Transient Ischemic Attack (TIA)

Transient Ischemic Attack (TIA)

• TIA is a sudden onset of focal neurologic symptoms lasting less than 24 hours due to transient decreased blood flow
• This definition is inadequate because even brief symptoms can cause permanent tissue injury
• A tissue-based definition describes TIA as transient neurologic dysfunction caused by ischemia in the brain, spinal cord, or retina without acute infarction

Mechanisms of TIA

• Embolic TIA has two subtypes: artery to artery and cardio-embolic
• Artery to artery embolic TIA involves lipid plaque rupture where clots travel to other arteries
• Cardio-embolic TIA is caused by conditions like Atrial Fibrillation, Valvular disease, Infective endocarditis, Patent Foramen ovale/Atrial Septal Defect, and Myocardial infarction with low ejection fraction (blood pooled)
• Lacunar TIA involves a blood clot blocking a small, deep artery in the brain
• Lacunar arteries are also referred to as penetrating arteries.
• Lacunar TIA has less widespread symptoms than large artery TIA
• Large artery TIA happens when blood flow affects a major artery supplying the brain which causes a wide range of symptoms
• Atherosclerosis is usually involved in large artery TIA which usually causes more widespread symptoms

Investigations

• Lab tests include:
  • FBC for infection and white cell count and anemia detection
  • Lipid-profile to detect hypercholesterolemia
  • HbA1C to check glycemic control
  • ESR/CRP to check for vasculitis
  • Renal-profile to check for hyponatremia
  • Liver-profile to start patient on statin
  • Coagulation to keep a baseline and if surgery is indicated
• Brain Imaging should be done within 24 hours of symptom onset
  • MRI with diffusion-weighted imaging (DWI) is the preferred modality since it can differentiate between TIA (no infarction) and stroke (infarction) to exclude other diagnoses like space occupying lesion
  • Non contrast CT Brain is also used to exclude a haemorrhagic stroke or other intracranial pathology
  • The brain imaging can show up as normal
• ECG/ Heart monitoring is done to detect cardiac arrhythmias like Afib
  • ECG shows characteristics of Afib such as tachycardia, absent P waves, and an irregularly irregular rhythm
• Telemetry/Holter/loop recorder to detect paroxysmal (sudden) Afib
• Echocardiography such as Transthoracic/Transoesophageal (TTE/TOE) to rule out mural thrombi, valvar diseases, cardiomyopathies, patent foramen ovale (PFO)
  • This can show up as ABNORMAL
• Neurovascular Imaging, like CT-angiography (CTA), Carotid doppler, and MRA (magnetic resonance angiography) are done to identify large artery cause
  • CTA is widely available
  • The neurovascular imaging an show up as normal

Management

• The patient has Afib which is the cause of the TIA

• There are 2 objectives of treatment:

  • Control Afib by addressing the heart's rate (tachycardia) and rhythm (non-sinus)

    • If the patient has been having palpitation symptoms for more than 48 hours, pharmacological or electrical cardioversion (returning the heart to sinus rhythm) is associated with a high risk of embolism

    • Cardioversion can cause mechanical dislodgement of a thrombus (clot) in the heart

    • Should treat heart rate first to prevent further embolism by drugs like -​ Classes II (Metoprolol, Bisoprolol, Carvedilol)

      -​ , III, IV (Diltiazem, Verapamil)
      -​ , and V (Digoxin) to lower heart rate
      - Class III drugs Amiodarone or Dronedarone are not used because they can result in cardioversion to sinus rhythm
      

    • Rachel was given Bisoprolol

  • Prevent future thromboembolic events with

    • Anti-platelet therapy (APT) using dual antiplatelet therapy (DAPT) for 21 days consisting of Aspirin and Clopidogrel, then monotherapy with either one of them
    • Anti-coagulant therapy can be used when not in combination with APT
      • Recommended for patients with Afib if they have a moderately high stroke risk (CHA2DS2VASc Score) AND a low bleeding risk (HAS-BLED Score)
      • Two options: IV Heparin followed by Oral Warfarin OR New Oral Anti-Coagulant (NOAC) either Direct thrombin inhibitors (Dabigatran) or Factor Xa Inhibitors (Apixaban, Rivaroxaban, Edoxaban)

• Mrs. Rachel scores in both criteria for anti-coagulant therapy, with a CHA2DS2VASc Score of 6 and a HAS-BLED Score of 2

• She was therefore discharged with a heartrate controlling drug (Bisoprolol 5 mg PO daily) and oral anti-coagulent (Dabigatran 150 mg PO twice daily) but not dual anti-platelet therapy

• Other prescriptions at discharge included:

  • Hypertension = Ramipril 5 mg PO daily
  • Hypercholestermia = Atorvastatin 80 mg PO nocte
  • Type II diabetes = Metformin 850 mg twice daily

Case Continued

• Six weeks later, the patient returned to the cardiology clinic, feeling well but aware of the continuous irregularity of her heartbeat
• An ECG was repeated and shows rate controlled atrial fibrillation
• A transesophageal echocardiogram shows normal LV size, good LV function (ejection fraction of 60%), and no intra-cardiac thrombus

Cardioversion

• Electrical or pharmacological cardioversion can now be considered, because
  • The patient has received 6 weeks of anticoagulation
  • Left atrial thrombus has been ruled out
• The possible benefits of restoration of sinus rhythm include
  • Symptom relief
  • Improved cardiac function because of coordinated atrial and ventricular contraction
  • Possible reduced risk of thromboembolism
  • Possible avoidance of the need for long-term anticoagulation

Types of Cardioversion

1. Electrical cardioversion involves having the patient fasted, under adequate sedation, and an electric shock (100 – 200 J) synchronized with the intrinsic activity of the heart

2. Phramacalogical cardioversion involves:

   • Class I Sodium Channel Blockers like Flecainide, Propafenone, or Vernakalant
   • Class III K Channel Blockers like Amiodarone or Ibutilid

Steps After Cardioversion

• Anticoagulation is continued for at least 4 weeks, and possibly indefinitely
• Anti-arrhythmic therapy is generally not recommended except with frequent symptomatic recurrences.
• Recurrent or persistent atrial fibrillation may be corrected by - Left atrial catheter ablation of fibrillation foci / pathways using radiofrequency energy – pulmonary vein isolation (PVI) - Surgical ablation of fibrillation foci / pathways (Maze operation