Distinction of thrombus from pannus formation as underlying causes of mechanical prosthetic valves obstruction: clinical and transesophageal echocardiographic criteria

Mechanical prosthetic valves obstruction could be caused by thrombus or pannus formation. Distinction between thrombus and pannus formation as the underlying etiology of valve obstruction is essential because thrombolytic therapy has emerged as an alternative to reoperation. The aim of this study was to determine the clinical and transesophageal echocardiographic [TEE] criteria that differentiate thrombus from pannus formation as the etiology of mechanical prosthetic valves [PVs] obstruction. 28 consecutive patients with obstruction of mechanical PVs detected by TTE Doppler who underwent a TEE just prior to surgical redo valve replacement [reoperation] were retrospectively studied. Patients with suspected infective endocarditis, double valve replacement, both thrombus and pannus and patients who were not found at surgery to have thrombus or pannus formation were excluded from the study 18 patients had prosthetic mitral valves [MVs] and 10 patients had prosthetic aortic valves [AoVs]. All the patients studied had mechanical prosthetic bileaflet tilting disc valves. All the patients had surgical confirmation of thrombus or pannus. Surgical results revealed that the underlying cause of obstruction was thrombus in 17 patients [60.7%] [Group I] and pannus formation in 11 patients [39.3%] [Group II]. In conclusion, clinical criteria are helpful in differentiating thrombus from pannus formation in obstructed mechanical prosthetic valves. Clinical criteria show that patients with thrombus have frequent recent thromboembolism, shorter time from valve insertion to malfunction, shorter duration of progression of symptoms of heart failure [HF] and inadequate antico-agulation compared to patients with pannus formation. The use of TEE identifies the mechanism and etiology of PVs obstruction. TEE criteria show that thrombus is larger, often has a mobile portion and often extends into the LA in prosthetic MVs and with softer ultrasound intensity compared to pannus formation. It is recommended that combination of clinical criteria and TEE criteria should be used for the differentiation of thrombus from pannus formation. This differentiation is essential in refining the selection of patients for thrombolytic therapy, since pannus formation is an indication for immediate surgery without prior thrombolytic therapy, particularly when presenting with homodynamic instability