Syncope

Question 1

define syncope

Answer 1

1. sudden transient loss of consciousness associated with loss of postural tone, from which recovery is spontaneous
2. importance:
   -may be foreshadowing of a serious cardiac problem
   -impact on quality of life
   -may lead to injuries
   -distressing to owners
   -sign of a wide range of conditions, impossible to treat without a diagnosis, lots discharged without a diagnosis

Question 2

when does syncope occur? (FRANK = on exam)

Answer 2

1. when cerebral flow is briefly interrupted

OR

2. when oxygen or nutrient delivery is impaired for other reasons

the main determinant of cerebral blood flow is cerebral perfusion pressure (CPP), which is determined by mean arterial blood pressure and by intracranial pressure

CPP = MAP - ICP (WILL BE ON EXAM)

-cerebral perfusion pressure can be reduced, and syncope can result from either a decrease in MAP or an INCREASE in ICP

Question 3

describe cardiogenic versus noncardiogenic syncope

Answer 3

cardiogenic: decreased MAP due to either decreased CO or decreased SVR

noncardiogenic:
-neurologic: increased intracranial pressure via cerebral edema, brain tumor, inflammation, vascular obstruction
–usually occurs gradually, NOT TRANSIENT

-metabolic: abrupt decrease in oxygen or nurtient delivery to brain (unrelated to perfusion)
–decrease in O2-carrying capacity (anemia)
–hypoglycemia: more commonly weakness and seixzres

also neurally mediated reflexes can cause! but usually lead to cardiogenic changes

Question 4

describe cardiogenic causes of syncope

Answer 4

1. arrhythmias: MOST COMMON
2. reduced preload
3. structural heart diease

-bradyarrhythmias: pause. in rhythm >6-8 seconds = loss of consciousness
–a fixed, low HR decreases SV which decreases CO
–most common clinically significant bradyarrhythmias: sick sinus syndrome (pause >6-8 sec), 3rd degree AV block, high grade 2nd degree AV, atrial standstill

-tachyarrhythmias (FRANK)
–severe tachycardia (>300bpm) causes reduced diastole (inadequate ventricular filling time) which causes reduced SV and reduced CO

–most common clinically significant:
-ventricular arrhythmias due to cardiomyopathy: DCM (dobies), ARVC (boxers), aborted sudden death)
-supraventricular trachyarrhythmias (including atrial fibrillation): less likely to result in sudden death

Question 5

describe arrhythmic causes of syncope

Answer 5

1. bradyarrhythmias:
   -pause in rhythm >6-8 seconds = loss of consciousness

-a fixed, low HR decreases SV which decreases CO

-most common clinically significant bradyarrhythmias:
–sick sinus syndrome (pause >6-8 sec)
–3rd degree AV block, high grade 2nd degree AV
–atrial standstill

2. tachyarrhythmias: (FRANK)

-severe tachycardia (>300bpm) causes reduced diastole (inadequate ventricular filling time) which causes reduced SV and reduced CO

-most common clinically significant:

–ventricular arrhythmias due to cardiomyopathy: DCM (dobies), ARVC (boxers), aborted sudden death)

–supraventricular trachyarrhythmias (including atrial fibrillation): less likely to result in sudden death

Question 6

describe reduced preload leading to syncope

Answer 6

1. ventricular filling determined by:
   -venous return
   -diastolic compliance
   -ability of ventricles to hold adequate blood volumes
2. inadequate ventricular filling causes decreased stroke volume which decreases CO
3. pulmonary hypertension:
   -increased pressure pulmonary arteries causes strain to right ventricle which decreases CO by impairment of left ventricular filling (decreased preload to left heart due to restricted pulmonary arteries)

Question 7

describe structural heart disease leading to syncope

Answer 7

1. associated with an increased risk of death
2. patients usually have exertional (long walk, going to the vet, etc.) syncope;
   -normal: vasodilation in exercise is countered by an increased CO
   -diseased heart: unable to sufficiently increase CO to meet needs
3. CHF patients may have increased risk of syncope due to:
   -poor CO
   -hypoxemia
   -associated arrhythmia
   -treatment with vasodilatory agents

Question 8

describe specific structural heart diseases leading to syncope

Answer 8

1. DCM:
   -eccentric hypertrophy + poor systolic function leads to reduced contractility
   -decrease SV, CO
2. HCM:
   -concentric hypertrophy causes reduced LV filling space reduced compliance
3. LEFT obstructions: aortic stenosis, intracardiac tumors, dynamic outflow (SAM with HCM)
   -increases afterload
4. RIGHT obstructions: pulm alve stenosis, HWD, PTE
   -decreased venous return
5. congenital right to left shunting
   -poorly oxygenated blood enters systemic circulation (brain gets desatHgb)
   -kidneys sense lack of O2 and cause polycythemia so sludgey blood causes brain to pass out

Question 9

describe neurally mediated reflexes leading to syncope(FRANK)

Answer 9

1. benign group of conditions in which CV reflexes inappropriately respond to a trigger by signaling vasodilation and bradycardia
2. 2 types in animals:
   -neurogenic bradycardia: triggered by exercise, extreme excitement, emotional stress, BOXERS predisposed

-situational syncope/vasovagal: triggered by events that increase vagus nerve stimulation
–cough syncope/cough drop, micturition syncope, syncope following vomiting, defecation pulling on lead

Question 10

describe historical findings of syncope (syncope versus seizure; FRANK(

Answer 10

1. syncope versus seizure: must differentiate! (FRANK)

-syncope: sudden loss of consciousness associated with postural tone from which recovery is spontaneous
–transient hypoperfusion (5-20 sec) of portion of brain responsible for consciousness
-characteristics: may be precipitated by certain situations, motionless or extensor rigidity, opisthotonus, spontaneous urination/defecation, jerking limbs, SHORT duration, RAPID recovery of normal mentation

-seizure: physical manifestation of abnormal, excessive cerebral electrical activity
–characteristics: prodromal symptoms, rhythmic movements, hypersalivation, chomping, variable duration (>5 min suggests seizure), SLOW return of consciousness, prolonged disorientation

-convulsive syncope: seizure activity from cerebral hypoperfusion
-complex partial seizures: decreased/lost consciousness, varying degrees of motor activity

Question 11

describe physical exam/diagnostics for syncope

Answer 11

1. cardiogenic syncope is most common and greatest risk, determine presence of heart diease
2. careful PE, thoracic ausucltation
3. ECG: for ALL cases even if no arrhythmia heard!
4. thoracic rads
   -TFAST is available: remember pericardial effusion
5. minimum database:
   -BP, PCV/TS, glucose, USG, chem
6. be breedist!
   -boxers (ARVC), dobermans (DCM): at high risk for arrhythmogenic CM

-labs (SVT), schnauzers, WHWT, cocker spaniels (SSS): predisposed to tachy/bradyarrhythmia

-syncope with exertion/exercise
-episodes of increased frequency
-dogs who do not return to normal between episodes