This was a decision of the Ontario Superior Court of Justice arising from a life-altering stroke suffered by the patient, William Johnson.

On October 17, 2012 the patient was admitted to hospital following an initial stroke. He was put on antiplatelet therapy to prevent a secondary stroke. On October 23, 2012, Mr. Johnson was discharge from hospital by the defendant physician, Dr. Rose-Anne Vieira. The defendant doctor admitted she was negligent in failing to review a critical imaging report prior to discharge.

The only issue at trial was causation, and specifically, whether in reviewing the critical imaging report, the patient would have remained in hospital and received anticoagulation therapy instead of antiplatelet therapy thereby preventing the secondary stroke.

Two experts testified on the issue of causation. Dr. Louis Caplan, a world-renowned expert in stroke and professor at Harvard University, testified on behalf of the plaintiffs. Dr. David Gladstone, a leading Canadian expert in stroke, testified on behalf of the defendant. The expert evidence revealed the existence of a debate in the medical community around the comparative efficacy of anticoagulation therapy versus antiplatelet therapy in the prevention of secondary strokes stemming from vertebral artery dissections. 

Background on Stroke and Cervical Artery Dissection

An ischemic stroke occurs when there is blockage of blood flow in part of the brain. When deprived of blood, which carries oxygen and glucose, brain cells die. This is known as an infarction.

There are many different causes of stroke. Dissections of the cervical arteries (vertebral and carotid arteries) are a well-established cause of stroke, and a relatively common cause of strokes in young and middle-aged adults.

A dissection refers to a tear that develops within an artery wall, leading to blood entering and splitting the inner layers of the vessel wall. This is known as an intramural hematoma. At the site of a dissection, the vessel diameter usually becomes narrowed from compression by the intramural hematoma. This can result in a mild, moderate, or severe narrowing of the vessel that can limit blood flow, or a complete vessel occlusion in which blood flow ceases. Blood clot formation inside the artery, known as thrombosis, can occur.

The most common mechanism of stroke related to a dissection is thromboembolism, whereby clots that form at the site of a dissection can subsequently dislodge, travelling upstream and block blood flow within the brain. Strokes may also result from hemodynamic ischemia, (i.e., diminished blood flow), if the injured vessel becomes severely narrowed or occluded. 

There are four main arteries that carry blood to the brain: two carotid arteries travel up the front of the neck and into the head and two vertebral arteries travel up the back of the neck and into the head where they join to form the basilar artery. The vertebral and basilar arteries supply blood to the brainstem, cerebellum and back of the brain.

Cervical artery dissections typically result from some form of head or neck injury, either major or minor trauma, or they may appear to occur spontaneously or associated with unrecognized or trivial trauma. The mechanism is usually a rapid or excessive neck movement (e.g., rotation or hyperextension) in a way that stretches and injures the artery wall. Dissections are usually painful (neck pain, headache, or facial pain) but may also be asymptomatic.

The diagnosis of dissection is established by characteristic abnormalities on imaging studies of the blood vessels using CT, MRI, ultrasound, or catheter angiography.

A stroke occurring as a complication of a dissection may occur immediately, but most often occurs in a delayed fashion (i.e., hours, days or weeks following the initial vessel injury). The typical temporal sequence is neck trauma, leading to artery dissection causing neck pain/headache and vessel narrowing/clotting, leading to a stroke.

Antithrombotic Medications for Stroke Prevention

As most strokes arise from blood clots that originate from the blood vessels or the heart, medications are typically prescribed to lower the risk of clots that could lead to strokes. There are two main classes of anticlotting medications in clinical practice: antiplatelet drugs and anticoagulant drugs.

Antiplatelet drugs include Aspirin and clopidogrel (Plavix). These drugs work by inhibiting blood platelets so they are less ‘sticky’ and less likely to form a clot.

Anticoagulant drugs include Heparin and Warfarin. They work by inhibiting specific coagulation factors to interfere with the body’s ability to produce thrombin, thereby inhibiting the formation of fibrin clots.

Heparin and Warfarin require monitoring with blood tests. The main advantage of antiplatelet drugs is that they have a lower risk of bleeding when compared to anticoagulants and are easier to use.

As of 2012, the Canadian Stroke Best Practice Recommendations contained no specific recommendations pertaining to the treatment of cervical artery dissections.

Decision of the Trial Judge

After reviewing the evidence of the two experts, the trial judge was satisfied that had Dr. Vieira viewed Mr. Johnson’s MRI and MRA imaging on October 23, 2012, she would have consulted with another physician who would likely have advised against discharge and would likely have placed Mr. Johnson on anticoagulation therapy. If anticoagulation therapy had started at that time, Mr. Johnson would have been fully “Heparinized” by October 30, 2012. In other words, Mr. Johnson’s PTT values would reached therapeutic levels of anticoagulation, though it is unclear when precisely this would have happened.

However, the trial judge was not convinced that anticoagulation therapy would have prevented the secondary stroke. At best, the trial judge concluded that it may have possibly resulted in a different outcome, either better or perhaps even worse than the actual outcome.

While cognizant that the plaintiffs need not prove causation with scientific precision, this was not a case where a common-sense inference could be used to bridge the evidentiary gap. The evidence taken as a whole simply did not support the conclusion either directly or by inference that Mr. Johnson’s second stroke would likely have been prevented had he been placed on Heparin instead of Aspirin at the time of his initial discharge from hospital. 

As such, the plaintiffs have failed to prove causation and the case was dismissed.

Decision Date: May 1, 2023

Jurisdiction: Ontario Superior Court of Justice

Citation: Johnson v Lakeridge Health Corporation, 2023 ONSC 2575 (CanLII)