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I.
Landmarks for Optimal Puncture Site
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To select an optimal transseptal puncture site, there are 2 imaginary reference lines that need to be defined first: 1) the vertical "mid-line" and 2) the horizontal M-line. The target site for septal puncture is, as a rule, located at the intersecting point of the vertical "mid-line" and the horizontal M-line.
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II. Definition of the Vertical "Mid-line":
A. Inoue's angiographic method
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Inoue has devised a specific transseptal puncture technique designed for the Inoue-balloon BMV, incorporating the concept of a vertical “mid-line,” a line assumed to divide the intra-atrial septum into anterior and posterior halves. This line is defined based on the landmarks obtained from right atrial angiography (with levophase) during normal respiration in the frontal plane (see figure at right).
On a stop-frame frontal right atrial angiographic image (Figure 1, left panel), the upper end of the tricuspid valve at systole (point T, marked as asterisk) is assumed to be the anterior limit of the |
Definition of "Mid-line"
Inoue's Angiographic Method
(Figure 1)
 Frontal View
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atrial septum, and the T point is translated to a stop-frame left atrial image (Figure 1, right panel) and translated to a stop-frame left atrial image (Figure 1, left panel). On the latter image, an imaginary horizontal line is drawn from point T until point L, where the line intersects the lateral border of the atrium encountered first (usually the left atrium, as in this case). Point L is assumed to be the posterior limit of the septum because the lateral border of the right atrium is lateral to that of the left atrium, and there exists no atrial septum beyond the left atrial border.
The posterior limit is either the right or left atrial border, whichever is medial because there exists no atrial septum beyond the medial atrial border. In usual cases, the posterior limit is the left atrial border (refer to section, “Posterior Limit of Atrial Septum", below).
A vertical line, the “mid-line”, is drawn to cross at the mid-point (point M) between T and L (right panel).
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B. Hung's modified fluoroscopic method
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Because in most cases of mitral stenosis, the left atrial silhouette is visible under fluoroscopy, Hung has modified Inoue's method of defining the “mid-line”. In this method, the aortic valve instead of the tricuspid valve is used as a landmark because of their proximity. Therefore, point T is substituted with the tip of a pigtail catheter (Figure 2, point A) touching the aortic valve (usually the non-coronary sinus of Valsalva) in the frontal view. A horizontal line is drawn from point A to L, where the line intersects the right lateral edge of the left atrium.
The "mid-line" thus derived is usually identical to that from the Inoue's angiographic method
(Figure 3).
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Determination of "Mid-line"
Fluoroscopic Method
(Figure 2)
Determination
of "Mid-Line"
Fluoroscopic vs. Angiographic Method
(Figure 3)
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III.
Posterior Limit of Atrial Septum -- Left vs. Right Atrium
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The septum lies within the superimposed area between the two atria, and therefore there is no septum outside this area. The posterior limit is the lateral border of the medial atrium, usually the left atrium. Infrequently (such as in patients with giant left atria), the lateral border of the right atrium is medial to that of the left atrium, and thus the posterior septal limit should be on the right atrial border because there is no septum laterally beyond this point, as illustrated in the following cases (Figures 4-6).
In the case with a giant left atrium, (Figure 4) if the left atrial border is used as the posterior septal limit, the mid-line would be outside or near the right
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Giant
Left Atrium
(Figure 4)
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atrial border. Puncture on this false “mid-line” would result in cardiac perforation and tamponade.
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(Figure 5) 
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RA Angiogram
(Figure 6)
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IV.
Inoue's Angiographic Method vs. Fluoroscopic Method
Because in most cases of mitral stenosis, the left atrial silhouette is visible under fluoroscopy, the “septal line” and “mid-line”can be determined without angiographic aide.
However, angiography is recommended
in the following situations:
1) For operators
inexperienced with the transseptal puncture technique.
2) In cases
in which atrial silhouettes are not well visualized under fluoroscopy
(e.g. Figure 7).
3)
In extremely difficult cases of transseptal puncture, e.g.in the presence
of a giant left atrium or severe kyphoscoliosis (Figure 8). In these cases, it may
be necessary to perform biplane (frontal and lateral) right angiography
to properly visulize the atrial septal orientation and relative anatomic
relationships of both atria, the tricuspid valve, and the aorta.
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PTMC
in Kyphoscoliosis
(Figure 8)
Cath Cardiovasc Diag 30:40, 1993
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V.
Definition of the Horizontal "M-line"
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The
"M-line" is a horizontal line crossing the center of the mitral
annulus (point M). It is derived from a diastolic stop frame of diagnostic
left ventriculography obtained in 30-degree RAO projection (see figure).
The latter is identical to the
projection used when manipulating the catheter balloon across the mitral
valve. This line is memorized in relation to
the vertebral body.
The stop frame angiogram is also
used as a road map during transseptal puncture and balloon catheter manipulation.
NOTE: The above landmarks can be drawn in the mind, and therefore,
actual plotting and drawings on the image monitor is not necessary.
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Horizontal
M-line
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VI. Puncture Site
A. Inoue's Angiographic Method
The
puncture site (x) is determined on the "mid-line" at about 2/3
of a vertebral body height (h) above point C where the "mid-line"
intersects with the caudal edge of the left atrium (right panel).
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| B.
Modified Method |
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The
puncture is usually made also on the
"mid-line", but on the level of horizontal "M-line"
derived from left ventriculogram as discussed previously.
However, in individual cases the
puncture site on the "mid-line" may have to be adjusted. For example,
in a patient with a giant left atrium, the operator often is forced to make
septal puncture more caudally to the "M-line" because the septum
begins its curviliniear shape more caudally.
NOTE: BMV can be performed with the patient in |
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a
semi-recumbent position under an urgent setting. In this setting, the "mid-line"
can be defined in frontal view with appropriate caudal titling. The frontal
image intensifier needs to be tilted in a caudal angle corresponding to
the degree of semi-recumbency to negate the patient's tilt and "normalize"
the positional relationship of the various intrathoracic structures. For
example, if the patient is lying at 30 degrees to the horizontal, the frontal
image intensifier should be rotated to 30 degrees caudally.
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© 2002-2007 Dr. Jui-Sung Hung. All Rights Reserved.
Questions or Comments? Email shung@pipeline.com.
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