Anesthetic Management of Patients with Ischemic Heart Disease

Hemodynamic Goals of Induction and Maintenance of General Anesthesia

Core Pathophysiological Principle

Determinants of Myocardial O₂ Supply and Demand

• The left ventricle is perfused almost entirely during diastole
• Tachycardia disproportionately reduces diastolic time, simultaneously increasing demand and reducing supply - the most dangerous combination in IHD
• The right ventricle is perfused during both systole and diastole

HEMODYNAMIC GOALS

1. Heart Rate - THE MOST CRITICAL PARAMETER

• Tachycardia is the most common precipitant of perioperative ischemia; it increases demand and reduces supply simultaneously
• Disproportionate shortening of diastolic time at higher heart rates (diastolic time falls non-linearly with HR) directly limits coronary perfusion
• Bradycardia <45 bpm should also be avoided as it reduces cardiac output
• The most common hemodynamic abnormalities seen during ischemic episodes are hypertension and tachycardia - they are almost always the cause (not the result) of ischemia

• Adequate depth of anesthesia before laryngoscopy
• Opioid preloading (fentanyl 2-5 mcg/kg before intubation) to blunt laryngoscopy response
• Beta-blockers (esmolol 0.5-1 mg/kg IV) to treat intraoperative tachycardia
• Volatile agents (all have rate-lowering tendency at adequate MAC)
• Avoid anticholinergic tachycardia; if needed for bradycardia, use glycopyrrolate (less tachycardia than atropine)

2. Blood Pressure - Maintain in a Narrow Range

A. Hypertension

• Increases afterload → increases wall tension → increases O₂ demand
• Hypertension during laryngoscopy/intubation is one of the most dangerous moments
• Down-sloping/horizontal ST depression almost always accompanies severe hypertensive responses in IHD patients
• Management: adequate depth (volatile agent titration), iv fentanyl, β-blockers, nitroglycerin, nicardipine

B. Hypotension

• Reduces coronary perfusion pressure (Aortic DBP - LVEDP)
• Hypotension is a late and ominous manifestation of progressive ventricular dysfunction
• Higher diastolic pressures are preferable in patients with high-grade coronary occlusions
• The endocardium is most vulnerable to ischemia during hypotension (highest intramural pressures during systole)
• Management: vasopressors (phenylephrine preferred - pure α-agonist, does not increase HR; norepinephrine if cardiac output low); treat cause (hypovolemia, vasodilation from anesthetics, myocardial depression)

3. Preload (LVEDP / Filling Pressures)

• Excessive preload (fluid overload): Increases LVEDP → reduces coronary perfusion pressure (supply falls) AND increases ventricular wall tension (demand rises) - a double jeopardy
• Elevated LVEDP specifically reduces subendocardial perfusion
• Hypovolemia: Reduces preload → reduces cardiac output → hypotension → reduces coronary perfusion
• Optimal filling: guided by clinical assessment, arterial waveform variation, or TEE (LV chamber size)
• PAC-measured PCWP rises abruptly with ischemia (though PAC rarely used now)

4. Contractility

• Increased contractility = increased O₂ demand
• Excessive anesthetic-induced depression → low CO → hypotension → reduced perfusion
• Most volatile agents are mildly negatively inotropic - this is acceptable and even beneficial at moderate doses (reduce demand, reduce preload/afterload)
• Volatile agents also exert anesthetic preconditioning - activate ATP-sensitive K⁺ channels, reduce reperfusion injury, help "stunned" myocardium recover
• Avoid catecholamine surges (laryngoscopy, surgical stimulation) - they massively increase contractility and HR simultaneously

5. Systemic Vascular Resistance (Afterload)

• High SVR → increased wall tension → increased O₂ demand
• Low SVR → hypotension → reduced coronary perfusion pressure
• The goal is stable SVR within normal limits

6. Arterial Oxygen Content (CaO₂)

• Maintain adequate oxygenation and ventilation throughout
• Anemia → compensatory tachycardia → worsens supply-demand balance
• Most clinicians are reluctant to allow Hb <7 g/dL in CAD patients; transfusion decision is individualized
• Hypoventilation with resulting hypoxia and hypercarbia (both cause sympathetic stimulation and tachycardia) must be avoided

INDUCTION - SPECIFIC GOALS AND STRATEGIES

The Critical Period: Induction and Laryngoscopy

1. Anesthetic agents cause vasodilation/myocardial depression → risk of hypotension
2. Laryngoscopy causes intense sympathetic stimulus → tachycardia and hypertension

Induction Agents

• Propofol: Most commonly used; causes vasodilation and mild myocardial depression - titrate slowly to avoid sudden hypotension; use with opioid preloading
• Etomidate: Hemodynamically most stable (minimal CVS effects) - preferred when LV function is compromised; causes minimal change in HR, BP, and SVR; however does not blunt laryngoscopy response
• Ketamine: Generally avoided in IHD - sympathomimetic properties increase HR, BP, and O₂ demand; occasionally used when hemodynamics are very compromised
• Thiopental: Historically used, causes vasodilation and mild myocardial depression

Blunting Laryngoscopy Response

1. Opioid preloading - fentanyl 2-5 mcg/kg, remifentanil infusion
2. Lignocaine IV - 1.5 mg/kg given 90 seconds before intubation
3. Beta-blockers - esmolol 1-2 mg/kg bolus before laryngoscopy
4. Topical laryngeal analgesia - 4% lignocaine spray
5. Adequate depth - deep enough volatile anesthetic or propofol before laryngoscopy
6. Keep laryngoscopy brief - <15 seconds; use video laryngoscope

MAINTENANCE - SPECIFIC GOALS

Choice of Anesthetic Agents

• All are coronary vasodilators
• Reduce myocardial O₂ requirements
• Provide anesthetic preconditioning (cardioprotection via KATP channels)
• Reduce preload and afterload at moderate doses
• Caveat: Desflurane causes sympathetic stimulation during rapid increases in concentration → avoid rapid up-titration in IHD

• ACC/AHA Class IIa recommendation: either volatile or TIVA is reasonable (LOE: A)
• Propofol reduces preload and afterload but lacks preconditioning benefit

• High-dose opioid techniques provide excellent hemodynamic stability
• Fentanyl, sufentanil, remifentanil - blunt sympathetic responses, minimal direct cardiac depression
• Remifentanil infusion is particularly useful for moment-to-moment titration

• Vecuronium or rocuronium preferred (minimal cardiovascular effects)
• Avoid pancuronium (vagolytic - causes tachycardia)
• Avoid succinylcholine as primary agent if not needed urgently (fasciculations → transient increases in IOP and oxygen demand)

Maintaining Hemodynamic Stability During Surgery

• Increase depth of anesthesia
• Esmolol (short-acting β-blocker) or metoprolol
• Address pain/light anesthesia
• Ensure adequate analgesia

• Deepen anesthesia, increase volatile agent
• Nicardipine, labetalol, or GTN infusion
• Ensure adequate opioid analgesia

• Reduce anesthetic depth
• IV fluid bolus if hypovolemic
• Phenylephrine (if BP low, HR normal/high)
• Ephedrine (if BP low, HR low)
• Check ECG for new ischemia immediately

Temperature

• Maintain normothermia - hypothermia → shivering post-op → massive increase in O₂ demand; ACC/AHA Class IIb recommendation

MONITORING REQUIREMENTS

SUMMARY TABLE: Hemodynamic Goals in IHD

KEY EXAM POINTS TO REMEMBER

1. Tachycardia is the enemy - it simultaneously increases demand and reduces supply by shortening diastole
2. Coronary perfusion pressure = Aortic DBP - LVEDP - both sides of this equation matter
3. The myocardium cannot increase oxygen extraction (already near-maximal at rest) - supply must match demand
4. Volatile agents are cardioprotective via preconditioning (KATP channel activation) - this is a pharmacological advantage over TIVA
5. Hypotension is a late sign of ventricular dysfunction - by the time BP falls due to ischemia, significant myocardium is already compromised; the goal is to prevent this from happening
6. Induction and laryngoscopy are the highest-risk periods - use opioid preloading, adequate depth, and short laryngoscopy time
7. Etomidate is the hemodynamically most stable induction agent - preferred in compromised LV function
8. Pancuronium is contraindicated - vagolytic tachycardia
9. TEE > ECG for early ischemia detection (RWMA precede ST changes)
10. ACC/AHA: Either volatile or TIVA is acceptable (Class IIa, LOE A); prophylactic intraoperative nitroglycerin is not recommended (Class III: No Benefit)

Goldman's Cardiac Risk Index (CRI)

Short Note for MD Anaesthesia Exam

Introduction

The Nine Risk Factors and Their Point Values

Memory aid: "MI, S3, ECG, Age, Aortic stenosis, Poor status, Big surgery, Emergency" Point values (high to low): S3/JVP (11) > Recent MI (10) > PAC/non-sinus rhythm (7) = PVCs (7) > Age >70 (5) > Emergency op (4) > Aortic stenosis (3) = Big surgery (3) = Poor status (3)

Risk Classification and Cardiac Event Rates

• Class I and II = Low risk - proceed with surgery with standard precautions
• Class III = Intermediate risk - consider optimization and enhanced monitoring
• Class IV = High risk - surgery only if absolutely necessary; aggressive optimization; ICU care

Key Observations from the Original Study

1. Congestive cardiac failure (S3 gallop/raised JVP) carried the highest point value (11) - reflecting the importance of ventricular dysfunction as a risk determinant
2. Recent MI (<6 months) was the second highest risk factor (10 points). This gave rise to the classic teaching to defer elective surgery for 6 months following MI (now revised downward to 30-60 days with modern revascularization)
3. Arrhythmias - non-sinus rhythm and frequent PVCs were independent risk factors even without structural disease
4. Hypertension alone was NOT found to be an independent predictor of perioperative cardiac risk in this study (a surprising and controversial finding at the time)
5. Type of surgery mattered: major abdominal, thoracic, and aortic operations were higher risk than peripheral procedures

Limitations of the Original Goldman Index

1. Single-centre study - Massachusetts General Hospital; may not be generalizable
2. Small sample size (1,001 patients) with relatively few outcome events
3. Dated - does not include modern risk factors such as diabetes, renal insufficiency, or cerebrovascular disease
4. Does not account for functional capacity (METs) - a powerful predictor now incorporated in modern guidelines
5. Does not include type of anaesthesia or quality of intraoperative management
6. 6-month MI rule has been revised - with modern PCI, elective surgery may be considered at 30-60 days post-MI with appropriate precautions
7. Aortic and vascular surgery population was poorly represented - performs less well in vascular patients
8. No provision for echocardiographic or stress testing data

Subsequent Modifications and Evolution

Detsky Modified Cardiac Risk Index (1986)

• Modified Goldman's index to incorporate unstable angina (class III/IV), pulmonary oedema, and suspected critical aortic stenosis
• Applied as a pretest probability combined with a nomogram based on surgery type
• Was the preferred index in American College of Physicians guidelines

Revised Cardiac Risk Index - RCRI (Lee et al., 1999) - THE CURRENT STANDARD

• Score 0: ~0.4%
• Score 1: ~1%
• Score 2: ~2.5%
• Score ≥3: ~5-11%

ACS-NSQIP / MICA Calculator (2011, Gupta et al.)

• Uses 5 variables: type of surgery, dependent functional status, abnormal creatinine, ASA class, and age
• Better discrimination than RCRI, especially for vascular surgery
• Provides numerical probability (%) rather than class

Historical Significance and Exam Points

1. First multifactorial index - moved preoperative assessment from subjective impression to objective scoring
2. S3 gallop/JVP = highest-weighted single sign (11 points) - reflects overt CCF
3. Recent MI (within 6 months) = 10 points - led to "6-month rule" (now replaced)
4. Hypertension NOT a risk factor in Goldman's original study - controversial
5. Total = 53 points across 9 variables
6. Class IV (≥26 points) = 56% cardiac mortality
7. RCRI is the current preferred index - simpler (6 equal-weight variables), better validated in modern surgical populations
8. The Goldman index established the principle that preoperative optimization of CCF (the highest-weighted factor) reduces perioperative risk - a principle that remains valid today
9. The index is not designed for cardiac surgery patients - applies only to non-cardiac operations
10. Goldman's study also showed that elective surgery in the context of recent MI should be deferred whenever possible

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