Robert C. Neely, MD, Linda Mongero, CCP, James Beck, CCP, and Michael Argenziano, MD
Concept
- Cardioprotection strategies for the arrested heart during cardiopulmonary bypass
- Common errors and troubleshooting techniques
- Cardioplegia solutions
Chief complaint
“You are doing an aortic valve replacement on a 65-year-old man for severe aortic stenosis with moderate aortic insufficiency who has a history of previous triple vessel CABG (LIMA-LAD, SVG-PDA, SVG-OM). Discuss your options for cardioprotection.”
In general, options for cardioprotection for an arrested heart include antegrade and retrograde delivery, continuous or intermittent. Types of cardioplegia include crystalloid or blood-based solutions that can be warm or cold. The most common practice is to use a solution that has a 1:4 blood to crystalloid ratio and is cooled to a temperature of 4° C and infused intermittently every 15-20 minutes.
This patient has important issues that influence the approach, namely a reoperation with prior LIMA conduit and the presence of moderate aortic insufficiency. Standard re-operative measures should be taken, including external pacing pads and prepped groins bilaterally in the event that emergent peripheral cannulation is needed for bypass (refer to redo CABG chapter).
In order to achieve adequate cardiac arrest with sufficient cardioprotection, one must ensure 4 things in this scenario – #1 excellent drainagethrough standard atrial, groin or bicaval cannulation (this can be augmented by an LV vent if needed) #2 ability to cross clampthe aorta – need enough room on the ascending for the placement of a cross clamp, axillary cannulation may be needed if the proximals are patent and high on the aorta #3 Identify the LIMAconduit – prior to arresting the heart, the LIMA should be clamped to prevent continuous perfusion during aortic cross clamping (NOTE: could avoid clamping LIMA in favor of cold bypass flow). #4 retrograde and antegradecardioplegia access. Antegrade would perfuse the OM and PDA territories but not the LAD. Retrograde would perfuse the LAD territory. Adjunctive measures include moderate hypothermia (28-32° C) and direct cardioplegia down the vein grafts but again that would not supply the LAD territory.
In the setting of aortic insufficiency, a retrograde cardioplegia catheter should be inserted in order to ensure cardioplegia delivery. The downside of this approach is incomplete right heart protection when the tip of the retrograde cannula is distal to the middle cardiac vein. Direct retrograde insertion can circumvent this issue. The other downside is that if you get a perforation of the sinus during insertion you are in a difficult situation as the posterior part of the heart is likely to be stuck from the prior operation. On the other hand, any dissection that you do to facilitate retrograde insertion risks damage to the grafts. Do what you are most comfortable with but demonstrate thoughtfulness in either direction.
Index scenario (additional information)
“After cross clamping and delivering 500 mL of antegrade cardioplegia, you note poor distension of the aortic root, incomplete arrest, and left ventricular distension on transesophageal echocardiogram (TEE). How would you proceed?”
Switch to retrograde and turn on the aortic root vent. An aortotomy would also allow decompression. Another option is placing an LV vent in order to decompress the left heart as cardioplegia crosses the incompetent aortic valve and fills the LV. However, it may be difficult to get the vent in during a redo.
“You place an LV vent. The LV is decompressed but electrical activity persists. As planned, you give retrograde cardioplegia, but you note persistent activity and your perfusionist notes inadequate line pressure. You are unable to reliably palpate the retrograde catheter in the coronary sinus. Transesophageal echocardiography suggests the catheter is not in the coronary sinus. How would you proceed?”
Remember that this is a redo situation. Open the aorta (if you haven’t already) and deliver additional antegrade cardioplegia directly down the vein grafts to get the best arrest that you can and cool to moderate hypothermia. Get around the cavas if you can and insert the retrograde catheter directly to get perfusion of the LAD distribution. The other alternative to getting excellent cardioplegia down the LAD territory is to cool to 20° and leave the L-LAD open.
“How do you ensure adequacy of retrograde cardioplegia delivery?”
Look for cessation of electrical and myocardial activityby checking the EKG and looking at the heart. Additionally, confirm with the perfusion team that you have adequate line pressure and flow. Most retrograde cannula tips have pressure monitor probes that report the pressure in the coronary sinus. A conservative upper limit of appropriate pressure is approximately 40 mmHg. This reflects a flow of 50-100 cc/min. Observe flow through the coronary veins and arteries during retrograde cardioplegia. Check the RCA and LCA ostia after the aorta is opened and retrograde is running to ensure adequate distribution of the retrograde to the right and left circulations. The myocardial temperature can also be a guide to the adequacy of cardioplegia delivery. You should notedecreasing myocardial temperature assessed either manually or with a direct temperature probe.
Operative steps
Antegrade cannula placement
- Identify a favorable area on anterior curvature of ascending aorta with adequate room for aortic cross clamp cephalad and proximal anastomosis or aortotomy—if needed—caudad.
- Can check for plaque by palpation or evaluate with epiaortic ultrasound.
- Antegrade needle and cannula should be snared securely.
- After securing the line in place it must be flushed to deair. After cross clamping, run your induction dose and inspect the root for evidence of dissection and inspect the LV for distention. A fast arrest is a good sign.
Retrograde cannula placement
- A purse-string suture is placed in the inferolateral aspect of right atrium.
- Retrograde cannula is placed with a gentle L shaped curve and directed toward the orifice of the coronary sinus with guidance from the operator’s opposite hand.
- The final placement is confirmed by palpation and/or transesophageal echocardiographic imaging, and further substantiated by distal pressure readings during infusion.
- Some cannulae have self-inflating balloons; others must be inflated manually. These balloons are rarely completely occlusive. This lack of complete occlusion is helpful in avoiding edema during CABG procedures when giving simultaneous cardioplegia down the retrograde catheter and a saphenous vein graft.
- If indirect retrograde placement is problematic, then direct retrograde placement can be used. This requires bicaval cannulation, caval snares for atrial isolation, small atriotomy, handheld retractor, identification of the coronary sinus ostium, purse string and direct placement of the coronary catheter. This is usually done with the clamp in place on the aorta.
- The standard catheters may be used for direct retrograde although an 8 mm flexible polystan catheter may be less traumatic. The purse string is secured which leads to occlusion of the coronary sinus. Thus, giving direct retrograde and cardioplegia down a vein graft simultaneously may theoretically lead to myocardial edema.
- Direct retrograde is a good way to ensure delivery down the right and left since the catheter is not advanced beyond the middle cardiac vein.
Potential questions/alternative scenarios
“How does the presence of a left sided Superior Vena Cava (LSVC) change your approach to cardioprotection?”
The presence of a left sided SVC poses an issue of volume returning to the right side of the heart (directly or via the coronary sinus) that is not drained by a venous cannula. This volume of blood then enters the pulmonary circulation and returns to the left atrium and ventricle and may cause distension. In addition, this blood is warmer than the cardioplegia solution and may negate cooling effects on the myocardium. The other issue is that in cases in which the LSVC drains into the coronary sinus, it is difficult to administer retrograde cardioplegia. In these cases, the LSVC can be occluded or cannulated directly and added to the venous drainage circuit. The latter technique is advisable if the LSVC is very large and is mandatory if there is an interrupted innominate vein.
“Upon infusing antegrade cardioplegia, the perfusionist notes high line pressure. What are your next steps in management?”
This raises concern for a dissection. Stop your antegrade flow. Check for kinks or clamps obstructing flow along the line, ensuring that the cardioplegia is flowing down the appropriate path to the aortic root. Also check to make sure that the pressure monitoring line is connected correctly. With regard to a potential dissection, visualize the aortic root and look for distension or discoloration/bruising around the cannula. Ask the anesthesiologists to visualize the ascending and descending aorta with transesophageal echocardiography. If dissection is confirmed start cooling with your original aortic cannula which is distal to the clamp (assuming the dissection is contained within the root. Prepare for a dissection repair (see chapter on Iatrogenic Aortic Dissection).
“After unclamping the aorta during a case with retrograde cardioplegia, you notice the myocardium is slow to regain electrical activity. Prior to placing pacing wires, what should you check?”
Check that the retrograde catheter is removed and/or that the balloon is down (if not automatically deflated after infusion) in order to allow for adequate coronary sinus flow.
“While sewing the distal anastomosis on a coronary artery bypass graft, you notice increase bleeding from the coronary arteriotomy, how do you proceed?”
The concern is that the arrested myocardium is getting perfused. First check that the aortic cross clamp is occlusive, and the aortic root vent is on. A possible explanation for mild bleeding at the arteriotomy site is the presence of collateral circulation. If unable to identify a correctable cause, monitor for signs of electrical activity and consider cold topical saline, cooling the patient (mild hypothermia – 32° C), reducing flows as tolerated or more frequent administration of cardioplegia solution.
“Discuss the principles of cardioplegic arrest, how this is achieved by components of the cardioplegia solution and name some common types of cardioplegia.”
Minimizing myocardial oxygen demand is the primary principle of cardioplegic arrest. This is best achieved by rapid diastolic arrest after the aortic cross clamp is applied, thereby minimizing time of high ventricular work against a fixed afterload. Potassium is the most common electrolyte employed to produce diastolic arrest, and there are several common additional components, including sodium, citrate, and magnesium. Magnesium has been associated with decreased ventricular arrhythmias and improved cardiac performance in some studies. Histidine, Tryptophan, and Ketoglutarate (HTK) also comprises commonly used cardioplegia formulas. The cardioplegia solutions are cooled to 4° C which decreases myocardial oxygen consumption and diminishes contractile activity. Dextrose is used for glucose uptake and control of myocardial edema. Lastly, there are several iterations of blood and crystalloid ratios, but no evidence to support superiority, and preferences tend to be surgeon and/or institution specific.
“After placing the retrograde catheter, you encounter some dark blood emerging from behind the heart. You check and notice a perforation of the coronary sinus.”
The rigid catheter can perforate the sinus especially in older and frail patients. If this happens, initiate cardiopulmonary bypass, cross clamp and arrest with antegrade. Repair the perforation directly with prolene suture or with a pericardial patch (see chapter on Venous Injuries).
Pearls/pitfalls
In general, there are a few things to consider when thinking about persistent activity which can be broadly grouped under “Access,” “Collateral flow,” and “Myocardial mass.”
Access
- Are your retrograde and antegrade cannulasin place and properly connected?
- Is the retrograde too far and not protecting the RV despite antegrade?
Collateral flow
- Is the cross clamp completely occlusive?
- Is the right sided drainage adequate or do you need an additional cannula?
- Is there a persistent left sided SVC filling the right atrium?
- Is the left sided drainage adequate (is the root vent on or additional basket suckers in place; is there so much collateral flow that you need an LV vent)?
- Once drainage is optimized do you need systemic moderate hypothermia to 28-32° C to keep the residual collateral flow cool?
Myocardial mass
- Is the heart so hypertrophied that myocardial delivery of cardioplegia is inadequate – if so address all of the above and try topical hypothermia?
Suggested readings
- Chambers DJ and Fallouh HB. Cardioplegia and cardiac surgery: Pharmacological arrest and cardioprotection during global ischemia and reperfusion. Pharmacology and Therapeutics. 2010. Issue 127 (41-52).
- Levitsky S and McCully J. Myocardial protection. Sellke FW et al (ed). Surgery of the Chest. Saunders. 8th Edition.
- Mentzer RM, Salik Jahinia M, Lasley RD. Myocardial Protection. Cohn L (ed). Cardiac Surgery in the Adult. McGraw Hill. 2008.
- Sa et al. Is there any difference between blood and crystalloid cardioplegia for myocardial protection during cardiac surgery? A meta-analysis of 5576 patients from 36 randomized trials. Perfusion. 2012. July.
