Is stroke volume high or low in aortic regurgitation?

Stroke Volume in Aortic Regurgitation

Total stroke volume is HIGH in aortic regurgitation, while effective (forward) stroke volume may be normal or reduced depending on disease severity and compensation.

Understanding Stroke Volume Components in AR

The key to understanding stroke volume in AR is recognizing that there are two distinct measurements 1:

• Total LV stroke volume: The entire volume ejected by the left ventricle during systole (LV end-diastolic volume minus LV end-systolic volume)
• Effective (forward) stroke volume: The volume that actually reaches systemic circulation (total stroke volume minus regurgitant volume)

In chronic severe AR, the total LV stroke volume is markedly elevated because the ventricle must eject both the normal forward flow AND the regurgitant volume that leaked back during diastole 1, 2.

Hemodynamic Mechanisms

Why Total Stroke Volume Increases

• The regurgitant volume returns to the LV during diastole, increasing preload and LV end-diastolic volume 3
• To maintain adequate forward cardiac output, the LV compensates by ejecting a larger total volume with each beat 1
• This high total stroke volume produces systolic hypertension and the characteristic wide pulse pressure seen in chronic AR 2, 3
• The elevated stroke volume accounts for peripheral physical findings like bounding pulses 3

Clinical Implications of High Stroke Volume

The high total stroke volume creates a substantial transvalvular gradient across the aortic valve, even in the absence of stenosis 1. This is particularly important in mixed aortic valve disease:

• In patients with severe AR and mild AS, the high total stroke volume may produce misleading pressure gradients 1
• The gradient varies with the square of transvalvular flow, so excess flow (not stenosis) drives the elevated gradient 1
• This can lead to overestimation of stenosis severity if not properly interpreted 1

Quantification Methods

Doppler Volumetric Assessment

The elevated total stroke volume in AR can be measured using the pulse wave Doppler method 1:

• Total stroke volume is derived from LVOT measurements
• In the absence of significant mitral regurgitation, mitral inflow calculates systemic (effective) stroke volume 1
• Regurgitant volume = LVOT stroke volume - mitral stroke volume 1
• A regurgitant fraction >50% indicates severe AR 1

CMR Quantification

Cardiac magnetic resonance provides the most accurate assessment when AR coexists with other valvular lesions 1:

• LV stroke volume = LV end-diastolic volume - LV end-systolic volume 1
• Aortic forward flow and regurgitant volume measured by phase-contrast imaging 1
• This method accounts for the high total stroke volume while accurately separating forward from regurgitant flow 1

Important Caveats

Acute vs. Chronic AR

In acute severe AR, the hemodynamic picture differs dramatically 3:

• The sudden volume overload occurs on a normal-sized, non-compliant ventricle 2
• The LV cannot acutely dilate to accommodate increased volume 3
• Total stroke volume may not be as elevated as in chronic AR 3
• Pulse pressure may not be widened because systolic pressure is reduced and diastolic pressure equilibrates rapidly with elevated LV diastolic pressure 2

Impact on Gradient Interpretation

When assessing prosthetic or native aortic valves, high stroke volume states (including AR) significantly affect pressure gradient measurements 1:

• Peak velocity and mean gradient criteria are only valid for near-normal stroke volumes (50-90 mL) 1
• These parameters are more affected by high flow states including concomitant AR 1
• Flow-independent parameters (EOA, DVI) should be prioritized in high stroke volume conditions 1

Heart Rate and Regurgitant Fraction

Increasing heart rate significantly reduces the regurgitant fraction by shortening diastolic time 4:

• At 40 bpm, regurgitant fraction was 88% in an ex vivo model 4
• At 120 bpm, regurgitant fraction decreased to 42% 4
• This explains why beta blockers should be avoided in AR—they prolong diastole and increase regurgitant volume 2, 5
• Vasodilators that maintain or increase heart rate (ACE inhibitors, dihydropyridine calcium channel blockers) are preferred 2, 5

Clinical Decision-Making

Monitoring LV Response

A normal LV size almost excludes severe chronic AR, while LV dilatation is sensitive for chronic significant AR 1:

• If LV volumes fail to decrease after valve replacement for AR, suspect significant residual leak 1
• Progressive LV dilatation with hyperdynamic function suggests hemodynamically significant regurgitation 1
• Chamber geometry helps distinguish stenotic from regurgitant lesions—a small LV is inconsistent with chronic severe regurgitation 1