The evolution of cardio-protective strategies during “Open Heart” surgery, through numerous years of empirical trial-and-error, has evolved into two primary factors: utilizing cardioplegia (to quiet a beating heart) that one trained with in medical school vs. a cardioplegia solution with demonstrated superior global protective qualities.
It is necessary to discuss the myriad of present day cardio-protective strategies available to all Cardiac programs in order to effectively provide a “menu” of available options. The fascinating cornucopia of cardioplegia solutions literally runs the gamut. From all crystalloid solution, pink tinged crystalloid, crystalloid with blood to all blood with no crystalloid.
We have ratios of delivery: 4:1 (4 parts blood, 1 part, crystalloid), 1:1, 1;4, 8:1...all the way to 66:1. You have frequency of delivery: Every 10 to 20 minutes, after every graft, after one hour to one hour 30 minutes and longer to just one large dose.
The benefits conferred by either warm or cold blood cardioplegia (or any compounded formulation) are viable only if solutions are delivered to all myocardial regions in sufficient amounts to exert their desired effects. Maldistribution of flow unfortunately is commonplace with patients experiencing coronary artery disease when principle reliance is solely placed upon antegrade delivery of perfusion. This is especially true when arterial conduits are utilized, and precluding delivery from the newly constructed vein grafts.
Retrograde cardioplegia has neutralized this limitation. This is due to excellent left ventricular protection following coronary sinus or right atrial perfusion. The development of transatrial coronary sinus cannulation techniques has provided simple, safe and rapid access to the coronary sinus utilizing antegrade/retrograde technique.
Of paramount importance and never to be confused: Simplicity and Safety are not synonymous.
A cogent analysis: arterial conduits such as internal mammary artery (IMA) or gastricepiploic artery, along with mitral valve repair have now reached a nexus where they are superior to implanting all saphenous vein grafts or routine mitral valve replacement. Once again, time thereby longevity, will provide validation into the advantages and limitations from various operations. A similar situation now exists regarding methods of intra-operative global myocardial reanimation.
Longevity of patency is a key indices in determining whether or not you have achieved superior repair and/or replacement on the Cardiac muscle. As of this writing, a Starr/Edwards Aortic Ball Valve is still operating flawlessly after sixty years implanted.
During the 1970’s an explosion of interest in different methods protecting the Heart evolved across the Planet. From the introduction of multi-dose crystalloid cardioplegia in 1976. Cold blood cardioplegia in 1977, warm blood cardioplegic reperfusion and warm induction in 1977 and 1983. Alternating between antegrade and retrograde delivery in 1989...and the most recent technique of antegrade/retrograde delivered simultaneously in 1994. During this same time period, the concept of continuous cold non-cardioplegic blood perfusion was introduced. Primary endpoint: Full restoration of Normal Sinus Rhythm; without impeding surgical progress.
Of paramount importance, seldom appearing in print- extreme diligence in providing global myocardial protection is to ensure your surgeon repeatedly has uneventful spontaneous conduction into NSR when the cross-clamp is removed. To that end, the onus is upon Perfusion to become creative enough and “tailor” the appropriate myocardial protection strategy to the particular dynamics of the surgical procedure.
Pioneered by Norman Shumway at Stanford University in 1957, “normothermic ischemic arrest” became standard arresting practice for myocardial management prior to the acceptance of intra-cardiac cardioplegia solutions.
This moment in history is well documented due to the robust political rancor from two distinct camps that emerged with Cardiac Surgeons Worldwide over how best to “quiet” the beating human heart.
One vocal group of Surgeons maintained that “normothermic ischemic arrest” should be the primary technique when striving for total quiescence of the heart. The second group believed empirically that normothermic arrest did not provide a “safety valve” to guard against the onset of ischemia. They preferred a cold water solution, either circulating or static, or an ice-slush filling the pleural cavity. The major proponent of this technique was Stanford with Dr. Norman Shumway...and he maintained a very large coterie of disciples.
With the advent of electro-chemical arrest utilizing high doses of potassium, it seemed only natural for topical ice-slush to coalesce with potassium cardio manifesting a quiescent heart. This technique radically reduced the metabolic uptake, allowing for approximately two hour window to complete the necessary operation.
Unfortunately, it was discovered that it was not uncommon with ice-slush remaining in the pleural cavity for two hours plus the lungs would not tolerate extreme cold very well and periodically developed atelectasis. Of note; during the 1960’s, 70’s and 80’s it was not unusual for individuals to smoke unfiltered cigarettes. From air pollution to self-abuse, our lungs took quite a beating.
At this moment in time there is a plethora of varied compounded compositions achieving electro-chemical arrest of the myocardium. This is an updated sample:
1) Hypothermia: First viable and reproducible method of preservation
2) Hypothermia with fibrillation
3) Only fibrillation
4) Pure crystalloid solution
5) Crystalloid solution w/ “pink tinge” (small amount of whole blood)
6) High K+ or Low K+ delivery
7) Warm vs. Cold, intermittent and/or continuous, with or without substrate enhancement
8) Warm, Cold, Warm, with or without substrate enhancement
9) Continuous vs. Intermittent perfusion
10) Flowing through vein grafts
11) Antegrade and/or Retrograde delivery
12) Pure whole blood (cold and warm) w/ micro titrations of drugs (microplegia)
13) del Nido single dose low K+ with Lidocaine and Magnesium
14) Bretschnider single cross clamp
The results from a recent survey of more than 1800 surgeons in the United States indicated that blood cardioplegia emerged as the preferred cardio-protective strategy due to its versatility. This directly correlates with voluminous research indicating blood cardioplegia blends onconicity, buffering, rheology plus antioxidant benefits. It has also been established to augment oxygen delivery and its ability to “resuscitate the heart” plus attenuate ischemic injury, “limit reperfusion injury” and the potential to reverse “ischemic/reperfusion injury”.
“One shot” non-blood cardioplegia, by its delivery time-frame and composition cannot provide the same assurance.
Over the last several years, cold crystalloid 1:4 (one part blood, 4 parts crystalloid) cardioplegia has gained widespread favor. Primarily this is due to the advocacy of giving one large (1000ml +) cardio and then zero replenishment for over an hour. Since the surgical team is not required to stop the procedure to periodically replenish the heart, they are free to continue the operation un-tethered by periodic administration of cardioplegia.
In a perfect World scenario, this technique would be the panacea to all cardioplegia drawbacks. However, “a heart knows what a heart wants”. And a Heart that has endure years of less-than-ideal blood flow and oxygen is by far less tolerant than a young vibrant virgin baby heart. Therefore, it is not unusual for surgeons to experience a heart that refuses to spontaneously conduct when the cross clamp is removed It is questionable if the route response to a heart that does not conduct is to just say:
“Oh, we just start the pacemaker”. Becoming reliant on artificial electrical excitation to establish a rhythm would not be considered “Best Practices”.
The logic behind multi-dose blood cardioplegia derives from the occurrence of non-coronary collateral flow in all in-sit u hearts. This non-coronary collateral flow rewarms the heart by replacing any carefully formulated cardioplegic solutions with systemic (non-cardioplegic) blood at the temperature prevailing in the extracorporeal circuit. It enters the heart via open mediastinal connections and becomes evident as blood fills the coronary arteries or the coronary ostia while the aorta is cross clamped and the heart decompressed.
Rewarming can be circumvented by topical hypothermia. However, voluminous evidence has proven this technique is not only a cumbersome adjunct...but may well create pulmonary complications without supplementing the cardio-protective effect of multi-dose cold cardioplegia with warm induction and reanimation.
To clarify another misconception that should be easily rectified: Routine use of Cold Induction.
Cold induction has gained widespread acceptance Worldwide. The reasoning behind it is multifaceted and held onto tenaciously. And yet, the logic behind the technique is not only counter-intuitiveit is also counter-productive.
Cold creates constriction! Anyone who has fallen into snow or ice is familiar to what extreme cold is like on your bare skin. Constriction, when coupled with severe coronary disease makes it extremely difficult to adequately flow cardioplegia past blockages down to the myocyte. In essence, you are creating precisely what you should be preventing; that is the inability to flow cardioplegia adequately down to the myocyte.
Warm induction is nature’s wondrous dilator, opening the coronaries and periphery to facilitate adequate flow.
Finally: In defense of multi-dose administration versus single “one shot”: Lab testing has not been able to quantify a scientific model nor gather empirical evidence as to a time point when exactly ischemia begins in human hearts. It is noted that some patients display signs of ischemia at three minutes. While other patients show signs of ischemia at one hour.
Oxygen demands rise rather quickly if electro-mechanical activity (ie. beating or fibrillating) recurs in the under-perfused right ventricle. The use of cold blood, therefore, provides for the shifting of high K+ to Low K+ to No K+ during the same procedure while maintaining an arrested state.
In order for an operation to be considered a success, one must maintain a quiet, dry operative field. A prerequisite ensuring a precise cardiac surgical procedure. Unfortunately, most surgeons create “intentional ischemia” during non-delivery of any form of adequate protection.
All in-sit u hearts derive some non-coronary unpredictable flow that will effectively “wash away” cardioplegic solutions. Therefore, intermittent replenishment is mandatory to restore washed out metabolites, counteract acidosis and edema, and restore a cardioplegic composition to attenuate reperfusion injury prior to the next period of planned ischemia.
With every occurrence of “breakthrough beats”, unintended electro-mechanical activity while the aorta is clamped and cardioplegic administration has ceased; is not only a surgical nuisance, but signifies the retained capacity of producing sufficient ATP to allow robust contractility to resume.
Coronary artery bypass grafting is the most frequently performed procedure in the United States. The issue of intra-operative cerebral atheroemboli is becoming ever more evident as the patient population exceeds 70 years of age and undergoing revascularization. The atherosclerotic process in the aorta may lead to potential cerebral atheroemboli when the aorta if clamped. This potential is compounded if the aorta is repeatedly clamped tangentially to construct proximal anastamosis.
Anticipating infusing the final cardioplegic dose; delivery temperature is set at 37 degrees C, essentially to correspond when all anastomoses are complete. This provides for warm reperfusate, both antegrade and retrograde to be delivered without stopping the continuity of the operation. This will also avoid needless delays waiting for rewarming prior to terminating bypass.
The final cardioplegic dose is delivered warm with or without K+. This should be followed immediately by warm blood with zero cardioplegia, zero K+. This provides administration of warm blood while checking for any leaks, de-airing of grafts and washing out metabolites and any extraneous potassium.
Please keep in mind; there is zero downside to replenishing the heart with as much oxygen-rich blood as you deem feasible. Studies have indicated this whole blood washout procedure enhances the recovery period, dilating the heart and vasculature thereby replenishing any energy stores down to the myocyte.
In the 1970’s we had a rather macabre expression: “Surgery was a success. But the patient died”. This was in reference to utilizing a patient and family member who would act as the heart-lung machine.
It has been the goal since this forgetful period in time to strive for any patient in any condition to undergo revascularization and never look like they endured surgery.