Cardiac Considerations Post MI

7/29/2019 Cardiac Considerations Post MI

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Noncardiovascular Surgery for the

Cardiac Patient

Wayne E. Ellis, Ph.D., CRNA





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Preoperative Assessment

• History

• Physical exam

• Laboratory findings and other

tests



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History - Do a good one!!!

• Stability of angina

– NYHA

• Class I: Mild angina without impairment

• Class IV: Angina at rest

– Exercise tolerance!

– Ventricular function

– Associated cardiovascular diseases

– Medication



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Recent Myocardial Infarction

Less than three months

Patient < 70 years of age

Location of surgery

Duration of surgery

Poor LV function

CHF

Enlarged heartArrhythmias

Increased risk of morbidity and MORTALITY



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Perioperative Predictors

Recent MI

< 6 months

Current CHFOnly consistent predictors of

perioperative outcome



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Challenge of anesthesia

Adequately evaluate the patient

Provide adequate anesthesia

Prevent myocardial injury

Maximize postoperative pain management



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RISK FACTORS

• genetic predisposition

• age

•gender

• obesity

• hyperlipedemia

•

diabetes mellitus• hypertension

• stress, tobacco, and smoking



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Smoking

• Increases the risk of an initial cardiac event

and doubles the rate of subsequent infarction

and death.

• Risk rapidly declines after stopping and by 3

years reaches that of survivors who have

never smoked.



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Assessment of risk factors

Cigarette smoking

HypertensionDiabetes

Family history

May have a normal physical



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Perioperative estimation of cardiac risk

Recent preoperative MI

average 8% reinfarction if within 3 months

Optimal preparation

Invasive Monitoring

Without monitoring

> 30%

Age

> 7010 fold increased risk



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Coronary Artery Disease

• Most common cause of premature death for males

between 35-45years of age.

• Each year 1.5 million MI’s occur in the U.S.

• 280,000 OHS every year in the U.S.• $60 billion spent annually to treat CAD

• OHS represents 80% of the total adult operations

performed at most medical centers in the U.S.



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Atheroscelerosis

• begins as crystals of cholesterol adheres to

the intima.

• These crystals then form a larger matrix that

stimulates surrounding fibrous and smooth

muscle tissue growth to create additional

layers i.e.) larger plaques can grow



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Atheroscelerosis

• Larger plaques then develop into total obstructive

lesions, resulting in sclerosis(fibrosis)

• Atherosclerosis lesions become symptomatic with 75%

stenosis of one or more coronary vessels = ischemia,which depresses the myocardial function, causes chest

pain (angina pectoris).



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CAD

• Modulated by 3 factors

– 1) Myocardial oxygen demand

– 2) Myocardial oxygen supply

– 3) Coronary blood flow



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Myocardial Oxygen Demand (MvO2)

• Heart extracts more 02 than any other organ, 50-70% at

rest

• BP and HR provides a basic guideline for Mv02• contractility and myocardial wall tension are primary

determinants of Mv02

• wall tension can be lowered by decreasing preload

• contractility can be lowered by beta blockers or pain

management relief



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Determinants of Oxygen Supply

Degree of muscular contractility

Frank Startling PrincipleThe more stretch placed on a muscle fiber

before contraction, the more forceful the

contraction.

Ventricular preload



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Wall tension of the left ventricle

Afterload

With increased resistanceHypertrophy

Increased muscle mass

Maintain normal wall tension



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Heart rate

The faster the rate the more oxygen required

The faster the rate there is less time for tissueoxygenation



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Myocardial Oxygen Supply

• Any increase in myocardial oxygen

requirements can be met only by raising

coronary blood flow

• Maintaing the bloods oxygen carrying

capacity is the secondary objective for

cardiovascular perfusion



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• Oxygen content = Ca02

• CaO2 = (hgb x 1.34) x Sa02 + (Pa02 x 0.0003)

•

1.34 = milliliters of 02 per gm of hgb• Sa02 = % of oxyhemoglobin of total

hemoglobin(fractional saturation)

•

0.003 = oxygen solubility in plasma



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Influences affecting oxygen supply

Coronary blood flow

Left ventricle during diastole

With increased heart rate diastole is shortened

Coronary perfusion pressure

Diastolic pressure minus left ventricular end

diastolic pressure

CPP = DP-LVEDP



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Oxygen Supply

With coronary stenosis

Improve CPP

Increase systemic pressure

Lower elevated LVEDP

Nitroglycerin

Hgb Level

Oxygen saturation



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• Any increase in myocardial oxygen

requirements can be met only by raising

coronary blood flow

• Maintaing the bloods oxygen carrying

capacity is the secondary objective for

cardiovascular perfusion



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Coronary blood flow

• Perfusion of the left ventricle takes place

almost entirely during diastole, whereas the

right ventricle occurs mostly with systole.

• Not only is diastole important, but the length

of diastole is critical in determining the

volume of left ventricular subendocardial

flow



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Coronary blood flow

• Coronary perfusion psi = aortic diastolic

pressure(AoDp) - LVEDP

• Note hypotension is more likely to produce

ischemia than hypertension



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Temperature

Keep warm

Decreasing temperatureShift Oxygen dissociation curve to left

Hgb retains oxygen at tissue level

Prevent alkalosis



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Evaluation

Select patients at highest risk of difficulty

Reinfarction in 1st 6 months post MI high

High fatality rateCABG or Angioplasty first

Choice of monitoring



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Physical exam: Not a lot here

• Vital signs

• Cardiac exam

– PMI

– Gallops

• S4: HTN, S3: increased LVEDP

– Apical systolic murmur

• Papillary muscle dysfunction

– Precordial bulge

– Other signs of LV function

• JVD, pulmonary signs



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Physical Examination

Cardiovascular

JVD

Carotid Bruits

Murmurs

S3, S4, Click, Rub

Pitting Edema

Pulses

Vascular Access



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Physical Examination

Pulmonary

Wheezes

Rales

Rhonchi

A-P Diameter



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ECG

• How many msec after the J point??

• How many mm??

• A resting 12 lead is not a whole lot of good for detecting ischemia



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Chest X-Ray

• Cardiomegaly

• Signs of ventricular dysfunction

– Edema, effusions

• Complicating diseases

– Calcification of vessels, valves

– Pulmonary disease



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Blood tests

• CK, other cardiac enzymes

– R/O after surgery: Usually an MB of about 5-

7% of total CK

• Triponin >7 positive

• Associated diseases

– Diabetes, thyroid disease



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Primary Treatment

• Antiplatelet agents(abciximab,eptifibatide, tirofiban,

integullin)

•

GPIIb-IIIa antagonists• inhibit platelet function by blocking the GPIIb-IIIa

receptor, the final pathway of platelet aggregation

• thereby decreasing thrombi development and prevents

arterial vessel occlusion



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Percutaneous Coronary Intervention

• Advantages include: higher recanulazation

rates

• improved blood flow through the infarct-

related vessel

• improved LV function

• lower in-hospital mortality rates



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Normal Hemodynamic Measurements

RA (mean)

RV (mean)

PA (sys/dys)LA or wedge (mean)

LV (sys/dys)

Systemic arterial (sys/dys)

2 - 8

15 - 30/2 - 8

15 - 30/4 - 122 - 10

100 - 140/3 - 12

100 - 140/60 - 90



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Monitoring

Routine

Pulse Oximetry

PNS

Capnography

Temperature

Core and peripheral

ECGLeads V5 and II



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Monitors of Cardiac Performance

Arterial Line

Standard of Care

Site selection

Pulmonary Artery Catheter

Provides means for assessing filling pressures

Reliable site for drug administration

Transesophageal Echocardiography



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Physical signs

Jugular distentionChest sounds

Rales

Extra heart sounds



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Preoperative Evaluation

History

Physical assessment

EKG evaluation

Exercise tolerance

Chest X-ray

Lab studies



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Preoperative Evaluation

Current Medication

Beta-blockers

Calcium Channel Blockers

Antidysrhythmia agents

Nitrates

Diuretics

Antihypertensive agents



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Dyspnea

Activity

Rest

What starts it

How long lasts



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Dynamic Predictors

Acute imbalances in myocardial oxygen supply and

demand may produce ischemia that may result in

irreversible cardiac morbidity

HypertensionHypotension

Tachycardia



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Dynamic Predictors

Hypertension

No conclusive correlation

Intraoperative Hypertension

MI

Acute Hypertension

Precedes intraoperative ischemic events

50% of time



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Dynamic Predictors

Hypotension

25 % of ischemic events associated with > 20 % decrease in

systolic blood pressure

6 % decrease in MAP

Important predictor of PCM

Higher reinfarction rate

15.2 % vs. 3.2 %

Intraoperative hypotension

> 30% decrease in systolic BP

> 10 minutes duration



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Dynamic Predictors

TachycardiaCombination with hypotension

Ominous

Significant indicator of PCM

Myocardial Ischemia

ST changesNot a clear indicator of PCM

TEE

Most sensitive, earlier indices of ischemia

Before ST segment changes



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Treatment of ischemia

• Is it real?

• Optimize oxygenation and hemodynamics

• IV NTG

• SL Nifedipine• Diltiazem

• Intra-aortic Ballon Pump

– Improves systolic run off

– Provides diastolic augmentation



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Anesthesia Goals

Balance supply and demandControl heart rate

Normal to slow range

Maintain CPP

Prevent hypotension

Prevent increased LVEDP

Optimize arterial oxygen and carbon dioxide

statusKeep patient normothermic

Higher threshold for transfusion



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Anesthesia

• Goal

• Does technique make a difference?

•

Laryngoscopy• Maintenance

• Regional anesthesia



Preoperative Preparation

AnginaMedications to control it

Blood pressure controlled

Diastolic < 95 torr

Congestive heart failure treated

Diuretics

Afterload reduction

Bedrest if indicated

Control diabetes



Preoperative Medications

SedationPrevent tachycardia

Hypertension

Prepared for hypoxiaSupplemental oxygen

Calcium channel blockers not protective of

perioperative ischemia

Antihypertensives continue on day of surgery

Stop Diuretics



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Antianginal medications

Beta-blockers

Calcium Channel BlockersNitrates

Nitropaste morning of surgery



Beta Blockers

Negative inotropic effects

Withdrawal following stoppage of betablocker

Unstable angina

Myocardial infarction



Monitoring

EKG

Blood Pressure

Temperature

Pulse oximetry

End tidal CO2



Arterial Catheter

Beat to beat blood pressure monitoring

ABGsEarly detection of hypotension



Laboratory studies

HGB & HCT

Electrolytes

Liver function studiesCreatine clearance

Osmolality



Noninvasive beat to beat

analysis

Finapress

Ohmeda



PA catheter

Assessment of LV Function

Early detection of ischemia

“v” waves

Increased PCWP

More accuracy than CVP

Intravascular volume problems

Especially in patients with severe lung disease

Transesophageal



Transesophageal

Echocardiography

Demonstrates regional wall motion

abnormalitiesSuggestive of ischemia

Most accurate measure of left ventricular

volume

Non-invasive Continuous Cardiac



Non invasive Continuous Cardiac

Output Monitors

Transesophageal Doppler

Thoracic impedance

Limited

Accuracy is controversial

No information about systemic

vascular resistance

Measure CVP

Improved outcomes



Improved outcomes

Aggressive monitoring & treatmentVasoactive drugs

Reduced intraoperative ischemia

MI < 6 months has better survival rateOccurrence reduced from 30-5%

Multi-institution study over last 10 years

5000 patients

Continued for 3 days post-operatively

Decision to use Invasive



Decision to use Invasive

Monitoring

Patients with severe inoperable CAD

Chronic stable angina undergoing significant

abdominal or thoracic surgery

Large blood loss

History of remote MI with stable angina

Not necessary to use invasive monitors



Anesthetic Management

Regional vs general

Anesthetic management skills more

important than technique

Safest technique is the one the practitioner

does best

General anesthesia



General anesthesia

Avoids sympathectomy

Risks with intubation

Sympathetic stimulation

Hypoxia

Increased catecholamines

Loss of subjective monitor

Chest pain

Ischemia



General Anesthesia required

Narcotics

Effective control of catecholaminesRespiratory depression

Prolonged ventilation



Avoid Ketamine

Hypertension

TachycardiaUse in trauma



Etomidate

Painful to inject

More CV stability



Barbiturate

Direct depressant

Extended duration of activity

Smaller doses1-2 mg/kg

Add benzodiazepines and narcotic



Benzodiazepines

Quell anxiety

Hemodynamic stability

Extended duration of actionPotential for hypoxia

Lidocaine

Esmolol



Muscle Relaxants

Avoid pancuronium

Tachycardia

ST segment changes consistent with ischemia

Doxacurium

Duration similar to pancuronium

No cardiovascular effects



Avoid Histamine releasing drugsCurare

Atracurium

Mivacurium <15 mcg/kg

Hypotension

Tachycardia



Inhalation Agents

Potential for coronary steal

Alters coronary autoregulation

Alters regional blood flow

Little influence on outcome



Nitrous Oxide

Constricts coronary arteries

Aggravates myocardial ischemia

High FiO2 recommended

Maintain saturation at 95-100%



Regional Anesthesia

Monitor patient more accurately

Control sympathetic responsesFluids

Esmolol



Intraoperative predictors

Choice of anesthetic

Site of surgery

Duration of AnesthesiaEmergency Surgery




Choice of AnestheticNo difference in infarction rate GETA vs. Regional

No significant hypotension

No significant tachycardia

TURP

Regional decreased risk post MI

Reinfarction rate

SAB < 1%

GETA 2-8%




Choice of AnestheticPatient with CHF will benefit from regional technique

Sympathectomy

Decreased preload

Coronary Steal

Potent inhalation agents vs. narcotics




Site of SurgeryThoracic and upper abdominal

2-3 X’s risk of extremity procedures

Duration of Anesthetic

> 3 hours > risk of morbidity & mortality

Emergency Surgery

2 - 5 X’s greater risk than nonemergent surgery



Cardioactive drugs

Nitroglycerin

Lower LVEDPVasodilator

Poor ventricular function



Esmolol

Control heart rate and blood pressure

InductionEmergence



Labetalol

Mixed alpha and beta

Control hypertensionHeart rate management



Lidocaine

Blunt effects of intubation

1.5 mg/kg 4-6 minutes prior to

intubation



Clonidine

Less hypertension

Decreased anesthesia requirements



Nifedipine

Controlling hypertension

Manage coronary artery spasm



Postoperative Management

Maintain analgesia

Balance supply and demand

Supplemental oxygenContinue monitoring into postoperative

period

Early transfusion





Major GoalBalance Supply and Demand

Primary Determinants of Myocardial Oxygen

DemandWall tension and Contractility





Factors modifying coronary blood flowdiastolic time

perfusion pressure

coronary vascular tone

intraluminal obstruction





Myocardial O2 Extractioninfrequently the cause of ischemia intraoperatively

Arterial O2 Content

Correction of anemia

High FiO2

Hemodynamic Goals for the




Patient with CADP - keep the heart small, decrease wall

tension, increase perfusion pressure

A - maintain, hypertension better than

hypotension

C - depression is beneficial when LV function is

adequate

R - slow, slow, slow





patient with CADRhythm - usually sinus

MVO2 - control of demand frequently not

enough, monitor for and treat “supply

ischemia

CPB - elevated ventricular filling pressure

usually not needed after CABG

Anesthetic Technique



Anesthetic Technique

Goals of Anesthesialoss of conciousness

amnesia

analgesia

suppression of reflexes (endocrine and autonomic)

muscle relaxation

Inhalation Agents



Inhalation Agents

AdvantagesMyocardial oxygen balance altered favorably by

reductions in contractility and afterload

Easily titratableCan be administered via CPB machine

Rapidly eliminated

Inhalation Agents



Inhalation Agents

DisadvantagesSignificant hemodynamic variability

May cause tachycardia or alter sinus node function

Possibility of “coronary steal syndrome”

Coronary Steal



Coronary Steal

Arteriolar dilation of normal vessels diverts bloodaway from stenotic areas

Commonly associated with adenosine, dipyridamole,

and SNPForane causes steal and new ST-T segment depression

May not be important since Forane reduces SVR,

depresses the myocardium yet maintains CO

Opioids



Opioids

AdvantagesExcellent analgesia

Hemodynamic stability

Blunt reflexes

Can use 100% oxygen

Opioids



Opioids

DisadvantagesMay not block hemodynamic and hormonal

responses in patients with good LV function

Do not ensure amnesiaChest wall rigidity

Respiratory depression

Induction Drugs



Induction Drugs

Barbiturates

Benzodiazepines

Ketamine

Etomidate

Nitrous Oxide



Nitrous Oxide

Rarely used due to:increased PVR

depression of myocardial contractility

mild increase in SVR

air expansion

Muscle Relaxants



Muscle Relaxants

Used to:facilitate intubation

prevent shivering

attenuate skeletal muscle contraction duringdefibrillation

Postoperative predictors



Postoperative predictors

Ischemia does occur most commonly in thepostoperative period

Persists for 48 hours or longer following non-cardiac

surgery

Predictor value is unknown

Goldman, L., (1983) Cardiac Risk and Complications of

noncardiac surgery, Annals of Internal Medicine.

98:504-513



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Cardiac Considerations Post MI