KING AND MILLS CARDIAC UMBRELLA

King and Mills were the first to introduce percutaneous closure technique for atrial septal defect when they designed a closure device which was first implanted in dogs in 1972.⁴ This device was made of paired Dacron-covered stainless steel umbrellas collapsed into a capsule at the tip of a catheter. ASD closure was initially attempted in dogs by punching atrial septal defects, and complete closure of ASD and endothelialisation was noted during follow-up. Following experience in canine models this technique was extended to human studies.⁵ Stretched ASD diameter was measured by sizing balloon and a device larger than 10 mm of stretched diameter was deployed. The device was delivered through femoral venous cut down. The catheter tip was positioned in left atrium through ASD. The device is extruded in left atrium and catheter withdrawn into right atrium. The distal umbrella is fixed against left atrial side and right-sided umbrella deployed in right atrial side of septum with a special locking mechanism both umbrellas were fixed. Then obturator wire is withdrawn releasing the device. Successful implantation was done in 50% of patients.⁵ Later with help of Edward laboratories, some modifications were made and the device was successfully implanted in humans in 1975. It was a paired umbrella-type device with six stainless steel struts ending in hooks. Despite initial positive results, the device was not used again due to lack of self-centring and irretrievability and the need for surgical removal in case of suboptimal device placement. Also requirement of large sheaths of 23 F due to a bulky device and complex manoeuvrability did not help. However, the King and Mills device paved the way for newer technology in ASD devices.

RASHKIND SINGLE UMBRELLA

Almost at the same time of King and Mills work, Rashkind developed a different type of ASD device which had a single umbrella consisting of medical grade foam covered with three stainless steel ribs attached to central hub.⁶ He modified it into six ribbed device with three hooks attached to alternate ribs. The central hub was attached to 6-F catheter. The umbrella was held by five arms on the tip of guide wire. Rashkind’s device did have a centring mechanism and, by retracting the guidewire through the septal defect, its five arms could bend to produce an outward curve. The umbrella bends and hooks onto the left atrial side of the septum and, by further retracting the guidewire, the delivery system unlocks from the umbrella. This centring mechanism required a 14-F (or) 16-F sheath. After encouraging animal experiments, this device was deployed in 23 patients in whom only 60% was successful. Due to poor outcomes Rashkind developed a double umbrella version of the device, but, pending clinical trials, the device did not reach clinical use. Several disadvantages, such as the requirement of a large sheath and instantaneously permanent positioning due to anchoring hooks and the inability to reposition, might have discouraged further use. Sometimes the device got attached to mitral valve, requiring surgical intervention. Also complete endothelialization and damage to adjacent structures after successful implantation requiring surgical intervention discouraged its use. But the double-disc version was picked up by other investigators, and after further modifications the device was renamed as Lock Clamshell Occluder.

LOCK CLAMSHELL OCCLUDER (CR BARD INC, MURRAY HILL)

Lock et al., co-investigators in the development of Rashkind double umbrella, made certain modifications with a spring in the middle of all four umbrella arms and renamed it as the Lock Clamshell Occluder device.² These springs helped by holding both umbrellas against each other, producing clamshell-like appearance. The device was made of non-hooked stainless steel frame covered with Dacron and delivered through an 11-F sheath. Although device had technical improvement and retrievability, 40–84% of them had arm fractures, device embolization, residual shunt and new stroke. Hence it went out of clinical use. Later device was modified due to proven superiority compared with older devices. The device was modified into CardioSEAL and then later STARFlex.

BUTTONED DEVICE (CUSTOM MEDICAL DEVICES, ATHENS, GREECE)

Sideris et al. introduced buttoned ASD device in 1990.¹³ A number of modifications led to four generations of left-sided occluders and counter occluders with different shapes. The button occluder was a squared polyurethane disc with an x-shaped Teflon-coated stainless steel frame and a button that is a loop knot and counter occluder containing buttonhole and Teflon-coated steel wire in its foam disc. When both discs were deployed, a button on left atrial side was pulled through right-side button hole to connect them. The device required an 8-F to 9-F loading sheath. None of the four generations of devices had self-centring mechanism. Hence a centring mechanism introduced because of demand. Effective closure was achieved in 90% defects, as the device got pulled through in cases of large defects. Extensive single and multiple clinical trials were done between 1990 and 2001, and the buttoned device was found feasible and effective in closing atrial septal defects. Initial implantations were done in piglets and later in humans. During initial implantation in a child, after buttoning the device during deployment, it spontaneously dislodged due to tearing of the tie between the occluder and counter occluder due to excessive force used while buttoning. The first three generation of devices had a problem of unbuttoning post-procedure and subsequent surgical retrieval. This led to device modification, replacing silk tie with nylon tie and a radio-opaque marker on the button so that no excessive force can be used while buttoning. Further refinements were made, such as incorporation of additional nylon thread, reducing eccentricity of the buttoning and converting it into a straight one; this improved fourth-generation version could be directly loaded onto the delivery sheath, and an over-the-wire delivery technique was developed. Despite incidents of fewer unbuttoning and fewer residual shunts, these problems were a cause of concern. Despite widespread clinical experience, the device never received FDA approval and was discontinued.

ATRIAL SEPTAL DEFECT OCCLUDER SYSTEM (GERMANY)

A European ASD closure device called an atrial septal defect occluding system (ASDOS) 2001 was developed in 1990 by Babic et al. Device went through several modifications and finally got licensed in 1994.⁷ Two separate umbrellas with polyurethane frames and nitinol arms were implanted through an 11-F sheath by forming an arterio-venous loop. The first umbrella deployed in the left atrium. A metal plug was used to prevent distal migration and for centring the device, after which it was pulled into right atrium. Another catheter with a screw mechanism was used to deploy the second umbrella. Two umbrellas were screwed after correct positioning using a metal plug. Despite obtaining CE approval in 1995, the device was abandoned in 2001 in view of high incidence of frame fractures, Thrombus formation and atrial wall perforation. However, introduction of nitinol frame led to era of devices with reduced risk of fracture and ability to reshape after deployment.

NITINOL DEVICES—TECHNOLOGICAL LEAP

In 1962 William Buehler (US Naval Labs) found that an alloy containing equal amounts of nickel and titanium exhibited a strange character which allowed catheter-based devices to take a big step forward. The property of assuming a distorted shape inside the delivery catheter and regaining the preformed shape when deployed led to its use for ASD closure. These alloy materials have proven useful in devices with better centring characteristics and considerably lesser risk of stress fractures. This is considered a technological leap with unlimited boundaries in device engineering.

MONODISK

Pavcnik et al. (1993) designed a Monodisk⁸ (Figure 7.1) consisting of a single disc of stainless steel rings constructed from spring coil wire covered by double-layered nylon mesh with three hollow pieces of stainless steel wires sutured onto the right side of the device. Three strands of monofilament nylon pass through each of the hollow wires. The nylon thread passes through the delivery catheter. The entire device can be loaded over 9-F sheath. Once the device was positioned it was deployed by cutting the wires. The device was successfully implanted in dogs and subsequently in two patients. But no clinical trials were planned and pending long-term studies the device was discontinued. Pavcnik further introduced a modified version like a biodisc and double biodisc, but it fell out of favour for unknown reasons.

MODIFIED RASHKIND PDA UMBRELLA DEVICE

The Rashkind PDA umbrella device was modified by bending the arms of the device such that there is better apposition of the device to the atrial septum. The device was used to close four ASDs, two of which were removed with subsequent surgical closure. The use of this device for ASD closure was questioned and subsequently went out of use.

ANGEL WINGS (MICROVENA CORP, WHITE BEAR LAKE, MINNESOTA, USA)

In 1993 Das et al. developed a new device called the DAS Angel Wings device which had two polyester fabric-covered square frames and a nitinol frame with mid-point torsion spring eyelets.¹¹ The nitinol frame served as a torsion spring to provide a folding mechanism. A circular hole with a diameter equal to one-half the size of the disc was punched from right disc, with the margins sewn to left disc forming a conjoined ring, the centring mechanism. Device sizes ranged from 12 to 40 mm and were delivered transvenously through 11-F or 12-F sheath. Most device required 12-F sheath. Device did not cross phase II trials and was modified to become the Guardian Angel Wings device, but the device was shelved. Device malpositioning during deployment was the main reason for its discontinuation.

CARDIOSEAL AND STARFLEX

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