What are the differences in definition, pathophysiology, and management between HASCVd (Hypertension and Atherosclerotic Cardiovascular Disease) and IHd (Ischemic Heart Disease)?

ASCVD vs IHD: Definitions and Pathophysiology

Key Distinction

IHD (Ischemic Heart Disease) is a specific cardiac condition caused by reduced myocardial blood flow, while ASCVD (Atherosclerotic Cardiovascular Disease) is a broader term encompassing all atherosclerotic vascular disease including IHD, stroke, and peripheral arterial disease. 1

Definitions

Ischemic Heart Disease (IHD)

• IHD represents myocardial ischemia resulting from an imbalance between myocardial oxygen demand and coronary blood flow 2
• IHD is the leading cause of death and morbidity in both men and women, manifesting as stable angina, unstable angina, myocardial infarction, heart failure, and sudden death 3
• Encompasses approximately 17 million Americans with coronary heart disease and nearly 10 million with angina pectoris 3
• IHD accounts for nearly 380,000 deaths annually in the United States with an age-adjusted mortality rate of 113 per 100,000 population 3

Atherosclerotic Cardiovascular Disease (ASCVD)

• ASCVD is the umbrella term for all manifestations of atherosclerotic disease across vascular territories, including coronary arteries (IHD), cerebrovascular disease (stroke), and peripheral arterial disease 1
• ASCVD continues as a growing global health concern with ischemic heart disease and stroke as leading causes of years of life lost 1

Pathophysiological Mechanisms

Shared Atherosclerotic Foundation

Both conditions share the fundamental pathophysiology of atherosclerotic plaque formation, but IHD specifically involves coronary arterial involvement while ASCVD encompasses systemic atherosclerotic disease 2

Atherosclerotic Process

• The atherosclerotic process begins with endothelial dysfunction, followed by lipid accumulation, inflammatory cell infiltration, and smooth muscle cell proliferation in the arterial wall 2
• Plaques prone to rupture contain a large lipid core, low smooth muscle cell density, high macrophage density, and thin fibrous cap 2
• Unstable angina and myocardial infarction share a common anatomical substrate: atherosclerotic plaque rupture or erosion with differing degrees of superimposed thrombosis and distal embolization 3

IHD-Specific Pathophysiology

Three Main Etiologic Mechanisms

1. Atherosclerotic plaque formation in epicardial arteries (predominant cause) 2
2. Coronary microvascular dysfunction 2, 4
3. Epicardial coronary vasospasm 2

Myocardial Supply-Demand Mismatch

• Myocardial ischemia results from an imbalance between myocardial oxygen demand and coronary blood flow, influenced by both coronary factors (stenosis, thrombosis, vasospasm) and systemic conditions (anemia, tachycardia, blood pressure changes) 2
• Functional and structural microcirculatory abnormalities cause angina and ischemia through impaired coronary flow reserve and reduced microcirculatory conductance, even with non-obstructive epicardial disease 2, 4

Hypertension's Role in Both Conditions

When hypertension coexists with IHD or ASCVD, it creates distinct pathophysiological interactions that worsen outcomes 3

Hemodynamic Mechanisms

• Elevated systolic blood pressure increases left ventricular output impedance and intramyocardial wall tension, raising myocardial oxygen demand 3
• Wide pulse pressure and systolic hypertension result from inappropriately high aortic impedance due to decreased aortic diameter or increased effective stiffness from aortic wall thickening 3
• Increased wave reflection leads to central systolic pressure augmentation, which increases left ventricular pressure load and cardiac work, potentially causing angina pectoris and left ventricular hypertrophy 3

Structural and Functional Changes

• Hypertension induces endothelial dysfunction, exacerbates the atherosclerotic process, and contributes to making atherosclerotic plaques more unstable 5
• Left ventricular hypertrophy (the usual complication of hypertension) promotes decreased coronary reserve and increases myocardial oxygen demand, both contributing to myocardial ischemia 5
• The combination of IHD with severe hypertension presents a new qualitative state requiring specific therapeutic approaches 6

Sex-Specific Pathophysiology

Women with IHD more often have non-obstructive disease, coronary vasospasm, and abnormal vasodilator reserve compared to men, with up to 37% showing non-obstructive CAD on angiography despite positive biomarkers 2

• Sex affects pathophysiology, incidence, clinical presentation, diagnosis, treatment, and outcome of IHD 3
• HIV infection has been associated with up to twice as high risk of IHD in females as in males 3
• Autoimmune diseases are more frequent in women and are characterized by cardiovascular inflammation promoting development of hypertension, left ventricular hypertrophy, and atherosclerosis 3

Risk Factor Interactions

The five primary reversible risk factors (hypertension, dyslipidemia, glucose intolerance, cigarette smoking, and left ventricular hypertrophy) operate independently but increase risk in a multiplicative rather than additive fashion 3

• Hypertension and abdominal obesity are components of the metabolic syndrome, which also includes characteristic dyslipidemia (high triglycerides and low HDL cholesterol) and elevated fasting blood glucose 3
• Classic risk factors for atherosclerotic CAD include smoking, diabetes mellitus, hypertension, hyperlipidemia, family history of premature CAD, and postmenopausal state 2

Clinical Implications

Diagnostic Considerations

• Different ischemic mechanisms frequently act concomitantly in the same patient, requiring comprehensive evaluation beyond simple angiographic assessment 2
• Persistent ST-segment elevation generally reflects acute total coronary occlusion, while transient ST-segment depression or T-wave changes suggest non-ST elevation acute coronary syndromes 3

Treatment Thresholds

• The blood pressure threshold for initiating antihypertensive therapy is lowered to 130/80 mm Hg in patients with diabetes mellitus or chronic kidney disease, compared to 140/90 mm Hg for other hypertensive patients 3
• Complications and mortality following myocardial infarction are greater in hypertensive patients 5