Podcast
Questions and Answers
What is the approximate resting coronary blood flow?
What is the approximate resting coronary blood flow?
Which coronary artery supplies the anterior wall of the left ventricle?
Which coronary artery supplies the anterior wall of the left ventricle?
What is the purpose of the collateral circulation in the coronary system?
What is the purpose of the collateral circulation in the coronary system?
What is the ratio of myocardial capillary blood vessels to myofibrils in the coronary microcirculation?
What is the ratio of myocardial capillary blood vessels to myofibrils in the coronary microcirculation?
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Which coronary artery supplies the posterior third of the interventricular septum?
Which coronary artery supplies the posterior third of the interventricular septum?
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What determines right or left coronary artery dominance?
What determines right or left coronary artery dominance?
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What is the recommended timing for initiating perioperative beta-blockade?
What is the recommended timing for initiating perioperative beta-blockade?
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What type of testing is recommended in patients who are unable to exercise?
What type of testing is recommended in patients who are unable to exercise?
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In which condition is medical therapy with ACE inhibitors recommended?
In which condition is medical therapy with ACE inhibitors recommended?
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What is the main purpose of revascularization (CABG) in the context of preoperative cardiac intervention?
What is the main purpose of revascularization (CABG) in the context of preoperative cardiac intervention?
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When should IV therapy for perioperative beta-blockade be administered?
When should IV therapy for perioperative beta-blockade be administered?
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Which type of non-invasive testing involves Dipyridamole-thallium scintigraphy according to ACC/AHA guidelines?
Which type of non-invasive testing involves Dipyridamole-thallium scintigraphy according to ACC/AHA guidelines?
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Which muscle relaxant has a minimal effect on heart rate and blood pressure?
Which muscle relaxant has a minimal effect on heart rate and blood pressure?
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What is the disadvantage of using pulmonary artery occlusion pressure monitoring?
What is the disadvantage of using pulmonary artery occlusion pressure monitoring?
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What is the gold standard for intraoperative diagnosis of ischemia?
What is the gold standard for intraoperative diagnosis of ischemia?
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What is the effect of the transplanted heart on the patient's ability to detect anginal pain?
What is the effect of the transplanted heart on the patient's ability to detect anginal pain?
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How does the transplanted heart's response to indirect-acting drugs differ from direct-acting drugs?
How does the transplanted heart's response to indirect-acting drugs differ from direct-acting drugs?
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Which of the following is not a particular concern for postoperative management of the patient with a transplanted heart?
Which of the following is not a particular concern for postoperative management of the patient with a transplanted heart?
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What is the general goal for managing coronary artery disease intraoperatively?
What is the general goal for managing coronary artery disease intraoperatively?
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Which induction agent is likely to be avoided for patients with coronary artery disease?
Which induction agent is likely to be avoided for patients with coronary artery disease?
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What is the recommended approach to minimize the sympathetic pressor response during laryngoscopy in patients with coronary artery disease?
What is the recommended approach to minimize the sympathetic pressor response during laryngoscopy in patients with coronary artery disease?
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Which of the following statements regarding volatile anesthetic agents is true for patients with coronary artery disease?
Which of the following statements regarding volatile anesthetic agents is true for patients with coronary artery disease?
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Which anesthetic technique is preferred for patients with coronary artery disease undergoing non-cardiac surgery?
Which anesthetic technique is preferred for patients with coronary artery disease undergoing non-cardiac surgery?
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What is the potential concern with the use of volatile anesthetic agents in patients with coronary artery disease?
What is the potential concern with the use of volatile anesthetic agents in patients with coronary artery disease?
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Which vessel runs with the Right Coronary Artery (RCA)?
Which vessel runs with the Right Coronary Artery (RCA)?
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What percentage of coronary venous blood empties into the right atrium via the coronary sinus?
What percentage of coronary venous blood empties into the right atrium via the coronary sinus?
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What primarily determines myocardial oxygen consumption?
What primarily determines myocardial oxygen consumption?
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Which factor decreases coronary flow reserve and causes autoregulation to fail?
Which factor decreases coronary flow reserve and causes autoregulation to fail?
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In ischemic heart disease, what is considered more important than the degree of stenosis?
In ischemic heart disease, what is considered more important than the degree of stenosis?
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What is the primary mechanism for ventricular arrhythmias following acute occlusion?
What is the primary mechanism for ventricular arrhythmias following acute occlusion?
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What is the condition where blood flow may be redistributed away from an ischemic area?
What is the condition where blood flow may be redistributed away from an ischemic area?
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"Silent ischemia" is most often associated with elevations in which physiological parameters?
"Silent ischemia" is most often associated with elevations in which physiological parameters?
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"Unstable angina / Non-ST Elevation MI" management goals typically include which of the following?
"Unstable angina / Non-ST Elevation MI" management goals typically include which of the following?
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Rocuronium and vecuronium are muscle relaxants that have minimal effects on heart rate and blood pressure.
Rocuronium and vecuronium are muscle relaxants that have minimal effects on heart rate and blood pressure.
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Pulmonary artery occlusion pressure monitoring is considered the gold standard for intraoperative diagnosis of ischemia.
Pulmonary artery occlusion pressure monitoring is considered the gold standard for intraoperative diagnosis of ischemia.
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Patients with a transplanted heart can experience anginal pain due to the lack of sensory innervation.
Patients with a transplanted heart can experience anginal pain due to the lack of sensory innervation.
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In the first 6-12 months after a heart transplant, the patient's heart rate response to laryngoscopy is blunted.
In the first 6-12 months after a heart transplant, the patient's heart rate response to laryngoscopy is blunted.
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Atropine, a direct-acting drug, may have a normal effect on a transplanted heart.
Atropine, a direct-acting drug, may have a normal effect on a transplanted heart.
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Glycopyrrolate may produce less tachycardia than atropine when used for reversal of neuromuscular blockade.
Glycopyrrolate may produce less tachycardia than atropine when used for reversal of neuromuscular blockade.
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In the presence of ischemia, $T$-wave inversion on the ECG correlates with the severity of ischemia.
In the presence of ischemia, $T$-wave inversion on the ECG correlates with the severity of ischemia.
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Pancuronium is a muscle relaxant that can increase heart rate and blood pressure.
Pancuronium is a muscle relaxant that can increase heart rate and blood pressure.
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Nitroglycerin can be used for coronary vasodilation in the absence of hemodynamic derangements during intraoperative management of ischemia.
Nitroglycerin can be used for coronary vasodilation in the absence of hemodynamic derangements during intraoperative management of ischemia.
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The transplanted heart is unable to compensate for hypovolemia with an increased heart rate due to the disruption of the autonomic nervous system.
The transplanted heart is unable to compensate for hypovolemia with an increased heart rate due to the disruption of the autonomic nervous system.
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Study Notes
Cardiac Risk Assessment
- The Lee Revised Cardiac Risk Index assesses the risk of cardiac complications in high-risk surgery patients.
- High-risk surgery patients have:
- Ischemic heart disease
- Congestive heart failure
- Cerebrovascular disease
- Insulin-dependent diabetes
- Preoperative serum creatinine > 2.0 mg/dl
Preoperative Cardiac Intervention
- Options for preoperative cardiac intervention:
- Revascularization (CABG) - only if the risk of planned surgery exceeds the risk of cardiac cath + CABG + planned surgery
- Percutaneous Coronary Intervention (PCI) - angioplasty + stenting
- Optimizing medical management
Medical Therapy Intervention
- Recommendations for medical therapy intervention:
- Perioperative beta-blockade: oral therapy initiated at least 30 days preop, IV therapy intraop and postop
- Statin therapy: initiated at least 45 days preop, extended-release form on the day of surgery, and resumed postop
- ACE inhibitors: Class I
- Ca++ channel blockers: Class IIb, limited evidence for use in vascular surgery
- Nitroglycerin: Not indicated for prophylaxis or initial treatment of myocardial ischemia
Intraoperative Management
- General principles:
- Optimize the myocardial oxygen supply/demand ratio
- Monitor for ischemia and treat aggressively
- Maintain heart rate and blood pressure within 20% of baseline
- Induction and laryngoscopy:
- Most any induction technique is acceptable if done properly
- Avoid ketamine as the primary induction agent
- Minimize the sympathetic pressor response
- Maintenance:
- Volatile anesthetics: widely used, decrease myocardial oxygen requirements
- Narcotic technique: may be used with nitrous oxide, benzodiazepines, and low-dose volatile or propofol infusion
Coronary Artery Disease
- Anatomy of the coronary circulation:
- Coronary arterial system: origin, distribution, dominance, and collateral circulation
- Coronary venous system: great cardiac vein, anterior cardiac vein, and middle cardiac vein
- Coronary blood flow:
- Mechanical effects: coronary perfusion pressure, vascular resistance, and vessel length and blood viscosity
- Regulation of coronary blood flow: metabolic control, neural control, and autoregulation
- Pathophysiology of ischemic heart disease:
- Atherosclerosis: an inflammatory process, intimal lipid plaque, and acute coronary syndromes
- Coronary steal: ischemic area distal to a high-grade stenosis, maximally dilated microvasculature, and redistribution of blood flow
Management of Ischemic Heart Disease
-
ST elevation MI (STEMI):
- Management goals: hemodynamic stability, increase O2 supply, decrease myocardial O2 demand, and reperfusion
- Thrombolytic therapy, PCI, and CABG
-
Unstable angina/NSTEMI:
- Management goals: low risk patients managed medically, increase myocardial O2 supply, and prevent ongoing thrombus formation
- High-risk patients considered for early invasive evaluation and intervention
-
Predictors of long-term prognosis:
- Degree of left ventricular dysfunction
- Degree of residual ischemia
- Potential for malignant ventricular dysrhythmias### Coronary Blood Flow and Metabolism
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Decreased capillary density in the interventricular septum and AV node, which may explain the vulnerability of these tissues to ischemia.
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The coronary venous system consists of the great cardiac vein, anterior cardiac vein, and middle cardiac vein, which terminate in the coronary sinus and empty into the right atrium.
-
The coronary sinus receives approximately 75% of coronary venous blood, while the remainder empties directly into the atria and ventricles via thebesian veins.
Factors Affecting Left Ventricle Blood Flow
- Coronary perfusion pressure is determined by aortic pressure minus left ventricular end-diastolic pressure (LVEDP).
- Vascular resistance is related to the radius of the vessel to the fourth power, vessel length, and blood viscosity.
Regulation of Coronary Blood Flow
- Mechanical effects, metabolic control, and neural control regulate coronary blood flow.
- The Barash Guyton effect states that intense left ventricular muscular contraction limits systolic capillary blood flow, particularly to the subendocardial region.
- Large epicardial coronary vessels act as capacitors, and driving pressure for perfusion is essentially the average aortic root pressure during diastole.
Factors Compromising Subendocardial Blood Flow
- Coronary artery disease, left ventricular hypertrophy, tachycardia, decreased aortic-intraventricular pressure gradient, decreased aortic diastolic pressure, and increased LVEDP can compromise subendocardial blood flow.
Myocardial Oxygen Consumption
- Heart rate, myocardial contractility, and wall stress are major determinants of myocardial oxygen consumption.
- The Kaplan DPTI/SPTI ratio provides a more accurate picture of myocardial oxygen consumption in normal animal models.
Regulation of Coronary Blood Flow
- Myocardial blood flow is primarily under metabolic control, which is tightly linked to myocardial oxygen consumption.
- The exact mechanism or mediator of metabolic control has not been identified, but it is likely dependent on local mechanisms such as depletion of oxygen or accumulation of products of metabolism.
Neural Control
- Direct effects of neural control on coronary blood flow are minimal, but indirect effects are more significant, particularly changes in heart rate and contractility.
- The sympathetic nervous system has a greater influence on coronary blood flow than the parasympathetic nervous system.
Autoregulation and Failure
- Increasing occlusion results in dilation of capillary beds to maintain flow, but when coronary flow reserve is exhausted, autoregulation fails, and coronary blood flow becomes dependent on pressure gradients.
- Tachycardia markedly increases the mean arterial pressure at which autoregulation fails due to increased myocardial oxygen consumption and decreased diastolic perfusion time.
Pathophysiology of Ischemic Heart Disease
- Atherosclerosis is an inflammatory process that produces chronic stenosis and episodic thrombosis, often occurring in epicardial arteries.
- Characteristics of a vulnerable plaque include high lipid content, thin fibrous cap, decreased number of smooth muscle cells, and increased macrophage activity.
- Acute coronary syndromes result from sudden decreases in coronary blood flow, nearly always caused by thrombosis of a coronary artery.
- The degree of stenosis is less important than the extent of plaque rupture.
Management of Ischemic Heart Disease
- Management goals for ST-elevation myocardial infarction (STEMI) include hemodynamic stability, increasing oxygen supply, decreasing myocardial oxygen demand, and reperfusion.
- Management goals for unstable angina/non-ST-elevation myocardial infarction (UA/NSTEMI) include decreasing myocardial oxygen demand, increasing oxygen supply, and preventing ongoing thrombus formation.
- Predictors of long-term prognosis include the degree of left ventricular dysfunction, degree of residual ischemia, and potential for malignant ventricular dysrhythmias.
Arrhythmias and Ischemia
- Ventricular arrhythmias are most likely to occur in the first 10 minutes following acute occlusion.
- Three primary mechanisms of ventricular arrhythmias include failure of repolarization of ischemic myocytes, activation of the sympathetic nervous system, and left ventricular dilatation or aneurysm formation.
Coronary Steal and Silent Ischemia
- Coronary steal occurs when blood flow is redistributed away from an ischemic area via collateral vessels.
- Silent ischemia is often associated with elevations in heart rate or blood pressure and is closely related to circadian sleep-wake cycles.
Preoperative Assessment and Management
- Preoperative assessment should include a cardiac history, physical exam, preoperative testing, and risk stratification algorithms.
- Preoperative intervention may include revascularization, percutaneous coronary intervention, and optimizing medical management.
Intraoperative Management
- General principles of intraoperative management include optimizing the myocardial oxygen supply/demand ratio, monitoring for ischemia, and treating aggressively.
- Induction and laryngoscopy should be performed carefully to minimize the sympathetic pressor response.
- Maintenance anesthesia should focus on decreasing myocardial oxygen requirements, and muscle relaxants should have minimal effects on heart rate and blood pressure.
Postoperative Management
- Postoperative management should focus on increasing the potential for myocardial ischemia, particularly in the first 6-12 hours after surgery.
- Particular concerns include hypothermia, pain, inadequate ventilation, infection, and unreplaced or ongoing blood loss.
The Transplanted Heart
- The transplanted heart lacks parasympathetic, sympathetic, or sensory innervation for the first 6-12 months.
- After 6-12 months, partial reinnervation may occur, but results in a higher than normal resting heart rate and an inability to detect anginal pain.
- The transplanted heart is dependent on preload and the Frank-Starling mechanism to maintain cardiac output.
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Description
Learn about the anatomy of the coronary circulation, coronary blood flow, pathophysiology of ischemic heart disease, and coronary artery disease in this quiz for NRAN 80413 Spring 2024 with Dr. Ron Anderson, M.D.
