[Methods for evaluating vasodilator agents in cardiac failure]

Invasive cardiac catheterisation remains the reference technique for the evaluation of the effects of vasodilator drugs in cardiac failure. The arterial, venous or mixed site of action can be determined. Venous vasodilators induce a fall in left ventricular end diastolic volume (EVD), left ventricular end diastolic pressure (EDP), and stroke volume (SV). Arterial vasodilators decrease left ventricular end systolic pressure (ESP), end systolic volume (ESV) and increase the stroke volume. Mixed vasodilators associate the effects of both, leading to a fall in left ventricular filling pressures and an increase in SV. It is not always easy to determine the exact site of action of a given vasodilator drug. Arterial vasodilatation can only be confirmed when peripheral arterial resistances and systemic blood pressure decrease simultaneously. Venous vasodilatation can only be formally confirmed by using other techniques such as pethysmography. Hemodynamic investigations have other fundamental objectives in the evaluation of the effects of a vasodilator, especially the demonstration of possible associated positive inotropic effects. This would be relatively easy in the case of a venous vasodilator which induces an increase in SV but more difficult in the assessment of an arterial vasodilator. Studying the distribution of regional blood flow after the administration of a vasodilator is another important objective of cardiac catheterisation. Although coronary flow can be studied properly, the hemodynamics of other regions can only be assessed approximatively. The phenomenon of tolerance at an early or late stage of vasodilator therapy can also be demonstrated by hemodynamic monitoring.