Case Discussion - CABG

Case Discussion - CABG

 

Q. What is Acute Coronary Syndrome (ACS) ?

ACS comprises of these 3 -

ST elevation myocardial infarction (STEMI)

Non- ST elevation myocardial infarction (NSTEMI)

Unstable angina (USA)

Q. How is ACS different from Stable angina ?

Stable angina develops during exertion and resolves with rest

Unstable angina occurs suddenly, at rest or with minimal exertion.

Q. Which coronary is dominant ?

 Dominance of coronary system is defined by the origin of posterior descending artery (PDA) through which septal perforators supply the inferior one third of ventricular septum.

 Right dominant coronary circulation -

 When PDA originates from right coronary artery (RCA) it is called right dominant coronary circulation. It occurs in 85-90 % patients.

 Left dominant coronary circulation - When Left circumflex artery gives rise to PDA it is called left dominant circulation.It occurs in 10-15% patients.

 Co-dominant circulation - Contribution from both LCX and RCA can occur and is defined as when septal perforators from both vessels arise and supply the posterior-inferior aspect of the left ventricle.

Super-dominant circulation - Absent left circumflex coronary artery with superdominant right coronary artery is a very rare anomaly wherein the left main coronary artery continues as left anterior descending artery. There is complete absence of the left circumflex artery and obtuse marginal artery.

The RCA is superdominant with its distal branches coursing retrogradely in the left atrioventricular groove (in the course of the normal left circumflex artery) and supplying the left ventricle. In this case, the right posterior descending artery is prominent continuing retrogradely in the left atrioventricular groove.

Q. What is the etiology of Diastolic Dysfunction ?

Hypertension

Diabetes

Obesity

Coronary artery disease

Hypertrophic Cardiomyopathy

Infiltrative cardiomyopathy – amyloidosis

Volume overload – severe anaemia, aeteriovenous fistula.

Q. What can worsen diastolic dysfunction ?

AF : as atrial kick important in DD

Tachycardia : truncates last phase of diastolic filling – important for adequate LVEDV

Hypertension : increased LV wall tension worsens DD

Ischaemia : Increased LA pressure and increased pulmonary venous pressure leads to respiratory symptoms, they are ANGINAL EQUIVALENTS in DD

Q. What is the importance of DD from Anesthesia point of view ?

DD – LVEDP increases – Flash Pulmonary edema ensues

LVH- aims of anesthesia are to: avoid tachycardia

avoid/minimize the effects of negative inotropic agents, in particular anesthetic drugs

prevent increases in afterload

maintain adequate preload in the presence of elevated LVEDP.

Q. What are anesthesia concerns of DD ?

• Tachycardia


• Loss of atrial contraction


• Volume excess


• Myocardial ischemia
  
  
  
  • Directly affects relaxation
  
  
  • Induces rhythm disturbances
  
  
  
  


• Post-op sympathetic stimulation


• Post-op hypertensive crisis


• Rhythms other than sinus


• Shivering


• Anemia


• Hypoxia


• Electrolyte imbalances


• Anaesthesia Management DD- Cardiac Grid


• Hypertension


• AF – sinus rhythm important


• CAD – Ischaemia causes increased LVEDP.Myocardial oxygen supply is the key to energy using processes of active relaxation so decrease in myocardial oxygen demand can improve ventricular compliance.


• Volume overload – BAD , small increase in LVEDV lead to marked increase in LVEDP in DD.

Q. What are the indications for stress echocardiography ?

Assessment of CAD

Risk stratification after AMI

Viable myocardium assessment.

Q. What is positive stress echo ?

1) New RWMAs occur

2) LV systolic dilatation

3) Development of MR with stress indicating myocardial ischemia

But, worsening of wall motion abnormality like from akinesis to dyskinesis is not considered positive stress test.

Q. What risks are associated with dobutamine stress echocardiography (DSE) ?

Risks associated with DSE include:

• Chest pain


• Severely high blood pressure


• Irregular heartbeats


• Dizziness


• Nausea


• Extreme tiredness


• Heart attack (rare)

Q. What is the normal response to stress echocardiography ?

Increase in wall thickening and endocardial excursion

Decrease in LV end systolic volume.

Q. When can false negative stress echo happen ?

Suboptimal stress is given - < 85% of age predicted maximum heart rate for dobutamine or < 90% for treadmill exercise

Delay in imaging after exercise

Single vessel disease

RWMAs produced during stress echo can be masked by hypercontractile LV in MR and AR patients.

Q. When can false positive result occur in stress echo ?

Coronary artery spasm

LV hypertrophy

Diabetes

Myocarditis

Idiopathic dilated cardiomyopathy

Q. What is the resting myocardial metabolic rate  cardiac muscle  ?

High resting myocardial metabolic rate - Cardiac muscle  1 ml/min/g flow  Skeletal muscle  0.1 ml/min/g flow

Q. What will you see in transthoracic echocardiography ?

Regional wall motion abnormalities

LV hypertrophy

Ejection fraction

Ischemic MR

Pulmonary hypertension

Systolic dysfunction

Diastolic dysfunction

Thrombus in LV

Aortic atherosclerosis

Q. How to diagnose culprit vessel on ECG ?

LAD stenosis - Anterior MI – ST elevation in V1-V6

LCX stenosis – Lateral MI – ST elevation I, aVL, V5, V6

RCA stenosis- Inferior MI – ST elevation II,III,aVF

Q. What does Chest Xray show in IHD patients ?

LV Hypertrophy if long standing hypertension is present.

Q. What is the role of Intra aortic balloon pump (IABP) in OPCAB management ?

Main indication is low cardiac output syndrome.

IABP increases diastolic blood pressure and therefore an improvement in coronary perfusion and decrease in ventricular afterload occurs, thus increasing stroke volume and cardiac output.Hence, it is also useful in the situations of high oxygen demand during heart displacement in OPCAB.

Q. What are the indications of IABP regarding CABG ?

Severe LV dysfunction, Left main disease, Diffuse coronary artery disease, Redo Operation are few indications regarding CABG

Q. What advantage does IABP have over Inotropes ?

Inotropes increase cardiac output by increasing myocardial contractility but have effect on rhythm, preload, afterload,ventricular relaxation and myocardial oxygen demand. Whereas IABP decreases myocardial oxygen demand and increases its supply, improves ventricular afterload and improve the perfusion to the other vital organs.

Q. Which other drug can be used in low cardiac output syndrome (LCOS) ?

Levosimendan is a calcium sensitizer used to prevent postoperative low cardiac output syndrome. Levosimendan pretreatment (24 h infusion) in patient for OPCAB with poor LVEF shows better outcomes and hemodynamics in terms of inotropes, CPB and IABP requirements.

Q. How does Levosimendan act ?

 Levosimendan is a calcium sensitizer. It increases myocardial contractility by binding to the troponin C of myocytes without increasing intracellular calcium concentration.It has vasodilatory and anti-ischemic properties (pleitropic effects) because of its effects on ATP dependent potassium K ATP channels.It has favorable effects on coronary blood flow as it overrides coronary auto-regulatory vasodilation and dilates coronaries.

Q. What is Warm up phenomenon ?

Patients with coronary artery disease show improvement in cardiac performance after doing first exercise test, is called as warm up phenomenon.

Causes being –

Myocardial adaptation similar to ischemic preconditioning

Increased oxygen supply due to collateral recruitment, redistribution of myocardial performance.

Decrease in oxygen consumption due to down regulation or myocardial stunning.

Q. Which are the cardiac performance indicators ?

Pulmonary artery occlusion pressure, Right ventricular end diastolic volume index, Left ventricular end diastolic volume index, Stroke volume index and Cardiac index

Q. What are the trials associated with Angioplasty versus CABG ?

BARI TRIAL - Bypass Angioplasty Revascularisation Investigation

It enrolled 1829 patients who were randomized to undergo either PTCA or CABG

It found:-

1) No significant differences in survival at both 1 and 5 years

2) With a survival rates of 89.3% in the CABG group and 86.3% in PTCA group.

3) The rates of in-hospital myocardial infarction and stroke were greater in the CABG patients compared with the PTCA group- 4.6% and 2.1% for Q wave MI

-0.8% and 0.2% for stroke

4) For patients with diabetes – 5 year survival was 80.6% in CABG compared with 65.5% in PTCA group.

The difference in mortality was seen in insulin dependent and non-insulin dependent diabetes

5) The need for repeated revascularisation after initial intervention was greater in PTCA group-

At 5 years - only 8% of the patients in CABG group had undergone additional revascularisation procedures

-Compared to 54% of those assigned to PTCA

31% of PTCA patients eventually underwent CABG.

BARI 2D –

Patients with Type 2 diabetes have an increased risk of suffering a cardiovascular event over non-diabetic patients.

The 5-year death rate for the group receiving insulin sensitization therapy was 13.2% vs. 13.5% in the group receiving insulin provision therapy.

The rates of MI, stroke and the combined secondary endpoint of death, MI, and stroke were similar between the group receiving revascularization plus optimal medical therapy vs. the group receiving optimal medical therapy alone.

Neither revascularization nor optimal medical therapy demonstrated a significant reduction in death or major cardiovascular events at 5 years.

42.1% of patients in the optimal medical therapy alone treatment group eventually required revascularization within 5 years.

FREEDOM Trial - was a prospective, randomized, multicenter superiority trial comparing multivessel PCI to CABG in diabetic patients on optimal medical therapy.

CABG was superior to PCI with first generation drug-eluting stents.

CABG caused reduction in all-cause mortality and non-fatal MI but had increased rates of stroke.

Higher major adverse cardiac and cerebrovascular event (MACCE) in the PCI group (26.6% vs 18.7%) and a number needed to treat (NNT) of 12.6 favored CABG.

SYNTAX Trial - Synergy between PCI with Taxus and cardiac surgery (SYNTAX).

The goal was to assess the optimal revascularization strategy for patients with 3VD or LMD, by randomization to either CABG or PCI with TAXUS Drug Eluting Stent.

The trial was a multicenter, prospective randomized clinical trial with an “all-comers” design. Patients with angina or asymptomatic myocardial ischemia were eligible.

1800 patients (41% of those enrolled in the study) were deemed suitable for revascularization by either strategy and were randomized

The principal finding of SYNTAX was that patients treated with PCI by DES reached the primary end point of the study at 12 months after randomization: 17.8% suffering one of death (all causes), stroke, MI, or repeat revascularization compared with 12.4% of patients treated by CABG.

The conclusion was that CABG remains the standard of care for patients with 3VD or LMD. The composite of all-cause death, MI, and stroke was no different between the groups at 12 months (7.6% with PCI and 7.7% with CABG. Although stroke rate after CABG was higher as compared with PCI (2.2% versus 0.6%).

Q. What are the advantages of OPCAB over On pump CABG ?

OPCAB has advantages such as

• decreased blood loss and thereby less blood transfusion


• decreased myocardial enzyme release upto 24 hours


• less early neurocognitive dysfunction


• decreased incidence of renal insufficiency


• OPCAB surgery in patients with severe atheromatous aortic diseases is associated with reduced risk of stroke and death 


• Reduction in the complications and allows rapid recovery leading to early ICU and hospital discharge.Avoiding CPB accelerates immediate postoperative recovery and shortens ICU length of stay.

Q. What are the merits  of OPCAB ?

Merits of beating heart surgery are patient is not exposed to unphysiologic surface of CPB so no endothelial injury, RBC and platelet dysfunction. Systemic inflammatory response, neurological and renal dysfunctions due to CPB are avoided.

Morbidity is decreased which otherwise increases as the duration of  CPB and cross clamp increases. Aortic manipulations are less. OPCAB is associated with less bleeding and decreased incidence of atrial fibrillation,blood transfusions,need for inotropes.All leading to reduced length of stay in ICU and hospital.

Q. What is the rationale behind avoiding CPB ?

prevent deleterious effects of CPB such as systemic inflammatory response syndrome, global myocardial ischemia and the risks of aortic manipulation.

Q. What are the demerits  of OPCAB ?

Demerits  of OPCAB - are due to various positions of the heart during grafting and lifting of heart for adequate exposure of targets.It is a technically demanding skill with a greater learning curve. The quality of grafts sewn is less superior and number of grafts sewn with OPCAB are less than with standard CABG.The graft occlusion incidence is high.It also has lower rate of long term graft patency. Patients are more prone for hypoperfusion,hypotension,arrhythmias. Therefore OPCAB may result in less complete revascularization which may influence long term outcome.

Q. Discuss Trials in OPCAB

ROOBY Trial – The Randomized On/Off Bypass trial showed  no difference in 30-day mortality or short-term major adverse cardiac event (MACE).OPCAB patients received significantly fewer grafts per patient. After 1 year, cardiac-related death (8.8% versus 5.9%) and MACE (9.9% versus 7.4%) were significantly higher in the OPCAB group. The graft patency was significantly lower in the OPCAB group (82.6% versus 87.8%).

SMART Trial - The Surgical Management of Arterial Revascularization.Therapy is a prospective, randomized, single center, single-surgeon trial. Long-term survival and graft patency in 297 patients after isolated elective CABG was determined.After 7.5 years of follow-up, no difference in mortality or late graft patency between OPCAB and on-pump CABG was noticed.

CORONARY Trial - The Coronary Artery Bypass Surgery Off or On Pump Revascularization Study  stated that the rate of crossover from the off-pump to the on-pump group was lower (7.9% versus 12.4%). No significant difference in the incidence of recurrent angina (1.0% off-pump versus 0.9% on-pump).The need for repeat revascularization was higher in the off pump group(1.4% offpump versus 0.8% on-pump).

Q. Which Preoperative medications patient is on ?

Statins, Beta blockers, Angiotensin-converting enzyme inhibitors, Calcium channel blockers, Aspirin, Glycoprotein IIb/IIIa.

Q. What are the advantages of Statins ?

Statins have multiple “pleiotropic” actions.They are potent anti-inflammatory, vasculoprotective, antioxidative agents which increase nitric oxide release, attenuate myocardial “reperfusion” injury, have anti-thrombotic and lipid-stabilizing action.They also have beneficial effects on endothelial function. Statins decrease the circulating levels of adhesion molecules (ICAM) which are implicated in endothelial dysfunction after CPB, help in ventricular remodelling after acute myocardial infarction. They also decrease mortality after surgery, decrease the need for postoperative renal replacement therapy and decrease atrial fibrillation in cardiac surgery.

Q. How are Beta blockers beneficial ?

They decrease myocardial oxygen demand and the rate of atrial and ventricular arrhythmias.

Q. What are the indications and contraindications of preoperative cardiac drugs ?

Aspirin

Indications: All patients undergoing CABG

Contraindications:  Allergy or intolerance, Bleeding (active or recent), Thrombocytopenia.

Beta blockers

Indications:  All patients undergoing CABG

Contraindications: Allergy or intolerance, severe bradycardia or hypotension, Bronchospastic disease (asthma or COPD with bronchospasm), Heart failure (decompensated, NYHA IV), Cardiogenic shock, Conduction abnormality, Peripheral vascular disease, Pulmonary edema.

ACEI /ARBs

Indications: History of MI, reduced EF.

Contraindications:  Allergy or intolerance, Hyperkalemia, Hypotension, Acute renal failure, Aortic stenosis, Pregnancy.

Statins

Indications: All patients undergoing CABG

Contraindications: Allergy or intolerance, Liver disease,History of statin induced muscle soreness/myopathy/rhabdomyolysis.

Q. What Investigations are carried out before undergoing CABG surgery ?

Blood investigations – Routine and Specific Investigations.

Routine Investigations -

Hemoglobin -  is important as anaemia causes tachycardia.Tachycardia has deleterious effects as it increases myocardial oxygen demand, decreases diastolic filling time and hence decreases coronary filling which occurs during diastole.This leads to decrease in myocardial oxygen supply causing myocardial oxygen supply-demand mismatch which may further induce ischaemia.

Total leucocyte count,platelet count,electrolytes,coagulation profile, liver function tests, kidney function tests,thyroid function tests,serology are advised.

Specific investigations – Angiography,Echocardiography,Carotid doppler. Screening of peripheral vascular diseases, ultrasonography abdomen are optional.

Q. What monitoring is recommended during OPCAB ?

Monitoring – is done with 5 lead ECG with automated ST analysis,invasive blood pressure monitoring ( Radial or Femoral artery),pulse oximetry,Endtidal CO2,CVP monitoring,pulmonary artery pressure monitoring,transoesophageal echocardiography,continuous cardiac output monitoring,temperature monitoring,urine output monitoring,neuromuscular monitoring,coagulation profile.Transcranial Doppler,SvO2 monitoring are added monitoring modalities.

ECG – 5 lead ECG monitoring is done but the limitation is when the heart is lifted it has no contact with the surface hence amplitude of ECG is reduced to judge the signs of myocardial ischemia

12 lead ECG, with simultaneous monitoring of lead II and the lateral precordial (V4 and V5) leads increases the efficacy of ischaemia detection.

PA Catheter – Indications -  are ejection fraction < 40 %,significant LV regional wall motion abnormalities,LVEDP > 18 mm Hg at rest,recent myocardial infarction and unstable angina,emergency surgery,combined procedures and redo surgeries.

It effectively detects decrease in cardiac output,mixed venous oxygenation or increase in PAOP which is associated with myocardial ischemia.

It can also measure mixed venous oxygen saturation (SvO2) to detect global tissue oxygenation.SvO2, partial pressure of carbon dioxide (PaCO2) and central venous pressure (CVP) act as surrogates of changes in jugular bulb oxygen saturation (SjO2) which inturn predicts postoperative cognitive dysfunction(POCD).

Transoesophageal echocardiography(TEE) - provides information on new regional wall motion abnormalities (RWMAs),LV and RV function,mitral and tricuspid regurgitation,pulmonary hypertension and atheromatous aortic disease. New RWMAs can occur because of ongoing myocardial ischemia,poor myocardial preservation,changes in loading conditions,conduction abnormalities and myocardial stunning.

Q. How are RWMAs classified ?

RWMA are classified as -

Normokinesia – Endocardium moves toward the center of LV during systole > 30 %

Mild Hypokinesia – < 30 % but > 10 %

Severe Hypokinesia - < 10 %

Akinesia – Endocardium does not move or thicken

Dyskinesia – Endocardium moves away from the center of LV.

Grading of myocardial contractility –

Wall thickening -Normal 30 – 50 %

Mild Hypokinetic 30 – 50 %

Severe Hypokinetic < 30 %

Akinetic < 10 %

Dyskinetic None / Thickening

Q. What are the advantages of Epidural Anesthesia and analgesia during OPCAB ?

Advantages of epidural anesthesia –

It reduces total anaesthetic drug requirement, exhibits antianginal effect, reduces myocardial work.

It maintains hemodynamic stability,also increases the luminal diameter of dynamic coronary stenosis.

It decreases tachycardia and hypertension.Cardiac index is maintained. Adequate blood and tissue oxygenation parameters are maintained.

It provides excellent intraoperative analgesia.

Other advantages are - Early extubation, less respiratory complications, less atrial arrhythmias, preservation of fibrinolytic system, decrease in stress response,postoperative pain relief.

Thoracic epidural anesthesia causes coronary vasodilatation, increases blood flow in collaterals, decreases myocardial oxygen demand and also the rate of chest infection.

Q. What are the anesthetic considerations in OPCAB ?

Goals of anesthesia – are to maintain hemodynamic stability and coronary perfusion without increasing myocardial oxygen demand.

According to cardiac grid –

Heart rate is maintained, tachycardia is particularly avoided as it increases myocardial oxygen demand and decreases diastolic filling time during which coronary filling occurs.

Rhythm - sinus rhythm is important, no arrythmias.

Contractility – maintained as various heart positions tend to produce hypotension.

Preload – is maintained. Any increase in preload is detrimental as it increases left ventricular end diastolic pressure (LVEDP).

Afterload –is kept on a lower side as vertically positioned heart has to pump against gravity.

Induction agents – Etomidate is the drug of choice. Opoid induction can also be done along with Inj Propofol and Inj Midazolam.Inj Vecuronium  and Sevoflurane or Isoflurane are preferred for anaesthesia maintenance.

Intraoperative management-Inj Heparin 200 units/kg is given to achieve ACT of  250-300 seconds.After procedure, heparin is reversed with Inj protamine sulphate 1-1.5 mg  for every 100 IU of  heparin.ACT is kept in the range of 130-140 seconds.

Hypothermia should be avoided by keeping OT temperature around 24 degrees, warm blankets,warm IV fluids.Hypothermia increases morbidity and can cause shivering leading to increased metabolic rate and potential to myocardial ischaemia.

Q. Which coronary grafting has maximum hemodynamic instability ?

Grafting of Obtuse Marginalis

Q. Which coronary grafting has least hemodynamic instability ?

Left anterior descending coronary artery

Q. Discuss Management during Grafting.

Management during Grafting –

Octopus Tissue Stabilizer restricts the motion of the small area of the heart where the bypass graft is to be attached while the rest of the heart continues to beat normally.

Starfish is the positioner attached at the cardiac apex which locks the longitudinal axis of the heart, thereby allowing access to coronary vessels of the lateral and posterior walls.

Intracoronary shunts secure the blood flow through the coronary vessels during the procedure.

Left Anterior Descending (LAD) grafting – The position given to the heart during LAD and Diagonal grafting is called ‘displacement’.Displacement of the heart forward and superior to facilitate LAD anastomosis by placing pericardial stay sutures and mops underneath the heart.

Left Circumflex Artery (LCX) grafting  is the most critical anastomosis.

Exposure is difficult needs lifting the heart and placing it in an unphysiologic position called as “verticalization” for which heart is displaced to right side. Placing octopus stabilizer system leads to compression of right ventricle and distortion of tricuspid and mitral annuli.

Steps to combat hypotension and hypoperfusion are opening of right pleura to accommodate RV, application of starfish apical suction device,trendelenburg position, use of vasopressors and inotropes, judicious volume expansion as excess volume administration causes increase in left ventricular end diastolic volume (LVEDV) and hence LVEDP. This leads to decrease in coronary perfusion pressure.

Coronary perfusion pressure (CPP) = Diastolic blood pressure (DBP) – LVEDP

Right Coronary artery (RCA) grafting – Severe ischaemia during clamping of  RCA can result in complete atrioventricular block attributable to interruption of the blood flow in the AV node artery.

RVEF is decreased signi?cantly during the OM anastomosis as compared to during the LAD and RCA anastomosis. When the stabilizer is placed for the OM anastomosis, the LV was compressed but the RV is compressed more, thus causing a disturbance in diastolic expansion, and so the decrease in RVEF is not attributed to impaired contractility or ischemia, but is secondary to direct compression with reduced stroke volume.

Q. What measures are taken to minimise the hemodynamic instability during grafting ?

Positioning during OPCAB leads to hemodynamic compromise. Heart is lifted, tilted to expose the posterior and lateral walls which displaces atria below the corresponding ventricles and this leads to increase in atrial pressures.Also, vertical positioning causes distortion of mitral and tricuspid annuli leading to incompetent valves and regurgitation. The application of stabilizer device restricts the regional myocardial wall motion. All these changes contribute to  decrease in preload and stroke volume resulting in a reduced mean arterial pressure and cardiac index, especially during exposure of the posterior wall.

Q. What are the indications for Nitroglycerin (NTG) ?

• Hypertension >20 %


• PCWP > 18-20 mmHg


• ST elevation > 1mm


• A,C and V waves > 20 mmHg in JVP


• New RWMAs


• Acute LV or RV failure


• Coronary artery spasm

After CPB NTG is given for intraoperative myocardial ischemia,incomplete revascularisation,increase in systemic vascular resistance and pulmonary vascular resistance and for volume infusion.

Q. Which inotropes are preferred during OPCAB grafting ?

Inotropes – Inj Dopamine 5-10 mcg/kg/min,Inj Adrenaline 0.05-0.1mcg/kg/min or Inj Noradrenaline 0.03–0.05 mcg/kg/min

Other considerations – Electrolytes – Potassium and magnesium should be supplemented Inj Xylocard – for ventricular ectopics due to myocardial ischemia IABP – for intractable hypotension.

Postoperative goals -are early emergence and ambulation Excellent postoperative analgesia.

Q. What is Ultrafast tracking of anesthesia ?

Ultrafast tracking of anaesthesia (UFTA) includes shortening of prolonged ventilatory support or even immediate extubation,reducing ICU stay and early discharge from hospital. The essence of UFTA is titration of short acting anaesthetic drugs, maintenance of body temperature,early extubation with effective analgesia.

Q. What are the advantages of ultrafast tracking ?

The term ultrafast tracking includes shortening of prolonged ventilatory support or even immediate extubation,reducing ICU stay and early discharge. Also,shortening of the postoperative monitoring phase in the intensive care unit.

Benefits of early extubation after cardiac surgery are reduced lung trauma with decrease in the stress and discomfort of endotracheal tube suctioning and weaning from ventilation.Sedative drugs and ventilator disposables requirement is lessened.Patients are transferred early to lower dependency units. Nursing staff required to manage each patient is less.By this,cost saving is achieved.

Q. What are the concerns of UFTA ?

Concerns of UFTA are early extubation may increase respiratory and cardiac workload causing myocardial ischaemia,reintubation,hypothermia,shivering, inadequate analgesia,mortality.

Q. What is Emergency conversion to on pump CABG and Elective conversion to on pump CABG ?

Emergency conversion to on pump CABG is urgent institution of CPB to manage clinical instability after the commencement of coronary anastomoses.

It may lead to significant increase in morbidity, stroke, renal failure,pulmonary and gastrointestinal complications resulting in prolonged hospital stays and increased medical costs.

Elective conversion  is a semi-planned measure to prevent clinical instability before coronary anastomoses.

When conversion is  elective, the results are same as elective OPCAB procedures.

Higher rate of conversion is seen in patients with -

MI <24 hours

critical left main disease

redo CABG

significant mitral regurgitation

low ejection fraction and

emergent surgery.

Emergency cross-over from OPCAB to on-pump CABG increases the risk of early mortality and morbidity.

Q. What is Ischemic Reperfusion (I/R) injury ?

Cellular damage after reperfusion of previously viable ischemic tissues is defined as ischemia–reperfusion injury.

Q. When can I/R injury occur ?

It can occur with thrombolytic therapy, organ transplantation, coronary angioplasty, aortic cross-clamping or cardiopulmonary bypass.

When aortic cross-clamp is released, heart is suddenly and globally reperfused with blood that is fully anticoagulated, immunologically primed by exposure to the CPB circuit, and characterized by a very high partial pressure of oxygen.As a result, the post-cardiac surgery myocardium is exposed to extremes of ischemia and reperfusion and it results in myocyte damage through myocardial stunning, microvascular and endothelial injuries and irreversible cell damage and necrosis called as lethal reperfusion injury.

Q. Discuss Pathophysiologic Mechanism of I/R injury.

Ischemia leads to accumulation of intracellular sodium, hydrogen and calcium ions causing tissue acidosis.And, reperfusion causes rapid alterations in these ion flux.

Loss of electrical potential across the mitochondrial membrane is “permeability transition” mediated through the mPTP (mitochondrial permeability transition pore). Triggers for mPTP include Ca²⁺ overload , rapid normalization of pH and oxidative stress.

Free radical formation/reactive oxygen species (ROS)

Dysregulated nitric oxide (NO) metabolism

Apoptosis

Endothelial dysfunction

Platelet aggregation and microembolization

Immune activation

Q. What are the clinical manifestations of Ischemia - Reperfusion Injury ?

Clinical Manifestations of I/R Injury are -

 1)Vascular Injury and the “No Reflow” Phenomenon

 2)Myocardial Stunning

 3)Reperfusion arrythmias

 4)Lung I/R injury

 5)Multiorgan dysfunction syndrome

 6)Central Nervous System I/R injury–

 

Q. What are the strategies to attenuate I/R injury ?

 

• Controlled, graded reperfusion


• Use of metabolic additives in cardioplegia like pyruvate and glutamate/aspartate provide the arrested myocardium with energy substrates


• Ischemic preconditioning


• Leukocyte filters,steroids


• Pyridoxal-5′-phosphate (MC-1), pyridoxine metabolite and purinergic receptor antagonist prevents intracellular calcium overload and decreases I/R injury.


• Cariporide prevents intracellular Ca²⁺ overload by antagonising the sodium-hydrogen exchanger.


• Acadesine, a purine analog increases tissue adenosine levels.It is undergoing Reduction in cardiovascular Events by acaDesine in subjects undergoing CABG (RED-CABG) trial.


• Aspirin Triggered Lipoxin Analogues


• Antioxidant Therapy : Superoxide Dismutase SOD, Iron chelators, Mannitol, N-acetylcysteine, Vitamin E, Thiols,Allopurinol, Catalase.


• Calcium antagonists


• ACE inhibitors


• Metabolic stimulation with Insulin.


• Anti complement Therapy : Recombinant,Humanized,Single-Chain Anti-C5 Antibody and Soluble Complement Receptor


• Anti cytokine or Leukocyte Adhesion Molecule


• Endothelin receptor antagonists


• Platelet Activation Factor (PAF) Antagonists

 

Q. What are the recommendations for a patient for CABG & Non cardiac surgery ?

Recommendations for doing CABG earlier than non cardiac surgery include patients with:

• Acceptable coronary revascularization risk and suitable viable myocardium with left main stenosis


• 3 -vessel CAD with LV dysfunction


• 2 -vessel disease involving severe proximal left anterior descending (LAD)artery obstruction


• Intractable coronary ischaemia despite maximal medical therapy.

If major non-cardiac surgery is indicated following recent CABG, timing appears crucial.Postpone elective major surgery for at least 4–6 weeks possibly for even up to 6 months after CABG

 

 

References –

Navin C Nanda - Manual of Echocardiography

Editorial Warm up phenomenon and preconditioning in clinical practice F Tomai Heart 2002;87:99–100

Kay Maeda ,Marc Ruel.Prevention of ischemia-reperfusion injury in cardiac surgery: Therapeutic strategies targeting signaling pathways.,March 2015 Volume 149, Issue 3, Pages 910–911 J Thorac Cardiovasc Surg.

Aslan T.Turner Pathogenesis of Myocardial Ischemia-Reperfusion Injury and Rationale for Therapy Am J Cardiol. 2010 Aug 1; 106(3): 360-68

Charles D. Collard, Simon Gelman Clinical concepts and Commentary. 67ytygfAnesthesiology 2001; 94:1133–8  Pathophysiology, Clinical Manifestations, and Prevention of Ischemia–Reperfusion Injury

Subodh Verma, Paul W.M. Fedak, Richard D. Weisel, Jagdish Butany, Vivek Rao, Andrew Maitland et al Fundamentals of reperfusion injury for the clinical cardiologist. ‎Circulation. 2002 May 21;105(20):2332-6.

KE Okonta et al Intra-aortic balloon pump in coronary artery bypass graft - factors affecting outcome. J West Afr Coll Surg. 2011 Oct-Dec; 1(4): 28–40.

Tariq AR et al The FREEDOM Trial: Revascularization in Diabetics with Multivessel Disease: A Population-Based Evaluation of Outcomes May 13 2016 Expert Analysis American College of Cardiology.