The pressure that the ventricle (right or left) must overcome to eject blood (i.e. the left ventricleThe left ventricle ejects blood into the aortic arch to the body. Within the arch, the coronary arteries branch off first followed by three main arteries that branch to the brain (carotids) and the upper thorax (subclavian artery). The chambers... More pumps against aortic diastolic pressure and systemic vascular resistance.
The resistance to the ejection of blood by the ventricle is called afterload. The left ventricle, for example, must create sufficient pressures during systoleA contraction phase of the cardiac cycle; systole takes about 1/3 of the time of the cardiac cycle (2/3 of the time is taken by diastole). A complete cardiac cycle occurs with each audible ‘lub-dub’ that is heard with a... More to overcome diastolic arterial pressure and systemic vascular resistance before any blood is ejected. While preloadTechnically the end-diastolic pressure of either the left or right ventricles; simplified as the blood volume supplied to the left or right ventricles; note that the more volume or preload, the greater the myocardial stretch and forceful the contraction; increased... More enhances contractilityA muscle cell’s ability to shorten or contract through the action of actin and myosin - mediated by the calcium ion; the faster the influx of calcium, the more forceful the contraction. 1. Six Second ECG Guidebook (2012), T Barill, p. 194 More and stroke volumeThe amount of blood ejected by either the right or left ventricle with one beat (contraction). While heart rate is an undisputed contributor to cardiac output, stroke volume is the other major player. As heart rates vary to changes in... More, high pressures in the arterial vessels during ventricular end diastoleThe phase of relaxation during the cardiac cycle; occurs for the atria and the ventricles; blood enters the heart’s chambers and the coronary arteries during diastole; note that diastole is as important as systole – the negative pressure created by... More is inversely related to stroke volume (see Figure 2.4).
While systemic vascular resistance is not easily determined without a pulmonary arteryMain vessels carrying blood from the heart; the arteries have minimal elasticity and contain approximately 20% of the blood supply. Major Vessels 1. Six Second ECG Guidebook (2012), T Barill, p. 15, 190 More catheter, diastolic blood pressure is easily measured. So while an accurate estimate of afterload is often not clinically practical, a patient’s diastolic pressure provides a good indication of the resistance the left ventricle must overcome (afterload). In general, the higher the diastolic pressure, the higher the afterload.
And the higher the afterload, the more difficult a job it is for the left ventricle to eject sufficient stroke volumes. Similar to preload, increased afterload causes increased myocardial workload, a factor to consider for those with advanced cardiac disease and/or cardiac ischemiaThe ability to identify cardiac ischemia, injury and infarction is vital in the management of the majority of cardiac emergencies. Most sudden cardiac deaths are associated with an ischemic episode. Patient deaths due to an acute myocardial infarction (MI) typically... More.
The explanation for the walls of the left ventricle being three times the thickness of the walls of the right ventricleThe right ventricle ejects blood through the main branches of the left and right pulmonary arteries to the lungs. The chambers of the heart are the main drivers within an intricate pathway, delivering blood to the lungs for gas exchange... More rests squarely with the concept of afterload. At birth, the wall thickness of the right and left ventricle are equal. Soon after birth, though, the pressures in the systemic circulation begin to surpass those of the pulmonary system. The lower pressures (typically about 24/8 mm Hg) of the pulmonary system mean a lower afterload for the right ventricle than the left ventricle. As a result, the muscle mass required of the right ventricle is also less than the left ventricle.
Afterload is also tied to cardiac hypertrophy. As the resistance to chamber contraction increases, the chamber adapts to this increased workload with the accumulation of increased fibre within the myocardial cells. This makes the cells stronger but also bulks up the cells, ultimately resulting in chamber hypertrophy. Unfortunately, these thicker chamber walls can be associated with additional complications such as decreased contractility, reduced stroke volume, and cardiac dysrhythmiasUsed interchangeably with arrhythmia, refers to any abnormal rhythm – not normal sinus rhythm or sinus tachycardia. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 More.
As the resistance to the ejection of blood from the left ventricle increases, stroke volume tends to decrease as does cardiac outputWhat is it? Why is it Vital? The amount of blood pumped out of the ventricle in a minute (most often refers to the blood pumped by the left ventricle) What is cardiac output? Simply, cardiac output is the amount... More. Perhaps as important, cardiac workload increases with increases in afterload.
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... More (2012), T Barill, p. 34-35, 189