|Year : 2020 | Volume
| Issue : 2 | Page : 138-140
A negative preoperative 99mTechnetium tetrofosmin myocardial perfusion imaging scan with postoperative acute coronary syndrome - A case of balanced ischaemia
Indira Gurajala, Padmaja Durga
Department of Anaesthesiology and Critical Care, Nizams Institute of Medical Sciences, Punjagutta, Hyderabad, Telangana, India
|Date of Submission||14-Aug-2019|
|Date of Decision||30-Aug-2019|
|Date of Acceptance||31-Oct-2019|
|Date of Web Publication||4-Feb-2020|
Dr. Indira Gurajala
1-9-485/2, Lalithanagar, Jamai Osmania, Hyderabad, Telangana
Source of Support: None, Conflict of Interest: None
Perioperative myocardial infarction (PMI) is an important indicator of outcome after noncardiac surgery. Identifying patients at risk of PMI helps in risk stratification and modification. Myocardial perfusion imaging (MPI) is an established diagnostic modality for detection and prognostication of coronary artery disease (CAD). We report a case wherein preoperative MPI was negative for CAD but patient presented with acute coronary event in the postoperative period. We identify and evaluate the reasons for the failure of MPI in detection of CAD in our patient.
Keywords: Balanced ischaemia, myocardial perfusion imaging, postoperative acute coronary syndrome
|How to cite this article:|
Gurajala I, Durga P. A negative preoperative 99mTechnetium tetrofosmin myocardial perfusion imaging scan with postoperative acute coronary syndrome - A case of balanced ischaemia. Indian J Anaesth 2020;64:138-40
|How to cite this URL:|
Gurajala I, Durga P. A negative preoperative 99mTechnetium tetrofosmin myocardial perfusion imaging scan with postoperative acute coronary syndrome - A case of balanced ischaemia. Indian J Anaesth [serial online] 2020 [cited 2020 May 25];64:138-40. Available from: http://www.ijaweb.org/text.asp?2020/64/2/138/277759
| Introduction|| |
Myocardial perfusion imaging (MPI) with Thallium 201 or Technetium 99 is one of the preferred investigations for preoperative non-invasive workup of ischemic heart disease. A normal MPI has high negative predictive value for postoperative myocardial infarction or cardiac death. However, a false negative MPI study can result due to the phenomenon of “balanced ischaemia,” leading to adverse perioperative cardiac events.
| Case Report|| |
A 78-year-old male with known history of diabetes and hypertension for the past 20 years was posted for elective laparoscopic cholecystectomy. He was preoperatively on insulin for diabetes and amlodipine-atenolol combination (5/50 mg) for control of blood pressure. He had breathlessness on exertion (New York Heart Association class II). A more formal assessment of the functional capacity in terms of metabolic equivalents could not be performed as the patient had severe osteoarthritis of both knees. There was no history of chest pain, palpitations, or syncope. Three months prior, the patient had undergone endoscopic retrograde cholangio-pancreaticogram and common bile duct stenting for choledocholithiasis. On examination, his pulse rate was 70/min and blood pressure 138/80 mm Hg. A baseline electrocardiogram (ECG) showed T wave inversions in leads V1 to V6, a 2D transthoracic echocardiogram revealed good left ventricular function with no regional wall motion abnormalities (RWMA). In view of the age, long standing diabetes, preoperative ECG changes and unknown functional capacity, a99m Technetium tetrofosmin MPI scan was performed on the advice of the cardiologist and was found to be negative for dobutamine stress induced left ventricular myocardial ischaemia [Figure 1]. Preoperatively, the antihypertensive medication was continued. Anaesthesia was induced with inj fentanyl 100 μg, thiopentone sodium 200 mg and atracurium 35 mg given intravenously. After endotracheal intubation, anaesthesia was maintained with air/O2 mixture (60:40%), isoflurane 0.7–1.2 MAC, and intermittent boluses of atracurium. Intraoperative monitoring included ECG, non-invasive BP, pulse oximetry, and capnography. Laparoscopic cholecystectomy was performed uneventfully and the patient extubated after adequate reversal of muscle relaxation. On 1st postoperative day, patient was found to be irritable and complained of severe diffuse pain over the sternal and epigastric region. A 12 lead ECG revealed ST depression in leads V1 and V2 [Figure 1]. Troponin T was negative and other cardiac enzymes were borderline elevated. ECHO showed RWMA in the distal interventricular septum, apex, apicolateral wall. A diagnosis of unstable angina was made and patient posted for coronary angiogram (CAG). CAG showed distal left main coronary artery stenosis of 30%, type III left anterior descending artery with diffuse long segment disease, a non-dominant left circumflex artery with proximal 80% stenosis, and a totally occluded right coronary artery with retrofilling from the left system. The patient was referred for surgical revascularisation.
|Figure 1: A normal preoperative MPI scan and a postoperative ECG showing ischemic changes|
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| Discussion|| |
Myocardial perfusion imaging (MPI) is useful for non-invasive evaluation of coronary artery disease (CAD). It is a valuable tool in diagnosing cardiovascular disease, assessing viability, and establishing prognosis. According to the 2014 American College of Cardiology/American Heart Association guidelines for perioperative cardiovascular evaluation and management of patients undergoing noncardiac surgery, non-invasive pharmacologic stress testing (dobutamine stress echocardiogram or MPI) is indicated in patients with elevated risk and poor (<4 METs) or unknown functional capacity, if the results will change surgical management. A large meta-analysis study that compared MPI, positron emission tomography, and cardiac magnetic resonance found MPI has overall sensitivity of 88% and specificity of 61% for diagnosing obstructive CAD. A moderate to large defect on MPI is a positive predictor for postoperative cardiac events, while a normal MPI has high negative predictive value for postoperative myocardial infarction or cardiac death.
However, there are several pitfalls that can limit the utility of the MPI study. These could be patient related, errors due to equipment or due to technologist. Among the patient related factors, one area of low sensitivity for MPI is balanced or multivessel ischaemia. This is because MPI can only measure relative uptake, not absolute activity and assumes that the best perfused areas are normal. If there is decreased perfusion to all walls, the abnormalities may not be recognised, particularly if the decrease is of a similar magnitude throughout. This is termed as diffuse normalisation of decreased perfusion or so-called ''balanced ischaemia.” In our patient, all the myocardial segments showed normal tracer uptake and the MPI study did not show any defects either at rest or with stress. However, the patient had unstable angina postoperatively and CAG revealed triple vessel disease.
Though the sensitivity of MPI for identifying multivessel disease is only approximately 60%, there is usually some abnormality present, so that the identification of CAD in this setting still remains high at 95–98%. A decline in left ventricular ejection fraction with stress increased pulmonary or right ventricular uptake and transient ischemic dilation should be looked for during MPI as these are indicators of possible balanced ischaemia. None of these were identified in the MPI of our patient. Interpreting physicians must be familiar with these to ensure proper evaluation of the MPI study. Conditions such as balanced ischaemia are classified as “interpretation errors” as the issues do not arise from any limitation of the procedure but rather its interpretation itself.
| Conclusion|| |
Though MPI has a high negative predictive value, significant CAD can be missed due to balanced ischaemia. Other markers of balanced multivessel disease should be looked for during a negative study and in case of doubt, a coronary angiogram should be undertaken.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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