Coronary tortuosity: a long and winding road

Abstract

Coronary tortuosity is a phenomenon often encountered by cardiologists performing coronary angiography. The aetiology and clinical importance of coronary tortuosity are still unclear. Coronary tortuosity without fixed atherosclerotic stenosis in patients with angina pectoris and an abnormal exercise stress test has never been described in the literature.This article describes three cases of patients with anginal complaints, an abnormal exercise stress test and coronary angiography without the presence of a fixed atherosclerotic lesion.It is hypothesised that coronary tortuosity leads to flow alteration resulting in a reduction in coronary pressure distal to the tortuous segment of the coronary artery, subsequently leading to ischaemia. Future studies will be necessary to elucidate the actual mechanism of coronary tortuosity and its clinical significance. (Neth Heart J 2007;15:191-5.).

Figure 1.

Coronary angiography performed in patient 1 showed tortuosity of the left anterior descending artery and the circumflex artery without a fixed coronary stenosis.

Figure 2.

Coronary angiography performed in patient 2 showed tortuosity of the left anterior descending artery and the circumflex artery without a fixed coronary stenosis.

Figure 3.

The energy loss in a straight tube will be determined by the friction loss (ΔE_fr). This can be calculated with Poiseuille’s law. Bends give extra energy loss almost entirely caused by eddies, which originate because the flow has to separate from the wall due to a sharp bend (separation). Because of the increase in centrifugal overpressure (P_co) on section AB in the outside bend and the decrease in the underpressure (Pci) on section CD in the inside bend, areas will be built up where the flow may separate from the wall; this is accompanied by eddies and extra energy losses (ΔE_sep). The fastest particles are pressed outwards by the centrifugal effect, the original symmetrical velocity profile will be asymmetrical and perpendicular to the main flow a secondary transverse flow is generated.

Figure 4.

Nippert concluded from model measurements that sharp bends will generate high energy losses caused by separation.He showed a relation between R (=radius)/D (=width tube) and ΔE_sep/ΔE_frfor turbulent flow in a 90° bend of a rectangular wooden tube. The loss by separation ΔE_sep is at R/D = 2 equal to the friction loss ΔE_fr ; so the total energy loss in the bend is twice as high as in a straight tube. At R/D = 1 the total energy loss is even five times higher (ΔE_sep = appr. 4 ΔE_fr).

Figure 5.

Two 90° bends with R₁/D=3 and R₂/D=1 are drawn. From figure 4 we may conclude that the total energy loss at R₂is much higher than at R₁.

Figure 6.

The pressures, velocities and energy losses are related in the energy equation. The basic assumption is that the sum of potential energy (pressure P), kinetic energy (local velocity v) and energy losses (shear stress: ΔE_fr, separation: ΔE_sep) is constant. While v₂ is higher than v₁ and ΔE_1-2fr is relatively small, P₂ is smaller than P₁ (see also figure 3). After the bend the velocity v2 decreases to v₃ (=v₁): the pressure increases but will be lower than p1 because of the energy loss by the eddies of the separation.