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Why is LIMA graft superior to saphenous venous graft in CABG ?

Posted in cardiac surgery, Infrequently asked questions in cardiology (iFAQs), tagged , , , , , , , , , , , , , , , , , , , , , , , on November 6, 2008| Leave a Comment »

          During CABG arterial grafts are always preferred over venous grafts , for the simple reason the grafted vessel has to carry arterial blood and not the venous blood. Saphenous veins are tuned to carry venous blood at low pressure.The mean coronary arterial pressure is around 40mmhg and this will damage the saphenous venous endothelium more quickly. The reocculsion rate at 10 years for venous grafts  can reach  60%.


                                                    Left internal mammary artery (LIMA) is the most commonly used arterial graft. This is usually anastamosed with LAD. The lumen of LAD &  LIMA are more or less equal and they match well in character also !

The other advantage  of  LIMA graft  is ,   blood    tends to  flow  both during systole and diastole in a smooth fashion.. Since the venous graft which  hangs from the root of aorta , the  ostium  of venous graft lacks the  hemodynamic benefits of   coronary sinus . (We know the coroanry sinus acts like a  reservoir for  the smooth release of  blood flow into coronary arteries.)

Finally ,  the most important feature of LIMA is

  It is a live graft

LIMA’s proximal origin from subclavian is left intact, so LIMA acts as a live vessel with it’s  vasa vasorum intact ,  which means the endothlium derived relaxing factor (EDRF-Nitric oxide) secretion is not interrupted.This makes the LIMA  an excellent graft , self protected against reocclusion.One may call it a drug eluting graft !

 What is the patency rate for LIMA ?

LIMA patency rates at 10 years is nearly 90 %  .But the graft patency depends on many factors , like diabetes, age, gender, surgical technique ,(Now , beating heart CABG is very popular , where the LIMA patency is said to be slightly lower than conventional CABG) Sequential LIMA grafts, free LIMA graft ( Which  loses the advantage of being  a live graft) have relatively lower patency rates.

What are the other arteries used in CABG ?

Other arteries that could be used are radial artery, right internal mammary artery, and gastro epiploic artery.The patency rates of all these arteries far less than LIMA .

cabg-2

A surgeon testing LIMA flow before Anastomosing it to LAD.

Image courtesy Dr.Mannoj Aggny .You tube

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What are the most common indications for coronary arery by pass surgery?

Posted in cardiac surgery, cardiology -Therapeutics, tagged , , , , , , , , , , , , , , , , , , , , on November 5, 2008| Leave a Comment »

                                Coronary artery  by pass graft surgery has become the most common cardiac surgery done world over ever since it was first introduced by Favalaro in 1969.The common indications  are, triple vessel disease and left main disease in any of the following situationsE.

Elective CABG(Non emergent)

1.Chronic stable angina

Either emergent or elective

1.Unstable angina

Emergency CABG*

1.Acute myocardial infarction.-Cardiogenic shock

2.Failed thrombolysis

3.Failed primary PCI

4.Complications during routine PCI(Cath lab crashes !  etc)

5.As an associate procedure after a  mechanical complication during MI (Septal rupture, Acute MR etc)

*In emergency situations even a single vessel disease would require a  CABG

Hybrid CABG

Combining CABG and PCI in the same patient is followed in very few centres .(Example LAD graft and RCA angioplasty)This is done in patients who have co morbid conditions who can not tolerate prolonged surgical times.Further there can be situations  one lesion is very ideal for PCI  while for other grafting is the only solution.

Controversial CABG

1.CABG as a primary revascularisation  in STEMI*

(Rarely done now , almost obsolete , primary PCI has almost replaced it  . . . but it is still  useful if performed within 6 hours of MI )

2.Incidentally detected CAD*  following routine coronary angiogram.

( *CABG for incidentally detected asymptomatic CAD is  increasing in many parts of world )

Inappropriate CABG

         If it’s triple vessel disese it must be CABG -CASS study (1980s)

                       Coronary artery surgery study (CASS) still has considerable influence among the  cardiology  community in the decision making process  for CABG , even though it is many decades old .There has been a phenomenal development in both medical as well as interventional techniques since  CASS . (Thrombolysis, Statins, ACEI, PCI  DES to name a few) .

                     When CASS study was done many decades ago,it was believed triple vessel disese constitute a  homogeneous population and  carry  the same clinical significance . For example a 90% proximal LAD , 50% RCA and 50% OM technically qualify for a CABG and unfortunately , some of them are  subjected to it even in  2008 !  Now we clearly know, it is not the number of diseased vessels  that is important, but it’s location, severity , LV function, presence or absence of diabetes . Finally , the presence of revascularisation eligible myocardium must be documented in all post MI patients . (Technically referred to viable & ischemic myocardium ).              

              Currently , with the  PCI  & medical management has grown so much, CABG should be reserved only for, critical triple vessel disese , with at least one proximally located lesion (Mostly  LAD  or Left main ), especially in diabetic individuals.

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