Why Preload is Beneficial in Aortic Regurgitation
In chronic aortic regurgitation, maintaining adequate preload is essential because the enlarged, compliant left ventricle requires increased end-diastolic volume to generate the large total stroke volume needed to maintain forward cardiac output despite the regurgitant volume. 1
Compensatory Mechanisms in Chronic AR
The left ventricle adapts to chronic aortic regurgitation through specific structural changes that fundamentally alter its preload requirements:
Eccentric hypertrophy develops with new sarcomeres laid down in series, increasing individual myocardial fiber length and creating a larger chamber that can accommodate increased volume 1
Chamber compliance increases dramatically, allowing the ventricle to accept greater end-diastolic volumes without proportional increases in filling pressures 1
Preload at the sarcomere level remains normal or near-normal despite the enlarged chamber, preserving the ventricle's preload reserve capacity 1
The Total Stroke Volume Requirement
The fundamental hemodynamic challenge in AR explains why preload must be maintained:
The left ventricle must eject both forward stroke volume AND regurgitant volume in a single systolic contraction, requiring total stroke volumes far exceeding normal 2, 3
Forward cardiac output depends on adequate preload to generate this enhanced total stroke volume—reducing preload compromises the ventricle's ability to maintain systemic perfusion 1
The enlarged chamber size permits ejection of large stroke volumes through normal performance of each contractile unit along the enlarged circumference, but only if filling is adequate 1
Clinical Implications for Preload Management
Avoid Excessive Preload Reduction
Aggressive diuresis or vasodilators that reduce preload excessively will decrease forward cardiac output in patients with compensated AR 1
The compensated ventricle operates on a different portion of the Frank-Starling curve, requiring higher filling volumes to maintain adequate forward flow 1
Perioperative Considerations
Intravascular volume must be maintained at levels ensuring adequate forward output during anesthesia and surgery, though excessive rises in left atrial pressure should be avoided to prevent pulmonary edema 1
Appropriate intraoperative hemodynamic monitoring is reasonable for patients with severe AR undergoing elevated-risk procedures to optimize preload 1
Important Caveats
This principle applies to chronic compensated AR—acute severe AR behaves completely differently. In acute AR, the normal-sized, non-compliant ventricle cannot accommodate sudden volume overload, and dramatic increases in left ventricular end-diastolic pressure occur regardless of preload, leading to pulmonary edema and cardiogenic shock 2
Preload maintenance does not mean volume overload. The goal is adequate filling to support the enhanced stroke volume requirement, not excessive volume that increases left ventricular end-diastolic pressure and precipitates pulmonary congestion 1
As AR progresses to decompensation, preload reserve becomes exhausted and the hypertrophic response inadequate, at which point further volume loading may worsen rather than improve hemodynamics 1