Michael Schinlever
Cardiac radiofrequency (RF) ablation is the use of energy to damage specific cardiac tissue in an effort to inhibit pathologic conduction sources or tracts. Numerous arrhythmias can be treated with RF ablation. The success and complication rates of these ablations are highly dependent on the etiology of the arrhythmia and the targeted anatomic location. Arrhythmias that have a specific and localizable ectopic focus or conduction tract respond to RF ablation therapy with the highest rates of success. These include Wolf–Parkinson–White (WPW) syndrome, paroxysmal supraventricular tachycardias (AVNRT, unifocal atrial tachycardia, and accessory pathway–mediated tachycardia), type I atrial flutter, idiopathic ventricular tachycardia (VT; in structurally normal heart), and bundle branch reentrant tachycardia. On average, these carry success rates of 80% to 95% and have low rates of recurrence (<10%).
Ablation may be indicated for patients in whom pharmacologic management has failed, significant symptoms develop, or definitive treatment is desired. Cardiac RF ablation can be employed for atypical atrial flutter, inappropriate sinus tachycardia, and junctional tachycardia. However, RF ablation has a lower success rate in treating these rhythms; therefore, it is often reserved for cases that are refractory to drug therapy. Although controversial, asymptomatic patients who have an underlying arrhythmia prone to dangerous paroxysmal changes may benefit from ablation.
When cardiac ablation was first developed, direct current (DC) was used. With time, techniques using different forms of energy (RF, cryotherapy, laser, and acoustic) have been developed, which provide higher success rates with fewer complications. The most common energy form used for cardiac ablation is RF. RF is a low-voltage, high-frequency energy that causes resistive heating at the catheter tip and damages focused areas of cardiac tissue. The width and depth of these resultant lesions are typically 3 to 9 mm. With different approaches (eg, femoral vein, femoral artery, internal jugular vein, or subxiphoid), a variety of target sites can be reached for ablation.
FIGURE 9.3
This fluoroscopic image (left anterior oblique orientation) was obtained during cardiac RF ablation with multiple catheters at different sites; A is a coronary sinus electrode, B is an endocardial ablation catheter, lead C is situated at the bundle of His, and lead D is located in the right atrium.
The detailed mapping of cardiac conduction is a critical component of catheter ablation. Multiple catheter tips are passed through a major vessel under fluoroscopic guidance and positioned in the left or right heart. Electrophysiologists use the catheters to record internal ECG tracings, to pace different internal locations in an attempt to recreate the arrhythmia, or to locate classic areas of ectopy. Real-time fluoroscopic and ECG data can also be combined with prior CT or MR images and incorporated into mapping software. This software can create three-dimensional representations of the cardiac conduction pattern, thereby further defining ablation targets.
Cardiac ablation is relatively safe with a serious complication rate of about 1% for typical interventions. Vascular complications related to major vessel access, such as hematoma or pseudoaneurysm, can occur. Disruption of native cardiac conduction tracts may lead to heart block or new arrhythmias. Additional complications include pulmonary vein stenosis, atrial-esophageal fistulae, and cardiac perforation, resulting in tamponade.
In patients with history of cardiac ablation, consider the possibility of recurrent/new arrhythmia, or the rare above-mentioned complications.
Justin B. Joines
Cedric Lefebvre
Peripheral arterial disease (PAD) is the narrowing and obstruction of arteries within the peripheral vascular system. Risk factors for the development of PAD include smoking, hyperlipidemia, and diabetes mellitus. The incidence of PAD increases with age. PAD causes claudication (painful cramping of leg muscles), changes in skin color and temperature, loss of hair, and delayed healing of soft tissue wounds in the extremities.
Symptomatic patients with or without decreased peripheral pulses or bruits should be screened for PAD. The ankle brachial index (ABI) is a simple test that can detect evidence of PAD and can be performed easily in the emergency department or clinic setting. The ABI is a ratio of systolic blood pressures in the ankles/legs relative to the arms. To perform an ABI, first position a blood pressure cuff just above the ankle. Next, auscultate either the dorsalis pedis (DP) or posterior tibial (PT) artery with a Doppler device. Inflate the blood pressure cuff to just above the pressure at which the Doppler sound disappears. Allow the pressure in the cuff to release slowly until the pedal signal returns and record this systolic pressure. Repeat the measurement on the contralateral extremity using the same vessel (ie, DP or PT). Next, obtain bilateral systolic brachial artery pressures using a similar process with the blood pressure cuff located just above the elbow.
Calculating the ABI is achieved by dividing the higher ankle systolic pressure (DP or PT) by the higher of the two brachial artery systolic pressures (see Table 9.1 for a sample calculation). The resultant number is the ABI for the leg in question. An ABI of 0.9 to 1.3 is considered normal while an ABI of less than 0.9 is diagnostic of PAD (Table 9.2). Patients with abnormal ABI measurements should be referred to a vascular specialist for additional evaluation and treatment. Patients with an abnormal ABI should also undergo appropriate testing and treatment for other forms of atherosclerotic disease. The timing of consultation depends on the degree of ABI abnormality, the severity of symptoms, and other clinical factors.
An abnormal ABI is associated with a higher risk of coronary artery disease (CAD), stroke, transient ischemic attack, renal disease, and all-cause mortality.
Consider obtaining ABIs in trauma patients with lower extremity injury.
ABI of greater than 1.3 suggests calcified vasculature that is not easily compressible, leading to falsely elevated results and warrants further testing.
P. Matthew Belford
Sanjay K. Gandhi
Cardiac catheterization is an invasive procedure used to access the heart and its vessels percutaneously. It can be used to perform diagnostic coronary angiography to define anatomical and hemodynamic characteristics of the cardiac chambers, great vessels, and coronary arteries. Cardiac catheterization can also be used to perform therapeutic percutaneous coronary intervention (PCI). Indications for diagnostic cardiac catheterization include acute coronary syndromes, valvular heart disease, congestive heart failure, and pulmonary hypertension (see Table 9.3 for appropriate use criteria). The most common indication for cardiac catheterization is the evaluation, diagnosis, and treatment of CAD. Indications for right heart catheterization (described later) include the need for hemodynamic assessment of cardiac and pulmonary function, or for the evaluation of valvular heart disease. Contraindications for cardiac catheterization include acute renal failure, allergy to contrast media, and active severe bleeding (Table 9.4).
APPROPRIATE USE CRITERIA FOR DIAGNOSTIC CATHETERIZATION∗
| Indication | Appropriate Use Score |
|---|---|
| STEMI/suspected STEMI | A |
| Cardiogenic shock due to ACS | A |
| UA/NSTEMI | A |
| Symptomatic suspected CAD without stress imaging | I = if symptomatic with low pretest probability |
| A = if symptomatic with high pretest probability | |
| New LV systolic dysfunction | U = if asymptomatic |
| (EF<40) | A = if symptomatic |
| Any coronary calcium score | I = if asymptomatic Not rated if symptomatic |
| Known CAD with intermediate risk noninvasive study findings | U = if asymptomatic or stable |
| A = if worsening or limiting symptoms | |
| After VF or sustained VT without symptoms | A |
| After cardiac arrest with ROSC | A |
| After NSVT with normal LV function | U |
| Preoperative assessment for noncardiac surgery | I = for low risk surgery |
| I = for >4 METS without symptoms | |
| U = prior to solid organ transplant | |
| New LBBB | U |
CONTRAINDICATIONS TO CARDIAC CATHETERIZATION∗
| Uncooperative patient or patient refusal |
| Uncontrolled severe hypertension |
| Decompensated congestive heart failure or pulmonary edema |
| Acute trauma, bleeding (including GI), or severe anemia |
| Acute stroke |
| Profound electrolyte disturbance (particularly hypokalemia) |
| Medication toxicity or overdose |
| Anticoagulation with INR > 1.8, severe coagulopathy, moderate-severe thrombocytopenia |
| Anaphylactic reaction to contrast medium or documented contrast allergy |
| Acute renal failure or severe kidney disease (in patients who are not dialysis dependent) |
| Active infection or unexplained fever |
| Limited or no peripheral venous access |
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