Cardiac Arrhythmias

only if the hemodynamic status of the patient is being affected

when cardiac output is reduced and causes sustained tachycardia or are progressing to life threatening cardiac electrical instability

• preexisting medical conditions
• administration of premedications
• anesthetic induction and maintenance agents
• surgical stimulation

• sinus tachycardia
• second degree AV block

• sinus bradycardia
• sinus tachycardia
• first and second degree AV block

• low cardiac output states
• bradycardia
• decreases the epinephrine threshold for premature ventricular contractions(VPCs)

• bradycardia
• second degree AV block

bigeminy (a VPC following each normal beat)

• a normal heart beat
• nothing wrong with the conduction pattern

• dogs
• not normal in cats

• cyclic slowing and speeding of the sinus rate that is usually assoicated with respiration
• the rate tends to increase on inspiration and decrease on expiration because of changes in vagal tone
• end of expiration there is a pause in the heart beat

• need to watch the patient breath and listen to the heart at the same time
• must be able to assoicate with the respiratory rate

• slow heart rate, but has a regular rhythm
• <60 bpm in large breed dogs
• <80 bpm in small breed dogs
• <120 bpm in cats

• drugs that increase vagal tone (alpha 2 agonists, opioids, xylazine, acepromazine)
• mediated reflexes (pulling on ovarian pedicles, oculocardiac reflex)
• hypothermia
• hypothyroidism
• Addison's disease
• deep planes of anesthesia

decrease

only happening from time to time

• pause in conduction in SA node
• absent of PQRST from time to time
• basically it is a missing heart beat because the SA node has to fire for anything  esle to happen so if it does not fire (arrested) then the beat is missing

not usually a problem but can lead to something worse

sinus arrhythmia

arrest

• PR interval is > 0.2 seconds
• conduction block at the AV node

no, but it is important to recognize because it can lead to second and third degree AV block

• PR interval becomes increasingly long with each heartbeat
• the pattern accummulates until we lose a QRS complex and then it starts all over again

Mobitz 1

• random absence of QRS complex and T wave
• the PR interval is always the same and we just miss a QRS complex every now and then unlike type 1 where the PR interval gets longer with each beat until we miss a QRS complex

Mobitz 2

depends on how frequently it is happening

• lots of P waves and no QRS waves
• patient is about to die because the ventricles are not contracting therefore blood is not being circulated throughout the body

• normal conduction but happening fast
• >160 bpm for large dogs
• >180 bpm for small dogs
• >220 bpm for cats

• when the rate becomes so high that there is insufficient time for ventriclar filling.
• this decreases cardiac output and blood pressure and can have serious hemodynamic consequences for the patient

happening above the ventricles in the heart

• atrial flutter
• atrial fibrillation

• multiple P waves
• sometimes seen in cats, post induction
• we usually don't worry about it

no because there is still a QRS complex so the patient is still having regular ventricular contractions

• absence of a P wave and heart beat makes a different sound
• will have a pulse deficit - no pulse associated with a heart beat
• not a normal, healthy ventricular contraction - it is weak, poor, and pushes no blood out dispite being large on the EKG

VPC

trauma patients who have sustained myocardial bruising and dogs presenting for correction of gastric dilation and colculus (GDV) surgery

• if they are happening every no and then they are not a problem
• they become a problem when there are "runs" of VPCs - this can lead to ventricular fibrillation and death

• every other beat is a VPC
• only 50% of the beats are produces perfusion to the patient

every 3rd beat is a VPC

• normal beats and then a bunch of VPCs back to back
• frequency of the runs determines if it compromises the patient
• can lead to worse problems - more than 6 in a run with increasing frequency

• ventricular tachycardia means the patient is dieing
• Unifocal:  VPCs are firing all from one spot and they all look the same
• Multifocal:  VPCs are firing from different places

ventricular fibrillation

• no pulse, no mechanical activity
• ventricles are fluttering but not contracting of pushing out any blood

flat line

normal sinus rhythm

• sinus arrhythmia
• normal in dogs, not normal in cats
• pause in heart beat at the end of expiration

• sinus bradycardia
• conduction/pattern is normal just happening slower

• transient sinoatrial block
• pause in conduction at the SA node
• absent PQRST in an otherwise normal rhythm strip

• first degree AV block
• PR interval is > 0.2 seconds

• second degree AV block type 1 (mobitz 1)
• PR interval becomes increasingly long with each heartbeat until a heartbeat is skipped (QRS) and then it starts back over

• second degree AV block type 2 (mobitz 2)
• PR interval is always the same instead of getting longer with each beat - the heart just skips a beat every now and then

• sinus tachycardia
• normal conduction/pattern just happening faster

• atrial flutter
• multiple P waves

atrial fibrillation

• premature ventricular contraction (PCV or VPC)
• contraction is weak and poor with not blood being pushed out
• will have a pulse deficit - no pulse associated with a heart beat

• bigeminy
• a VPC every other beat

• Run of VPCs
• normal beats and then a bunch of VPCs back to back

• ventricular tachycardia - unifocal
• VPCs are firing from one spot and all look the same

• ventricular tachycardia - multifocal
• VPCs firing from different places

• ventricular fibrillation
• no pulse or mechanical activity
• ventricles are just fluttering but not contracting or pushing out any blood

• what is the rate and is it normal? (sinus tachycardia or sinus bradycardia)
• normal rhythm?  regular rhythm?  irregular rhythm (does the irregularity follow a regular pattern like a sinus arrhythmia)? 
• is there a P wave prior to each QRS? (if no...VPCs)
• is there a QRS to follow every P? (if no...second or third degree AV block)