Myocardial protection facts Flashcards
What is the benefit of systemic hypothermia on myocardial oxygen consumption
For every 1 degree of systemic hypothermia the myocardial oxygen consumption tissue decreases by 7%.
Benefits of Cooling for myocardium
Decreased metabolic rate decreased enzyme function decreased membrane stability increase calcium sequestration increased glucose utilization decreased ATP generation decreased tissue oxygen uptake decreased osmotic homeostasis increased hyperviscosity with rouleaux formation
What are options for myocardial protection during cardiac surgery
Cardioplegic arrest
Aortic cross-clamping with electrically-induced fibrillation
Hypothermic arrest with fibrillation (where the aorta remain unclamped)
Off pump coronary bypass surgery
What are advantages and disadvantages of using retorgrade cardioplegia
Advantage
Useful in patients with severe aortic regurgitation
Significant proximal coronary disease
Useful in patients with patent previous bypass grafts
Disadvantage
concerns regarding protection of the right ventricle
less predictable distribution then antegrade cardioplegia
What are methods of delivery for cardioplegia
Antegrade cardioplegia (down the root) usually at a pressure of 60 to 100 mmHg at 250ml/min
Retrograde cardioplegia (in coronary sinus) Usually at a pressure of 30 to 50mmHg at 150 ml/min. Usually takes longer (2-4 minutes)
How does cardioplegia cause arrest
Regardless of solution they alter the resting potential and cause a diastolic arrest
Extracellular solution— St. Thomas solution—prevents cardiomyocyte repolarization by increasing the potassium concentration in the extracellular fluid.
Intracellular solution–Bredtschneiders solution–blocks deploraization by lowering extracellular sodium concentrations
Main components of cardioplegia solution (Crystalloid cardioplegia contains)
Sodium 110 mmol/L Potassium 16 mmol/L Calcium 1.2 mmol/L Magnesium 16 mmol/L Chlordie 160 mmol/L
Blood cardioplegia contains st.thomas solutaion at a ration of 4:1 in addition it has
1) Procaine 2) Glutamate 3) aspartate 4) oxygen free radical scavengers 5) adenosine
Potential benefits of blood cardioplegia over crystalloid
Provides oxygen and nutrients
Buffering capacity
minimises intracellular edema due to its oncotic proteins
Scavengers of oxygen-free radicals as it contains superoxide dismutase, catalase, gluthione and vit C and E.
What are myocardial protection techniques for redo cardiac surgery with a patent LIMA
Dissect out the LIMA and temporarily occlude when giving cardioplegia
moderate hypothermia and fibrillatory arrest (without occluding the LIMA)
cooling to 28C with either continuous retrograde cardiopplegia or intermittent cold blood caridoplegia without isolation of LIMA
What is principle of terminal warm blood cardioplegia
Dose of warm cardioplegia immediately before removing cross clamp
allows washout of the products of anaerobic metabolism
provides substrate resuscitation of ischemic myocytes with oxygen and ATP
has been shown to improve myocardial metabolism and contractility once ventricular contractions resume.
What is Buckberg technique for protection of myocardium during acute MI
Establish extracoporeal circulation as quickly as possible with venting of the left ventricle
initially antegrade cardioplegia using either a warm buckberg solution or cold high potassium to achieve rapid diastolic arrest
Temperatures of anterior and inferior wall of the ventricles
after each distal anastomosis–cold cardioplegia is infused into each graft and the aorta at 200ml/min over 1 minute
followed by retrograde through the coronary sinus for 1 minute
After final distal warm substrate-enriched blood cardioplia is given at 150ml/min for 2 minutes into each anastomosis and the aorta.
Cross clamp removed-18 minutes of blood cardioplegia is given at 50ml/min into the grafts
The proximal vein grafts are then completed
Heart allowed to beat for 30 minutes (empty)
then come off
What percentage of retrograde cardioplegia returns to left coronary ostia and to the right coronary ostia
2/3 of total retrograde provides nutritional support (think 70%)
80% returns via LC (so total of 55%)
20% returns via RC (so total of 15%)
1/3 is non nutrictive cardioplegia (30%) and this just returns to RA/RV/LV via thebesian veins, ven-ven collaterals
What is dose of cardioplegia induction needed
10ml/kg to 15ml/kg
The typical aortic root perfusion pressure should be 60 to 80 mmhg
What are the two types of crystalloid cardioplegia
Intracellular—low sodium based solution
Extraceullular—high concentrations of sodium
most have K+ concentrations of < 40mmol/L
What is a potential negative of continous warm blood cardioplegia
one study showed worsening neurological function (3.1 vs 1.0 percentage)
What are goals of cardioplegia
Protect against ischemic injury
provide a motionless, bloodless field
allow effective post-ischemic myocardial resuscitation
What is most common form of cardioplegia
Blood
Greater oxygen content
superior buffering–b/c of blood protein histidine
reduced oxygen-mediate injury from erythrocyte free radical scavengers during reperfusion
reduced coronary vascular resistance and edema
improved oxygen extraction and energy delivery
List advantages of retrograde cardioplegia
benefit for high-grade coronary stenoses or obstruction (left main, acute coronary syndrome) More convenient during aortic and mitral valve operations Redo CABG (particularly with diseased SVGs or with patent LIMA to occluded LAD
Disadvantages of retrograde
various degrees of maldistribution to the RV
unrecognized persistent LSVC
Coronary sinus rupture
maybe less satisfactory in hearts with severe LV hypertrophy
What are benefits of intermittently(every 15 to 20 minutes) giving cardioplegia
Maintains arrest restores desired levels of hypothermia buffers acidosis washes away metabolites replenishes high-energy phosphates restores depleted substrates counteracts edema with hyperosmolarity
What are differences with neonates and adults in terms of cardioplegia
Usually single dose cardioplegia with ischemic times of 65-85 minutes
with stand hypoxia better
greater glycogen stores
more amino acid utilization
slower ATP breakdown
amino acid substrate enhancement is beneficial
DHCA is more commonly used
What is protection strategy in Acute LAD occlusion
Initial administration of warm blood cardioplegia
Retrograde and antegrade
can use a vein graft to LAD
Warm hot to come off
Which chamber is prone to hypoperfusion with RCP
Right ventricle
When RCP is administered roughly what percentage of nutrient flow drains by the routes indicated below
Left coronary ostium (30 +/- 10&)
Right Coronary Ostium (3 (+/- 3%)
Ventricles 67 +/- 10%
By what anatomical pathway does RCP perfusion drain into the ventricular cavities
Thebesian veins
What’s one surgical modification that can improve retrograde perfusion
purse string suture surrounding the coronary sinus and direct placement
What are cardiac metabolic demands at various conditions
Beating loaded heart 10ml of oxygen per 100 mg myocardium per minute
Unloaded heart 6ml of oxygen per 100 mg myocardium per minute
(On CPB)
Arrested heart 1ml of oxygen per 100 mg of myocardium per minute
(cardioplegia)
