Abstract
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Introduction: Pulmonary embolism (PE) is a significant source of morbidity and cardiovascular mortality. The severity of PE is stratified into 3 main categories: high-risk or massive, intermediate-risk or sub-massive and low-risk according to 2019 European Society of Cardiology (ESC) Guidelines developed in collaboration with the European Respiratory Society (ERS). Anticoagulation is adequate treatment for most cases of acute PE including sub-massive PE. However, thrombolytic therapy or embolectomy is reserved for patients with sub-massive PE who are at increased risk for clinical deterioration. Systemic thrombolytic therapy is recommended as the standard treatment for massive PE. Surgical embolectomy or percutaneous catheter-directed treatment are alternative options in patients with contraindications to thrombolysis. The PE response team (PERT) offers a multidisciplinary approach for rapid PE assessment with careful risk stratification and optimal treatment based on individual clinical scenario, as well as follow-up. Appropriate follow-up care of patients with PE following hospitalization helps to identify complications of PE including post-PE syndrome and chronic thromboembolic pulmonary hypertension (CTEPH). The current guideline recommends evaluation with TTE and/or V/Q scan in patients complaining of continued dyspnea and poor physical performance. If there are persistent mismatched perfusion defects on V/Q scan beyond 3 months after acute PE, referral to a PH/CTEPH expert center is recommended. Usually, follow-up imaging is done 3-6 months after thrombectomy to assess for treatment response. In our institution, we found additional benefit in obtaining a baseline V/Q scan with SPECT/CT soon after treatment. Due to COVID-19 pandemic, ventilation scan is discontinued and lung perfusion only imaging protocol with SPECT/CT is adopted. There is no consensus on the utility of Q-SPECT/CT for evaluation of PE, especially post-treatment. The aim of this educational exhibit is to demonstrate the application of lung perfusion scan with adjunctive Q-SPECT/CT in patients with PE after being treated with surgical or catheter-based thrombectomy during the COVID-19 pandemic.
Methods: Since April of 2020, the nuclear medicine division at our institution has adopted a Tc-99m MAA perfusion only lung scanning protocol with SPECT/CT for evaluation of PE or other indications including post-treatment follow-up. The SPECT/CT is coupled with a 16-slice diagnostic CT, using 110 mA for low-dose CT (GE Discovery 670). The lung perfusion scan was performed following 2-4 mCi of Tc-99m MAA administered intravenously. The pre-treatment chest CT pulmonary angiography (CTPA) and post-treatment lung perfusion imaging of these patients are reviewed to assess evolution of perfusion defects and correlate the lung findings with patient's clinical course.
Results: The Q-SPECT/CT allows for a detailed evaluation of regression or progression of the thrombotic disease by recognizing both small and large perfusion defects. The low-dose CT also helps to show nonthromboembolic abnormalities such as emphysema, pneumonia and other parenchymal changes or extrinsic vascular compression. Through literature review and case examples, this exhibit will further identify the advantages of Q-SPECT/CT over planar imaging as well as other modalities including CTPA used for post-treatment evaluation of PE. We will also highlight how the low dose CT helps to identify the nature of lung perfusion defects to narrow down the differential diagnosis, which may further affect clinical management.
Conclusions: The knowledge of the lung Q-SPECT/CT helps readers to be more familiar with its utilization for evaluation of PE, especially post-treatment follow-up. This is particularly useful during the COVID-19 pandemic and even beyond this era. The value of Q-SPECT/CT in follow-up of post-treatment PE remains to be further illustrated and promoted for routine clinical practice.
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