exam 4: ischemic heart disease

Ischemia

Condition where demand for oxygenated blood in the heart muscle is higher than the supply. Usually occurs due to atherosclerosis of coronary arteries.

Main determinants of O2 demand

• heart rate

• contractility

Pathophysiology of ischemia

• stenosis less than 60% = adequate blood flow in response to exertion

• stenosis more than 70% = resting blood flow is normal, but maximum blood flow is reduced even with vessels dilated & o2 demand increases

• stenosis more than 90% = blood flow inadequate even at rest; ischemia develops at rest

Causes of myocardial ischemia

• decreased perfusion due to hypotension

  • septic shock (life threatening; arises from sepsis- immune response to infection)

• severely decreased blood o2 content

  • increase in myocardial o2 demand even in absence of CAD. can occur with rapid tachycardias, acute hypertension, or severe aortic stenosis

Consequences of ischemia

• stunned myocardium: tissue demonstrates prolonged systolic dysfunction even after the return of normal myocardial blood flow.

• hibernating myocardium: tissue that manifests chronic ventricular contractile dysfunction due to persistently reduced blood supply, usually because multivessel CAD

• myocardial infarction: region of myocardial necrosis usually caused by prolonged cessation of blood supply.

Ischemia syndromes

Stable angina: occurs with physical exercise or emotionally upset, relieved by rest within minutes or meds

• relieved by rest

• pressure in chest

• predictable

• lasts 1-5 mins

Ischemia syndromes

Unstable angina: chest pain occurs suddenly & unexpectedly at rest and/or pain that is more severe, prolonged, or frequent than previous episodes

• more severe

• immediate medical attention

• rest, meds may not relieve pain

• strong indicator of myocardial infarction

Ischemic syndromes

Variant angina: typical angina discomfort, usually at rest, which develops because of coronary artery spasm rather than increase of myocardial demand

• AKA Prinzmetal angina

• coronary artery Vasospasms

• caused by reduction of o2 supply vs a higher demand

• may occur at rest

Ischemic syndromes

Silent ischemia: asymptomatic episodes of myocardial ischemia

• episode of ischemia without pain

• diagnosed through abnormalities on echo/stress echo testing

Diagnostic studies

• STEMI (ST segment elevation MI) indicated a complete blockage of a coronary artery, leading to ST segment elevation on an EKG & heart muscle damage. SEVERE.

• NSTEMI (non ST segment elevation MI) typically involves a partial blockage or temporary clot, resulting in ST segment depression or T wave inversion on EKG, & potentially less severe muscle damage.

What is circled?

ST depression (horizontal)

What is circled?

ST depression (downsloping)

What is circled?

T wave inversion

What is circled?

ST elevation

What is this?

STEMI (regional transmural infarction)

Ischemia diagnostic studies

Stress testing

• Test is continued until angina develops, signs of myocardial ischemia appear on EKG, a target heart rate is achieved (85% of maximal predicted heart rate)

• Patient becomes too fatigued to continue

Ischemic diagnostic studies

Coronary angiography

• insert catheter into BV (groin/arm) & guide it to the heart

• then, contrast dye is injected, making the arteries visible on xray images (fluoroscopy)

Treatment for ischemic heart disease

Beta blockers

Surgical treatment for ischemic heart disease

• PCI (percutaneous coronary intervention)

  • thin catheter with balloon inserted into narrowed artery, balloon inflated to widen artery, & stent is placed to keep artery open

• CABG (coronary artery bypass graft)

  • grafting healthy BV (leg, chest, arm) to bypass blockage & restore blood flow

Complications & findings of ischemic heart disease

• 45 minutes of ischemia leads to cardiac muscle death

• aneurysm