Discussion
Our results demonstrated that RV dysfunction is an important clinical feature in COVID-19 pneumonia patients with ARDS, which is related to the severity of COVID-19 pneumonia and ARDS. Bedside echocardiography allows an early integrated assessment of the RV function through the evaluation of TAPSE. The echocardiographic parameters of RV function and cardiac cavity in COVID-19 pneumonia patients show abnormity to different extents compared to healthy subjects.
Viral pneumonia is the one of the most common causes for ARDS and is associated with high morbidity and mortality worldwide, such as SARS, H1N1 flu and so on [13-15]. RV dysfunction is frequently presented in these patients, and leads to left-right asymmetry of the heart, which can worsen hemodynamic stability and is associated with a poorer prognosis [6, 16, 17]. In our study, a higher incidence of RV dysfunction was found in critically severe group who had more severe ARDS patients, which is similar to that in the severe ARDS population caused by SARS and H1N1 viruses [15, 18, 19]. Thus, RV dysfunction is common in viral pneumonia patients, especially in patients with severe ARDS.
TAPSE, as the most commonly used index for evaluating RV function, has been widely used in patients with ARDS [20]. A TAPSE less than 17 mm was recommended as a major parameter of RV dysfunction by ASE guidelines. In present study, we found the TAPSE in patients with COVID-19 pneumonia was significantly decreased compared to healthy people, and the proportion of patients with TAPSE <17 mm was significantly higher in critically severe patients (35.7%) than that in severe patients (8.6%), indicating that there was a correlation between the occurrence of RV dysfunction and the severity of COVID-19 pneumonia. Patients in critically severe group appeared to be more severely ill in terms of APACHE II, decreased MAP and increased HR. Moreover, invasive ventilation and vasopressors are frequently required in these patients.
The function of the RV is to keep proper pulmonary perfusion pressure and systemic venous pressure to maintain normal blood flow [21]. The main factors affecting the RV function in patients with ARDS are impaired RV contraction and increased pulmonary vascular resistance. It is known that the increase of pulmonary vascular resistance may be induced by vasoconstrictor, hypoxemia, hypercapnia, acidosis and so on, which cause the deterioration of right heart structure and function [22-24]. Recent studies have shown that the clinical characteristics of severe and critically severe COVID-19 pneumonia patients are severe hypoxemia, hypercapnia and microthrombosis, which may lead to the increase of pulmonary vascular resistance [3-5].
In our study, the values of TRPG and PASP were higher than normal ranges and increased in COVID-19 pneumonia patients. Although the majority of patients in critically severe group received mechanical ventilation, there were no significant differences in TRPG and PASP between the severe and critically severe patients. This may be because pulmonary vascular resistance is reduced by positive pressure mechanical ventilation and is not seriously deteriorated in the early stages of the disease [25-27]. The right heart had a poor ability to regulate pressure load [16]. In this study, the right heart cavity and pulmonary artery were enlarged soon after the increase of pulmonary vascular resistance in patients with COVID-19 pneumonia.
Patients with critically severe COVID-19 pneumonia are often accompanied by organ dysfunction and shock. The results of the present study have shown that both RV and left ventricular systolic function in critically severe patients with COVID-19 pneumonia are impaired. The hemodynamic instability of decreased LVEF and MAP is associated with more severe RV dysfunction, which present significantly decreased TAPSE, enhanced diameters of IVC and reduced ICV-CI. Therefore, the monitoring and protection of right ventricular function need to be strengthened in the management of patients with COVID-19 pneumonia. There are limitations in the present study. This is a retrospective study with limited sample size. The results need to be further confirmed by prospective clinical studies. In addition, although the assessments of echocardiography were performed by ultrasonologist, it became more challenged and difficult than usual to obtain parameters since three-level isolation and protection measures must be taken when contacting patients with COVID-19 pneumonia. However, in this case, echocardiography is the most important bedside examination method for evaluation of patients with COVID-19 pneumonia.