Acute Coronary Syndrome Catheter Interventions

Etiology

The establishment of catheter-based interventions first occurred in the late 1970s. The idea behind catheter-directed interventions for acute coronary syndrome flourished due to its ability to use the circulation as a "vascular freeway" to approach occlusive coronary disease without the use of open-heart surgery. The ability to gain percutaneous vascular access and intervene on an occluded vessel with a catheter completely revolutionized cardiovascular medicine. A cardiac catheter, first characterized by Werner Forssmann in 1929, was described as a plastic tube that allowed the delivery of substances (medications or contrast) for imaging and monitoring of intracardiac pressures. Catheters continued to evolve from purely diagnostic tools for pressure measurements to therapeutic tools, as described by Gruentzig's breakthrough in the late 1970s.

Throughout the 1970s and 1980s, balloon angioplasty remained controversial and primarily indicated for stable ischemic lesions. ACS patients continued to rely on the use of intravenous thrombolytic therapy and coronary artery bypass grafting (CABG) surgery for treatment. Then in the late 1990's Stone, Grines, in collaboration with the other PAMI (primary angioplasty in myocardial infarction) investigators, demonstrated the safety and efficacy of using balloon angioplasty for the primary treatment of acute coronary syndrome. PAMI demonstrated that patients that presented with ACS treated with percutaneous balloon angioplasty compared to tissue plasminogen activator (t-PA) demonstrated reduced rates of in-hospital mortality (2% vs 7%, P = 0.03), as well as recurrent ischemia (11% vs 29%, P < 0.001) and stroke (0% vs 4%, P = 0.02), and demonstrated shorter hospital stays (7.6 vs 8.4 d, P = 0.04).[5]

Again in the late 1990s, two more landmark trials, BENESTENT, and STRESS were published demonstrating the use of a metal scaffold, termed a stent, was efficacious and safe for implantation in the coronary arteries and exhibited a lower rate of major cardiovascular adverse events when compared to balloon angioplasty.[6] These stents, however, were bulky, prone to restenosis, and need for repeat revascularization. Additionally, the procedure itself correlated with many vascular complications limiting its utility and widespread adoption. These issues were addressed and in the early 2000s with the development of a new stent design with the ability to elute antiproliferative agents (i.e., sirolimus, paclitaxel, etc.).[7] This discovery once again revolutionized the field of cardiology and how both stable ischemic heart disease and acute coronary syndrome could be treated. As time has progressed, the catheter and catheter delivery system designs have undergone a variety of changes allowing for more capabilities like delivery of equipment, such as stents and balloons, over a wire or monorail system, as well as improved deliverability to target vessels with fewer rates of major adverse cardiovascular events.

Epidemiology

Acute coronary syndrome is consistently a leading global cause of morbidity and mortality. In the United States, the estimated annual incidence of ACS is approximately 550000 new events and greater than 200000 recurrent cases. ACS primarily occurs in adults and varies by gender, with men being affected on average more often and early with an average age of 65 years vs. 72 years for women.[8] Per the National Cardiovascular Data Registry (NCDR), over 600000 percutaneous coronary interventions (PCI) are performed in the United States yearly. In 2014 the registry reported 667424 procedures performed in 1612 hospitals across the United States. Additionally, NCBR reports in 2014, approximately 64% of procedures were for acute coronary syndrome.[9]

Pathophysiology

Acute coronary syndrome comprises a spectrum of obstructive coronary artery disease that most commonly arises from plaque rupture and/or erosion, leaving the vulnerable lipid-rich core exposed to the circulation, resulting in activation of platelets and the coagulation cascade leading to acute thrombotic occlusion. There are three major subtypes of ACS: Unstable Angina, non-ST elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI). Each of these subtypes represents a different stage in the spectrum of the disease. Plaque erosion with subendocardial ischemia represents the majority of cases of unstable angina and NSTEMI. In contrast, plaque rupture and complete thrombotic occlusion, of an epicardial coronary, with associated transmural infarction, is characteristic of STEMI.[10]

History and Physical

History and physical exam remain the cornerstone for the initial diagnosis and management of the acute coronary syndrome. Patients will often present in the field to first responders with limited access to medical records. Rapid recognition of this syndrome is vital to good patient outcomes.  

Common symptoms of Acute Coronary Syndrome are:

• Angina (typical)
  • Constant (less than 30 min) and worsened with exertion  
  • Often described as substernal, radiating to the abdomen, back, jaw, or upper extremities
  • Improved with nitroglycerine 
  • Worsening in quality or quantity from previous anginal episodes 
• Dyspnea  
  • Often at rest or with mild exertion 
  • Sudden onset or worsening over a short period
• Diaphoresis 
  • Often described as sudden onset, cold sweat 
• Other nonspecific symptoms 
  • Dizziness, abdominal pain, nausea, vomiting, paresthesia, palpitations, and headache 

Common signs of Acute Coronary Syndrome are:

• Tachycardia 
• Bradycardia 
• Hypertension 
• Hypotension 
• Hypoxia 
• Tachypnea 
• A new cardiac murmur 
• Orthopnea
• Lower extremity edema 
• Jugular venous distention 

Physical exam findings for ACS can vary depending on the patient's presentation on the extent and severity of the disease. In general, a complete physical exam is recommended for all patients presenting with ACS requiring catheter-based interventions, with particular attention paid towards the cardiovascular, respiratory, neurologic, and vascular systems. Due to the need for vascular access, the need for various anticoagulants and antiplatelet medications, and the use of percutaneous equipment, the risk for bleeding and mechanical complications of myocardial infarction must be ruled out before proceeding to the catheterization laboratory. 

Allergies must undergo an assessment before any catheter-based intervention to treat and sedate the patient throughout the procedure. Patients often will report adverse reactions to many of the medications used for moderate conscious sedation (i.e., fentanyl) as well as to medications administered post-procedure (i.e., statins, angiotensin-converting enzyme inhibitors, etc.). Additionally, many patients report adverse reactions, allergies, or anaphylaxis to the iodinated contrast used for angiography. Thus, a thorough and detailed history and physical is mandatory prior to any cardiac catheter-based procedure.

Evaluation

To understand what pre-procedure evaluations are needed, one must understand what a cardiac catheterization procedure entails and what complications can arise from the procedure itself as well as a patient with an acute coronary syndrome. The procedure itself entails gaining vascular access and cannulation of the coronary arterial tree. Large doses of anticoagulant medications as well as antiplatelet medications will be administered, significantly increasing the bleeding risk of the procedure. Additionally, iodinated contrast is used for imaging in angiographic procedures, most of which are consider nephrotoxic. Other patients can present with a large anterior myocardial infarction or right ventricular infarction that can often present in cardiogenic shock or advanced atrioventricular heart block. A thorough peri-procedural evaluation is vital before sending a patient for cardiac catheterization.

Vitals

• The first step for all patients presenting with ACS is to assess for hemodynamic instability. There should be continuous monitoring of the heart rate, along with blood pressure readings every 3 to 5 minutes. Pulse oximetry should be performed on arrival and continuously monitored. The temperature should be taken to assess for fever or other signs of systemic infection. The respiratory rate should undergo continuous monitoring in cases of respiratory distress. 

12 Lead Electrocardiogram (ECG)

• Generally performed in the emergency room when a patient first presents with acute coronary syndrome. Typical ECG findings for ACS vary based on subtype and presentation. Unstable angina and NSTEMI can present with a normal ECG or with ECG concerning for ischemia, such as ST depressions, T wave inversion, or sustained or nonsustained arrhythmias (premature ventricular complexes, nonsustained ventricular tachycardia, sustained ventricular tachycardia, etc.) STEMI will present most commonly as J point elevation.

Continuous Telemetry

• Every patient with ACS should have continuous monitoring with telemetry, most commonly portable cardiac resuscitation devices with defibrillation pads placed before presenting to the cardiac catheterization laboratory.  

Labs

• Complete Blood Count (CBC) - Due to the use of high-dose anticoagulant and antiplatelet medications, a complete blood count is needed to assess baseline hemoglobin and platelet levels to help quantify the bleeding risk.
• Basic Metabolic Profile (BMP) - A baseline blood urea nitrogen and creatinine level are necessary to evaluate for post-procedure contrast nephropathy as well as the ability to use other cardiac medications that are renally cleared due to the use of nephrotoxic agents during the procedure, specifically iodinated contrast
• Partial Thromboplastin Time (PTT) - To assess baseline anticoagulation levels and for appropriate dosing and monitor of medications during the procedure
• Prothrombin Time (PT) and International Normalized Ratio (INR) - To determine baseline anticoagulation levels and for proper dosing, monitoring of medications during the procedure
• Troponin - To assess the baseline degree of cardiac damage and allows for quantification of the timing of the initial event. 
• CKMB - Sometimes used to help assess for acute or subacute stent thrombosis in a patient that has recently undergone PCI 
• Brain Natriuretic Peptide (BNP) - Generally not needed. However, it can help assess and establish a baseline for treatment and prognosis in patients with congestive heart failure in the setting of acute myocardial infarction.

Imaging

• Chest X-ray (CXR) - Generally not needed but can assist in assessing for acute pulmonary edema and evidence for cardiogenic shock
• CT Chest with contrast - Generally not required unless there is a concern for possible aortic dissection, pulmonary embolism, or other causes of acute chest pain
• CT Brain without contrast - Generally not needed unless there is a concern for possible acute ischemic or hemorrhagic CVA

Treatment / Management

Approach and Access[11][12][13][14](A1)

• Transradial - Generally preferred for acute coronary syndromes. In this approach, access is gained via the right or left radial artery, with sheath insertion to maintain vascular access. Diagnostic and guiding catheters are then used from this approach for both diagnostic and therapeutic management. Transradial approach has been shown in a large meta-analysis of multiple trials to be safer with significantly less bleeding risk and vascular complications (hematoma formation, pseudoaneurysm formation, retroperitoneal bleeding) to a transfemoral approach. However, transradial is associated with high radiation to both the patient and the operator compared to a transfemoral approach. 
• Transfemoral - Left or right common femoral artery is accessed and sometimes preferred over transradial access because of less anatomical variations and the ability for large bore access if needed; however, associated higher rates of major adverse cardiovascular events driven by significant bleeding. It also correlates with increased mortality in acute coronary syndrome when compared to a transradial approach.  
• Transbrachial -  A seldom-used approach; this is due to possible limb occlusion with compromised vessel patency.  
• Transulnar - Very rarely used due to the size of the vessel and lack of evidence and operator experience. Emerging literature does suggest that transulnar can be a viable option if needed. 
• Distal Radial Access- Very rarely used due to the size of the vessel and lack of randomized control trials and operator experience. Emerging literature does suggest that the distal left or right radial can be a viable option if needed. Evidence, though limited, does support less radial artery occlusion post-procedure compared to transradial as well as improved operator and patient comfort. 

Types of Coronary Wires

• Coronary wires are generally 0.014mm in diameter and are introduced to the coronary tree via a guiding catheter. 
• Multiple different coronary wires exist- described as "workhorse," "extra supportive," or "hydrophilic,"  among many other terms that are beyond the scope of this article. 

Types of Coronary Catheters

• Diagnostic Catheter - Smaller sized (5F-6F) and only used for diagnostic purposes for coronary angiograms and hemodynamic assessment. 
• Guiding Catheter - Large size (5-8F)  and used primarily to deliver coronary interventional equipment (i.e., coronary wires, balloon, and stent catheters, etc.)
• Balloon Catheter (monorail) - Used for percutaneous balloon angioplasty. Often described by their ability to comply with the vessel. Compliant balloons are useful for the pre-dilation of a lesion and sizing purposes. Noncompliant balloons are often used for post-dilation to ensure stent apposition and full deployment or for dilation of severely stenotic lesions non-responsive to other therapies. 
• Balloon Catheter (over the wire) - Often smaller in size when compared to the monorail system and are generally used for pre-dilation. These catheters can also be used for wire exchanges, medication injection, and delivery to the distal coronary bed, as well as for extra guide and wire support. 
• Stenting Catheter - A stent (bare-metal or drug-eluting) mounted on a balloon is inserted via a monorail system and used for percutaneous coronary intervention

Adjunctive Catheter Therapy

Multiple other adjunctive catheter therapies exist; however, they are beyond the scope of this document and are not discussed in detail. Some examples of these therapies are listed below: 

• Thrombectomy Catheter - Used for aspiration of thrombus during acute coronary syndrome.  
• Atherectomy Catheter - Used for plaque debulking before angioplasty and stenting. However, multiple different atherectomy technologies exist beyond the scope of this document and are not discussed in detail. These are but are not limited to rotation, orbital, laser, and excisional atherectomy.  
• Intravascular Ultrasound Catheter (IVUS) - An imaging catheter; allows deep penetration of vascular tissue with ultrasound within the coronary tree. It is often used to visualized and assess target vessels pre and post-intervention. Further description of this device is beyond the scope of this document. 
• Optical Coherence Tomography Catheter (OCT) - Similar to IVUS, this catheter is used for intravascular imaging with the use of light waves, allowing for excellent spatial resolution within the coronary vasculature. Excellent visualizing within the vessel lumen for assessment for intraluminal irregularities such as dissection, stent thrombosis, etc. Further description of this device is beyond the scope of this document. 
• Scoring Balloon Catheters - These devices are also known as cutting balloons. Their predominant use is for balloon angioplasty in severely diseased and calcified lesions in which balloon slippage is an issue. These devices are also useful in areas of in-stent restenosis. 
• Distal Embolization Device - A wire "basket" device, which is placed distally in the target vessel in cases in which distal embolization of vascular debris (atheroma, thrombus, etc.) is expected to avoid the no-reflow phenomenon. Most commonly indicated in cases involving atherectomy or saphenous vein graft interventions.  
• Guideliner - This is a coaxial guiding catheter extension delivered to the target vessel over a guidewire monorail system. This device is useful in cases where guide support due to guide catheter seating is an issue. 
• Support, Micro, and Crossing Catheter - These are small catheters that can be inserted into a guiding catheter via an over-the-wire system to assist in crossing a complex and often chronic total occlusion in the coronary and peripheral vascular tree. 

Mechanical Support Devices

Mechanical support catheters and therapies exist; however, these are beyond the scope of this document and not discussed in detail. These are but are not limited to intra-aortic balloon pump counterpulsation therapy, ventricular support devices, tandem heart support devices, and extracorporeal membrane oxygenation.

Differential Diagnosis

Pathologies that can be mistaken for acute coronary syndrome:

• Aortic dissection 
• Acute pulmonary embolism 
• Pneumothorax 
• Acute pericarditis 
• Myocarditis
• Esophagitis 
• Esophageal perforation 
• Critical aortic stenosis

Prognosis

Six-month mortality rates recorded in the Global Registry of Acute Coronary Events (GRACE)  for patients with STEMI were estimated close to 17%, 13% for patients with NSTEMI ACS, and 8% for those with unstable angina. These numbers have continued to decline as percutaneous coronary intervention continues to evolve and operator experience increases. Additionally, the broad adoption of transradial PCI has continued the trend in the decrease in mortality in both NSTEMI and STEMI. This adoption has support from the results of the MATRIX, STEMI-RADIAL, and numerous other studies in the past decade.

Complications

Complications that arise from coronary intervention can vary from minor to major, depending on their hemodynamic significance. The most common complication of coronary intervention is access site bleeding. Due to a large amount of anticoagulation given and the occasional need for large bore access, access site complications (hematoma, pseudoaneurysms, dissection, etc.) can arise and most commonly result in transfemoral access. Additional complications seen are contrast-induced nephropathy, vessel dissection or perforation, acute cerebrovascular accident or other embolic phenomena, myocardial infarction, need for emergent cardiothoracic surgery, and rarely death. The rates of complications vary by center and operator volume; however, for the most part, the risk of the procedure is generally low (between 1 to 2%), and the benefit of the procedure far outweigh the risk.[15]