Answer: C

The ECG showed atrium-ventricular (AV) dissociation with narrow QRS complex escape at 40 bpm, findings which are compatible with complete AV block and not with Mobitz II second-degree AV block (figure 2A).

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Figure 2

(A) ECG showing that atria activity (p waves→blue arrows) is independent of the ventricle activity (QRS complex→red arrows), suggesting atrium-ventricular (AV) dissociation which is a typical finding of complete AV block. (B) Long-axis parasternal view from the transthoracic echocardiogram (TTE) showing hyperechogenic nodular image infiltrating the lateral wall of the left atrium (yellow arrow). (C) Four-chamber view from the TTE showing hyperechogenic nodular image infiltrating the roof from the right atrium and the interatrial septum (yellow arrows).

On the other hand, the patient did not feel chest pain, the ECG also showed no changes in repolarisation, and the serial determination of markers of myocardial damage (creatine kinase, troponin I) was negative, which rules out a non-ST elevation myocardial infarction.

In the TTE we observed a hyperechogenic nodular image infiltrating both atria and thickening of the interatrial septum (figure 2B,C). The fact that the image infiltrates underlying tissue, affecting several cardiac chambers, increases the likelihood of a malignant process and it made less likely that it was a benign tumour like myxoma (characterised by a pedunculated and mobile image in any of the atria without infiltration).

Although our first impression was a malignant process that was infiltrating the heart, a thoracic CT was performed, first to rule out pulmonary embolism, which was discarded, and second to characterise better the image observed in the TTE. The CT findings supported that with high probability it was a lymphoproliferative process (online supplementary figure 1).

Unfortunately, on the sixth day of admission, the patient died, and the autopsy confirmed that it was a diffuse large B-cell type lymphoma (online supplementary figure 2).

Of all primary cardiac tumours, lymphomas are extremely rare and type B is the most prevalent.1 2 They usually remain asymptomatic until the very advanced stages of the disease. Atrial arrhythmias and conduction abnormalities are not very common, each occurring in approximately 25% of patients.3 TTE is the tool that establishes the diagnosis of suspicion and CT provides more information about the type of tumour (eg, vascularisation, necrosis).4 But despite all the diagnosis of certainty is always histological.