Why does atherosclerosis cause isolated systolic hypertension and not diastolic hypertension?

Why Atherosclerosis Causes Isolated Systolic Hypertension and Not Diastolic Hypertension

Atherosclerosis causes isolated systolic hypertension (ISH) but not diastolic hypertension primarily because it reduces arterial elasticity, increases arterial stiffness, and alters pressure wave reflection patterns, which specifically impacts systolic blood pressure while allowing or even lowering diastolic pressure. 1

Pathophysiological Mechanisms

Arterial Stiffness and Structural Changes

Atherosclerosis leads to several structural and functional changes in the arteries that specifically affect systolic pressure:

• Loss of Elasticity: Atherosclerosis accelerates the thinning, fragmentation, and fracture of elastin fibers in arterial walls while increasing collagen deposition, resulting in decreased arterial compliance 1

• Increased Arterial Wall Thickness: The atherosclerotic process causes arterial wall thickening and changes in wall composition, leading to increased effective stiffness 1

• Endothelial Dysfunction: Develops over time as a consequence of both aging and atherosclerosis, contributing functionally to increased arterial rigidity 1

Hemodynamic Consequences

The stiffened arteries create specific hemodynamic effects:

1. Increased Pulse Wave Velocity: Stiff arteries transmit pressure waves faster, causing reflected waves to return during systole rather than diastole 1

2. Pressure Wave Reflection: In stiffened arteries, reflected pressure waves from the periphery return to the central arteries during systole rather than diastole, augmenting systolic pressure 1

3. Widened Pulse Pressure: The combination of elevated systolic pressure and normal or decreased diastolic pressure creates a characteristic widened pulse pressure 1

4. Decreased Diastolic Pressure: Arterial stiffness can actually lead to decreased diastolic pressure because the rapid runoff of blood during systole and reduced elastic recoil during diastole fails to maintain diastolic pressure 1

Clinical Implications

The isolated systolic hypertension pattern has significant clinical implications:

• Prevalence: After age 70, isolated systolic hypertension accounts for >90% of all hypertension cases 1

• Cardiovascular Risk: ISH is a major risk factor for coronary heart disease, stroke, and cardiovascular mortality 1

• Organ Damage: Augmentation of central aortic systolic blood pressure increases left ventricular work and pressure-related cardiac pathology, including coronary artery disease and left ventricular hypertrophy 1

• Coronary Perfusion: The decreased diastolic pressure that may accompany ISH has the potential to compromise coronary perfusion pressure, which occurs primarily during diastole 1

Evidence from Imaging Studies

Research has confirmed the relationship between atherosclerosis and arterial stiffness:

• Studies using ultrasound have shown that patients with isolated systolic hypertension have significantly higher carotid intima-media thickness (a marker of atherosclerosis) compared to normotensive individuals 2

• Arterial distensibility is markedly reduced at atherosclerotic plaque sites, but importantly, this effect extends proximally beyond the actual plaque location 3

Common Pitfalls in Understanding ISH

• Misperception: There's a lingering misperception that ISH is an adaptive physiologic phenomenon in older adults required to ensure organ perfusion, which has been disproven by clinical trials 1

• Treatment Challenges: Despite evidence supporting treatment benefits, ISH remains the major subtype of untreated and uncontrolled hypertension 4

• Measurement Issues: Proper measurement techniques are essential as ISH can be overdiagnosed due to transient elevations in blood pressure during clinic visits ("white coat effect") 5

In summary, atherosclerosis causes isolated systolic hypertension through a cascade of structural and functional changes in the arterial system that specifically impact systolic pressure while maintaining or lowering diastolic pressure. The stiffened arteries lose their ability to buffer pressure changes during systole and have altered wave reflection patterns that augment systolic pressure, creating the characteristic pattern of isolated systolic hypertension.