Preload in Cardiac Function

Physiological Basis of Preload

The American Heart Association suggests that preload represents the initial stretching of cardiac myocytes before contraction, which directly affects sarcomere length and subsequent contractile force 1
The American College of Cardiology states that at the sarcomere level, preload determines the initial length of myocardial fibers, influencing the force of contraction through the Frank-Starling mechanism 2
Preload is a key determinant of stroke volume, as it establishes the starting volume from which the ventricle ejects blood during systole, according to the American Thoracic Society 3

The European Society of Cardiology recommends that echocardiography provides direct visualization of ventricular dimensions, allowing assessment of end-diastolic volume as a measure of preload 4
The American College of Emergency Physicians suggests that inferior vena cava (IVC) diameter and collapsibility during respiration can provide qualitative estimates of preload status - collapse of 50-99% is normal, complete collapse may indicate volume depletion, and <50% collapse may suggest volume overload 5
Static pressure measurements like central venous pressure and pulmonary capillary wedge pressure are generally insensitive indicators of preload status, as low values may reflect hypovolemia but high values don't necessarily indicate volume overload, according to the Society of Critical Care Medicine 6

The American Heart Association states that in heart failure, the ventricle may develop eccentric hypertrophy with addition of new sarcomeres to maintain preload reserve despite chamber dilation 1
The American College of Cardiology suggests that preload reserve represents the heart's ability to increase stroke volume in response to increased venous return, which can become exhausted in advanced heart failure 2

The Society of Critical Care Medicine recommends that dynamic indicators of preload responsiveness (like stroke volume variation) are more reliable than static parameters for predicting fluid responsiveness in critically ill patients 6

The European Society of Cardiology suggests that in hypovolemic shock, echocardiography can rapidly document a small hyperdynamic unloaded ventricle with reduced left ventricular end-diastolic area, indicating decreased preload 7
Optimal preload management is crucial in perioperative cardiac surgery, as heart failure cannot be properly assessed unless volume loading is optimal, according to the American Association for Thoracic Surgery 4
The American Heart Association states that in right ventricular failure, patients may require higher right ventricular end-diastolic pressure (preload), though reduced left heart filling is more likely caused by right ventricular dilation and ventricular interdependence than reduced right ventricular forward output 8

The American College of Cardiology suggests that ventricular interdependence refers to forces directly transmitted from one ventricle to the other through the myocardium and pericardium 8
The American Heart Association states that in right ventricular volume overload, right ventricular dilation can compress the left ventricular cavity, impeding left ventricular filling and equalizing biventricular diastolic pressures 9
Increased transmural pressure caused by right ventricular dilation with pericardial constraint impairs left ventricular filling (preload), affecting overall cardiac output, according to the American College of Cardiology 8

The American College of Cardiology acknowledges that in chronic aortic regurgitation, the left ventricle compensates for volume overload by increasing end-diastolic volume and developing eccentric hypertrophy, which maintains preload at the sarcomere level near normal despite chamber enlargement, allowing the heart to maintain normal ejection performance for years or even decades 10, 11
In patients with beta-thalassemia major, a chronic high-output state with volume-loaded ventricles (high preload) occurs due to severe anemia, requiring increased end-diastolic volume, stroke volume, and heart rate to maintain tissue oxygen delivery, with the body compensating by lowering systemic vascular resistance through peripheral vasodilation 12

The American College of Cardiology recommends that in patients with mitral stenosis undergoing noncardiac surgery, preload must be maintained high enough to allow adequate forward flow across the stenotic valve but low enough to avoid pulmonary edema, requiring invasive hemodynamic monitoring with measurement of cardiac output and pulmonary wedge pressure 13
For patients with aortic stenosis, it is crucial to avoid hypotension and tachycardia perioperatively, as decreased coronary perfusion pressure combined with inadequate preload can precipitate myocardial ischemia, arrhythmias, or circulatory collapse 13
In cases of regurgitant lesions like mitral regurgitation, maintaining adequate preload while avoiding increased afterload and bradycardia is essential 13

During high-intensity dynamic exercise, stroke volume increases primarily through elevation of end-diastolic volume (the Frank-Starling mechanism), making increased preload the most important factor for athletes, as noted by the American Heart Association 14