Does the stroke clock reset with worsening of symptoms in a patient with an evolving acute stroke?

Does the Stroke Clock Reset with Worsening Symptoms?

No, the stroke clock does not reset when symptoms worsen—the clock starts from the initial symptom onset or "last known well time," regardless of subsequent clinical deterioration. 1, 2

The Fundamental Principle of Stroke Timing

The American Heart Association explicitly defines stroke onset time as when the patient was last known to be normal or without neurological deficits—this is the "last known well time." 1 This time determines eligibility for all acute therapies, including IV thrombolysis and mechanical thrombectomy.

In your patient's case, the stroke clock began when they first experienced left arm numbness (before 6 p.m.), NOT when they developed dysarthria at 12:30 a.m. or facial droop/aphasia at 3:30 a.m. 1

Critical Exception: When the Clock DOES Reset

The American Heart Association states that if transient neurological symptoms completely resolved and the patient returned to baseline, the therapeutic clock resets and time of onset begins anew when new symptoms appear. 2 However, this exception does NOT apply to your patient because:

• The MRI showed acute stroke in cerebellar and lacunar regions 2
• The patient had complete basilar artery occlusion with collaterals 2
• The initial symptoms (left arm numbness) represented actual stroke, not a TIA that fully resolved 2

Why Symptom Progression Doesn't Reset the Clock

Worsening neurological symptoms in acute stroke represent expected disease progression through several mechanisms 3:

• Collateral failure in the setting of large vessel occlusion (your patient has basilar occlusion with collaterals) 3
• Infarct core expansion into the penumbra 3
• Brain edema developing over hours 3
• Hemodynamic insufficiency in watershed territories 3

The Canadian Stroke Best Practice guidelines classify patients with fluctuating symptoms as highest risk for recurrent stroke, but this refers to risk stratification for TIA patients, not resetting the treatment window for acute stroke. 1

Clinical Implications for Your Patient

Your patient's timeline:

• Before 6 p.m.: Left arm numbness (initial symptom = stroke onset time)
• 6 p.m.: Presentation with symptom resolution (but imaging shows acute stroke)
• 12:30 a.m.: Dysarthria develops
• 3:30 a.m.: Facial droop and aphasia develop

The stroke clock started before 6 p.m. when left arm numbness began. 1 By the time of worsening symptoms (12:30 a.m. and 3:30 a.m.), the patient was already 6.5-9.5 hours from onset—well beyond the standard IV thrombolysis window (4.5 hours) and likely beyond most mechanical thrombectomy windows. 1

Common Pitfall to Avoid

Never mistake symptom fluctuation or progression for a "new" stroke that resets the clock. 2 This is particularly dangerous in basilar artery occlusion, where patients classically present with stuttering symptoms over hours to days before catastrophic deterioration. 3 The imaging findings (subacute/chronic hypoattenuation on CT, acute stroke on MRI, complete basilar occlusion) confirm this is a single evolving stroke process, not multiple discrete events. 4

Documentation Requirements

The American Heart Association mandates that the date and time should be defined as when the stroke symptoms that brought the patient to the hospital first occurred—in this case, the left arm numbness. 1 If precise timing is uncertain, use standardized time parameters (morning, afternoon, evening, overnight), but the earliest symptom onset must be used. 1