Coronary artery calcification

# Overview
The coronary angiogram is fairly insensitive to the presence of lesion calcification, particularly to the presence of deep vessel wall calcification.  Intravascular ultrasound is much more sensitive in the assessment of vessel wall calcification. Conventional coronary angiography has limited sensitivity for the detection of smaller amounts of calcium, and has moderate sensitivity for the detection of extensive lesion calcium (sensitivity 60% and 85% for three- and four-quadrant calcium, respectively). Calcification is often associated with older saphenous vein graft age, insulindependent diabetics, and smoking. Calcified lesions pose several challenges to the interventional cardiologists as they are sometimes difficult to cross with the angioplasty equipment, they are less likely to fully dilate, prone to recoil, and often do not allow for full expansion of the stent. Failure to fully expand the stent may result in restenosis. Stents should be deployed only after ensuring that the lesion can be fully expanded by a conventional balloon angioplasty.

# Grading System
- None: no radiopacity.
- Mild: faint radiopacities noted during the cardiac cycles.
- Moderate: dense radiopacities noted only during the cardiac cycle.
- Severe: dense radiopacities noted without cardiac motion before contrast injection generally compromising both sides of the arterial lumen.

# Diagnosis
- The coronary angiogram is fairly insensitive to the presence of lesion calcification, particularly the presence of deep vessel wall calcification.
- Intravascular ultrasound is much more sensitive in the assessment of vessel wall calcification.
- Conventional coronary angiography has limited sensitivity for the detection of smaller amounts of calcium, and has moderate sensitivity for the detection of extensive lesion calcium (sensitivity 60% and 85% for three- and four-quadrant calcium, respectively).
- Presence of calcium deposit thicker than 500 mm or presence of calcium involving an arc of the vessel >270 degree on intravascular imaging requires lesion modification to facilitate stent delivery.
- Calcification of SVGs is generally within the reference vessel wall rather than within the lesion itself. Calcification is often associated with older graft age, insulindependent diabetics, and smoking. 

# Treatment
- Calcified lesions pose several challenges to the interventional cardiologists as they are sometimes difficult to cross with the angioplasty equipment, they are less likely to fully dilate, they are prone to recoil, and they often do not allow for full expansion of the stent. It is critical to notice that failure to fully expand the stent may result in restenosis.
- The following methods could be used to modify calcified lesions:
Rotational atherectomy
Orbital atherectomy
Cutting balloon atherotomy
Intracoronary lithotripsy
Angioplasty
- Rotational atherectomy
- Orbital atherectomy
- Cutting balloon atherotomy
- Intracoronary lithotripsy
- Angioplasty
- Rotational atherectomy is frequently employed following unsuccessful pre-dilating PTCA to perform plaque modification. Stents should be deployed only after ensuring that the lesion can be fully expanded by a conventional balloon angioplasty.

# PCI Complications and Technical Challenges

## Reduced Compliance of the Vessel
The presence of coronary calcification reduces the compliance of the vessel, and it may predispose calcified plaquenormal wall interfaces to dissections after balloon angioplasty.

## Reduced Ability to Cross the Lesion
- The lack of flexibility in calcified arteries makes it difficult to advance balloons and particularly stents down a tortuous vessel. This is often observed in a tortuous and calcified right coronary artery.
- The presence of coronary calcification also reduces the ability to cross chronic total occlusions and severely stenotic lesions.

## Reduced Ability to Fully Dilate the Lesion
- Stent strut expansion is inversely correlated with the circumferential arc of calcium on intravascular ultrasound. 
- Extensive coronary calcification is associated with muscle rigidity requiring higher balloon inflation pressures to obtain complete stent expansion.

# PCI Techniques

## Guidewire Technique
Often times hydrophilic guidewires with a core that extends to the tip are necessary to cross heavily calcified lesions.  Once the lesion is crossed, then a more flexible and less traumatic wire can be inserted distally to minimize vessel, and to minimize the potential for vessel perforation.  If there is the difficulty in delivering the equipment, then a more rigid wire such as a stabilizer wire can be used to facilitate passage of devices. Sometimes two wires are used in the "buddy wire technique" to straighten the vessel and facilitate delivery of devices.

## Balloon Dilation
Calcified plaques usually require higher balloon pressures to fully expand than normal plaques.  Because of this, non-compliant balloons may be a better choice than compliant or semi-compliant balloons.  Differential expansion of compliant or semi-compliant balloons inside a particular lesion may jeopardize less diseased segments if the balloon expands greater than the vessel's native diameter.  On the contrary, non-compliant balloons allow for a more uniform expansion at high pressures and therefore may be a better choice to apply focused pressure at the calcified plaque.  Another option is to place a second "buddy" wire adjacent to the balloon to improve the ability to dilate calcified plaque.
If pre-dilatation fails to fully expand a calcified stenosis, then the risks and benefits of stent deployment should be carefully considered due to the risk of incomplete expansion and future restenosis.

## Intravascular Ultrasound (IVUS)
IVUS is a medical imaging methodology that uses a specially designed catheter with a miniaturized ultrasound probe attached to the distal end of the catheter.  The proximal end of the catheter is attached to computerized ultrasound equipment. It allows the application of ultrasound technology to see from inside blood vessels out through the surrounding blood column, visualizing the endothelium (inner wall) of blood vessels in living individuals.  IVUS is used in the coronary arteries to determine the amount of atheromatous plaque built up at any particular point in the epicardial coronary artery.
While coronary angiography by fluroscopy is limited in its detection and severity assessment of coronary calcification, IVUS can assess the extent of calcification and may be particularly useful for instances when the reason for poor balloon expansion is uncertain.  Although this approach has its advantages over angiography, heavy involvement of superficial, sub-endothelial calcification may require rotational atherectomy.

## Cutting Balloon and FX MiniRailTM
A cutting balloon is an angioplasty device used in percutaneous coronary interventions. It has a special balloon tip with small blades, that are activated when the balloon is inflated. This procedure is different from rotational atherectomy, in which a diamond tipped device spins at high revolutions to cut away calcific (chalky) atheroma usually prior to coronary stenting.
This technique can be useful in treating calcified lesions because the microsurgical blades on the surface of the balloon may help to score and modify calcified plaques.  Generally, if a cutting balloon will cross the lesion, a stent can be delivered.  Although this technique has its advantages, there are certain additional considerations that must be made before deciding to use this procedure.  For one, despite their usefulness, these balloons are often more difficult to deliver past tortuous or calcified segments, so extra care must be used.  Also, there were no significant differences observed in rates of restenosis when using this procedure.

## Rotational Atherectomy
Rotational atherectomy is an invasive method of removing plaque and blockages from an artery and subsequently widening arteries that have been narrowed by arterial disease.  Unlike angioplasty and stents of blocked arteries that simply push blockages aside into the wall of the artery, rotational atherectomy involves inserting a thin catheter with a rotating blade on its end into the artery.  The rotating edge is used to remove plaque buildups, thereby opening the artery and restoring normal blood flow.
Rotational atherectomy is frequently employed following unsuccessful pre-dilating PTCA to perform plaque modification.  This procedure facilitates PTCA by creating micro-fractures, removing calcified plaque, and increasing vessel compliance.  Despite its usefulness in treating calcified lesions, certain precautions should be taken.  In an effort to limit the risk of vessel laceration, smaller diameter burrs are now preferred.  A general guideline to use is that the initial burr to luminal ratio should be 1:2.  Additional caution should be taken when a coronary dissection is present, as rotational atherectomy may propagate the dissection.
- Rotational atherectomy in severe lesion calcification: Rotational atherectomy is the preferred pretreatment method in patients with severe lesion calcification, particularly ostial lesions, and facilitates the delivery and expansion of coronary stents by creating microdissection planes within the fibrocalcific plaque. Yet even with these contemporary methods, the presence of moderate or severe coronary calcification is associated with reduced procedural success and higher complication rates, including stent dislodgement.
- Rotational atherectomy in mild-moderate calcifications: In less severely calcified lesions, no differences in restenosis rates were found after paclitaxel-eluting stent implantation in calcified and non-calcified vessels. 
Caution should be used in the patient with a low ejection fraction as distal embolization from rotational atherectomy can result in a decline and LV function. Also, tortuous segments with acute bends should not be treated with rotational atherectomy is there is an increased risk of vessel dissection at the site of acute bends and turns.

## Directional Coronary Atherectomy (DCA)
DCA involves inserting a thin, flexible catheter with a small blade on its end into the artery, which cuts off plaque buildups.  These plaque shavings are caught with the catheter and are subsequently removed from the artery.
One problem that may arise during the procedure is that heavy calcification proximal to the target lesion may limit deliverability of the device and its success.

## Excimer Laser Coronary Atherectomy/Angioplasty (ECLA)
ECLA uses a laser, instead of a traditional blade, to perform atherectomy and angioplasty.  The excimer laser is a pulsed ultraviolet laser that can erode calcified plaque while also causing minimal thermal tissue injury.
One advantage of using ELCA is that it fractures calcified plaques, thereby facilitating PTCA.  However, it also has a higher equipment cost and has a lesser ease of use than rotational atherectomy.  Furthermore, it is more commonly used in lower extremity peripheral arterial disease than in coronary artery disease (CAD).

## Stents
In cardiology, a stent is a tube that is inserted into an artery to counteract significant decreases in vessel diameter by acutely propping it open.
In the treatment of calcified lesions, stents are frequently used in conjunction with PTCA or atherectomy to decrease the risk of restenosis.  Extra care should be taken in deploying stents in lesions where incomplete expansion occurs following pre-dilation, as incomplete expansion of a target lesion will increase the likelihood of restenosis.  Stents should be deployed only after ensuring full balloon expansion.

# 2011 ACCF/AHA/SCAI Guidelines for Percutaneous Coronary Intervention (DO NOT EDIT)

## Calcified Lesions (DO NOT EDIT)

# ACA 2021 Revascularization Guideline