Cardiac Catheterization & Electrical Therapies

Objectives 2.1 / 3.1 — Understand cardiac catheterization indications and procedure, diagnostic and therapeutic interventions, radionuclide studies, synchronized cardioversion, and pacemaker/ICD function and interrogation.

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Unit 2: Cardiac Catheterization

Overview

Cardiac catheterization is a procedure to examine the heart by passing a catheter through an artery — usually the femoral artery — to examine structures of the heart.

• Considered primarily a diagnostic study, though therapeutic interventions may be performed during the same procedure
• The most common indication is identification of CAD and assessment of its extent and severity

Catheters

• Different catheters are selected based on the type of disease process expected, guided by prior assessments (echocardiography, CMRI)
• Each catheter is introduced via a guidewire
• The guidewire remains in place to allow rapid exchange of catheters by technicians as needed

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Equipment

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Procedure — Judkins Technique

The patient is placed on a flat table with a fluoroscope capable of a 360° view of the heart, projected on a screen visible to all clinicians.

Judkins Technique — Percutaneous entry into the femoral artery:

1. Palpate for the inguinal ligament
2. Measure 1–3 cm (one or two fingers) below the inguinal ligament
3. Make a small nick in the skin above the vessel
4. Puncture the femoral artery and introduce the catheter via guidewire

Femoral arterial access is the most common route for cardiac catheterization.

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Diagnostic Studies

Coronary Angiography

Coronary angiography is the gold standard for evaluating the anatomy of the coronary artery tree and diagnosing CAD.

• Normally a same-day procedure
• Most widely used invasive procedure in cardiovascular medicine
• Can be performed via the femoral or radial arteries

How It Works

1. Direct injection of radiopaque contrast agent into the coronary arteries
2. Contrast enhances x-ray absorption, producing sharp visualization of arterial anatomy
3. Catheter is inserted and guided up the aorta to the coronary artery ostium
4. Contrast is injected and images are captured on high-resolution digital radiographic systems

Indications

Contraindications

There are no absolute contraindications to coronary angiography.

Relative risk factors requiring risk/benefit analysis:

• Active bleeding
• Abnormal coagulopathy (elevated INR)
• Fever
• (And others)

Catheter Types

Judkins catheters between 5F and 6F are standard for diagnostic arteriography.

Patient Preparation

• Conscious sedation:
  • Fentanyl
  • Midazolam (Versed)
• Heparin anticoagulation
• Nitroglycerin — used to dilate vessels in patients with an active or recent coronary event

Contrast Agents

• Injected into coronary arteries to enhance x-ray absorption and produce sharp contrast with surrounding tissue
• Typically contain iodine — which may cause an allergic reaction in some patients

Assessing the Lesion

The composition, distribution, and location of atherosclerotic plaque are unique to each patient. Because every patient has a unique coronary tree, the lesion's location may complicate stenting or atherectomy.

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Cardiac Electrophysiology (EPS)

Invasive electrophysiology studies (EPS) use a multi-lead catheter with electrodes to record or stimulate cardiac electrical activity.

• Performed by an electrophysiologist (a subspecialty cardiologist)
• Has both diagnostic and therapeutic functions
• Effective at initiating VT and SVT when these tachyarrhythmias have occurred spontaneously

Diagnostic EPS

By stimulating specific portions of the electrical pathway, the technician can:

• Measure specific electrical dysfunctions (e.g., third-degree AV block)
• Initiate arrhythmias (SVT, tachycardia) for characterization
• Help determine if a patient requires a pacemaker or cardioversion device

Cardiac Mapping

Cardiac mapping records electrical potentials from the heart and depicts them spatially as activation times and electrical amplitudes of myocardial tissue.

• A computer algorithm detects the electrical potential of the myocardium and how quickly muscle tissue is stimulated
• Displayed as a color chart
• Effective at identifying:
  • Foci causing SVT
  • Wolff-Parkinson-White (WPW) syndrome
  • Scar tissue

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Therapeutic Interventions

Percutaneous Coronary Intervention (PCI)

PCI provides relief of ischemic CAD symptoms and reduces the risk of mortality and subsequent myocardial infarctions.

• Mortality rate: < 1%
• Complications include:
  • Risk of restenosis of a stent
  • Risk of thrombosis
  • Risk of perforation of the coronary artery

Balloon Angioplasty

Balloon angioplasty expands the coronary lumen by stretching and tearing the atherosclerotic plaque and vessel wall.

• Does not remove atherosclerosis — it displaces it to the sides of the vessel wall
• Restenosis is common
• Rare but possible: arterial rebound and vessel swelling causing occlusion worse than initial stenosis

Stents

Stents are used in 90% of PCI procedures worldwide and are the predominant form of PCI.

• Tube-shaped devices placed in the artery to maintain vessel integrity and patency
• Deployed by being fed into the coronary artery on a balloon catheter and expanded within the stenosis
• Restenosis occurs in only ~1% of cases
• Some stents are drug-impregnated to help prevent thrombosis and plaque development

Coronary Atherectomy

Atherectomy refers to the removal (rather than displacement) of obstructing atherosclerotic plaque by grinding it.

• Allows for a larger final minimal lumen diameter than balloon angioplasty alone
• The rotablator rotational atherectomy system is the most commonly used device
• Restenosis remains a concern
• Complication: distal blockages as plaque is broken away from the artery

Ablation

Ablation destroys myocardial tissue by delivering energy through a catheter electrode placed on the myocardium at a targeted location.

• Energy types:
  • Radiofrequency (RF) — generates heat through the catheter tip, destroying targeted tissue
  • Cryo — destroys tissue through freezing
• Used to eliminate:
  • Foci causing SVT/arrhythmias
  • Bridging tissue between scar tissue that sustains reentrant arrhythmias (circular electrical signals)

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Radionuclide Studies

Also known as radionuclide angiography or blood pool imaging.

• Provides imaging of the heart to detect ejection fractions and chamber volumes

Key Concepts

Isotopes have an excess number of protons or neutrons, giving them excess nuclear energy, making them easy to identify on gamma imaging devices or x-ray.

Radionuclide Ventriculography

Using 99mTc-pertechnetate, the gamma camera — which can rotate around the patient — produces images in:

• Anterior-Posterior (AP)
• Left Anterior Oblique (LAO)
• Lateral views

Data is recorded in a computer synchronized with the R wave of the patient's ECG.

What Radionuclide Studies Can Identify

• Size of heart chambers and great vessels
• Regional wall motion
• Global function (qualitative assessment)
• Ventricular wall thickness
• Pericardial effusion
• Pericardial fat pad
• Paracardiac mass

Blood pool imaging — a reduced ejection fraction (EF) results in blood pooling within one of the ventricles, which is visualized on radionuclide imaging.

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Unit 3: Electrical Therapies

Synchronized Cardioversion

Synchronized cardioversion delivers a shock timed to the R wave to convert a fast, irregular heart rhythm to a regular rhythm.

• A synchronizing function (manual or automatic) times the shock delivery
• Marked as a 'Tic' mark on the R wave on the monitor
• Shock is delivered at a predetermined optimal moment (milliseconds after R wave detection)

Indications

Pulseless VT and VF are treated with unsynchronized shocks — this is called defibrillation, not cardioversion.

Procedure

Preparation:

1. Verify indication; explain procedure to the awake patient
2. Remove clothing from the upper body
3. Remove nitroglycerin paste/patches; wipe away any residue
4. Remove (shave) excessive hair from paddle/electrode sites
5. Do not apply alcohol, tincture of benzoin, or antiperspirant to skin
6. Print an ECG strip to document the rhythm
7. Ensure suction and emergency medications are available
8. Give oxygen and start an IV

Delivering the shock:

1. Ensure defibrillator is on
2. Apply defibrillation gel (standard paddles) or adhesive pads
3. Press the "Sync" control on the defibrillator
4. Select a lead with an optimum QRS amplitude and no artifact
5. Confirm sense markers appear on the R wave of each QRS (not on the T wave)
6. If sense markers are misplaced, adjust ECG size or select another lead
7. Administer sedation per protocol (if patient is awake and time permits)
8. Confirm machine is in Sync mode; select appropriate energy level
9. Charge the defibrillator; recheck rhythm
10. Place paddles/pads on the patient's chest
11. Call "Clear!" — ensure all personnel and equipment are clear; confirm oxygen is not flowing over the chest
12. Press and hold both discharge buttons simultaneously until the shock is delivered
13. Note: slight delay occurs while the machine detects the next R wave
14. Release controls after shock delivery; reassess rhythm and patient
15. If arrhythmia persists, confirm Sync mode is still active before delivering another shock

If the rhythm deteriorates to pulseless VT or VF, turn Sync off and defibrillate.

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Pacemaker Interrogation

Pacemakers & ICDs — Overview

Indications

Cardiac Electrical Stimulation

A stimulus that successfully stimulates local myocardium is said to have captured it.

Hardware

Leads:

• Have common cable structures inserted into a "Header"
• Bipolar leads are used more frequently — better sensing → better detection
• Both unipolar and bipolar leads are available

Generator (the "Can"):

• Clear plastic header where leads attach
• Titanium casing houses all electronic components:
  • Battery
  • RAM/ROM memory
  • Microprocessor
  • Essentially a tiny computer in the patient's chest

Sensing, Detection & Oversensing

Pacemaker Interrogation Checklist

A complete standard interrogation should document:

Noninvasive interrogation tools:

• Remote management of the pacemaker
• Short-range telemetry with an inductive wand

Precautions for Device Implantation

• Damage to cardiac vasculature during placement
• Cardiac perforation
• Device infection (e.g., MRSA)
• Lead displacement
• Stroke