to effusion itself and is associated with a decrease in left ventricular stroke power caused by fluid accumulation [12].

Sinus tachycardia is the most common compensatory mechanism in patients with pericardial effusion. As the amount of fluid increases, diastolic function is limited, ventricular filling is reduced, ejection fraction decreases, and the compensatory heart rate increases. These are also the most common abnormal electrocardiogram findings in MPE patients. Our study showed that 42.1% (91/216) of patients developed sinus tachycardia, which is slightly lower than in previous reports [13]. This may be related to the reduction in sinus node function caused by treatments such as radiotherapy and chemotherapy. Alternate or arbitrary combinations of P, QRS, ST, or T waveforms are specific ECG findings in a large number of patients with pericardial effusion. This study showed that 21.3% (46/216) of patients had evidence of electrical alternans. And other studies have shown that electrocardiographic evidence of electrical alternation has lower sensitivity in the diagnosis of pericardial effusion [14].

Echocardiography is the sensitive imaging technique for detecting pericardial effusion, and it perfectly shows a large number of pericardial effusion features [15]. And chest CT also has an irreplaceable advantage in the diagnosis of pericardial cavity occupation [16]. In our study, although chest CT had a diagnostic rate of only 79.4% for MPE yet it didn't indicate that the diagnostic efficacy of CT was weaker than that of echocardiography. It was difficult to ensure that all imaging examinations were performed within the same disease stage for each patient, so the corresponding positive diagnostic rates were not highly comparable. We speculated that the low diagnostic rate might be due to the fact that patients with tumors underwent routine chest CT at an early stage without demonstrating the pericardial effusion at that time. Diagnostic efficacy aside, compared to chest CT, echocardiography provides additional information on the impairment of cardiac function due to pericardial effusion [17].

This study confirmed the unsatisfactory prognosis of MPE. The in-hospital mortality rate was 9.3% (20/216), and the 5-year mortality rate after discharge was 46.8% (101/216). The Cox regression results showed that echocardiographic fluid signs (HR = 2.37, P = 0.010), electrocardiographic evidence of sinus tachycardia (HR = 1.76, P = 0.006) and echocardiographic evidence of cardiac tamponade (HR = 3.33, P < 0.001) had a significant relationship with patient survival. Moreover, they were all independent factors influencing the survival of patients. The treatment methods recorded in this study are more directed to the treatment of primary disease. It has been reported that systemic chemotherapy may be effective for lymphoma and breast cancer, and pericardial chemotherapy is the preferred treatment for lung cancer [18].

Lung cancer, a malignancy with high morbidity and mortality, was also the highest proportion of primary cancer type in this study. In recent years, the role of immune checkpoint inhibitors in the treatment of pericardial effusion caused by lung cancer is gradually being revealed. Cai et al. observed that immune checkpoint inhibitor, represented by nivolumab, reduced pericardial effusion in patients with advanced non-small cell lung cancer after 11 cycles of treatment [19].

As a single-center investigation, this study has limitations and the conclusions require confirmation in a large sample and multi-center trial. In addition, the results of imaging examinations that are not included in the same disease stage may restrict the comparison of diagnostic efficacy.

In summary, MPE has complex clinical manifestations, an unsatisfactory prognosis, and a lack of effective treatment. Due to the relatively low incidence of the disease, more clinical studies are needed to determine the risk factors for and to predict the incidence of the disease in order to achieve early diagnosis, individualization and comprehensive treatment for MPE.