What is Cardiac Surgery?
Any procedure performed on the ventricles, atria, cardiac valves, and great vessels
May be closed procedures which can be performed without opening major cardiac structures
May be open procedures which require circulatory arrest
Inflow occlusion (procedures < 5 minutes) with or without hypothermia
Cardiopulmonary bypass (not discussed in these lectures)
Perioperative Considerations
Must undergo a thorough diagnostic evaluation
Incomplete or inaccurate diagnosis can be devastating
Cardiac catheterization, CT or standard angiography (no longer routinely necessary)
Anatomic 2D, m-mode, color flow and spectral Doppler, live 3D and transesophageal echocardiography
Animals undergoing cardiac surgery usually have some degree of cardiovascular dysfunction
Wherever possible, cardiac abnormalities should be corrected medically prior to surgical intervention
Arrhythmias
Congestive heart failure (pulmonary edema, pleural effusion, etc.)
Not fundamentally different from other soft tissue surgery
All principles of good surgical technique apply
Motion from cardiac contraction is the aspect that makes cardiac surgery different
Strategies for arresting cardiac motion are available
Closure of cardiovascular structures require precise suturing techniques:
Typically use fine suture (4-0 or smaller) with swaged-on atraumatic needles
Avoid palming instruments when suturing vascular tissue
Hand tying of knots is fast and produces a tighter, more secure knot
Fundamental skill for cardiac surgery
One handed tie preferred
First 2 or 3 throws in same direction, and finish with a square knot
Suture and Instrumentation
Polypropylene, nylon, braided polyester, common sutures in 3-0 to 6-0 size ranges
Heavy gauge silk for ligatures
Swaged-on taper point needles
Double-armed suture (needles on both ends) very useful in cardiovascular surgery
Continuous horizontal mattress pattern oversewn with simple continuous is the most secure and generally preferred suture pattern
Proper instrumentation is essential
Basic surgical instruments along with
DeBakey atraumatic tissue forceps
Metzenbaum scissors
Potts 45 degree angled scissors
Long needle holders
Vascular clamps (variety of styles and sizes)
Conditions Amenable to Surgical Correction Without Inflow Occlusion/Bypass
Patent Ductus Arteriosus
Ductus arteriosus is a fetal vessel that shunts blood away from (pulmonary artery) lungs back to systemic circulation (descending aorta)
Closes shortly after birth
Continued patency of the ductus arteriosus for more than a few days after birth is consistent with PDA
Most common congenital cardiac defect in dogs (25–35% of congenital malformations in dogs)
Exists, but rare in cats
More common in purebreds, slight predilection for females.
Poodles, Yorkshire Terriers, Maltese, Bichon Frise, Cocker Spaniels, Pekingese, Collies, Shelties, Pomeranians, Welsh Corgis.
Heritability documented in Poodle and Welsh Corgi
Pathophysiology
Allows left to right shunting, resulting volume overload, leading to left ventricular and atrial dilation, progressive myocardial deterioration, and left sided congestive heart failure
Most dogs with PDA die of heart failure before 1 year of age
Diagnosis
Continuous cardiac murmur (machinery murmur) at left heart base is classic PE finding, often with palpable thrill
Bounding femoral pulses
Radiography
Left atrial and ventricular enlargement
Enlargement of the vessels
Characteristic aortic bulge (dilatation of descending aorta)
ECG findings
May or may not show changes, more changes as cardiac dilatation occurs
Echocardiography:
Most diagnostic
Helps rule out concurrent defects
Helps rule out right to left shunts (although clinical signs of this are different)
Treatment
Standard surgical correction is ligation of the ductus
Left 4th intercostal thoracotomy
Vagus nerve is identified and isolated
Gently dissect ductus and pass two silk ligatures (O) around ductus
Excellent prognosis with surgical therapy
Less than 5% mortality
Aortic aneurysm or PDA rupture can cause complications
Transvascular occlusion now standard of care (coil embolization, Amplatz ductal occluder)
Surgery relegated to failures or very small dogs (rare)
Vascular Ring Anomalies
Can occur in any breed
German Shepherd and Irish Setter seem to have a predilection for PRAA
Pathophysiology
Developmental anomalies of the great vessel which result in entrapment of the trachea or esophagus in complete or incomplete ring of vessels
Diagnosis
Usually normal until weaning, when signs of post-prandial regurgitation occur
Clinical signs caused primarily by esophageal obstruction
Coughing and respiratory distress may be present with aspiration pneumonia, or with tracheal compression due to double aortic arch
Radiography:
Esophageal dilation cranial to heart base
Contrast esophagrams
Esophagoscopy
Angiography (rarely performed)
Treatment
Medical management unrewarding
Surgical intervention
Divide vascular ring and transect peri-esophageal fibrous bands
Most corrected via left lateral thoracotomy, except aberrant right subclavian
Prognosis
Persistent regurgitation is common
Loss of neuromuscular function and lack of aboral peristalsis
Earlier intervention is probably better, but many older dogs do well
Most report good or excellent outcomes
Ventricular Septal Defects
Failure of development of the intraventricular septum
Membranous defects more common than muscular
10% of congenital heart defects in dogs.
Most common congenital malformation in cats
English springer spaniels, Lakeland terriers, West Highland white terriers, basset hounds, English bulldogs, Akitas, and Shih Tzu have increased risk
Polygenic in keeshonden
Pathophysiology
Dependent on defect size and location
Restrictive defects allow left to right shunting
Left ventricular overload leading to CHF
High flow shunts
Progressive pulmonary arteriopathy
Pulmonary hypertension
Right to left shunting (Eisenmenger's syndrome)
Aortic valve insufficiency is associated with VSD
Prolapse of right coronary aortic leaflet into the defect
Diagnosis
Often not symptomatic in young animals
Eventually see signs of left-sided CHF
Coughing
Exercise intolerance
Systolic murmur at the right sternum/apex
Diastolic murmur due to aortic insufficiency can give the murmur a continuous quality ("to and fro")
Angiography (rarely done anymore)
Echocardiography with color flow Doppler
Higher velocity shunting equates with a smaller defect and a better prognosis
Treatment
Surgical correction indicated for hemodynamically unrestricted defects
Prevent CHF
Prevent worsening of aortic insufficiency if present
Radiological evidence of pulmonary vascular dilatation
Echocardiographic evidence of left ventricular dilatation
Shunt velocity > 3.5 m/sec (> 5 m/s for left to right defects)
Right ventricular outflow tract ejection velocity increased causing relative pulmonic stenosis
Pulmonary Arterial Banding
Increase right ventricular systolic pressure
Left 4th intercostal approach
Large cotton or Teflon tape passed around pulmonary artery just distal to pulmonic valve
Generally requires a 2/3 reduction in pulmonary arterial diameter
Attenuated pulmonary arterial pressure decreased to < 30 mm Hg
Open repair requires bypass
Interventional cardiac catheterization closure on the horizon
Complications
Minimal morbidity and mortality
Over-tightening of pulmonary band can lead to reversal of flow through defect
Progressive tricuspid regurgitation and RVO tract obstruction leading to reverse flow also reported
Prognosis
Long term data is not available
Short term palliation good. One report out up to 7 years.
Cats do better than dogs
Definitive open repair or closure via catheter occluder probably curative
Tetralogy of Fallot
Complex congenital defect
RVO tract obstruction
VSD
Over-riding aorta
Right ventricular hypertrophy
Genetic in keeshond
Pathophysiology
With large RVO obstructions:
Markedly elevated right ventricular pressure
Right to left shunting
Cyanosis
Progressive polycythemia
Sudden cardiac death
With large VSD
Similar to VSD alone
Balanced VSD and RVO obstruction
Similar to VSD that has been banded
Diagnosis
Cyanosis
Moderate to severe exercise intolerance
Exertional tachypnea
Syncopal episodes
Thoracic radiographs
Right ventricular enlargement
Dilation of pulmonary artery
Echocardiography
Indications for Surgery
Severe exercise intolerance
Polycythemia (HCT > 65%)
Resting hypoxemia (PaO2 < 70%)
Treatment
Goal of surgery is to alleviate right outflow obstruction and to create a left to right shunt
Animals with a natural left to right shunt have acyanotic tetralogy and rarely require surgery
Balloon valvuloplasty + modified Blalock-Tausig shunt
Definitive correction requires bypass
Prognosis
Short term palliation successful
Long term palliation has not been demonstrated
Successful definitive correction reported (2 dogs)