Pressure Wave Reflection at the Heart

1. Pressure Wave Reflection at the Heart Why arterial stiffness is the major cause of heart failure, stroke and myocardial ischemia.

2. Pressure Wave Reflection at the Heart • If there was no wave reflection (ie. the aorta was an open-ended tube providing a simple resistance to flow), then: • the pressure wave in the aortic root would be the same as the flow wave (see graph). Figure 1 Figure 1 Menu

3. Pressure Wave Reflection at the Heart • Now if we connect up the network of arteries with all its bifurcations and vascular beds, then: • as this primary wave travels along the arteries it will generate reflected waves from each bifurcation and from the peripheral vascular beds. • all these small reflect-ed waves return to the heart, summing to create a reflected wave as shown, starting even before the end of systole. Figure 2 Menu

4. Pressure Wave Reflection at the Heart • So the pressure in the aortic root is the sum of the outgoing and reflected wave (the green wave). • note importantly how the reflected wave boosts the coronary artery perfusion pressure – the aortic root pressure – during diastole when over 95% of perfusion of the sub-endocardium takes place. Figure 3 Figure 3 Menu

5. Pressure Wave Reflection at the Heart • The speed at which the outgoing and reflected waves travel is dependent on the stiffness of the arteries along which they are travelling. • So if a person has stiffer arteries, the waves will travel out and back quicker, arriving earlier back at the heart (see graph). Figure 4 Figure 4 Menu

6. Pressure Wave Reflection at the Heart • Now when the outgoing and reflected waves are added there is a very different aortic root pressure waveform. • there are three important clinical implications. Figure 5 Figure 5 Menu

7. Pressure Wave Reflection at the Heart • First, the central systolic pressure and central pulse pressure is increased. • an increase in the central pulse pressure that drives cerebral blood flow increasesstroke risk. • NOTE: this change in central systolic pressure can occur without any changes occurring in peripheral cuff systolic pressure. Increased Central Pulse Pressure Figure 6 Menu

8. Pressure Wave Reflection at the Heart • Second, there is an increase in left ventricular load(LV load). • increase in LV load accelerates increase in LV mass and increasesrisk of LV hypertrophy. • the area under the pressure-time curve during systole is by definition LV load. • this increase in LV Load (late systolic “afterload”) is shown by the black arrowed region. Increased LV Load D LVL Figure 7 Menu

9. Pressure Wave Reflection at the Heart • Third, the pressure that is perfusing the coronary arteries during the critical diastole period is reduced, increasing the risk of myocardial ischemias. • Conclusion: Increasing arterial stiffness independently increases the risk of all three major cardiovascular outcomes. Decreased Coronary Artery Perfusion Pressure in Diastole Figure 8 Menu