November 21, 2014

Innocentive Theoretical Challenge: Heart Implantation of a Medical Device

I must say that I am not authorized to share the details of the challenge, as per the agreement signed by me. Yet you can have a glimpse of the overall structure of the problem here. Once you have seen the salient points you may now look for the solution that I submitted to them way back in 2010. 

I am free to publish my proposed solution, which also sheds some light on the deeper requirements for the leadless device. However, I am omitting "My Solution: • Introduction and Background: " part, as it may divulge  information from the challenge itself. The truncated portion that appears below has not been altered post-submission, even though I could find some faults retrospectively. Below is the un-altered submission. 

"• Detailed Description of the Solution:

As is conventional with these procedures, the patient is venepunctured (using aseptic and anesthetic precautions) in the groin and the femoral vein is accessed.  The Leadless Device is introduced retrogradely to the inferior vena cava and thence to the right atrium of the heart. All these procedures should be undertaken while under fluoroscopic control is assisted by echocardiographic guidance.  

The LD may be conveniently delivered to its location, discussed later, by using a fiberoptic endoscope, which in addition to ‘being guided’ by the fluoroscopic/ echocardiographic screens; can visualize the anatomy of the right atrium and the right ventricle that lie proximally. 

In a study by Fujimura et al (fig 1, =Ref 3) a 3.6 mm diameter fiberoptic endoscope (with a latex balloon) was used to study the right heart anatomy of anesthetized dogs. The distal tip was inserted into the right atrium, where the balloon was inflated with air in 5 mL increments. Thus, it seems very likely that we could explore the human heart using a fiberoptic device having a diameter of around 4mm. The endoscope will, in fact, help to locate the best anatomical co-ordinates in the right heart (ventricle) where the LD may attach (reversibly). 

The LD must be secured to the RV (septum, wall or the apex). This could be done in the following ways:

1. Modifying the LD shape (fig 1), so as to incorporate a ‘groove’ in it (fig 2) or as a ‘O’-ring at its ends (fig 2), which could act as an anchor for LD to the RV.

2. The ‘modified’ LD may then be either sutured to the right ventricular myocardium using:

a)atraumatic suture using fiberoptic guidance,
b)Better still; secure the LD, with the help of silastic rings, as is done in male sterilization.
c)An inflatable occlusion balloon (as in Foley’s catheter); that may be deflated, when necessary, for re-implantation (fig 3); BUT the volume of the balloon may interfere with the stroke output of the Right Ventricle, though that is miniscule, by physiological standards.
d)Or, depositing the device in the pocket of the moderator band (septomarginal trabecula) (fig 4)

Whichever way the LD is secured, the LD should be preferably anchored in a transversely approach, as a longitudinal placement may enable the LD to a ‘greater strain’ (RV axis; Ref 1) while the ventricle is contracting.

It is quite obvious that some coverage of anti-thrombotic episodes must be provided during the procedure. This may include low molecular weight heparin therapy or therapy by aspirin or other pharmaceutical agents, so that the implant does not initiate a thrombotic episode, due to the LD’s irregular (or, perhaps its wettable surface) surface terrain.

However, once the LD is implanted in the cardiac tissue; the irregularities in surface may, in fact, stimulate cell growth and adhesion (chronic endothelialization) (Ref 2; Patent application number: 20100063562 )

Thus, the LD will finally adapt to the cardiac tissue in a way that the LD will not be a deterrent to normal functioning of the heart.


• References and Notes: 

Ref 1: Septomarginal trabecula (also see wikipedia: http://en.wikipedia.org/wiki/Septomarginal_trabecula), the septomarginal trabecula (or moderator band))
Ref 2: Chronic endothelialization (LEADLESS TISSUE STIMULATION SYSTEMS AND METHODS)

Fig 1
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Fig 2

Fig 3

Fig 4


• Conclusion

The LD being 25mm/7mm will have no problem negotiating a catheter of 8mm diameter (24 Fr catheter). The volume of the LD (962.5 mm3 or 0.0009625 L) is too small to have any practical hemodynamical impact on the stroke volume of the Right Ventricle (5 L) which is equal to the output of the left ventricle. Moreover, the implanted payload is expected not to interfere with the right heart function hemodynamically (0.0009625 Liter of the vol. of the LD vs. 5L of cardiac output), antigenically (medical grade polymer) or thrombogenically (clotting). The non-metal, silastic ring or atraumatic sutures will not cause undue ‘electromagnetic shielding’ of any electromagnetic radiation the LD might emanate, neither would they pick up stray electromagnetic disturbances. The securing of the device by silastic ring or atraumatic sutures will keep our options open regarding the choice of re-implanting elsewhere, if needed. 

Thus it seems that the present approach is arguably one of the best approaches possible for a reversible implant of a Leadless Device onto the right chamber of the heart."

Addendum: Ref 2 link
Fig 1, Fig 2, Fig 3, Fig 4

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