CTPA – the key to diagnosing pulmonary emboli

11th March 2024, NIA Diagnostic Imaging

It is actually not that difficult to diagnose pulmonary embolism. Patients with chest pains, shortness of breath, tachycardia and perhaps, light headedness might suggest pulmonary embolism. However, on their own, those symptoms may be from a number of medical conditions. Only with a high index of suspicion would you consider ordering more investigations looking for pulmonary emboli. Naturally, early diagnosis is vital. CT Pulmonary Angiogram (CTPA) is the key to diagnosing a Pulmonary Embolism.

Pulmonary emboli (PE) arises when the blood flow in the pulmonary artery or its branches is disturbed by a thrombus originally occurring elsewhere in the body. Commonly, PE will occur after a deep vein thrombosis (DVT) has occurred within the deep veins, usually in the lower limbs. A thrombus which has developed is susceptible to break off, in which a part of the thrombus may migrate into pulmonary circulation. Whilst rare, PE may occur due to embolisation of air, fat or tumour cells which have migrated into pulmonary circulation. (2)

In the body, all veins drain into larger veins which carry blood to the right side of the heart and into the pulmonary arteries. As such, this embolus will migrate to the right side of the heart through the venous system, entering the pulmonary artery. Moreover, if there are multiple clots, they can progress into one or both lungs in different areas (3). Usually, pulmonary emboli are multiple and more commonly occur in the lower lobes of the lungs (2). Hence, a PE is a medical emergency as the blockage prevents normal blood flow and gas exchange leading to reduced oxygen levels in the body, stressing and damaging organs such as the brain, kidneys and heart (3).

Symptoms of Pulmonary Embolism may include:
• Shortness of Breath especially on exertion
• Sudden onset of sharp chest pain
• Difficulty breathing
• Light headedness
• Dizziness
• Rapid Heart rate
• Haemoptysis

What is a CT Pulmonary Angiogram (CTPA)?
Multi-detector CT pulmonary angiography is the imaging modality of choice for the diagnosis of queried pulmonary embolism (PE) due to its high sensitivity and specificity. As a result of high morbidity and mortality rates it is essential that patients are diagnosed promptly. The scan involves using a bolus-tracking technique whereby iodinated contrast agent paired with a
saline chaser is injected through a vein using a 20G cannula, using a minimum flow rate of 4.5mls/s (5).

A monitoring slice is taken below the carina at the level of the pulmonary trunk, where a ROI is then place on the pulmonary artery. In this selected region, sequential axial slices are conducted whilst the injection of contrast occurs until enhancement reaches 150 HU which will immediately trigger the scan. The acquired scan range will be from apices to the costophrenic angle (4).

CTPA is performed using a shallow inspiratory breath hold, to reduce the Valsalva manoeuvre occurring with deep breath hold as it may lead to poor vascular opacification due to the contrast bolus being diluted with unopacified blood flowing from the IVC (6).

At NIA Diagnostic imaging, with our latest CT technologies we are able to diagnose PE quickly through multiplanar reconstruction techniques, maximum intensity projections (MIPs), multi planar reformation (MPR) and volume rendering (VR) (5).

Radiographic features suggestive of PE:
Acute pulmonary emboli will result in an intraluminal filling defect within the pulmonary vasculature on a CT pulmonary angiogram. They form a sharp interface with the iodinated contrast medium. Acute pulmonary emboli may completely occlude the vessel with the entire lumen not being opacified, the vessel may enlarge, a central filling defect may occur where IV contrast surrounds the emboli or a peripheral intraluminal filling defect may occur that makes an acute angle with the vessel wall (7).

(RADIOGRAPHING APPEARANCE: Above axial images sequentially showing extensive, bilateral pulmonary emboli in patient with clinical history of shortness of breath on exertion and sharp chest pain)

Contraindications:
CTPA scans are contraindicated in patients who have renal insufficiency (eGFR <30) or patients who have moderate to severe allergy to iodinated contrast. Evidently, due to the urgent nature of PE diagnosis, the risk of the contraindications must be weighed up against the clinical urgency of performing the scan. Alternative imaging modalities such as V/Q scans or premedication may be considered for patients who are allergic to iodine and intravenous pre hydration may be considered for renal insufficiency (2).
Conclusion
At NIA Diagnostic Imaging, we understand the importance of early diagnosis of PE and accept all urgent requests for CTPA examinations. All Medicare eligible examinations are bulk billed under Medicare, including CTPA scans. With having highly experienced radiographers and radiologists on site, CT services are readily accessible at all NIA Diagnostic Imaging clinics. Please contact us for any further information: NIA Glenquarie Radiology (02) 9158 8660 info@niaimaging.com.au NIA Ingleburn Radiology (02) 8104 0803 info.ingleburn@niaimaging.com.au

References:
1. Thrombosis and Haemostasis society of Australia and New Zealand (n.d.). Pulmonary Embolism: PE. Accessed 06 Mar 2024. https://www.thanz.org.au/documents/item/359#:~:text=A%20Pulmonary%20Embolism%20(PE)%20is,and%20stopped%20in%20the%20lungs.

2. Vyas V, Goyal A. Acute Pulmonary Embolism. 2022, StatPearls Publishing, viewed 06 Mar 2024 https://www.ncbi.nlm.nih.gov/books/NBK560551/

3. American Thoracic Society, Patient Education Series – Pulmonary Embolism (n.d.) Accessed 06 Mar 2024. https://www.thoracic.org/patients/patient-resources/resources/pulmonary-embolism.pdf

4. Murphy, A. (n.d.). CT pulmonary angiogram (protocol) | Radiology Reference Article | Radiopaedia.org. Radiopaedia. https://radiopaedia.org/articles/ct-pulmonary-angiogram-protocol

5. Liu, D., Cai, X., Che, X., Ma, Y., Fu, Y., & Li, L. (2020). Visibility and image quality of peripheral pulmonary arteries in pulmonary embolism patients using free-breathing combined with a high-threshold bolus-triggering technique in CT pulmonary angiography. The Journal of international medical research, 48(8), 300060520939326. https://doi.org/10.1177/0300060520939326

6. Bhalla, A. S., Das, A., Naranje, P., Irodi, A., Raj, V., & Goyal, A. (2019). Imaging protocols for CT chest: A recommendation. The Indian journal of radiology & imaging, 29(3), 236–246.https://doi.org/10.4103/ijri.IJRI_34_19

7. Wittram, C., (2007), How I Do It: CT Pulmonary Angiography. American Journal of Roentgenology, Volume 188, Issue 5. https://doi.org/10.2214/AJR.06.1104

PFO Closure

Furlan AJ, Reisman M, Massaro J, et al. Closure or medical therapy for cryptogenic stroke with patent foramen ovale. N Engl J Med 2012; 366: 991–

A multicenter, randomized, open-label trial of closure with a percutaneous device, as compared with medical therapy alone, in patients between 18 and 60 years of age who presented with a cryptogenic stroke or transient ischemic attack (TIA) and had a patent foramen ovale. The primary end point was a composite of stroke or transient ischemic attack during 2 years of follow-up, death from any cause during the first 30 days, or death from neurologic causes between 31 days and 2 years.

Results:

Primary end point was 5.5% in the closure group as compared with 6.8% in the medical-therapy group (adjusted hazard ratio, 0.78; 95% confidence interval, 0.45 to 1.35; P = 0.37)

Conclusion:

“In patients with cryptogenic stroke or TIA who had a patent foramen ovale, closure

with a device did not offer a greater benefit than medical therapy alone for the

prevention of recurrent stroke or TIA”

2 Saver JL, Carroll JD, Thaler DE, et al. Long-term outcomes of patent foramen ovale closure or medical therapy after stroke. N Engl J Med 2017; 377: 1022–

A multicenter, randomised, open-label trial ,randomly assigned patients 18 to 60 years of age who had a patent foramen ovale (PFO) and had had a cryptogenic ischemic stroke to undergo closure of the PFO (PFO closure group) or to receive medical therapy alone (aspirin, warfarin, clopidogrel, or aspirin combined with extended-release dipyridamole; medical-therapy group). The primary efficacy end point was a composite of recurrent nonfatal ischemic stroke, fatal ischemic stroke, or early death after randomisation.

Results:

Recurrent ischemic stroke occurred in 18 patients in the PFO closure group and in 28 patients in the medical-therapy group, resulting in rates of 0.58 events per 100 patient-years and 1.07 events per 100 patient years, respectively (hazard ratio 0.55; 0.31 – 0.999; P = 0.046)

Conclusion:

“Among adults who had had a cryptogenic ischemic stroke, closure of a PFO was associated with a lower rate of recurrent ischemic strokes than medical therapy alone during extended follow-up.”

Meier B, Kalesan B, Mattle HP, et al. Percutaneous closure of patent foramen ovale in cryptogenic embolism. N Engl J Med 2013; 368: 1083–

A prospective, multicenter, randomised, event-driven trial, randomly assigned patients to medical therapy alone (anti-platelet or warfarin therapy) or closure of the patent foramen ovale.

Results:

9 patients in the closure group and 16 in the medical-therapy group had a recurrence of stroke (hazard ratio with closure, 0.49; 0.22 – 1.11; P = 0.08). The primary analysis of the intentionto- treat cohort showed a nominal 51% hazard rate reduction with closure, but the reduction did not reach significance.

Conclusions:

” …there was no significant benefit associated with closure of a patent foramen ovale in adults who had had a cryptogenic ischaemic stroke.”

Sondergaard L, Kasner SE, Rhodes JF, et al. Patent foramen ovale closure or antiplatelet therapy for cryptogenic stroke. N Engl J Med 2017; 377: 1033–

Multinational trial involving patients with a PFO who had had a cryptogenic stroke, randomly assigned patients to undergo PFO closure plus antiplatelet therapy or to receive antiplatelet therapy alone.

Results:

During a median follow-up of 3.2 years, clinical ischemic stroke occurred in 6 of 441 patients (1.4%) in the PFO closure group and in 12 of 223 patients (5.4%) in the antiplatelet-only group (hazard ratio, 0.23; 0.09 to 0.62; P=0.002).

Conclusions:

“Among patients with a PFO who had had a cryptogenic stroke, the risk of subsequent ischemic stroke was lower among those assigned to PFO closure combined with antiplatelet therapy than among those assigned to antiplatelet therapy alone; however, PFO closure was associated with higher rates of device complications and atrial fibrillation.”

Mas JL, Derumeaux G, Guillon B, et al. Patent foramen ovale closure or anticoagulation vs. antiplatelets after stroke. N Engl J Med 2017; 377: 1011–

In a multicenter, randomised, open-label trial patients 16-60 years of age who had had a recent stroke attributed to PFO, to transcatheter PFO closure plus long-term antiplatelet therapy, antiplatelet therapy alone or oral anticoagulation.

Results:

No stroke occurred among patients in the PFO closure group, whereas stroke occurred in 14 of the 235 patients in the antiplatelet- only group (hazard ratio, 0.03; 0 to 0.26; P<0.001). Large number of patients discontinued anti-coagulation in the anti-coagulant group and statistical significance was not analysed because the study was not adequately powered to compare outcomes.

Conclusion:

“Among patients who had had a recent cryptogenic stroke attributed to PFO with an associated atrial septal aneurysm or large interatrial shunt, the rate of stroke recurrence was lower among those assigned to PFO closure combined with antiplatelet therapy than among those assigned to antiplatelet therapy alone. PFO closure was associated with an increased risk of atrial fibrillation.”

Lee PH, Song J-K, Kim JS, et al. Cryptogenic stroke and high-risk patent foramen ovale: the DEFENSE-PFO Trial. J Am Coll Cardiol 2018; 71: 2335–

Patients with cryptogenic stroke and high-risk PFO were divided between a transcatheter PFO closure and a medication-only group.

Results:

No events occurred in the PFO closure group. 12.9% of patients in the medication group had an event (p= 0.023).

Conclusion:

“PFO closure in patients with high-risk PFO characteristics resulted in a lower rate of the primary endpoint as well as stroke recurrence”