Antegrade, retrograde or combined cardioplegia delivery
For optimal myocardial protection, homogeneous distribution of the cardioplegic solution is integral. This is influenced by the mode of delivery of the cardioplegia and the most common approach is through  antegrade delivery of cardioplegia\sout via the aortic root(28). This leads to rapid diastolic cardiac arrest and administration of cardioplegia seems to be straight forward, easy and rapid(29).
However, antegrade cardioplegia may cause inhomogeneous distribution if occlusion or significant stenosis of coronary arteries is present.  This may lead to myocardial injury and delayed functional recovery as the myocardial areas distal to the lesion are poorly protected. Additionally, the antegrade perfusion can not only be delivered through the aortic root but also directly through the coronary ostia during aortic valve surgery, however it may cause coronary ostial injury during placement of the perfusion cannulae into each coronary ostia(30).
Retrograde cardioplegia delivery is via the coronary sinus. It can be used alternative to antegrade cardioplegia in the presence of occluded coronary arteries for better recovery of function in areas distal to the occlusion(31). There is also elimination of operative interruptions, reduced risk of aortic root air, and air and debris flushing from the coronary arteries, especially during aortic valve surgery(29).   Retrograde cardioplegia is particularly beneficial for valve operations and redo-CABG. During aortic valve surgery, the coronary ostia are not cannulated, thus the operative field is clear and there is no ostial damage, intraoperative dissection or late ostial stenosis(30).
Some limitations of retrograde cardioplegia include coronary sinus injury and delay of cardiac arrest(32). There is also requirement of large volumes of cardioplegic solutions(29) and myocardial oedema may occur(33). Additionally, retrograde cardioplegia leakage through the coronary arteriotomy site may obscure the surgical field and prolong the operation, therefore coronary suction may be a necessity(34).  Due to absence of any direct connection between the coronary sinus and anterior cardiac veins there is inadequate protection of the right ventricle, which is worsened in patient with right ventricular dysfunction or poor venous collaterals(34).
As retrograde cardioplegia is associated with under perfusion of the right ventricle and antegrade cardioplegia homogenous delivery is affected by coronary lesions, combined antegrade-retrograde blood cardioplegia was brought about. It combines the advantages of both techniques(30). Bhayana et al. found that compared to antegrade alone, combined cardioplegia lead to earlier recovery of left ventricular function and a shorter post-ischaemic stunned period so less damage to the myocardium(30).
Using combined cardioplegia may have a greater benefit in higher risk patients(30). It may also provide better distribution in patients with hypertrophied cardiac tissue(34). Radmehr et al. also found that there was reduced need for ionotropic support in combined cardioplegia compared to antegrade(34). However, in situations such as right coronary artery occlusion, both antegrade and retrograde delivery would be compromised so the combined method would not be drastically more beneficial.
As each approach has its own benefits and drawbacks, treatment must be individually tailored to each patient. The properties of different cardioplegic delivery methods are summarised in Table 4.