Small Animal Cardiac Surgery

Surgical Repair or Replacement of Mitral Valves in Dogs
Published: January 01, 2005
James Buchanan; Mike Pierdon; Laurel Frydenborg; Jay Hreiz

Mitral valve replacement or repair is the definitive treatment for mitral regurgitation but both procedures require cardiopulmonary bypass and are too expensive for most clients.

F. Netter, courtesy of Ciba Medical Illustrations

  

Courtesy of Kanemoto (Jpn J. of Vet. Sci., 1990)

  

External mitral annulus constriction (circumferential annuloplasty) with a purse-string suture (PSS) or a device inserted into the coronary sinus does not require cardiopulmonary bypass and can significantly reduce the severity of mitral regurgitation. This presentation demonstrates construction of a composite suture and a method for PSS annuloplasty.

Yellow = Purse String Suture
Green = Mitral Annulus
Red = Coronary Arteries
Blue = Coronary Sinus & Veins

  

Radiographs 2 hours after surgery showing the position of a radiopaque PSS around the mitral annulus in a dog with severe mitral regurgitation and cardiomegaly.

  

Circumferential Annuloplasty for Correction of Mitral Valve Disease in Dogs

Materials and preparation

A. 50 cm, medical grade Silastic tubing, one mm internal diameter.
B. 75 cm, #5 polyester sternotomy suture with the 3/8 curved needle tip cut off and smoothed by filing.
C. Barium sulfate marker thread removed from a surgical sponge
D. Electrical heat shrink tubing, 0.16cm diameter
E. Assembled PSS attached to straight guidewire, 0.09 cm X 46 cm

  

1. Soak the Silastic tube in xylene for 30 minutes to temporarily enlarge it.

2. Insert the polyester suture and barium sulfate thread into the Silastic tubing by tying them together at one end with a 75 cm long, 3-0 suture then withdraw the suture through the Silastic tube with a stiff wire snare. Passage is aided by moistening the polyester suture and barium sulfate thread with xylene and gently using peristaltic “milking” compression during the pull-through.

3. The assembled PSS is then air dried which shrinks the Silastic tubing back to its original size. To prevent PSS curling while the xylene evaporates, a hemostat weight is applied along with occasional peristaltic compression toward the center of the PSS during the first hour of evaporation. Air dry for 24 hours.

  

4. Attach the 46 cm straight guidewire to the non-needle end of the suture using heat-shrink tubing.

5. Taper the ends of the connections with silicone gel.

6. Sterilize the assembled PSS and a 30 cm tapered, open end 6F guide catheter with ethylene oxide gas.

  

Surgical procedure

1. Thoracotomy: Enter the thorax through the left 6th intercostal space and divide the 7th rib at the costochondral junction or remove the 7th rib if necessary to expose the caudal aspect of the heart.

2. Pericardiotomy: Elevate the phrenic nerve and expose the whole heart with a long cranio-caudal incision in the pericardium one or two cm ventral to the vagus nerve then extend the incision ventrally from the midpoint to the apex of the heart. Suture the dorsal pericardial edge to surrounding thoracic muscles to restrain the left lung lobes.

   

3. Caudal vena cava tourniquet: Bluntly break through the caudal mediastinal pleura and place a loose tourniquet around the caudal vena cava to temporarily reduce blood pressure intermittently during dissection and manipulation procedures. Pull encircling umbilical tape ends through a rubber tube to create a tourniquet around the caudal vena cava and intermittently reduce blood pressure during dissection and manipulation procedures.

 

4. Catheterization: Insert a balloon tip, open-ended catheter in the left atrial appendage to monitor atrial pressure before and after PSS tightening. Alternatively, catheterize a jugular vein before thoracotomy and position an open-ended balloon catheter in wedge position in a pulmonary artery branch for indirect assessment of left atrial pressure.

5. Marginal coronary artery dissection and tunnels: Make several small incisions in the epicardium below the great cardiac vein and coronary sinus between the marginal branches of the left circumflex CA and identify the caudal descending (subsinuosal) CA. It is located below the juncture of the coronary sinus and the caudal vena cava and it identifies the terminus of the LCx. It is critical to place the PSS under the LCx and not above it. Bluntly make tunnels under the marginal arteries and veins.

Postmortem photograph showing relationships of the purse-string suture (PSS) and cardiac structures after surgery is completed. 

S identifies the first marginal or the ventricular septal artery which occurs uniquely in many dogs as an initial branch of the left main, paraconal or left circumflex CA.

RAA = Right Atrial Appendage
PSS = Purse-String Suture
A = Aorta
TS = Transverse Pericardial Sinus
PA = Pulmonary Artery
L = Left Main Coronary Artery
LAA = Left Atrial Appendage
P = Paraconal Artery
Cx = Left Circumflex Coronary Artery
S = Septal Artery
V = Great Cardiac Vein

  

6. Left main coronary dissection: Elevate the left atrial appendage to expose the epicardium and fat pad over the left main and paraconal CA. Dissect a tunnel under the left circumflex CA distal to the paraconal branch of the left main CA.

Post mortem photograph of the caudal aspect of a normal canine heart.

1. Insert a 16-gauge, 5cm, over-the-needle Abbocath (A) under the terminal segment of the left circumflex coronary artery (Lcx) and into the coronary sinus (CS). Great cardiac vein (V). Caudal vena cava (Caud VC). Subsinuosal coronary artery (S).

  

2. After removing the needle, pass a J-tip, 0.09 cm x 46cm guidewire through the Abbocath into the coronary sinus and advance it into the right atrium and remove the Abbocath.

  

3. Pass a guide catheter (tapered-tip, 30-cm long segment of an open end 6F catheter to aid palpation) over the J-wire into the right atrial appendage (RAA). Palpate the right atrial surface to identify the J-wire and secure it in the RAA by clamping the RAA around the J-wire.

4. Partially release the RAA clamp, withdraw the J-wire into the catheter, advance the guide catheter against the RAA wall, reapply the clamp and remove the J-wire completely.

  

5. Insert the 46-cm long straight wire of the assembled PSS into the 30-cm guide catheter in the RAA as far as possible. Release the RAA clamp and advance the straight wire, puncturing the RAA wall.

6. Grasp the straight wire outside the RAA and pull it out of the RAA along with the guide catheter and the trailing PSS.

7. Cut off the straight wire and heat shrink tubing and clamp the cranial end of the PSS with a hemostat to prevent inadvertent retraction of the PSS into the right atrium.

The diagram shows the PSS in the right atrium after entering it through the coronary sinus and exiting through the RAA. 

  

PSS insertion outside and inside a patient. 

Catheter and wire exchanges outside the thorax demonstrate intrathoracic procedures. After Abbocath insertion (into the coronary sinus), advance a J-tipped guidewire (into the right atrium).  Remove the Abbocath, insert a guide catheter over the J-wire and advance both (to the right atrial appendage). Replace the J wire with the straight PSS wire, perforate (the right atrial appendage) and pull the PSS through (the right atrium). Click forward arrow for intrathoracic demonstration.

After Abbocath insertion under the left circumflex CA and into the coronary sinus, advance a J-tipped guidewire into the right atrium.  Remove the Abbocath, insert a guide catheter over the J-wire and advance both to the RAA guided by transmural right atrial palpation. Replace the J wire with the straight PSS wire, perforate the RAA and pull the PSS into and through the right atrium in front of the aorta. Cut off the straight needle and place a mattress suture around the PSS exit site in the RAA.

Necropsy photograph of the opened right atrium of a dog one-hour after surgery showing the PSS on the right side of the interatrial septum extending from the coronary sinus on the left to the atrial appendage on the right.

  

Pass the blunt curved needle attached to the caudal end of the PSS under each marginal branch of the left circumflex CA until it reaches an appropriate position for tying to the cranial end of the PSS. A ligature carrier can be substituted for the needle if desired. The tie should be positioned so the knot will not obstruct the origin of the paraconal artery. This usually requires passage of the cranial end of the PSS backward under the first marginal branch so the knot can be tied between the first and second marginal branches in a more lateral position.

Insert a large, curved ligature carrier though the transverse pericardial sinus(TS) caudal to the aorta (A) and pulmonary artery (PA). Grasp the end of the PSS and withdraw it and the RAA into the transverse pericardial sinus.  Click forward arrow to see demonstration.

  

Insert a large curved or double angled clamp through the transverse pericardial sinus caudal to the aorta. Grasp the end of the PSS and withdraw it and the RAA into the transverse pericardial sinus.

Insert a curved hemostat through the previously dissected tunnel under the left circumflex CA (CX) and withdraw the PSS through the tunnel.  Click forward arrow to see demonstration.

  

Insert a curved hemostat through the previously dissected tunnel under the left circumflex CA (CX) and withdraw the PSS through the tunnel.  Then withdraw it under the great cardiac vein to join the other end of the PSS.

Diagram of the heart showing the final PSS position around the mitral annulus. The suture goes through the coronary sinus and right atrium, then under the left main, paraconal, marginal, and circumflex coronary arteries and the great cardiac vein. The suture is usually tied between the first and second marginal branches of the left circumflex CA.
The green line outlines the mitral valve annulus
   
The coronary sinus and great coronary vein is highlighted in blue
The left coronary artery is highlighted in red.
   
fg5paracartery
The left anterior descending (paraconal) artery is highlighted in red.
The left circumflex artery and marginal arteries are highlighted in red.
   
The coronary vein is highlighted in blue.

  

Record left atrial or pulmonary capillary wedge pressure then withdraw the pulmonary artery catheter to the cranial vena cava to avoid PSS entrapment in the right atrium. Temporarily tighten the PSS to seat it more deeply near the annulus fibrosus and assess the effect on cardiac rhythm, blood pressure and myocardial color. Advance the pulmonary artery catheter to a wedge position to assess left atrial pressure.

Coronary angiograms in an anesthetized dog before (left) and after (right) tightening a contrast filled catheter placed in a mitral PSS position show continued patency of the left circumflex CA (arrow) even after extreme PSS tightening.

Aortic root angiogram highlighting the coronary arteries. The arrow indicates the left circumflex artery.
After tightening the ligature, the left circumflex artery continues to have flow, indicating that it has not been occluded by the ligature.

  

With no tension of the PSS, record an epicardial echocardiogram to assess mitral valve motion and measure the valve diameter. The diameter in this dog can be reduced from 3.25 cm to 1.98 cm (39% reduction). It was left at a diameter of 2.5 cm (23% reduction).

The amount that annulus diameter should be reduced is guided by several factors

1. Observe beneficial hemodynamic effects of PSS tension (rise in systemic pressure, fall in pulmonary capillary wedge pressure, softening of left atrial tension).

2. Palpate the left atrium for disappearance or reduced intensity of the mitral regurgitation jet with trial tension.

3. Evaluate regurgitant jet by epicardial Doppler echocardiography.

4. Assess the effects of arbitrary 25% and 33% reduction of annular diameter.

5. Compare annulus diameter (A) to aortic diameter (B). Normal mitral-to-aortic ratio is approximately 1.5:1

  

A: After settling the PSS in position but not under tension, remove the Silastic tubing beyond the crossover point.
B: Remove 5.6 cm of additional Silastic to yield a 37% diameter reduction in this example. (Diameter reduction is based on the equation: Circumference = 3.14 x diameter. Thus, if a 1-cm reduction in annulus diameter is desired, 3.14 cm of additional Silastic tubing must be removed.)
C: Tie only the polyester suture and transfix it with 3-0 prolene. Excluding the Silastic minimizes the bulk of the knot.

  

Deflate the balloon catheter, remove it from the left atrium and ligate the access site.  
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