Medical Quiz on Syncope and Cerebral Perfusion

Syncope

• Syncope is a sudden, temporary loss of consciousness caused by a drop in blood pressure and a decrease in cerebral blood flow
• The loss of consciousness is associated with a loss of postural tone, and recovery is usually spontaneous
• Syncope is a serious clinical sign that may indicate a serious cardiac problem
• It can lead to injuries and distress for owners

Learning Objectives

• Define syncope and its features
• Understand the pathophysiology of syncope
• Identify differential diagnoses of syncope
• Develop a plan for patient evaluation of syncope

Syncope Defined

• Sudden, transient loss of consciousness
• Spontaneous recovery
• Important because could be a premonitory sign of a serious cardiac problem
• Can impact quality of life
• Can lead to injuries
• Difficult to treat without clear cause of the event
• 33-50% dogs, 25-42% of people with syncope are discharged without diagnosis

CPP = MAP - ICP

• Cerebral perfusion pressure (CPP) is a critical determinant for cerebral blood flow
• CPP is determined by mean arterial pressure (MAP) and intracranial pressure (ICP)
• A reduction in CPP can trigger syncope, which may be due to a decreased MAP or increased ICP

Cardiogenic, Non-cardiogenic and Metabolic Syncope

• Cardiogenic: Reduced cardiac output (CO)
  • Arrhythmias (brady/tachy)
  • Reduced preload (Cardiac Tamponade, Hypovolemia)
  • Structural heart disease (Cardiomyopathy, Congenital Heart Disease)
• Non-cardiogenic: Increased ICP (intracranial pressure)
  • Cerebral edema
  • Brain tumors
  • Inflammation
  • Vascular obstruction
• Metabolic: Changes in oxygen or nutrient delivery unrelated to perfusion
  • Anemia
  • Hypoglycemia
  • Other conditions like seizures and weakness

Cardiogenic (Reduced Cardiac Output)

• Arrhythmias (bradycardia, tachycardia)
• Reduced preload (Cardiac tamponade, Hypovolemia)
• Structural heart disease (Cardiomyopathy, Congenital Heart Disease)

Bradyarrhythmia Leading to Syncope

• A pause in cardiac rhythm greater than 6-8 seconds can lead to loss of consciousness
• Fixed, low heart rate can cause syncope with exertion
• Decreased heart rate results in decreased cardiac output
• Decreased stroke volume

Bradyarrythmia Presenting Information

• Oreo, 10-year-old Miniature Schnauzer presented to ER with recurrent episodes of "falling asleep"
• The two ECGs show bradycardia

Tachyarrhythmia

• Brutus, 9 year old MN Boxer
• Owner reports he plays too hard and falls over
• His ECG and Holter monitor show tachycardia

How to Diagnose Syncope

• Historical findings
• Physical examination
• Step-wise diagnostic plan

Historical Findings (Example Questions)

• What was the animal doing just before the event occurred?
• How long did the event last?
• Did the animal lose consciousness during the event?
• Did the animal have motor activity during the event?
• Is the animal currently taking medication?
• Has the animal shown any unusual behavioral changes recently?

Transient Loss of Consciousness vs. Seizure

• Syncope: Characterized by a sudden loss of consciousness, associated with loss of postural tone and rapid recovery of normal mentation
• Seizure: Physical manifestations of abnormal, excessive cerebral electrical activity with varying degrees of behaviors (jerking, stiffening)
• Duration of cerebral anoxia can help distinguish between syncope and seizure
  • <5 seconds usually suggestive of syncope
  • 5-15 seconds can be either syncope or seizure, further evaluation needed -> >15 seconds likely a seizure

Syncope vs. Seizure (Differentiation Difficulties)

• Convulsive syncope
• Complex partial seizures
• History can be misleading
• Encouraging owners to video episodes helpful

Physical Examination/Diagnostics

• Careful physical examination, thoracic auscultation, ECG, possibly thoracic radiographs, etc
• Determine the presence of heart disease

Diagnostic Plan (Minimum Database)

• Blood pressure measurement
• PCV/TS, glucose
• Urine specific gravity
• Chemistry panel (BUN/creatinine, glucose, potassium)
• 24-hour ambulatory ECG (Holter monitor)

Diagnostic Plan (Additional Diagnostics)

• Breeds at risk for sudden death from arrhythmogenic cardiomyopathy (e.g., Boxer dogs, Doberman pinschers)
• Breed predisposed to tachy/bradyarrhythmias (e.g., Labrador Retrievers and some spaniel breeds)
• Exertional syncope
• Increasing frequency episodes
• Dogs that do not return to normal between episodes

Cardiac Tamponade Resulting in Reduced Preload

• This happens when fluid collects around the heart, reducing the space the heart has to fill
• The condition will reduce the preload

Pulmonary Hypertension Leads to Reduced Preload

• Increased pressure in pulmonary arteries strains right ventricle
• Decreased CO due to impairment of left ventricular filling

Structural Heart Disease: Cardiomyopathies

• Dilated Cardiomyopathy (DCM)
  • Eccentric hypertrophy, poor systolic function, reduced contractility
• Hypertrophic Cardiomyopathy (HCM)
  • Concentric hypertrophy, reduced LV filling space, reduced compliance

Structural Heart Disease: Obstructive Lesions

• Left obstructions: Aortic stenosis, Intracardiac tumors, dynamic outflow obstructions (SAM with HCM)
  • Increase afterload
• Right obstructions: Pulmonary valve stenosis, Heartworm disease, pulmonary thromboembolism
  • Decrease venous return

Congenital Right-to-Left Shunting

• Communication between the right and left sides of the heart, causing a direction of blood flow to bypass the lungs
• Oxygen-depleted (poorly oxygenated) blood enters the systemic circulation causing desaturation of the systemic circulation,
• Desaturated hemoglobin (hypoxia)
• Sludgy blood (polycythemia)

Neurally Mediated Reflexes

• Benign Conditions where cardiovascular reflexes respond to a stimuli leading to sudden drop in blood pressure
• Neurocardiogenic Bradycardia
  • Extreme excitement, exercise, emotional stress
• Situational Syncope
  • Events that stimulate vagus nerve stimulation (cough, urination, defecation)