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The Argument for Aggressive Coiling of Aortopulmonary Collaterals in Single Ventricle Patients

By Herbert J Stern MD, FAAP, FACC, FSCAI
Pediatric Cardiology Expert Witness Specializing In Adult And Pediatric Congenital Heart Disease
Aortopulmonary collateral vessels are extremely common in single ventricle patients. We present the rationale that these vessels are not innocent bystanders and can lead to significant hemodynamic, neurohormonal and mechanical perturbations ultimately leading to ventricular dysfunction.

Aortopulmonary collaterals (APCs) are present in up to 80% [1, 2, 3, 4] of single ventricle patients undergoing pre-Fontan catheterization. It has been theorized that hypoxia is a potent stimulus for their development [5]. There is generally no consensus as to their impact in the mid-long term course of single ventricle patients. Bradley et al. argued that their presence in the immediate post-operative period following Fontan repair had no impact on duration of pleural effusions or resource utilization in terms of length of mechanical ventilation, ICU stay or hospital stay [6], prompting many centers to ignore these vessels at the time of their pre-Fontan heart catheterization. While their findings were counter-intuitive, even to the authors, this single study has been used as justification to ignore aortopulmonary collaterals not only at the pre-Fontan catheterization but long-term in a number of centers [informal polling and personal communication]. In those centers performing catheter occlusion of APCs, the criteria for occlusion is subjective or based on hemodynamic data which has not been validated in terms of defining what is significant APC flow. MRI assessment of pulmonary artery and pulmonary vein flow using phase contrast velocity mapping [7] is a promising and accurate modality for calculating APC flow but is expensive, time consuming and usually requires general anesthesia. Finally, the long-term impact of permanently occluding vessels off the subclavian arteries and thoracic descending aorta is unknown. Given this backdrop, what is an interventionalist to do when he/she encounters APCs during the pre-Fontan catheterization?!

It is well known that chronic volume loading raises filling pressures, induces adverse remodeling, triggers apoptosis and activates neurohormones all of which conspire to cause progressive ventricular dysfunction. This pathophysiologic cascade has been well-described in the adult literature [8, 9] and there is compelling data to suggest that these same mechanisms apply to the single ventricle patient [10, 11, 12]. Additionally, Ascuitto et al., demonstrated that competitive flow and pressure elevation from APCs can lead to dramatic energy losses resulting in elevated filling pressures and decreased cardiac index in a hydrodynamic model further implicating APCs as pathologic entities [13].

Confusing matters further, the anatomy of APCs has been poorly described in the literature and therefore the techniques to effectively occlude these vessels have been sub-optimal. It is critically important to understand that arteries arising from the subclavian arteries (including the internal mammary arteries, thyrocervical trunk, lateral thoracic branches, etc.) and intercostal arteries normally have extensive connections between them (Figure1). Occluding only the origins of these vessels, which have APCs arising from them, is inadequate in occluding APC flow as distal feeder vessels will always revascularize them. The entire length of the feeder vessel, when applicable, needs to be occluded to prevent this phenomenon from occurring (Figures 2-5). This task has been simplified by the availability and use of coaxial microcatheters (Tracker-Target Therapeutics, Fremont, CA; Progreat-Terumo Interv. Systems Somerset, NJ-) and platinum microcoils (Micronester, Cook Inc.-Bloomington, IN; Target platinum coils, Target Therapeutics -Fremont, CA).

While methods to calculate APC flow need to be refined so that potentially important branches off the aorta are not occluded, we believe that the presence of APCs in single ventricle patients is detrimental to optimal ventricular function. Until those methods are developed, parameters including oxygen step-up and pressure elevation in the pulmonary arteries, upper lobe filling defects suggesting competitive flow (Figure 6), elevated ventricular end diastolic pressures, size of APCs, density of pulmonary capillary blush and pulmonary venous return (Figure 7) should all be considered when deciding to occlude these vessels. There is a disturbing trend towards gradual attrition in single ventricle patients partly due to ventricular dysfunction [14]. In addition to other well-described anatomical determinants for long-term survival [15], attention to elimination of APC flow is important and often overlooked. Using the rationale that early Glenn shunting (around 4 months) is preferred to unload the single ventricle and prevent deleterious long-term consequences [16], aggressive coiling of APCs should be viewed in this same light. Despite our opinions however, multicenter randomized prospective double-blind studies are needed to evaluate the impact of APCs on neurohormonal activation, volume loading, filling pressures, ventricular function and correlation with adverse consequences including protein losing enteropathy, atrial arrhythmias, pleural effusions, ascites and death.

References:

1. Ichikawa H, Yagihara T, Kishimoto H, et al. (1995) Extent of aortopulmonary collateral blood flow as a risk factor for Fontan operations. Ann Thorac Surg 59:433-437
2. Kanter KR, Vincent RN, Raviele AA. (1999) Importance of acquired systemic-to-pulmonary collaterals in the Fontan operation. Ann Thorac Surg 68:969-975
3. Spicer RL, Vzark KC, Moore JW et al. (1996) Aortopulmonary collateral vessels and prolonged pleural effusions after modified Fontan procedures. Am Heart J 131:1164-1168
4. Triedman JK, Bridges ND, Mayer JE, et al (1993) Prevalence and risk factors for aortopulmonary collateral vessels after Fontan and bidirectional Glenn procedures. J Am Coll Cardiol 22:207-215
5. Yu CH, Chen MR. (2008) Clinical Investigation of Systemic-Pulmonary Collateral Arteries. Pediatr Cardiol 29:334-338
6. Bradley SM, McCall MM, Sistino JJ, and et al. (2001) Aortopulmonary Collateral Flow in the Fontan Patient: Does It Matter? Ann Thorac Surg 72: 408-415
7. Valsangiacomo ER, Barrea C, Macgowan CK, et al. (2003) Phase-contrast MR assessment of pulmonary venous blood flow in children with surgically repaired pulmonary veins. Pediatr Radiol 33:607-613
8. Haas GJ, Leier CV. (2009) Are Hemodynamic Parameters Predictors of Mortality? Heart Failure Clin 5:229-240


ABOUT THE AUTHOR: Herbert J Stern MD, FACC, FSCAI
Dr. Stern is a board certified pediatric cardiologist specializing in congenital heart disease in adults and pediatrics, therapeutic cardiac catheterization with special interests in hybrid (surgical/catheter) procedures; in stroke and migraine patients who have been diagnosed with a patent foramen ovale; congestive heart failure management, patients with single ventricle physiology and pulmonary hypertension.

Copyright Herbert J Stern MD, FAAP, FACC, FSCAI

Disclaimer: While every effort has been made to ensure the accuracy of this publication, it is not intended to provide legal advice as individual situations will differ and should be discussed with an expert and/or lawyer.For specific technical or legal advice on the information provided and related topics, please contact the author.

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