From the Guidelines
Cardiac preload is the volume of blood stretching the ventricles of the heart at the end of diastole, just before contraction begins, and is a critical factor in determining stroke volume and cardiac output, as emphasized in the 2020 ACC/AHA guideline for the management of patients with valvular heart disease 1.
Definition and Determinants
Cardiac preload represents the initial stretching of cardiac muscle fibers before contraction and is a key determinant of stroke volume according to the Frank-Starling mechanism. It is primarily determined by venous return to the heart and can be clinically estimated using measurements such as central venous pressure (CVP), pulmonary capillary wedge pressure (PCWP), or end-diastolic volume.
Clinical Estimation and Factors Influencing Preload
Factors that increase preload include increased blood volume, venous constriction, and the horizontal position of the body. Conversely, factors that decrease preload include blood loss, vasodilation, and upright posture. Understanding preload is essential in managing conditions like heart failure, where excessive preload can lead to pulmonary congestion, or hypovolemic states, where insufficient preload reduces cardiac output.
Clinical Management
Clinicians manipulate preload using interventions such as fluid administration to increase it or diuretics to decrease it, based on the patient's hemodynamic status. As noted in the guideline, maintenance of LV preload and sinus rhythm should be the targets in the perioperative period for patients with valvular heart disease undergoing noncardiac surgery 1. Preload attainment can be challenging and requires measurement of cardiac output and pulmonary wedge pressure, highlighting the importance of invasive hemodynamic monitoring in certain clinical scenarios.
From the Research
Definition of Cardiac Preload
- Cardiac preload refers to the initial stretching of the cardiac myocytes prior to contraction, which is directly related to the volume of blood in the ventricles at the end of diastole 2, 3.
- It is an important determinant of cardiac output, as it affects the force of contraction of the heart muscle according to the Frank-Starling law 4.
Factors Affecting Cardiac Preload
- Cardiac preload is influenced by factors such as venous return, blood volume, and ventricular compliance 3, 5.
- Vasodilators, such as nitrates and nitroprusside, can reduce cardiac preload by decreasing venous return and increasing venous capacitance 2, 3.
Measurement of Cardiac Preload
- Cardiac preload can be measured indirectly by assessing left ventricular filling pressure (LVFP) or pulmonary capillary wedge pressure (PCWP) 2, 3.
- Echocardiography and Doppler imaging can also be used to evaluate cardiac preload and ventricular function 3.
Clinical Significance of Cardiac Preload
- Abnormalities in cardiac preload can contribute to heart failure and other cardiovascular disorders 5, 6.
- Understanding cardiac preload is essential for the management of patients with heart failure, as it guides the use of diuretics, vasodilators, and inotropic agents to optimize cardiac function 2, 3, 5, 4, 6.