Pathophysiology of Coronary Artery Disease (CAD)

From: Dr. A.P.Netraranjn

Cardiac Anatomy

Coronary Arteries

Coronary blood supplyArises from the ascending aortaEmpties into the coronary sinus

Coronary Arteries

Right Coronary Artery

• Acute Marginals • Posterior Descending

Artery (PDA)• Posteriolateral Artery (PLA)

Left Coronary Artery

• Left Main

• Left Anterior Descending (LAD)

– Diagonals

– Septals

• Left Circumflex (LCx)

– Obtuse Marginals (OM)

Coronary Artery Disease (CAD)

An imbalance in the myocardial oxygen supply:

• Impaired blood flow• Increased oxygen demand • Decreased supply

CAD - Etiology

• Subintimal deposition of atheromas in large and medium-sized coronary arteries (atherosclerosis).

• Less common - Coronary spasm.

• Rare - Coronary artery embolism, dissection, aneurysm (eg, in Kawasaki disease), and vasculitis (eg, in SLE, syphilis).

Myocardial Oxygen Supply and Demand

Factors that Impair Myocardial Oxygen Supply

• Atherosclerosis– Plaque rupture

• Thrombosis• Embolism• Spasm

Factors that Increase Myocardial Oxygen Demand

• Physical exertion• Stress

– Emotional – Physical

Progression of Atherosclerosis

Progression of Atherosclerosis

Progression of Atherosclerosis

Plaque

Progression of Atherosclerosis

Angina pectoris

Progression of Atherosclerosis

Plaque rupture reasons: unclear but probably related to

• Plaque morphology,• Plaque Ca content, and• Plaque softening due to an inflammatory process

Risk Factors

• Hypertension

• Elevated LDL/decreased HDL

• Smoking

• Obesity

• Diabetes

• Physical inactivity

• Advanced age

• Gender (Male >Female)

CAD – Clinical Presentation

Chest PainCommon non cardiac causes of chest pain

Angina pectoris

Atypical angina

Acute coronary syndrome

Other cardiac or vascular causes: pericarditis, Aortic dissection, pulmonary embolism

No Chest Pain = Silent Ischemia

Cardiac or non cardiac

MusculoskeletalRespiratory diseaseGastrointestinalAnxiety/Emotional

Angina Pectoris - Symptoms

• Angina may be a vague, barely troublesome ache or may rapidly become a severe, intense precordial crushing sensation. It is rarely described as pain.

• Discomfort is most commonly felt beneath the sternum, although location varies.

• Radiate to: – left shoulder and down the inside of the left arm, even to the fingers; straight

through to the back; – into the throat, jaws, and teeth; and, – occasionally, down the inside of the right arm. It may also be felt in the upper

abdomen.

• The discomfort of angina is never above the ears or below the umbilicus.

Angina Pectoris

Class Activities Triggering Chest Pain 1

 

Strenuous, rapid, or prolonged exertionNot usual physical activities (eg, walking, climbing stairs)

2

 

 

 

 

 

 

Walking rapidlyWalking uphillClimbing stairs rapidlyWalking or climbing stairs after mealsColdWindEmotional stress

3

 

Walking, even 1 or 2 blocks at usual pace and on level groundClimbing stairs, even 1 flight

4

 

Any physical activitySometimes occurring at rest

Symptom severity is often classified by the degree of exertion resulting in angina Canadian Cardiovascular Classification System of (Stable) Angina Pectoris.

Acute Coronary Syndrome

• Acute coronary syndromes result from acute obstruction of a coronary artery.

• Consequences depend on degree and location of obstruction and range from

– Unstable angina

– Non-ST-segment elevation MI (NSTEMI)

– ST-segment elevation MI (STEMI)

– Sudden cardiac death.

Myocardial Infarction

Blocked Blood Supply

OccludedCoronary

Artery

DamagedHeart Muscle

Myocardial Infarction

Stages of myocardial cell death due

to prolonged lack of oxygen • Ischemia - insufficient oxygen supply• Inflammation• Infarction - necrosis

Myocardial Infarction

Extent of Infarction• Subendocardial infarct- isolated in the subendocardial layer• Transmural infarct - involves

the full thickness of a portion of myocardium

MI Classification

Classification is based on ECG changes and presence of cardiac markers in blood.

• Non-ST-segment elevation MI (NSTEMI, subendocardial MI) is myocardial necrosis (evidenced by cardiac markers in blood; troponin I or T and CPK will be elevated) without acute ST-segment elevation or Q waves.

• ST-segment elevation MI (STEMI, transmural MI) is myocardial necrosis with ECG changes showing ST-segment elevation that is not quickly reversed by nitroglycerin or showing new left bundle branch block Q waves

may be present. Both troponin and CPK are elevated.

Acute Coronary Syndrome - symptoms

Unstable angina

Similar to angina pectoris except that the pain is

• more intense

• lasts longer

• is precipitated by less exertion

• occurs spontaneously at rest

• is progressive in nature

• or involves any combination of these features.

Unstable Angina

Classification Description Designation Severity

I New onset of severe angina or increasing† angina

No angina during rest

—

II Angina during rest within past month but not within preceding 48 h

Subacute angina at rest

III Angina during rest within 48 h Acute angina at restClinical situation

A Develops secondary to an extracardiac condition that worsens myocardial ischemia

Secondary UA

B Develops when no contributory extracardiac condition is present

Primary UA

C Develops within 2 wk of acute MI Post-MI UA

Unstable angina is classified based on severity and clinical situation

Braunwald Classification of Unstable Angina :

Acute Coronary Syndrome - symptoms

NSTEMI and STEMI

• Usually - deep, substernal, visceral pain described as aching or

pressure, often radiating to the back, jaw, left arm, shoulders, or all

of these areas.

• The pain is similar to angina pectoris but is usually more severe and

long-lasting; more often accompanied by dyspnoea, diaphoresis,

nausea, and vomiting; and relieved little or only temporarily by rest

or nitroglycerin.

Acute Coronary Syndrome - Investigations

• Serial ECGs

• Stress testing with ECG

• Serial cardiac markers

• Coronary angiography

ECG - Limb leads

• Three electrodes attached to the left arm, the right arm, and the left leg, respectively.

• The three bipolar limb leads:– lead I: right arm–left arm– lead II: right arm–left leg– lead III: left leg–left arm

• The unipolar leads: – aVR lead: right arm– aVL lead: left arm– aVF lead: left leg

ECG - Chest leads

• Another six electrodes, placed in standard positions on the chest wall, give rise to a further six unipolar leads –

• the chest leads (also known as precordial leads), V1–V6.

ECG

ECG – Normal tracing

ECG – ST Segment Depression

ECG demonstrating ST-segment depression (I, V3–V6). ST depression is diagnostic of ischemia.

ECG – ST Segment Elevation

ECG showing ST elevation on inferior leads (II, III, aVF).

Myocardial Infarction

Exercise Treadmill Test (ETT)

• Myocardial demand is increased by exercise and perfusion to the heart is examined by use of ECG.

• “Exercise” can be done by use of treadmill or bicycle; or by use of drugs that increase heart rate e.g., adenosine, dypiridamole, dobutamine.

• Clinical findings suggestive of ischemia:– BP falls below resting level– Significant arrhythmias– Typical chest pain (>5 on 0-10 scale)– Significant ECG changes.

Cardiac markers

Cardiac markers are cardiac enzymes (eg, CPK-MB) and cell contents (eg, troponin I, troponin T, myoglobin) that are released into the bloodstream after myocardial cell necrosis.

The amount of enzyme release depends on the severity of the injury.

Each enzyme follows a specific pattern of peak levels in blood.

Cardiac markers

Time Course of Cardiac Biomarkers after M.I.

Cardiac markers

Biomarker Range of time to initial

elevation (hrs)

Mean time to Peak

elevation

Time to return to normal

range

Notes

CK-MB 3-12 24 hr 48-72 hrHigh specificity and sensitivity to myocardial necrosis

cTnI 3-12 24 hr 5-10 dNear absolute specificity to myocardial necrosis

cTnT 3-12 12 hr – 2d 5-14 d

High sensitivity to even microscopic areas of necrosis

Not an index of acute injury because of prolonged time to return to normal

Coronary angiography

This diagnostic method outlines the lumina of the coronary arteries and can be used to

detect or exclude serious coronary obstruction.

However, coronary arteriography provides no information regarding the arterial wall, and

severe atherosclerosis that does not encroaches on the lumen may go undetected.

Angiography: Right Coronary Artery (LAO)

Filling defect: Lesion

CAD - Management

• General Measures

• Drugs

• Revascularization

Approach to acute coronary syndromes (ACS).

Revascularization

• Revascularization is the restoration of blood supply to ischemic myocardium

in an effort to limit ongoing damage, reduce ventricular irritability, and

improve short-term and long-term outcomes.

• Modes of revascularization include 1. Thrombolysis with fibrinolytic drugs 2. PCI with or without stent placement 3. CABG.

Percutaneous Coronary Intervention (PCI)

• PTCA, POBA, Angioplasty

• Cutting balloon angioplasty

• Stenting Bare metal stents Drug-eluting stents

• Brachytherapy

• Coronary rotablation and atherectomy

Coronary Artery Bypass Graft (CABG)

CABG is performed for certain groups:

• Patients with three or more blocked arteries

• If the left main artery is narrowed by 50% or more

• When the disease portion of the artery is very long

Thank you

For any feedback, please contact Dr. Netraranjn at ap_n@in.com