Post-OP MI in Noncardiac Surgery

1. Post-OP MI in Noncardiac Surgery Ri 洪宗民

2. Post-OP MI in Noncardiac Surgery • Pathogenesis • Risk factors • Clinical manifestations • Prevention • Treatment

3. Pathogenesis • Myocardial oxygen supply • Oxygen content of blood • Hemoglobin levels & Oxygen saturation of hemoglobin • Coronary blood flow • Coronary perfusion pressure • Viscosity of the blood • Anatomic factors (which modify the caliber) • Myocardial oxygen demand • Heart rate, Contractility, Wall tension • Wall tension direct to chamber radius & peak systolic pressure, inverse to wall thickness

4. Decreased oxygen supply • Low blood oxygen content • Severe anemia, hypoxemia • Decreased coronary perfusion pressure • Systemic hypotension, intraoperative hemorrahege, tachycardia, IVC compression, pooling of blood in the legs during spinal anesthesia • Increased blood viscosity (rare) • Anatomic obstruction to coronary flow (common) • Atherosclerotic plaque, coronary artery spasm, drugs causing coronary vasoconstriction, defect of EDRF production or response

5. Increased oxygen demand • Increased heart rate • Intravascular volume depletion, drugs with positive chronotropic effects • Increased contractility • Sympathetic NS activation (light anesthesia), administration of inotropes • Increased wall tension • Afterload increased (LV outflow obstruction due to AS, cross-clamping of abdominal aorta during vascular surgery), administration of pure α-agonists, LV intracavitary volume↑ (eg.DCM)

6. Risk factors • Risk stratification parameters and criteria for cardiac events following noncardiac surgery • Cardiac Risk Index System (CRIS) • From table 22.1 & 22.2 of “Surgery : basic science and clinical evidence”

9. CRIS class

10. Clinical manifestation • Peak incidence timing • Symptoms and signs • ECG • Cardiac enzymes

11. Clinical manifestation • Peak incidence timing • Peak during the first 24 hrs post-op, first night mostly • Symptoms and signs • Badner’s study • Only 17% experienced chest pain • Possible reasons for the absence of chest pain • Residual effect of anesthetis and analgesics • Competing somatic stimuli alter pain perception • Pain tolerance ↑ (nonsurgical pt with silent MI) • Features of perioperative MI • Arrhythmias, CHF, hypotension, impaired mental status, excessive hyperglycemia in diabetes

12. Clinical manifestation • ECG • Many perioperative MI are non-STelevation • ECG may be normal or only subtle changes • Cardiac enzymes • CKMB • ↑ within 4-8 hrs, remain for 48-72 hrs • Current studies show high false-positive rate • Troponins (Troponin I and T) • ↑ by 3 hrs, I for 7-10 days, T for 10-14 days • More specific than CKMB • Recommemded for high risk

13. Prevention • β-blockers • Nitrates or calcium antagonists • α2 –agonists • CABG • PTCA • Temperature

14. Prevention • β-blockers • Solid evidence for ↓ incidence of ischemia & MI • Titrate to HR＜70/min in OP, ＜80/min post-OP • Nitrates or calcium antagonists • No evidence of benefit • Prophylactic nitrates may be harmful (hypotension) • α2 -agonists (↓ central sympathetic activity) • No evidence to support their use • However, mivazerol may be of benefit (small group)

15. Prevention • CABG • Protective effect has been suggested • ACC/AHA advocate that CABG be performed to those who meet established criteria (left main , 3 + LV-dys., 2 with LAD Pro. , myo. ischemia despite Max. medical regimen) • PTCA • ↓ peri-OP cardiac morbidity • Possibility of elastic recoil and plaque disruption, delay surgery for days to stabilize endothelium • Temperature • Main normothermia in OP ↓ incidence of morbidity

16. Prevention • Patients with chronic stable angina (important to continue antianginal therapy) • β-blockers • Continue to the time of surgery • Long-acting preparation on the surgery morning • Resume therapy as soon as possible after OP • If unable to take PO 24 hrs after OP, give IV form • Calcium antagonists • The same as β-blockers, only the IV Ca antagonists change to IV or topical nitrates

17. Treatment • Immediate goals (same as nonsurgical setting) • Reperfusion of ischemic myocardium • Prevent rethrombosis (for subtotal stenosis) • ↓myocardial oxygen demand • Prevention of LV remodeling

18. Treatment • Thrombolytic therapy • PTCA • Aspirin • Heparin • β-blockers • Nitroglycerin • ACEi

19. Treatment • Thrombolytic therapy • Recent surgery → should not be used mostly • PTCA • Urgent PTCA be considered if evolving acute MIs • Aspirin • ↓ early mortality during the acute phase of MI • Can’t PO → rectal suppository; allergic → clopidogrel • Heparin • ↓ morbidity and mortality • Heparin and antiplatelet drugs, though benefit, but ↑ bleeding, consider benefit and risk before use

20. Treatment • β-blockers • Reduce post-MI morbidity & mortality • Titrate to HR＜70/min • Contraindication: sig. bradycardia or hypotension, sev. LV dys. , 2 & 3 AV block, sev. bronchospastic lung dz. • Nitroglycerin • Effective in ↓ pain, beneficial in CHF or Pul. edema, but no evidence of ↓ mortality in AMI • Start: 5-10μg/min, ↑ 5-10μg/min per 5-10 mins (close monitor vital signs)

21. Treatment • Nitroglycerin • Titration endpoints: (usually＜200μg/min) • Control of symptoms or↓ in MAP of 10% in normal, 30% in HTN (never systolic＜90 mmHg) • Max.↑10/min in HR (but＜110/min) • Pul. a. EDP↓10-30% • ACEi • Give early can ↑ survival, esp. in p’t with ant. MI or LVEF＜40% • All sustained MIs benefit from long-term ACEi

22. Reference • Weitz HH. Perioperative cardiac complications. [Review] [63 refs] Medical Clinics of North America. 85(5):1151-69, vi, 2001 Sep. (reference of Clinical manifestations, Prevention, & Treatment) • Ashton CM. Perioperative myocardial infarction with noncardiac surgery. [Review] [66 refs] American Journal of the Medical Sciences. 308(1):41-8, 1994 Jul. (reference of Pathogenesis) • Surgery : basic science and clinical evidence / edited by Jeffrey A. Norton ... [et al.] New York : Springer, c2001 page: 366-371 (reference of Risk factors)