The Heart of the Matter: Anesthesia for Patients with

Cardiac Disease

Molly Shepard DVM Dipl. ACVA

Continuing Education Seminar

Cobb Emergency Veterinary Clinic

October 3rd, 2012

Overview

• Cardiac function review

• Cardiovascular effects of anesthetic drugs

• Cardiac diseases

– General anesthetic considerations

– Case examples

Normal cardiac function

• It all starts with an action potential • Pacemaker cells

http://php.med.unsw.edu.au/embryolo

gy/index.php?title=Advanced_-

_Cardiac_Conduction

SA node 70-160 bpm

AV node/ His Bundle region

40-60 bpm

Bundle branches/

Purkinje network

20-40 bpm

Action potential – pacemaker cell

Craven 2006

Variable cardiac action potentials

http://healthyheart-sundar.blogspot.com/2011/03/cardiac-action-potential.html

Action potentials and ECG

http://www.pharmacolog

y2000.com/Cardio/antiar

r/antiarrtable.htm

Ventricular

muscle

Purkinje fibers

AV node

SA node

Atrial depolarization

http://www.sciencephoto.co

m/media/304266/view

AV node conduction

http://www.sciencephoto.co

m/media/304266/view

Bundle of His, bundle branches

http://www.sciencephoto.co

m/media/304266/view

Purkinje fibers

http://www.sciencephoto.co

m/media/304266/view

Ventricular depolarization

http://www.sciencephoto.co

m/media/304266/view

Ventricular repolarization

http://www.sciencephoto.co

m/media/304266/view

Two full cardiac cycles

http://web.squ.edu.om/med-Lib/MED_CD/E_CDs/anesthesia/site/content/v02/020536r00.HTM

Evaluation of cardiac function

• Physical exam/monitoring – Thoracic auscultation

• Heart rate and rhythm

• Presence of murmurs

– Mucous membrane color • Intestinal color

– CRT

– Pulse palpation • Pulse quality

• Pulse deficits

Evaluation of cardiac function

• Heart rate

• Heart rhythm

• Blood pressure – Indirect

– Direct

• Pulse oximetry

• Capnography

• Central venous pressure

Pressure – volume relationships

• Cardiac output = Heart Rate x Stroke Volume

Preload

Afterload

Contractility

Determinants of stroke volume

http://www.cvphysiology.co

m/Cardiac%20Function/CF

002.htm

Overview

• Cardiac function review

• Cardiovascular effects of anesthetic drugs

• Cardiac diseases

– General anesthetic considerations

– Case examples

Opioids

• Minimal CV effects (clinical analgesic dosing)

• Bradycardia

– Medullary vagal stimulation

– Responds to anticholinergics

• Histamine release hypotension

– Especially morphine (avoid rapid IV)

http://www.dailymedplus.com/monograph/view/setid/b325028e-0722-4c8c-9fdb-ab6fb0dc460c

Benzodiazepines

• Limited CV effects

• No appreciable change in HR, myocardial contractility, CO, ABP

– 0.5-2.5mg/kg IV (dogs)

• Generally cardio-protective

http://vurtpunk.deviantart.com/art/Mr-

Diazepam-13629111

Phenothiazines (acepromazine)

• Conscious dogs – Decreases SV, CO, MAP (20-25%, 0.1mg/kg IV)

– Increase or no change in HR

• Dogs on inhalant

• Ace premed then

isoflurane: 24% decrease

in MAP (0.1mg/kg IM)

• Conscious cats

• 30% decrease in MAP

(0.1mg/kg IM)

http://www.gopetplan.com/blogpost/petplan-pet-insurance-presents-a-

sedentary-life--pets-and-anesthesia

Alpha-2-agonists (dexmedetomidine)

• Dose-dependent CV effects

– Endogenous catecholamines antagonize the clinical effect

• Vasoconstriction hypertension

– Reflex bradycardia (e.g. HR<40-50 bpm)

– HR and CI decrease (60%, 5-20 micr domitor/kg, conscious dogs)

– Hypertension exacerbated by atropine when given simultaneously (Congdon 2011)

Dexmedetomidine

• ~35-45 minutes post injection

– Decreased vascular tone hypotension & decreased cardiac output

• CV effects lessened under inhalant

Imidazole hypnotics (etomidate)

• Metomidate in 35% propylene glycol – Can cause hemolysis (clin signif??)

• No change in HR, BP or myocardial performance (canine)

• Anti-convulsant properties – May be neuroprotective after global

ischemia (e.g. cardiac arrest)

• Should not be used as CRI – Cortisol suppression

http://www.safestchina.

com/wholesalers-

powder-injection/

Dissociatives (ketamine, tiletamine)

• Increased sympathetic efferent activity

– Positive inotropy

• Increased myocardial O2 demand

– 2 minutes post injection

• Increased HR, MAP, CO

– 15 min post-inj: normal HR, MAP, CO

– No change in vascular tone

http://www.adammaxwell.com/t

he-library/published-

online/special-k-and-the-

yorkshire-terrier-floatation/

Sedative hypnotic (propofol)

• Decreases arterial pressure

– Myocardial contractility

– Vasodilation (arterial and venous)

• Enhances catecholamine-associated arrhythmias

– Not inherently arrhythmogenic

http://www.za

zzle.com/got_

propofol_shirt

-

23546131003

3221603

Anticholinergics

• Block presynaptic muscarinic cholinergic receptors and parasympathetic nerve terminals

– facilitates NE and ACh release

– Sinus tachycardia

• Increased myocardial work

• Decreased myocardial perfusion

Volatile inhalants

• Dose-dependent CV effects – Direct myocardial depression

• Decreased CO, blood pressure

– Vasodilation HYPOTENSION

• Decrease sympathoadrenal activity – Renin/angiotensin system may not respond normally

to hemorrhage

• Partially obtunded baroreceptor reflexes – hypotension or hypovolemia may not cause

tachycardia

Cardiac diseases in dogs/cats

• Congenital – Patent ductus arteriosus – Aortic or pulmonic stenosis – AV valve dysplasia – Septal defects

• Acquired – Valvular endocardiosis – Hypertrophic cardiomyopathy (feline) – Dilated cardiomyopathy (canine) – Pulmonary hypertension

• Heartworm disease

– Dysrhythmias (noncardiac disease)

Overview

• Cardiac function review

• Cardiovascular effects of anesthetic drugs

• Cardiac diseases

– General anesthetic considerations

– Case examples

Cardiac murmurs

• Intensity: Grade (I-VI out of VI)

• Timing: systolic, diastolic

• Location (point of maximal intensity:

– Basilar/apical

– Left/right

http://en.wikipedia.org/

wiki/Heart_murmur

Innocent murmurs

• “Innocent” = functional – Mild turbulence within heart and great

vessels – Diminish by 4-5 months of age

• Characteristics – Systolic – < III or IV/VI intensity

• Intensity may change from day to day

– Short duration, low-pitched/vibrating

• Murmurs that are not innocent – >IV/VI intensity, precordial thrill, diastolic

Aortic and pulmonic stenosis

• Narrowed aortic or pulmonic outflow tracts

• Systolic basilar murmur

• CO depends primarily on HR – Positive inotropy doesn’t increase

CO

– Bradycardia decreased CO

– Tachycardia may predispose to ventricular arrhythmias • Very cautious use of anticholinergics

http://www.heart-valve-

surgery.com/aortic-stenosis-

valve-heart-narrowing.php

Pulmonic stenosis – Anesthetic recommendations

• Avoid drugs that drastically change heart rate – Anticholinergics

– Alpha-2-agonists (xylazine, dexmedetomidine)

• Maintain preload to maintain stroke volume – If fluid overload, result is ascites (this is less

critical than pulmonary edema)

– 5ml/kg/hr fluid rate

– 5ml/kg crystalloid boluses as needed for hypotension

Aortic stenosis – Anesthetic considerations

• Maintain heart rate

– Avoid: ketamine, alpha-2-agonists

– Use: opioids (maybe not fentanyl?)

• Maintain adequate stroke volume

– Fluid restriction

• Good monitoring is key

– TPR, ECG, Invasive blood pressure

– Capnography

Myxomatous Valvular disease

• Insufficiency or stenosis – impaired CO failure (if severe)

– Great variability in severity and valves involved

• Preanesthetic work-up – Min database, chest films, +/- echo

• Anesthetic goals – Maintain HR, contractility

– Avoid vasocontriction (increases in afterload)

http://www.dog-

obedience-training-

review.com/cavalier-king-

charles-spaniel.html

Valvular insufficiency – anesthetic guidelines

• Skip morning dose of ACE inhibitor

• Protocol: – Use opioids +/- benzodiazepines

– Induce with ket/val or propofol (mild) or etomidate/val (severe)

– Conservative IV fluid therapy

– Use anticholinergics with caution

– BP monitoring +/- CVP

• Contraindicated: α-2-agonists – Bradycardia, increased afterload

Hypertrophic cardiomyopathy (feline)

• Stiff LV, poor diastolic function

– Mitral regurg and hypertension

• Early disease

– symptomatic (+/- murmur)

• Progressive disease

– Murmur, arrhythmias, dyspnea, thromboembolic disease

– Heart failure, sudden death with stress

http://www.statesymbolsu

sa.org/Maine/cat_maine_

coon.html

Anesthetic management (feline HCM)

• Contraindicated drugs – Acepromazine

• Decreases afterload reduced coronary perfusion

– Ketamine and anticholinergics • Increases myocardial O2 demand

• Monitoring – TPR, indirect blood pressure, ECG

– Ideal if symptomatic: direct blood pressure, capnography, pulse oximetry

• Ventilation for Fozzy: peak airway pressure <15 cm H2O

Dilated cardiomyopathy (canine DCM)

• Features – Systolic dysfunction

– Increased end-systolic and end-diastolic volumes eccentric hypertrophy

– Poor myocardial contractility

– +/- dysrhythmias • Atrial fibrillation

– No atrial contraction (“kick”)

– No atrial-ventricular synchrony low stroke volume

DCM - Anesthetic recommendations

• Delay elective procedures

• Maintain contractility – Avoid negative inotropic drugs, e.g.

propofol, alpha-2-agonists

• Maintain normal heart rate – Avoid drugs that cause tachycardia

(anticholinergics)

– Avoid drugs that cause bradycardia (alpha-2-agonists, high dose opioids)

DCM – Anesthetic recommendations

• Pre-operative: measure blood pressure

• Premeds: opioid/benzo combo

• Induction drugs – Etomidate or neurolept combo

– Ketamine = okay if paired with benzodiazepine.

• Maintenance with inhalant – Opioids decrease inhalant requirement

http://balilandandvilla.blogsp

ot.com/2012/08/doberman.ht

ml

Pulmonary hypertension (e.g. heartworm disease)

• Pulmonary hypertension

– Avoid ketamine and dexmedetomidine

– Good monitoring

• Symptomatic HW disease

– Dysrhythmias

– Pulmonic embolic disease

– Possible decreased CO

https://www.msu.edu/~silvar/h

eartworm.htm?pagewanted=al

l

Heartworm disease: anesthetic recommendations

• USE benzodiazepines and opioids

• Avoid drugs that significantly increase afterload – Don’t use dexmedetomidine

• Cautious with acepromazine

• +/- Avoid drugs with documented link to pulmonary hypertension – Ketamine

– Oxymorphone

General anesthetic guidelines for cardiac patients

• Preoxygenate ~3-5 minutes

• Good monitoring (case-appropriate)

– TPR

– Blood pressure!!

– +/- ECG

– +/- capnography

– +/- pulse oximetry

• Use multi-modal approach!

Drugs to use carefully in cardiac patients

• Drugs that cause tachy- or bradycardia

• Drugs that significantly change SVR

• Drugs that decrease contractility

• Drugs/techniques with a narrow margin of safety

– Mask induction (no premed)

– High-dose acepromazine (>0.05mg/kg)

General anesthetic guidelines for cardiac patients

• +/- fluid restriction (2-5ml/kg/hr)

– Depends on disease and procedure

• Drugs almost always appropriate for cardiac patients (with good monitoring!)

– Opioids

– Benzodiazepines

– Etomidate

– Regional/local anesthesia

General anesthetic guidelines for cardiac disease

• Keep procedure as short as possible

• Post-op monitoring

• Skip morning dose of ACE inhibitors

–Reduce intraanesthetic

hypotension

http://shop.farmvet.com/P

harmacy/Pet_Pharmacy/E

nalapril-Maleate-Tablets

Summary…

• Anesthetic drugs have variable effects on cardiovascular function

– Safe anesthetic management depends on…

• Knowledge of these anesthetic drug effects

• Knowledge of cardiac pathophysiology

• Monitoring!

• Good planning and organization!

“There are no safe anesthetic

agents, there are no safe anesthetic

procedures. There are only safe

anesthetists.” -Robert Smith, MD

And for those lingering questions or difficult cases…

• The UGA Anesthesia service does phone consultations! 800-861-7456 – Erik Hofmeister, DVM MA DACVA, DECVAA

– Jane Quandt, DVM MS DACVA DACVECC

– Molly Shepard, DVM DACVA

– Cynthia Trim, BVSc, MRCVS, DVA, DACVA, DECVAA

– Residents: • Jill Maney, VMD

• Stephanie Kleine, DVM

References

• Congdon JM, et al 2011. Evaluation of the sedative and cardiovascular effects of intramuscular administration of dexmedetomidine with and without concurrent atropine administration in dogs. 1;239(1):81-9.

• Guyton and Hall. 2006. Textbook of Medical Physiology.

• Tranquilli, Thurmon, Grimm. 2007. Lumb and Jones’ Veterinary Anesthesia and Analgesia.

• Tilley, Smith, Oyama, Sleeper. 2008. Manual of Canine and Feline Cardiology.

• Lamont LA, et al. 2002. Doppler echocardiographic effects of medetomidine on dynamic left ventricular outflow tract obstruction in cats. JAVMA 221 (9): 1276-1281.

• Cardiac cycle diagram: http://www.google.com/imgres?imgurl=http://2.bp.blogspot.com/_uiyskjNZYt8/TJW2uBf-P2I/AAAAAAAACHc/efGjdpXNqwQ/s1600/Mechanical%2Band%2BElectrical%2BEvents%2Bof%2Bthe%2BCardiac%2BCycle.jpg&imgrefurl=http://medipptx.blogspot.com/2010/09/mechanical-and-electrical-events-of_501.html&usg=__0wpCdLXkpAFTj2CZG4YKEB-8MrQ=&h=816&w=1200&sz=149&hl=en&start=0&sig2=yv9g0Q1TS4vTCsIbQ9N9lw&zoom=1&tbnid=nsmBikvf3tCLTM:&tbnh=129&tbnw=179&ei=nhPLTbSiLYS2twfklvDhBw&prev=/search%3Fq%3Dcardiac%2Bcycle%26hl%3Den%26sa%3DX%26rls%3Dcom.microsoft:en-us:IE-SearchBox%26rlz%3D1I7TSNA_enUS371US371%26biw%3D1345%26bih%3D585%26tbm%3Disch%26prmd%3Divns0%2C34&itbs=1&iact=hc&vpx=382&vpy=225&dur=6942&hovh=185&hovw=272&tx=142&ty=105&page=1&ndsp=21&ved=1t:429,r:9,s:0&biw=1345&bih=585

• Aortic stenosis diagram: http://www.google.com/imgres?imgurl=http://petheatlhinfo.com/wp-content/uploads/2011/01/Aortic-Stenosis.gif&imgrefurl=http://petheatlhinfo.com/aortic-stenosis-dogs.html&usg=__FmP2lWIklHLRucmlNSbSVBqI2GE=&h=350&w=350&sz=38&hl=en&start=0&sig2=fxyOUSz2-w3ELXMk_rhPUg&zoom=1&tbnid=BpWaWJnxyDDMDM:&tbnh=160&tbnw=156&ei=6lnLTYfRIcXL0QGSvsCoBQ&prev=/search%3Fq%3Daortic%2Bstenosis%2Bcanine%26hl%3Den%26sa%3DX%26rls%3Dcom.microsoft:en-us:IE-SearchBox%26rlz%3D1I7TSNA_enUS371US371%26biw%3D1345%26bih%3D585%26tbm%3Disch%26prmd%3Divns&itbs=1&iact=hc&vpx=133&vpy=185&dur=9454&hovh=225&hovw=225&tx=108&ty=134&page=1&ndsp=12&ved=1t:429,r:0,s:0

• PDA diagram: http://www.google.com/imgres?imgurl=http://health.stateuniversity.com/article_images/gem_04_img0496.jpg&imgrefurl=http://health.stateuniversity.com/pages/1146/Patent-Ductus-Arteriosus.html&usg=__RHxfb65ZXDu3dBE2B1FP3kSHPN4=&h=282&w=370&sz=22&hl=en&start=0&sig2=mMcAqGG1Q_Q4RAjfFTB9xQ&zoom=1&tbnid=5QFzhJv9hR-JZM:&tbnh=121&tbnw=159&ei=glrLTd-mPKTY0QGy7sHCBQ&prev=/search%3Fq%3Dpatent%2Bductus%2Barteriosus%26hl%3Den%26sa%3DX%26pwst%3D1%26rls%3Dcom.microsoft:en-us:IE-SearchBox%26rlz%3D1I7TSNA_enUS371US371%26biw%3D1345%26bih%3D585%26tbm%3Disch%26prmd%3Divns&itbs=1&iact=hc&vpx=975&vpy=112&dur=10186&hovh=196&hovw=257&tx=144&ty=137&page=1&ndsp=23&ved=1t:429,r:5,s:0

• http://php.med.unsw.edu.au/embryology/index.php?title=Advanced_-_Cardiac_Conduction

• http://php.med.unsw.edu.au/embryology/index.php?title=Advanced_-_Cardiac_Conduction