Intracardiac echocardiography (ICE) is increasingly being used to guide percutaneous interventional procedures, principally the closure of interatrial septal abnormalities, and to support electrophysiological procedures. Clear views of intracardiac structures can help a number of other procedures, such as myocardial biopsy and paravalvular leak closure. The main advantages of ICE over transoesophageal echocardiography during closure of atrial septal defects are that the use of ICE eliminates the need for a general anaesthetic, affords clearer imaging, shorter procedure times and reduces hospital stays and radiation doses. The principal disadvantage is the additional cost of the catheter, though this can be offset by improved turnaround times and reduced personnel costs.
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The technology to perform intravascular ultrasound was developed in the early 1970s but it has taken nearly 30 years to overcome the limitations posed by poor tissue penetration, difficult manipulation and size of the probes to see intracardiac echocardiography (ICE) emerge into full-time clinical use.1 ICE is now a viable alternative to transoesophageal echocardiography (TOE) for imaging a number of interventional procedures and has proved particularly successful for guiding the closure of interatrial septal abnormalities. ICE systems currently available include the AcuNav catheter (Biosense Webster, California, USA), the ViewFlexcatheter (EP Medsystems, New Jersey, USA) and the Ultra ICE catheter (Boston Scientific, Boston, USA). At the John Radcliffe Hospital we currently use the AcuNav ICE catheter. This is an 8F or 10F single-use, multifrequency (5–10 MHz), 64-element, linear phased array, ultrasound catheter that can perform pulsed and colour Doppler imaging (fig 1). It is capable of tissue penetration of up to 10 cm and has four-way head articulation to allow multiple angle imaging.
VISUALISATION OF STRUCTURES WITH ICE
To perform ICE, venous access is usually gained via the right femoral vein under local anaesthesia and the catheter is gently advanced to the mid-right atrium. The catheter sometimes needs to be screened up to avoid catching on venous branches with gentle anteroposterior steering for tortuous vessels. Advancing a guidewire through an adjacent sheath can help guide the catheter to the right heart. The following suggestions will help image orientation but, as with all imaging modalities, adjustments need to be made to allow for varying cardiac anatomy and size. Once in position, the catheters usually afford an extremely stable position to guide interventional procedures with only minute per-procedural adjustments required for image optimisation.
The “standard view” is achieved with the ICE probe sited in the mid-right atrium and with the scan plane facing anteriorly. This gives excellent views of the right atrium, right ventricle and tricuspid valve (fig 2). From the “standard view” withdrawing the catheter to the inferior right atrium brings the eustachian ridge, the remnant of the eustachian valve and the tricuspid valve isthmus into view.
From the standard view, retro-flexing and rotating the catheter tip clockwise, and advancing the catheter slightly brings the interatrial septum and fossa ovalis into view (fig 3). A small amount of left to right manipulation may be required to open up the septum. Close inspection of the septum can then be performed, with and without agitated saline contrast into the femoral vein, to demonstrate if a patent foramen ovale (PFO) is present (fig 4). This ICE catheter position is then usually accepted as a “working position” for septal defect procedures as the catheter is out of the way for device deployment.
Increasing the depth in the atrial septum view will reveal the left superior and inferior pulmonary veins (fig 5). Pulse wave Doppler can be performed to examine venous flow if required (fig 6). Rotating the catheter clockwise past the left pulmonary veins and advancing slightly brings the right pulmonary veins into view. These can be difficult to visualise with ICE and advancing into the superior vena cava may be required to identify them.
The aortic valve is viewed by gently rotating clockwise and retroflexing from the “standard view” to bring the valve into short axis (fig 7).
Mitral valve and left ventricle
Advancing the catheter towards the atrial septum and rotating clockwise brings the left atrial appendage and mitral valve into view (fig 8). Rotating clockwise allows visualisation of the coronary sinus ostium. The left ventricle is poorly seen with ICE but small adjustments in this view will open up the ventricular septum (fig 9).
CLOSURE OF INTERATRIAL SEPTAL ABNORMALITIES
Visualisation of the interatrial septum and fossa ovalis with ICE allows a detailed assessment of the size and length of the PFO “tunnel” and additional information gained on the mobility of the atrial septum (fig 10). The ICE catheter is usually quite stable for guiding the percutaneous closure of PFO and atrial septal defects (ASDs).
There has been considerable interest in the role of PFO in cryptogenic stroke and migraine.2 3 Given the relatively high prevalence of PFOs and incidence of migraine and cryptogenic stroke, if the results of continuing controlled studies support defect closure, we are set to see an increase in the number of referrals for percutaneous closure. ICE is perfectly poised to provide imaging for these procedures as PFO closures can now be performed as a day case under local anaesthetic with total procedure times of around 30 min.4 As visualisation of the septum is so accurate, ICE has also been shown to reduce the need for fluoroscopy in comparison with TOE-guided procedures, with a reduction in radiation doses used, shorter procedure times and shorter hospital stays.5
The role of ICE in interventional electrophysiology is developing. Traditionally, these procedures have been performed using fluoroscopy and electrophysiological mapping catheters. Success in these procedures rests on the accurate identification of anatomical structures together with good lesion formation. The extra dimension of imaging provided by ICE confirms stable, complete catheter–tissue contact, ensuring more complete electrical isolation and reducing the incidence of catheter clot formation,6 preventing tissue overheating while allowing maximal safe delivery of treatment. This reduces the incidence of scar formation, thrombosis and stenosis that can result from tissue overheating.
ICE can also identify thrombus in the left atrium and left atrial appendage and complications occurring within the pulmonary veins. Left atrial ablation for atrial fibrillation has been shown to be more successful with fewer embolic complications than procedures performed without ICE.7 ICE has also been used to confirm needle positioning and to guide trans-septal punctures that are necessary where access to the left atrium is required.8 This may result in a reduction in the potentially serious complications of trans-septal punctures such as cardiac tamponade and aortic perforation seen even in the most experienced hands.
More recently, images acquired using ICE have been combined with three-dimensional electrophysiological mapping catheters to provide additional anatomical information during ablation.9 The SoundStar 3D catheter (Biosense Webster, California, USA) has an embedded position sensor to display the location and beam orientation of the transducer. Dedicated software allows incorporation of these images with those pre-acquired using CT or MRI (fig 11).
OTHER IMAGING ROLES
As described earlier, virtually all cardiac structures can be visualised using ICE and some structures, for example right sided ones, that are often poorly differentiated with transthoracic or transoesophageal echocardiography are well suited to ICE. The small size and versatile nature of the ICE probe has led to its use in a wide variety of interesting interventional as well as diagnostic imaging roles.
Percutaneous closure of perimembranous ventricular septal defects10;
Balloon mitral commisurotomy11;
Left ventricular pacing12;
Atrial septal pacing13;
Septal ablation for hypertrophic cardiomyopathy10;
Guiding the biopsy of cardiac masses14;
Pacemaker lead endocarditis for diagnosis as well as assessment of whether percutaneous or surgical lead extraction is appropriate15;
Evaluation of cardiac function after cardiac surgery via a modified mediastinal drain;
Diagnosis of arrhythmogenic right ventricular cardiomyopathy.16
Currently AcuNav ICE catheters are single use and cost approximately 2100 euros. Analysis in the USA has shown that the overall costs of using ICE and TOE for monitoring ASD closure were similar (US$33 563 vs US$32 812, p = 0.4).17 The extra cost of the ICE catheters is offset by performing the procedure under local anaesthesia avoiding the cost of the anaesthetist and the anaesthetic drugs. Savings are also made on the cost of the TOE operator and equipment as well as shorter hospital stays. Additionally, the catheter laboratory time saved in performing the procedure under ICE, and the extra inpatient bed space available to admit other patients for procedures, may allow revenue to be generated by performing additional catheter laboratory procedures. Analysis in our own centre has shown that the cost difference between ICE and TOE is marginal and the difference for patient turnaround and effect on list scheduling is considerable. Our current practice is therefore to routinely offer ICE guidance for all patients undergoing ASD and PFO closure.
The development of ICE has found a particular role for guiding the percutaneous closure of PFOs and ASDs. The advantages of ICE over TOE include clearer image quality, shorter procedure times and reduced need for fluoroscopy and reduced radiation doses. The main disadvantage is the initial cost of the single-use catheter, though this may be offset by reduction in the need for additional staff, reduced bed stay and increased catheter laboratory turnover and efficiency. The small size and versatile nature of the ICE probe has led to its use in a variety of electrophysiological, interventional and diagnostic roles. If the current trials on the role of PFOs in cryptogenic stroke and migraine support PFO closure, ICE will prove the perfect tool to help tackle the increased demand with the ability to perform the procedures as a day case under local anaesthesia.
Competing interests: None.
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