Intraoperative detection of left atrial clot using transoesophageal echocardiography in a patient undergoing off-pump coronary artery bypass grafting

Editor, Thrombus in the left atrium or left atrial appendage (LAA) or both is associated with an increased risk of patient morbidity and mortality [1]. If it remains undetected in the preoperative period, this can be life-threatening in patients undergoing coronary artery bypass grafting (CABG) where the heart is distorted while performing graft anastomoses. We present a case of incidental detection of LAA thrombus during intraoperative transoesophageal echocardiography (TOE) in a patient undergoing off pump CABG (OPCAB) resulting in change of surgical technique and subsequent management. A 65-year-old man, weighing 67 kg, presented with dyspnoea on exertion for 3 days with no associated complaint of chest pain, syncope or palpitation. He had a past history of type 2 diabetes mellitus and a family history of coronary artery disease (CAD). Twelve hours after admission, the patient developed atrial fibrillation with a fast ventricular rate (heart rate 150–160 min−1) and blood pressure (BP) of 104/56 mmHg that was treated with an intravenous bolus of amiodarone (150 mg) followed by its infusion at 60 mg h−1. Sinus rhythm was restored after 4 h. Intravenous unfractionated heparin was started at 1000 IU h−1. The patient had raised troponin T and creatinine kinase-MB levels. Transthoracic echocardiography revealed a left ventricular (LV) ejection fraction of 40–45%, hypokinesia of the inferior wall, pseudonormal diastolic dysfunction, mild mitral regurgitation, normal cardiac chamber dimensions, and no clot/vegetation/pulmonary embolism. Coronary angiography revealed triple vessel disease with involvement of the left main coronary artery (60%). The patient was scheduled for elective OPCAB. Meanwhile, he was medically optimized. The preoperative examination revealed a conscious alert and anxious person with BP of 136/80 mmHg and normal sinus rhythm. His cardiovascular examination was normal, whereas respiratory examination showed bilateral coarse crepitations on auscultation. Electrocardiogram revealed ST elevation in leads I, II, V5, and V6. Haematological and biochemical markers were unremarkable. Heparin infusion was stopped 6 h prior to surgery. The patient was premedicated with pantropazole 40 mg and lorazepam 2 mg the night before and on the day of surgery. A standard opioid-based anaesthesia technique was used. After induction of anaesthesia, a TOE probe was inserted atraumatically. Initial TOE examination revealed an ejection fraction of 35–40%, with lateral, anterior, and inferior wall hypokinesia, mild mitral regurgitation, no mitral stenosis and a mass in the LAA. Detailed examination of this mass revealed its size (18 mm × 14 mm) (Fig. 1) and a point of attachment in the LAA, whereas the rest of the portion was mobile. Immediately, the operating surgeon was informed. After reviewing the TOE images, it was decided to perform the surgery on cardiopulmonary bypass (CPB) instead of the earlier plan of OPCAB. TOE monitoring was continued as the patient was being prepared to undergo CPB. Because of the heart manipulation at the time of inspecting target vessels, the clot become dislodged from the LAA and moved into the left atrium cavity. The left atrial clot was now freely mobile (Fig. 2) and this was brought to the notice of the surgeon. CPB was initiated immediately and the aorta was clamped. The LAA was incised and the left atrial mass was taken out with help of forceps while being monitored using TOE. Following CABG, repeat TOE revealed an ejection fraction of 40–45% with no clot in the left atrium/LAA. The bispectral index (BIS) was monitored throughout the procedure so as to rule out any embolic phenomenon during the procedure. There was no episode of sudden fall in BIS value. After the operation, the patient was moved to the ICU and was extubated after 6 h. His postoperative stay was uneventful with no evidence of neurological deficit. The histopathology report showed this mass to be thrombus in nature. Low-dose warfarin was started in the immediate postoperative period in view of preoperative atrial fibrillation.Fig. 1Fig. 2Discussion Left atrial thrombus primarily affects patients with mitral stenosis, especially those with atrial fibrillation. Its incidence among patients with sinus rhythm is reported to be only 0.1% [2]. Patients who are at risk of having left atrial or LAA thrombus or both in the absence of mitral stenosis are those with dilated cardiomyopathy [3], moderated to significant LV dysfunction (ejection fraction 35–40%), a history of atrial fibrillation, and a history of stroke or transient neurological deficit [2]. Our patient was in sinus rhythm at the time of surgery but had a brief period of atrial fibrillation immediately after admission to the hospital. However, the possibility of occurrence of atrial fibrillation in the past could not be ruled out. In addition, the patient had moderate LV dysfunction. As LV dysfunction is usually associated with an abnormal mitral flow pattern and reduced filling in the LAA, a patient is at risk of stasis of blood in the LAA [4]. Patients with LV dysfunction are at risk of developing thrombus in the LAA. As our patient had a history of atrial fibrillation, LV dysfunction, and stopping heparin prior to surgery, he was a potential candidate for developing thrombus in the LAA. Preoperative detection of left atrial/LAA thrombus is always desirable so that subsequent management can be planned accordingly. Preoperative transthoracic echocardiography in our patient did not reveal any thrombus. Heparin was stopped 6 h prior to the surgery; whether this could have initiated the development of thrombus in this patient is a matter for speculation. Perioperative use of TOE is considered as a category I indication for valve repair, complicated cardiac surgery, and for the evaluation of acute haemodynamic instability in both the operating room and ICU. On the other hand, its use in patients undergoing CABG is considered as category II [5]. Many people do not use TOE for low-risk surgery such as CABG using the OPCAB technique. This case highlights the value of doing TOE intraoperatively before starting the surgical procedure. It is also well known that TOE has higher sensitivity and specificity for detecting left atrial thrombus than transthoracic echocardiography [6]. Detection of left atrial thrombus altered the surgical technique used in our patient, that is, OPCAB was converted to on pump CABG. It also changed the patient's subsequent management in the ICU where low-dose warfarin was started immediately in the postoperative period. Therefore, we feel that TOE should be used in such a group of patients who are at high risk of developing thrombus in the perioperative period. We suggest that TOE should be used not only to diagnose the problem but also continuously while CPB is being initiated. As this case report showed, left atrial thrombus can dislodge from its site while the heart is being manipulated and can become freely mobile with high risk of embolization. Continuous TOE monitoring in our case prevented the embolization of the thrombus and avoided the potential catastrophic sequelae.