Transcranial Doppler: Does Addition of Blood to Agitated Saline Affect Sensitivity for Detecting Cardiac Right-to-Left Shunt?

Adjunct Methods for the Detection of Patent Foramen Ovale: The Contribution of Transcranial Doppler and the Valsalva Manoeuvre

A patent foramen ovale (PFO) is present in 25% of the population. In some patients, especially those without traditional stroke risk factors and with no immediately apparent cause, a cryptogenic stroke may be caused by an embolus passing through the PFO to the systemic circulation. The identification, or indeed exclusion, of a PFO is sought in these patients, most commonly using contrast-enhanced transthoracic or transoesophageal echocardiography. Another method for detecting a PFO is transcranial Doppler, which allows the detection of PFO possibly without the need for an echo laboratory, and with arguably improved sensitivity. This review will focus on transcranial Doppler detection of PFO, with a brief summary of echocardiographic techniques and the use of ultrasound contrast agents, and the role of provocations to increase diagnostic accuracy, specifically the Valsalva manoeuvre. We discuss the phases alongside the direct and indirect signs of an adequate Valsalva manoeuvre.

Diagnostic Accuracy of Carotid Doppler Ultrasound for the Detection of Right-to-Left Cardiac Shunt

Background:

Right-to-left cardiac shunt is a condition anatomically related to patent foramen ovale (PFO) and potentially related to cryptogenic cerebrovascular events. As recent studies demonstrated a reduction of recurrent stroke in patients undergoing percutaneous PFO closure after a cryptogenic cerebrovascular event, it is now of pivotal importance to screen these patients for Right-to-left shunt(RLS) presence. At this regard, transcranial color Doppler (TCCD) with contrast has a good sensitivity (97%) and specificity (93%) compared to transesophageal echocardiography and became the test of choice to assess RLS presence, thanks to its noninvasive nature. However, temporal bone window is not accessible in 6%–20% patients. Several approaches have been explored to overcome this limitation with encouraging but not definitive results for extracranial internal carotid artery (ICA) approach, proposed in previous pivotal studies. Aims of this study were to further assess the diagnostic accuracy of ICA Doppler ultrasound with contrast for RLS detection compared to TCCD, with the two tests performed simultaneously.

Materials and Methods:

Sixty-four patients underwent simultaneously to TCCD and ICA Doppler ultrasound, both performed at rest and after Valsalva maneuver. Diagnosis of RLS was made, both for TCCD and ICA ultrasound, if=1 microembolic signals (MES) were detected during the examination (either at rest or after Valsalva maneuver).

Results:

ICA Doppler ultrasound sensitivity and specificity resulted respectively of 97% (confidence interval [CI] 95%) and 100% ([CI] 95%), while negative likelihood ratio was 0.03 (CI 95%).

Conclusions:

ICA Doppler ultrasound represents a valid alternative to TCCD for RLS screening in patients without adequate transcranial acoustic window.

Patent Foramen Ovale, the Role of Antiplatelet Therapy Alone or Anticoagulant Therapy Alone Versus Device Closure for Cryptogenic Stroke: A Review of the Literature and Current Recommendations

Cryptogenic stroke and its relation to the Patent Foramen Ovale (PFO) is a long-debated topic. Recent clinical trials have unequivocally established the relationship between cryptogenic strokes and paradoxical embolism across the PFO. This slit-like communication exists in everyone before birth, but most often closes shortly after birth. PFO may persist as a narrow channel of communication between the right and left atria in approximately 25-27% of adults. In this review, we examine the clinical relevance of the PFO with analysis of the latest trials evaluating catheter-based closure of PFO's for cryptogenic stroke. We also review the current evidence examining the use of antiplatelet medications versus anticoagulants for stroke prevention in those patients with PFO who do not qualify for closure per current guidelines.

Patent Foramen Ovale and Hypoxemia

Patent foramen ovale (PFO), an embryonic remnant of the fetal circulation, is present in 20-25% of adults. Although recent observational studies and clinical trials have established the link between PFO-mediated right-to-left shunting with cryptogenic stroke and migraine with aura, the role of a PFO in exacerbating hypoxemic medical conditions (ie, sleep apnea, chronic obstructive pulmonary disease, pulmonary hypertension, platypnea-orthodeoxia, pulmonary arteriovenous malformation, high-altitude pulmonary edema, and exercise desaturation) remains less understood. PFO-mediated hypoxemia occurs when deoxygenated venous blood from the right atrium enters and mixes with oxygenated arterial blood in the left atrium. Patients with an intracardiac right-to-left shunt may have profound hypoxemia out of proportion to underlying primary lung disease, even in the presence of normal right-sided pressures. The presence of right-to-left cardiac shunting can exacerbate the degree of hypoxemia in patients with underlying pulmonary disorders. In a subset of these patients, percutaneous PFO closure may result in marked improvement in dyspnea and hypoxemia. This review discusses the association between PFO-mediated right-to-left shunting with medical conditions associated with hypoxemia and explores the role of percutaneous PFO closure in alleviating the hypoxemia.

Prevalence of patent foramen ovale in cryptogenic transient ischaemic attack and non-disabling stroke at older ages: a population-based study, systematic review, and meta-analysis

BACKGROUND

Percutaneous closure of patent foramen ovale (PFO) has been shown to be superior to medical treatment alone for prevention of recurrent stroke after cryptogenic transient ischaemic attack or non-disabling stroke in patients aged 60 years or younger. The justification for trials in older patients with transient ischaemic attack or stroke depends on whether PFO is shown to be associated with cryptogenic events at older ages, for which existing evidence is conflicting, and on the population burden of PFO-associated events. Therefore, we did a population-based screening study using contrast-enhanced transcranial Doppler (bubble-TCD) to detect probable PFO as indicated by a right-to-left shunt (RLS); we also did a systematic review and meta-analysis to compare our results with previous studies.

METHODS

In this population-based study, nested in the Oxford Vascular Study (OXVASC), we established the prevalence of any RLS, and of large RLS (>20 microbubbles), in consecutive patients attending a rapid-access transient ischaemic attack and stroke clinic, or at 1-month follow-up after stroke unit admission, with transient ischaemic attack or non-disabling ischaemic stroke, comparing cryptogenic events with those of known cause (according to Trial of Org 10172 in Acute Stroke Treatment [TOAST] criteria). We stratified participants by age, and extrapolated data to the UK population. We also did a systematic review of published studies of PFO prevalence (using transthoracic or transoesophageal echocardiography or bubble-TCD) according to stroke subtype, which included older patients and reported age-specific results, and determined by meta-analysis (including the OXVASC data) the pooled odds ratio (95% CI) of finding PFO of any size in cryptogenic events compared with events of known cause, stratified by screening modality (transthoracic or transoesophageal echocardiography or bubble-TCD). The study protocol is registered with PROSPERO, number CRD42018087074.

FINDINGS

Among 572 consecutive patients with transient ischaemic attack or non-disabling stroke between Sept 1, 2014, and Oct 9, 2017 (439 [77%] patients aged >60 years, mean age 70·0 years [SD 13·7]), bubble-TCD was feasible in 523 patients (91%) of whom 397 were aged older than 60 years. Compared with those with transient ischaemic attack or stroke of known cause, patients with cryptogenic events had a higher prevalence of RLS overall (odds ratio [OR] 1·93, 95% CI 1·32-2·82; p=0·001), and in those aged older than 60 years (2·06, 1·32-3·23; p=0·001). When we pooled the OXVASC data with that from two previous smaller studies of bubble-TCD in patients aged 50 years or older, we found an association between RLS and cryptogenic events (OR 2·35, 95% CI 1·42-3·90; p=0·0009; pheterogeneity=0·15), which was consistent with the equivalent estimate from transoesophageal echocardiography studies (2·20, 1·15-4·22; p=0·02; pheterogeneity=0·02). No data on large RLS in patients with TOAST-defined cryptogenic events compared with other events were available from previous studies, but we found no evidence that the association was diminished in such cases. Of 41 patients with large RLS and cryptogenic transient ischaemic attack or non-disabling stroke in our study, 25 (61%) were aged older than 60 years, which extrapolates to 5951 patients per year in the UK (data from mid-2016).

INTERPRETATION

Bubble-TCD was feasible in most older patients with transient ischaemic attack or non-disabling stroke, the association of RLS with cryptogenic events remained at older ages, and the population burden of PFO-associated events is substantial. Randomised trials of PFO closure at older ages are required and should be feasible.

FUNDING

National Institute for Health Research, Oxford Biomedical Research Centre, Wellcome Trust, and Wolfson Foundation.

Identification and Quantification of Patent Foramen Ovale-Mediated Shunts: Echocardiography and Transcranial Doppler

Once deemed benign, patent foramen ovale (PFO)-mediated right-to-left shunting has now been linked to stroke, migraine, and hypoxemia. Contrast transesophageal echocardiography is considered the standard technique for identifying a PFO, allowing visualization of the atrial septal anatomy and differentiation from non-PFO right-to-left shunts. Transthoracic echocardiography is the most common method for PFO imaging, being cost-effective, but has the lowest sensitivity. Transcranial Doppler is highly sensitive but is unable to differentiate cardiac from pulmonary shunts; it is the best method to quantitate shunt severity, being more sensitive than transthoracic or transesophageal echocardiography so is our preferred screening method for PFO.