Ventricular Diastolic Dysfunction
Ventricular function is highly dependent upon preload as demonstrated by the Frank-Starling relationship. Therefore, if ventricular filling (preload) is impaired, this will lead to a decrease in stroke volume. The term "diastolic dysfunction" refers to changes in ventricular diastolic properties that have an adverse effect on stroke volume. About 50% of heart failure patients have diastolic dysfunction, with or without normal systolic function as determined by normal ejection fractions.
A second mechanism can also contribute to diastolic dysfunction: impaired ventricular relaxation (reduced lusitropy). Near the end of the cycle of excitation-contraction coupling in the myocyte, the sarcoplasmic reticulum actively sequesters Ca++ so that the concentration of Ca++ in the vicinity of troponin-C is reduced allowing the Ca++ to leave its binding sites on the troponin-C and thereby permit disengagement of actin from myosin. This is a necessary step to achieve rapid and complete relaxation of the myocyte. If this mechanism is impaired (e.g., by reduced rate of Ca++ uptake by the sarcoplasmic reticulum), or by other mechanisms that contribute to myocyte relaxation, then the rate and perhaps the extent of relaxation are decreased. This will reduce the rate of ventricular filling, particularly during the phase of rapid filling.
An important and deleterious consequence of diastolic dysfunction is the rise in end-diastolic pressure. If the left ventricle is involved, then left atrial and pulmonary venous pressures will also rise. This can lead to pulmonary congestion and edema. If the right ventricle is in diastolic failure, the increase in end-diastolic pressure will be reflected back into the right atrium and systemic venous vasculature. This can lead to peripheral edema and ascites. The rise in venous pressures also occur because of an increase in blood volume due to activation of the renin-angiotensin-aldosterone system, which causes renal retention of sodium and water. Therefore, diuretic drugs are commonly given to patients in diastolic failure; however, care must be taken not to reduce blood volume too much because elevated venous pressures are needed to fill the less compliance ventricle.