From the Guidelines
Patients with aortic stenosis are highly dependent on adequate preload and should avoid conditions that reduce venous return to the heart. Maintaining appropriate preload is crucial because these patients have a fixed cardiac output due to the narrowed aortic valve, which limits the heart's ability to increase stroke volume. When preload decreases (from dehydration, excessive diuresis, or vasodilation), these patients cannot compensate by increasing heart rate or contractility, potentially leading to hypotension and cardiovascular collapse, as highlighted in the context of valvular heart disease management 1.
The importance of careful management of preload in aortic stenosis patients is underscored by the fact that heart failure in severe AS is multifactorial and reflects myocardial damage secondary to valvulo–arterial impedance and myocardial ischemia 1. The prevalence of a left ventricular ejection fraction (LVEF) <50% in patients at greater than intermediate risk for aortic valve replacement is significant, estimated between 30–50% 1, emphasizing the need for cautious management to avoid further compromising cardiac function.
Conversely, excessive preload can worsen heart failure symptoms by increasing left ventricular end-diastolic pressure and pulmonary congestion. Management should focus on euvolemia—avoiding both hypovolemia and hypervolemia. In practice, this means:
- Cautious use of diuretics to avoid dehydration and reduced preload.
- Maintaining adequate hydration to support venous return.
- Avoiding rapid position changes that reduce venous return.
- Careful perioperative fluid management to prevent both hypovolemia and fluid overload.
- Vasodilators should be used with extreme caution as they reduce preload and can precipitate hypotension.
The physiological basis for this preload dependence relates to the fixed obstruction at the aortic valve, which forces the left ventricle to generate higher pressures to maintain cardiac output, making the heart particularly sensitive to changes in filling pressures 1. Therefore, maintaining optimal preload is critical in the management of patients with aortic stenosis to prevent complications and improve quality of life.
From the Research
Preload in Aortic Stenosis
- Preload refers to the initial stretching of the cardiac myocytes prior to contraction, which is essentially the volume of blood in the ventricle at the end of diastole 2.
- In patients with aortic stenosis, left ventricular hypertrophy and atrial augmentation of preload compensate for the increase in afterload caused by aortic stenosis during the asymptomatic latent period 2.
- However, as the disease worsens, these compensatory mechanisms become inadequate, leading to symptoms of heart failure, angina, or syncope 2.
- Fluid overload, which can be objectively quantified using bioimpedance spectroscopy, subjects patients with severe aortic stenosis to increased risk for heart failure and death after valve replacement 3.
- BIS-guided decongestion has been shown to improve prognosis and quality of life following transcatheter aortic valve replacement (TAVR) in patients with severe aortic stenosis and concomitant fluid overload 3.
Management of Preload in Aortic Stenosis
- Management of fluid overload is crucial in patients with severe aortic stenosis, and diuretics play an essential role in the treatment of heart failure 4.
- The choice of diuretic is guided by patient clinical situations and the presence of other co-morbidities, with azosemide and torasemide causing a significant reduction in brain natriuretic peptide (BNP) level and torasemide also causing a significant decrease in collagen volume fraction (CVF) and edema 4.
- Current guidelines for management of adults with aortic stenosis recommend aortic valve replacement for patients with clinical consequences due to hemodynamically severe valve obstruction, with transcatheter aortic valve replacement (TAVR) being recommended for patients with prohibitive surgical risk and reasonable in intermediate and high-risk patients 5.