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September/October 2010
Treating Coronary Artery Fistulas and Pulmonary AVMs
Transcatheter coil embolization for coronary and pulmonary arteriovenous malformations.
By Thomas A. Farrell, MD, and Ted E. Feldman, MD, FESC, FACC, FSCAI
Coronary artery fistulas (CAFs) and pulmonaryarteriovenous malformations (PAVMs) are relativelyrare but clinically important cardiovascularabnormalities that may require percutaneoustreatment. In most patients, the current preferred treatmentfor both lesions is transcatheter embolization usingtechniques that are well established in these two conditions.We present a review of CAF and PAVM treatment withemphasis on the technical aspects of transcatheterembolization.
TRANSCATHETER TREATMENT OFCAF AND PAVM
Coronary Artery Fistulas
CAFs are rare congenital malformations in which thereis a direct vascular connection from a coronary artery toa cardiac chamber, great vein, or pulmonary artery withoutan intervening capillary bed. CAF is the most commonhemodynamically significant congenital abnormalityof the coronary system and is seen in up to 0.22% ofadults undergoing coronary angiography. Most fistulasfound incidentally are small, single, and result in a leftto-right shunt. In adults, CAF may present as angina,myocardial infarction, or heart failure as a result of a stealphenomenon, with blood bypassing the distal myocardialcapillaries (Table 1).
Indications for Treatment and GuidelineRecommendations. Although spontaneous regression hasbeen documented, there are few long-term studies fromwhich to draw conclusions.1,2 CAFs have a class II indicationfor device occlusion therapy. American College ofCardiology/American Heart Association (ACC/AHA)consensus guidelines (based on level of evidence C) indicatethat a large CAF, regardless of symptomatology,should be closed via either a transcatheter or surgical route after delineation of its course and its potential tofully obliterate the fistula. Furthermore, a small-to-moderateCAF in the presence of documented myocardialischemia, arrhythmia, otherwise unexplained ventricularsystolic or diastolic dysfunction or enlargement, or endarteritisshould be closed via either a transcatheter or surgicalapproach after delineation of its course and its potentialto fully obliterate the fistula. Patients with small,asymptomatic CAF should not undergo closure of CAF.3
Small asymptomatic fistulas do not require a specificprocedure for closure simply because they are detectedincidentally (see Relative Contraindications to TranscatheterTreatment of CAF sidebar). However, closure of even smallfistulas may be recommended (1) if the there is a risk ofendocarditis, or (2) if longitudinal follow-up is not feasible,or (3) if the patient is undergoing an invasive procedurefor some other cardiac problem. In children, electiveclosure of any CAF that remains clinically apparent past 3to 5 years of age, even if the patient is asymptomatic, isrecommended.4
Of note in older patients, if the proximal coronaryartery has become grossly enlarged, closure of distal fistulashas been associated with a high incidence of latethrombosis of the permanently dilated and tortuousproximal coronary artery.5 Closure of the fistula results inrelative stasis in the giant coronary artery, and this is likelythe etiology of late thrombosis. If the older patient isasymptomatic, the best course of action in this scenariois unclear because late thrombosis may be no better thanlate development of coronary steal syndrome.
Transcatheter occlusion of a CAF with detachable balloonswas first reported by Reidy et al in 1983,6 whoalso reported occlusion of a CAF with coils in 1991.7Because of its minimally invasive nature and high successrate, transcatheter closure with either pushablecoils4,8-11 or an Amplatzer device (AGA MedicalCorporation, Plymouth, MN) is considered the procedureof choice in most patients requiring treatment. Inexperienced hands, residual leaks are rare (< 5%) andare usually amenable to retreatment. In our experience,the majority of patients are satisfactorily and safely treatedwith transcatheter coil embolization.
Technique for Coil Placement. Systemic heparin administration(100 units/kg) is recommended after the femoralvenous and arterial accesses are established. The choiceof catheter system is as important as that of coil type andsize in terms of facilitating precise coil placement in fistulasthat are often dilated and tortuous. We have used a triaxial (3-F/5-F catheters via an 8-F guide catheter) systemfor more stability and precise placement in tortuousvessels. A coaxial (5-F catheter/8-F guide) system shouldsuffice in less tortuous anatomy. A useful test of cathetertip stability is to advance the coil pusher wire (0.016 inchesin the case of microcoils, LLLT [Newton] guidewire for0.035/0.038-inch coils) to the tip of the catheter first as atrial run to gauge the likelihood of catheter displacementor backing out. We typically use pushable, as opposed todetachable, coils because they are less expensive and easierto stock in a shared interdepartmental inventory.Collaboration with interventional radiologists for choiceand deployment of coils is recommended for cardiologistswho do not implant coils regularly.
The choice of 0.018-inch versus 0.035-inch coils isdependent on the delivery catheter size, which in turn isdependent on the tortuosity of the fistula. We oversizecoil diameter by 20% relative to the CAF diameter. Nestercoils are composed of a platinum wire base and allowformation of a more compact coil ball than comparablestainless steel coils (Figure 1A). Tornado coils are madewith either the smaller end or larger end (LEF) deployedfirst (Figure 1B). With the delivery catheter in place, thecoil is deployed by using a gentle tapping motion on thecoil pusher, which permits visualization and control ofthe proximal coil end until it exits the catheter. We aimto create a compact coil ball or plug in the fistulabecause we believe that this promotes more rapid andcomplete occlusion (Figure 2).
Patience is essential while waiting for cessation offlow after embolization. Angiography performed afterembolization may reveal additional smaller fistulas dueto change in flow dynamics caused by embolization—which may not require immediate treatment. Placement of a covered stent across the origin acoronary fistula may be the appropriatechoice in adult patients withcoexisting coronary artery disease.9,10
Amplatzer Occluders. The mainadvantage of using an Amplatzerdevice is speed in deployment.However, its relative bulk and that ofits delivery system may prevent its usein smaller and more tortuous fistulas.This challenge is greatly facilitated byinitially advancing a guidewire throughthe fistula, where it is snared on thevenous side. This through-and-throughaccess can then be upsized, allowingthe use of a larger and more stableplatform for precise deployment ofthe plug device.11,12 Oversizing of the vessel by 30% to 50%is recommended for the current Amplatzer Vascular PlugII (AVP II). Deployment is a combination of unsheathing thedevice and then unscrewing the delivery wire. Advancementof the unsheathed device is not recommended.
Complications of Embolization. Complications associatedwith embolization include migration of coils, transientST-T wave changes,13 transient arrhythmias,14 distal coronaryartery spasm, and fistula dissection.8 Air embolizationmay occur, and careful sheath and delivery cathetermanagement is essential. Interventionists should befamiliar with the use of loop snares to retrieve coils thathave migrated through a fistula (Figure 3).
Surgical Treatment. Up to 30% of patients with CAFhave an additional congenital anomaly, most commonlytetralogy of Fallot, patent ductus arteriosus, and atrialseptal defect.15 Surgical closure is the preferred approachin patients who are undergoing operative repair of othercardiovascular problems. The surgical approach can alsoallow for reduction in the size of very large aneurysmaldilations of either the fistula or the proximal coronaryartery.16,17
Follow-Up. Most of the data on long-term coronarypatency are based on patients who have had surgical closureof CAF. The long-term patient outcomes after fistulaembolization remain unknown, but intermediate-termresults reveal persistent coronary artery dilatation inmany of these patients.5 Because there is little informationon the natural history of the patency of aneurysmalcoronary arteries after transcatheter embolization, it maybe wise to evaluate myocardial perfusion on follow-up. Based on limited experience, long-term anticoagulationwith at least one antiplatelet agent is suggested inpatients with aneurysmal dilatation, and some cardiologistssuggest warfarin.4,5,18
Pulmonary AVM
PAVMs are defined as direct, low-pressure, artery-toveinconnections that result in a right-to-left shunt. Theyare rare, usually congenital abnormalities, with a strongassociation with hereditary hemorrhagic telangiectasia(HHT), an autosomal dominant disorder in whichapproximately one-third of patients develop PAVM(Table 1). If untreated, complications of PAVM mayoccur in up to 50% of patients; these include transientischemic attacks, paradoxical embolization, massivehemoptysis, or hemothorax. The goals of treatment arethreefold: (1) improvement of dyspnea/hypoxemia, (2)prevention of lung hemorrhage, and (3) prevention ofneurologic sequelae.
Diagnosis. Initial screening with contrast echocardiography,followed by measurement of PaO2 while breathing100% oxygen, is the optimal screening procedure foridentifying patients with PAVM, whereas screening withchest radiography and pulse oximetry alone has beenshown to be insufficient.19,20
Computed tomography, magnetic resonance imaging,and pulmonary angiography are equivalent in accuracyfor the detection and confirmation of PAVM.21-23 Inpatients with HHT, PAVMs were diagnosed as a result ofsystematic screening procedures (29%), incidental imagingfindings (15%), dyspnea (22%), or central nervoussystem symptoms (13%).
We have previously described a method to diagnoseand localize PAVM during a catheterization procedureusing intracardiac echo in conjunction with selectiveinjection of bubble contrast into the pulmonary arteries.This allows for the rapid and accurate diagnosis of PAVF when a patent foramen ovale is sought but not foundand for the exclusion of associated PAVF when a patentforamen ovale exists.24
Coils. Pulmonary angiography with measurement ofpulmonary arterial pressures is typically done first. Thecatheter is then exchanged for a coaxial 80-cm, 7-F/100-cm, 5-F catheter system. The use of a guiding catheteravoids elongation of the coil during deployment, resultingin a more tightly packed mass of coils and bettercross-sectional occlusion of the vessel. More importantly,guiding catheters provide enhanced stability and controlduring coil deployment.
Although detachable coils offer a more controlled deliverywith a lower risk of coil migration, they are moreexpensive. White developed a technique of using coaxialcatheters to deliver less-expensive pushable coils, whichprovides safe and controlled deployment. These operatorsuse a 5-F coil delivery catheter within a 7-F guiding catheter.White states, “It is not the coil that is so important, but theuse of coaxial or triaxial catheters that allow for preciseplacement of the coil.”25 Cross-sectional occlusion is essentialfor embolization of PAVM and this is achieved using theanchor or scaffold coil technique. The anchor techniqueentails deploying the initial segment of coil in an adjacentvessel or side branch as an anchor before deploying thebulk of the coil in or adjacent to the PAVM itself.25
White also recommends that guidewires always bewithdrawn from catheters under saline flush to preventair embolism via the catheter. In addition, regular flushingof catheters and systemic periprocedural heparinizationto reduce the potential for embolization of particulatematter or clot is advocated.25
Amplatzer Device. The AVP II is a redesigned version ofthe original AVP, with the important modifications ofhaving a finer, more densely woven nitinol frame and alsoa multisegmented design. The device is available in sizes ranging from 4 to 22 mm in 2-mm increments, and canbe delivered through guide sheaths between 4 and 7 F,depending on the device size. The Amplatzer device producesalmost immediate complete closure, and recanalizationhas not been reported. The device is available in arange of five sizes, from the 4-6–mm device for small vesselsto the 12-14–mm device for large vessels, and requiresdelivery through 5- to 7-F sheaths, allowing its use insmall infants and neonates.26 Multiple devices can bedelivered through a single sheath, and the device can berepositioned or retrieved until the operator is sure ofproper positioning. A disadvantage of the device may beits relatively long length, which may preclude its use ifthe target vessel is short (Figure 4).
Hart reported successful embolization in 75% of 161PAVMs using AVP alone. Complete and rapid occlusion offeeding vessels was easily achieved at the site of arteriovenouscommunication without complication. Particularlysmall or tortuous feeding arteries supplying 27 complexand 14 simple PAVMs were occluded with coils. Therehave been no documented instances of recanalization onfollow-up.27
Detachable Occlusion Balloons. Before their removalfrom the United States market in 2002, detachable latexand silicone occlusion balloons were a useful and effectivemethod of treating PAVMs. Follow-up studies showed alow recanalization rate despite early balloon deflation.
Complications. Complications of transcatheter PAVMembolization include infections, lung infarction, pleural painand effusion, air embolism, cardiac arrhythmia, transientangina, and paradoxical embolization with cerebral infarction.28-31 Felix et al describe a patient who had a strokeimmediately after embolization treatment of a PAVM andrecommend antiplatelet drug use, such as low-dose aspirin,as the short-term primary stroke prevention after endovascularPAVM embolization.32
Outcomes. Trerotola et al report that outpatient singlesession (86%), with most patients discharged after a 2-hour period.33 Recurrence is rare (< 2%), with recanalization being embolization was achieved in 44 of 51 patientsthe most common mechanism of PAVM reperfusionaccounting for 88% of cases.34 Increased feeding arterydiameter, low number of coils, use of oversized coils, andproximal coil placement within the feeding artery are associatedwith reperfusion. Distal coil placement facilitates repeatembolization if reperfusion occurs. Repeat embolotherapyfor reperfused PAVMs was technically successful in 94% ofcases. In the remaining 6% of cases, insufficient feedingartery length prevented safe repeat treatment.35
Follow-Up. Clinical and anatomic evaluation after PAVMembolization is important to detect persistent or reperfusedlesions and enlarging lesions, with the latter morecommon. Patients with persistent, reperfused, or enlarginglesions often have symptoms, but many patients may beasymptomatic. More frequent assessment, such as annualpulse oximetry, contrast echocardiography, and chest radiographyhave been suggested to improve detection beforethe onset of symptoms.26,34
All patients should be assessed for other manifestationsof HHT before treatment, and they are best followed inone of the 20 HHT centers worldwide (www.hht.org).
SUMMARY
Transcatheter embolization of CAF and PAVM is effectivein reducing both anatomic shunt fractions and inreducing complications. The technique of transcatheterembolization is well tolerated and has a low complicationrate. Collaboration with interventional radiology/neuroradiologyfor choice and deployment of devices isrecommended.
Thomas A. Farrell, MD, is with the NorthShore UniversityHealth System in Evanston, Illinois. He has disclosed that heholds no financial interest in any product or manufacturermentioned herein. Dr. Farrell may be reached at(847) 570-2160; tfarrell@northshore.org.
Ted E. Feldman, MD, FESC, FACC, FSCAI, is Director ofthe Cardiac Catheterization Lab at Evanston Hospital inEvanston, Illinois. He has disclosed that he holds no financialinterest in any product or manufacturer mentionedherein. Dr. Feldman may be reached at (847) 570-2250;tfeldman@northshore.org.
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