Coronary revascularization

# Overview
Coronary revascularization is one of the most commonly used surgical procedures worldwide. Currently, coronary revascularization has three techniques including, percutaneous coronary intervention (PCI), coronary artery bypass surgery (CABG), and hybrid coronary revascularization. CABG is one of the most common techniques with an overall of more than 20 million operations performed. Treatment decisions regarding coronary revascularization should be done regardless of sex, race, and ethnicity. Decision regarding coronary revascularization must be affected by coronary anatomy of patient, and the percentage of stenosis. Based on ACC 2021 guideline, coronary angiography is still the default method to determine coronary anatomy and stenosis degree. Furthermore, significant stenosis could be described as a estimated diameter stenosis more than 70% for non-left main disease, or more than 50% for left main disease. It is recommended to consider more investigations for stenosis more than 40% but less than 69%. Although the lesion's length can affect the ischemia severity, there are no standard cutoffs for the length of the lesions when severe stenosis is determined. Furthermore, the presence of other comorbidities can affect decision-making. Although many indications are the same for performing either PCI or CABG, these two procedures have inherently different mechanisms. While PCI mitigates an obstruction, it can not prevent plaque progression or rupture in other involved segments of the artery, on the other hand, CABG is able to prevent future ischemic insults caused by plaque progression or rupture in other involved segments of the artery. Most studies report the same outcome with PCI and CABG, but there is a number of reports that favor CABG over PCI. 2021 ACA revascularization guideline published many recommendation for coronary revascularization among specific patients, such as those with diabetes, or chronic kidney disease, and elderlies, pregnants.

# Historical Perspective
- In 1948, Radner issued one of the first descriptions of transradial central arterial catheterization. Despite these early findings, limitations of present-day equipment were the reason behind the use of larger vessels such as the brachial, carotid, and femoral systems and not the radial artery.
- One of the coronary revascularization methods, CABG, was first introduced in the 1960s and rapidly became one of the most common surgical procedures around the world.
- In the late 1970s, PCI was introduced by mostly using 9-F guiding catheters.
- In the mid-80s Loop and Lytle introduced the internal thoracic artery (LIMA) as the best performing bypass graft conduit. They also announced the superiority of  LAD with LIMA as opposed to saphenous vein graft (SVG).

# Classification
Coronary revascularization may refer to;
- Percutaneous coronary intervention
- Coronary artery bypass surgery
- Hybrid coronary revascularization

# Indications
- Treatment decisions regarding coronary revascularization should be done regardless of sex, race, and ethnicity.
- Decision regarding coronary revascularization should be patient-centered, meaning that physicians should consider patient's wishes, health literacy, and cultural believes.
- Based on ACC/AHA/SCAI 2021 guideline, for patients with unclear optimal treatment strategy a Heart Team including an interventional cardiologist, cardiac surgeon, and clinical cardiologist is recommended to assess the patient's outcome. The following table demonstrates factors that can be considered by the Heart Team:

## Coronary Anatomy
- Based on ACC 2021 guideline, coronary angiography is still the default method to determine coronary anatomy and stenosis degree.
- Significant stenosis is one of the indications for the revascularization procedure, which has been defined as the following observations in coronary angiography:
An estimated diameter stenosis more than 70% for non-left main disease.
An estimated diameter stenosis more than 50% for left main disease.
For stenosis more than 40% but less than 69% more investigations are required.
- An estimated diameter stenosis more than 70% for non-left main disease.
- An estimated diameter stenosis more than 50% for left main disease.
- For stenosis more than 40% but less than 69% more investigations are required.
- The fact that whether visually estimated diameter stenosis or quantitative coronary angiography can better predict the functional significance of a coronary stenosis is controversial. 
- Although the lesion's length can affect the ischemia severity, there are no standard cutoffs for the length of the lesions when severe stenosis is determined.

# Coronary Revascularization Comparison to Medical Therapy
- Based on MASS II (Medicine, Angioplasty, or Surgery Study), CABG or PCI cohorts had lower 10-year mortality rate compared to those who received medical therapy. This was further supported by a meta-analysis of 25 studies with overall 19,806 participants.
- In contarst, there are some other studies that did not report any differences between the mortality rate of patients who was treated with medications to those who received a revascularization procedure.
- While coronary revascularization could be related to the increased incidence of procedural type 4a or type 5 MIs, it was able to decrease the incidence of late MI (spontaneous MI , demand-induced MI , or MIs associated with stent thrombosis  or with restenosis ) when compared to medical therapy alone.
- In contrast, a meta-analysis done on patients with stable ischemic heart disease did not report reduction in incidence of MI after coronary revascularization, while another study demonstrated reduction in the rate of MI with CABG, but not with PCI. 
- Although medical therapy is effective in reduction of patients' symptoms, numerous studies demonstrated that coronary revascularization is more effective in improving angina and quality of life compared to medical therapy alone.

# What Procedure to Choose?
- Although many indications are the same for performing either PCI or CABG, these two procedures have inherently different mechanisms.
While PCI mitigates an obstruction, it can not prevent plaque progression or rupture in other involved segments of the artery.
On the contrary, CABG is able to prevent future ischemic insults caused by plaque progression or rupture in other involved segments of the artery.
- While PCI mitigates an obstruction, it can not prevent plaque progression or rupture in other involved segments of the artery.
- On the contrary, CABG is able to prevent future ischemic insults caused by plaque progression or rupture in other involved segments of the artery.
- Most studies report the same outcome with PCI and CABG, but there are some reports that favor CABG over PCI:
The SYNTAX trial with 705 patients demonstrated a significantly higher rate of major adverse cardiovascular events and mortality rate among those who received PCI than the CABG cohort.
Two Studies reported that CABG is more effective in prevention of late spontaneous MI when compared to PCI.
- The SYNTAX trial with 705 patients demonstrated a significantly higher rate of major adverse cardiovascular events and mortality rate among those who received PCI than the CABG cohort.
- Two Studies reported that CABG is more effective in prevention of late spontaneous MI when compared to PCI.
- ACA 2021 revascularization guideline recommends to consider the following factors to decide whether to chose PCI or CABG:
SYNTAX Score
SYNTAX score derived from a clinical trial with the same name which predicts the grade of the anatomic complexity and can be used as a decision-making tool.
This score is a guide for selection of a revascularization procedure in patients with multivessel coronary artery disease.
All cause mortality rate among patients with a coronary artery disease-associated SYNTAX score equal or greater than 33 were significantly lower when undergone CABG than PCI
For patients with SYNTAX score lower than 33, no differences have been report in mortality rate of CABG and PCI
Compliance to medications
Preferences of patient
Individual factors, such as anatomic complexity, which is discussed in the following table:
- SYNTAX Score
SYNTAX score derived from a clinical trial with the same name which predicts the grade of the anatomic complexity and can be used as a decision-making tool.
This score is a guide for selection of a revascularization procedure in patients with multivessel coronary artery disease.
All cause mortality rate among patients with a coronary artery disease-associated SYNTAX score equal or greater than 33 were significantly lower when undergone CABG than PCI
For patients with SYNTAX score lower than 33, no differences have been report in mortality rate of CABG and PCI
- SYNTAX score derived from a clinical trial with the same name which predicts the grade of the anatomic complexity and can be used as a decision-making tool.
- This score is a guide for selection of a revascularization procedure in patients with multivessel coronary artery disease.
- All cause mortality rate among patients with a coronary artery disease-associated SYNTAX score equal or greater than 33 were significantly lower when undergone CABG than PCI
- For patients with SYNTAX score lower than 33, no differences have been report in mortality rate of CABG and PCI
- Compliance to medications
- Preferences of patient
- Individual factors, such as anatomic complexity, which is discussed in the following table:
- PCI would help patients with STEMI and ischemic symptoms for less than 12 hours.
- Rescue PCI is recommended for STEMI patients who failed re-perfusion after fibrinolytic therapy to improve the survival.
- PCI has been related to improved survival rate when done in STEMI patients who are stable and presented 12 to 24 hours after symptom onset.
- Regardless of time from MI, PCI can increase survival in STEMI patients who developed complications such as ongoing ischemia, acute sever heart failure, or life-threatening cardiac arrhythmia.
- Performing the PCI is not beneficial in stable and asymptomatic STEMI patients who have a totally occluded infarct artery >24 hours after symptom onset with no evidence for sever ischemia.
- The role of PCI in asymptomatic STEMI patients who are presenting after 12 to 24 hours after symptom onset is not well studied.
However, based on a small trial named BRAVE-2 a reduction in left ventricular infarct size has been reported among asymptomatic STEMI patients who were treated with an invasive strategy of coronary stent within 12 to 48 hours after symptom onset, compared to conservative therapies.
- However, based on a small trial named BRAVE-2 a reduction in left ventricular infarct size has been reported among asymptomatic STEMI patients who were treated with an invasive strategy of coronary stent within 12 to 48 hours after symptom onset, compared to conservative therapies.
- Both PCI and CABG are indicated in patients with STEMI, cardiogenic shock, and hemodynamic instability.
- CABG is recommended for patients with STEMI who have mechanical complications such as ventricular septal rupture, mitral regurgitation because of papillary muscle infarction or rupture, or free wall rupture.
- Emergent or urgent CABG is recommended in STEMI patients whose PCI is not feasible with a large area of myocardial involvement. On the other hand, emergent or urgent CABG should be avoided in these patients in the absence of ischemia or large myocardial involvement. Furthermore, CABG is usually avoided if patients' distal targets are poor.
- The following algorithm demonstrates the proper revascularization in STEMI patients.
- The sole condition that fibrinolytic therapies are superior to PCI is when the duration from hospital presentation to PCI is anticipated to be more than 120 minutes.
An early revascularization strategy could increase the survival rate in patients with STEMI complicated by cardiogenic shock.
- The sole condition that fibrinolytic therapies are superior to PCI is when the duration from hospital presentation to PCI is anticipated to be more than 120 minutes.
- An early revascularization strategy could increase the survival rate in patients with STEMI complicated by cardiogenic shock.

## Fractional flow reserve and instantaneous wave-Free Ratio
- Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are commonly used to assess the lesion significant. Fractional flow reserve (FFR) compares the maximal blood flow distal to the lesion to the normal maximal blood flow. On the other hand iFR compares the instantaneous wave-free ratio of the coronary pressure distal to the lesion during the diastole with the aortic pressure.
- Reported in numbers of trials which used FFR, FFR-guided PCI was successful in lowering the revascularization rate, procedure-related chest pain in patients with stable coronary artery disease and functionally significant stenosis.
- In one of these trials patients with abnormal FFR significantly benefited from PCI over medical therapy with lower rate of ischemia-driven revascularization and shorter procedural time. 
- FFR-guided revascularization with CABG was more off-pump with fewer anastomosis and simpler procedure compared to CABG with angiogram-guided revascularization in one of the clinical trials. Although other studies reported similar outcomes in both.
- iFR measure does not require the administration of adenosine has been also studied in clinical trials. Results supported that this measure is not inferior to FFR and also showed less adverse outcome related to the procedure.
- Lower rate of long-term major adverse cardiac events has been reported when PCI was deferred with FFR greater than 0.80 or iFR that is >0.89. One of the trials named DEFER (Deferral of Percutaneous Intervention) reported that the rate of adverse outcome cardiac outcomes is similar in both group of patients whose PCI has been deferred either with a FFR greater than 0.75 or intermediate angiographic measures.

# ACA 2021 Guidline Recommendations for Specific Patients

## Diabetics
- The following should be considered when making revascularization decision for diabetic patient:
Using Heart Team approach
Patient preferences
Left ventricular function
Other comorbidities
Ongoing symptoms
Expected survival
- Using Heart Team approach
- Patient preferences
- Left ventricular function
- Other comorbidities
- Ongoing symptoms
- Expected survival
- Diabetic patients experience a higher rate of mortality and repeat revascularization when undergone revascularization.
- PCI has been associated with a higher five-year-mortality rate compared to CABG. 
- Two years after CABG the survival advantages become edivent and it will decrease after 8 years.
- CABG is related to an overall increase in likelihood of stroke for five years.
- Need of repeated revascularization is higher in PCA compared to CABG regardless of the use of the new generation of drug eluting stent.

## Patients with Previous CABG
- The following factors should be considered when repeated revascularization is required:
Internal mammary artery accessibilty
A patent graft to the LAD
Other comorbidities
Patient's preferences
The quality of the target vessel
Anatomic complexity
Feasibilty of the revascularization procedure
Risks of the revascularization procedure
- Internal mammary artery accessibilty
- A patent graft to the LAD
- Other comorbidities
- Patient's preferences
- The quality of the target vessel
- Anatomic complexity
- Feasibilty of the revascularization procedure
- Risks of the revascularization procedure

## Non Adherence to Dual Antiplatelet Therapy
- Being adherent to dual antiplatelet therapy is vital after PCI and non-adherence is related to stent thrombosis, poor outcomes and high mortality rate. Therefore, PCA is not recommended in patients who can not access, tolerate, or adhere to dual antiplatelet therapy.

## Pregnant Patients
- An expanded Heart Team approach is recommended for identifying the appropriate coronary revascularization strategy with consideration of patient preferences. 
- There are not sufficient data about the effect of antiplatelet drugs in pregnant patients, especially on third trimester (due to high risk of performing such studies).
- Low dose aspirin is known to be safe during pregnancy.
- If clopidogrel is indicated then it should be prescribed for a short duration throughout pregnancy with close monitoring.
- CABG is recommended only when medication or PCI is not effective or safe. 

## Elderlies
- Based on studies, CABG can be more successful at delivering a complete revascularization, while PCI can minimize the risk of periprocedural events in fragile patients.

## Patients with Chronic Kidney Disease
- Cardiac mortality rate is inversely associated with estimated glomerular filtration rate in patients with chronic kidney disease.
- Chronic kidney disease is known to be on of the strongest risk factors of acute kidney injury, which is more common in higher stages of chronic kidney disease.
- The main strategies to prevent acute kidney injury are hydration and minimization of the contrast dose.
- The incidence of Contrast-induced acute kidney injury (AKI) before diagnostic catheterization can be reduced with high-dose statins.
Statins decrease systemic inflammation due to their pleiotropic effects.
They do it by decreasing endothelin-1 production and hindering tissue factor expression in macrophages.
- Statins decrease systemic inflammation due to their pleiotropic effects.
- They do it by decreasing endothelin-1 production and hindering tissue factor expression in macrophages.
- It has been reported that the risk of AKI is lower when radial access is used compared with femoral access. This could be due to the possible role of atheroembolism in the development of AKI after PCI since femoral access may increase the risk of atheroembolism in proximity to renal arteries.
- The following table represents the best practices for angiography in chronic kidney disease patients in catherization labs:

## Before Non-Cardiac Surgery
- The incidence of peri-operative cardiovascular events is higher among patients with coronary artery disease who are undergoing a high-risk surgery, such as solid organ transplantation or vascular surgery.
- The necessity of performing revascularization should be evaluated based on patient's conditions and circumstances, nevertheless not as a routine prophylactic method to reduce the risk of death or cardiovascular events.

## Ventricular Arrythmia
- Monomorphic ventricular tachycardia is often caused by reentrant rhythms due scars and not ischemia hence revascularization alone is not associated with any improvement in patients' outcomes.

## Spontaneous Coronary Artery Dissection

## Patients With Cardiac Allografts
- Although cardiac allograft vasculopathy patients have been not included in most clinical trials which compared drug eluting stent (DES) versus bare metal stents (BMS), there are clues suggesting a better outcome with drug eluting stent (DES).

# Outcome
- After controlling baseline comorbidities and treatment strategies, outcome of coronary revascularization were same among different races as well as males and females.