7C · Virtual Reality Lab: Heart Valves and Great Vessels

This VR walkthrough, also without slides, uses the same MRI scan as the previous video. That video focused on the chambers and their features. This one focuses on the great vessels and the valves, again starting at the right atrium and its structures and working through to the right ventricle, then the left atrium and left ventricle.

The venae cavae¶

From the front, the heart shows the right atrium, the right ventricle, the left atrium tucked around the side, and the left ventricle. To see what we want in the right atrium, we come around the back.

One opening into the right atrium is already visible from behind: the inferior vena cava. We think of it as coming up from the bottom, but the ventricle sits at the bottom. So the inferior vena cava does come up from the lower portion of the body, but in this individual it feeds in on the backside of the right atrium.

The superior vena cava is the vessel above. Cutting into the atrium confirms it: the vessel leads forward and pours right into the right atrium. Likewise, the inferior vena cava opening leads right into the back of the right atrium.

Tricuspid valve¶

The tricuspid valve sits between the right atrium and the right ventricle. The slide image shows it idealized; cutting in shows what it actually looks like, with the right atrium above and the right ventricle below.

Approaching from the ventricle side, coming up from the bottom, gives a different perspective. Cross-sections of papillary muscles come up, then chordae tendineae, then the valve itself. These are very thin flaps of tissue. As the lectures said, they are not muscular.

From another angle all three flaps are visible, along with the thin, string-like chordae tendineae and papillary muscles sprouting out of the ventricular wall, each sending chordae up to a different flap of the valve. Inside the right ventricle, from the front, the tricuspid valve and a papillary muscle coming up the side are both visible.

Pulmonary valve and pulmonary arteries¶

Out of the right ventricle, the outflow tract leads up to the pulmonary valve. Some blood remains in the ventricle and pulmonary trunk on this scan, so the view is not as clear as we would like. Adjusting the visualization settings removes some of that blood. It sacrifices some of the atrial wall and other structures, but shows much more of the papillary muscles and chordae in the right ventricle, including another set of chordae going to the third flap of the tricuspid valve.

Up the outflow tract is the pulmonary valve, with its three flaps, and from there blood moves right into the pulmonary trunk. From the slides, the pulmonary trunk should move backward a little and then split into right and left pulmonary arteries. Turning the heart to look near the back, with the tissue settings restored, shows exactly that: the trunk dividing into the left pulmonary artery, heading off to the left lung, and the right pulmonary artery, which wraps around and heads over to the right lung.

Pulmonary veins and left atrium¶

After the lungs, blood returns to the left atrium, which sits on the back of the heart. Two left pulmonary veins, beautifully visualized here, come in from the left lung, pouring oxygenated blood into the left atrium.

Twisting the heart so its right side faces us, we look for the right pulmonary veins. There are two from each lung, but this particular scan gives a really good visualization of only one of the two on the right side. Following its entrance and cutting further shows the flat, elongated left atrium on the back of the heart, and the vein leads right into it. Another vessel looks like it might be the other right pulmonary vein, and it does seem to lead in as well.

Coming around to a front view and in to the left atrium, the walls show the same kind of ridges pointed out on the right atrium. The pulmonary trunk sits nearby. We are really looking for where the left atrium empties down into the left ventricle, and this view sits toward the back of the heart, because the left atrium sits so far toward the back.

Mitral valve and left ventricle¶

The mitral, or bicuspid, valve is beautifully imaged here, along with the posterior papillary muscles. The mitral valve has a posterior flap and an anterior flap, so posterior papillary muscles send chordae up to the posterior flap.

Carving into the left ventricle shows the left atrium, the mitral valve, the left ventricle with its papillary muscles, and the outflow tract, where blood heads up out of the left ventricle toward the aortic valve.

Aortic valve¶

The aortic valve is beautifully visualized on this scan, with its three flaps: the right cusp, the left cusp, and the posterior cusp. Zooming in shows little white clumps here and there on the valve, which are calcification, with a little more on the posterior flap. Considering this is the heart of a 97-year-old woman, the valve is in remarkably good shape for that much wear and tear for that long.

Up the aorta¶

With the heart rotated back and the vessels restored, the final view swims retrograde, upstream, up the aorta. This is the perspective of the valves and catheters in transcatheter valve replacement and similar procedures. They come up the aorta backward against the flow of blood and access the valve from this side. From here the three cusps of the aortic valve are visible again, with some spots of calcification.