Cardiac metastasis is considered extremely rare with an incidence of 1.2% and often remains silent until autopsy [1, 2]. The most common origins of cardiac metastatic tumors are adjacent organs, including the lung, breast, and esophagus. Cardiac metastasis as the first site of metastasis is reported only in isolated cases. These tumors usually accompany other multi-organ seedings of the primary tumor and are often discovered by autopsy.
The most common sites of metastasis from gastric adenocarcinoma are the liver, peritoneum, lung, and bone. Cardiac metastasis with the origin of gastric adecarcinoma has a very slight chance of occurrence. The chances of this event to be solitary are very minute. In a report of 476 consecutive tumor deaths with cardiac involvement, young JM demonstrated that only 2 cases had metastatic cardiac lesions while none were solitary cardiac metastasis; they suggested a hematogenous path of spread for the metastasis. In contrast, Bussani et al. showed that only 8% of autopsies with cardiac metastases had a gastric origin. They described gastric metastases to tend to infiltrate the pericardium more often. Again there was no report of solitary cardiac metastasis. KY Lam et al., in a report on 12,485 autopsies, found that cardiac metastases with gastric origin have an incidence of 4%.
To our knowledge, there are no reports regarding gastric adenocarcinoma with solitary cardiac metastasis on the right side of the heart; only Peter B et al. reported a 60 mm left-sided cardiac metastasis that probably originated from gastric adenocarcinoma in the patient. The unique feature of the current case is the thrombotic of the tumor, which is extremely rare, leading to the floating and hypermobility of the lesion. Adenocarcinoma metastases to the heart tend to infiltrate the pericardium via the lymphatic pathway.
Several mechanisms are suggested to contribute to the rareness of cardiac metastasis in malignancies; These include the rigorous motion of the myocardium, metabolic features of myocardial cells, rapid flow of blood through the heart, and adequate deep and superficial lymphatic drainage from the heart. Despite the mentioned mechanisms, cardiac metastasis may occur due to direct, hematogenous, lymphatic spread, transvenous or a combination of these pathways; Regarding the malignancies in adjacent organs such as the lung, the lymphatic spread is offered as the most probable route. The lymphatic route of spread most probably leads to pericardial involvement, but in our case, considering the site and features of the metastatic mass in the right side of the heart (right atrium) with no infiltration, we assume it as a transvenous metastasis. The mechanism can be explained through seeding of the tumor cells from stomach into portal veins, liver, inferior vena cava and eventually atrium.
Cardiac metastatic lesions are only 10% symptomatic. In previous literature, the first sign of cardiac cavity metastatic tumor reported as progressive dyspnea, as in our case, the patient had NYHA class III-IV dyspnea with sufficient O2 Saturation and increased respiratory rate. Due to covid-19 pandemic, first diagnosis was the viral acute respiratory syndrome. But in the next stage the reverse transcriptase chain reaction test for covid-19 RNA showed negative results. Absence of other covid-19 infection symptoms,and the suspicion to cardiac causes due to hemodynamic changes, convinced us to perform transesophageal echocardiography that revealed the tumor in the right atrium. Other initial symptoms are hypotension, muffled heart sound in auscultation, tachycardia, arrhythmia, cardiomegaly, heart failure, and in one report, jugular vein distension and pulsus paradox[1, 11, 12]. The symptoms result from tumor obstructive mass effect in the atrial inlet, atrial cavity, inside the tricuspid valve and right ventricle, or other related infiltrative complications such as pericardial effusion or even cardiac tamponade.
Solitary metastasis to the heart is extremely rare, and cardiac metastasis is observed more frequently in autopsy studies of patients with extensive multi-organ metastases. The cardiac myxoma (benign primary cardiac tumor) is considered as the top differential diagnosis of solitary cardiac metastasis in the atrial cavity. Others include vegetation and thrombosis. In the presented case, the preoperative diagnosis was established via trans-esophageal echocardiography as a floating mass compatible with thrombi that later was observed in the IHC study to be a gastric adenocarcinoma metastasis. It is suggested that late gadolinium-enhanced cardiac MRI studies can help to improve the diagnosis and depth of tumor infiltration because it provides a definite distinction of heart layers from the tumor and limits the differential diagnosis. Besides MRI, in one study, Computed Tomography could detect the extent of a left-sided cardiac metastatic tumor of unknown origin with adjacent nodular densities .
Choi et al. discussed that with recent advances in diagnosis techniques, the incidence of cardiac metastasis would increase, urging the need for standard guidelines for diagnosis and treatment options of cardiac metastasis. Cardiac metastatic tumors yield an abysmal prognosis in the affected patients. The obstructive mass, low cardiac input and consequently low output, hypotension, possible arrhythmia, and in some cases pericardial effusion and tamponade —as mentioned above— and finally hemodynamic instability urges the immediate action for removing the metastatic mass to save the patient’s life. Due to complicated surgical procedures and compromised patient factors, this procedure is associated with an extreme risk of bleeding, ventricular dysfunction, tumor cells seeding, or death in some cases. However, several authors have suggested surgery to be helpful, particularly in solitary metastatic tumors, to relieve the symptoms or palliation [10, 11, 14]. In cases of inoperable cardiac tumors, it is worth considering palliative chemotherapy to shrink the size, maintain the cardiac output and increase survivability[10, 11].