Life With the Medtronic Closed Loop System for Diabetics

Medtronic MiniMed 670G

There are an estimated 86 million diabetics in the U.S. Of those, about 3 million have Type I Diabetes, a disease in which the body produces none of its own insulin. And millions of the Type II diabetics are on a full-insulin replacement. They spend countless hours injecting themselves and pricking their fingers to check their blood sugar, often chasing what can seem like an endless loop of highs and lows. Now there’s at least a partial solution.  Officially, it’s the Medtronic MiniMed 670G. Unofficially it’s been called the “artificial pancreas” (a name the American Diabetes Association and Medtronic would prefer you didn’t use since it overstates the system’s capabilities). Medtronic bills it as “the world’s first hybrid closed loop system; the first [and so far only FDA approved] system that constantly self-adjusts to automatically keep glucose levels in target range.”

Old Tech + Old Tech = Breakthrough

The two major components of the MiniMed System, the insulin pump and the continuous glucose monitor (CGM) are not new. The first wearable insulin pump was invented by Dean Kamen back in 1973 and came to market three years later. The first practical CGM came from MiniMed (later purchased by Medtronic) in 1999. So why has it taken so long to get these two devices to work with each other? The short answer is technology. Putting the two of them together required the development of complex algorithms that just didn’t exist before, and a microprocessor-based platform capable of making the connection. You can read some of the development history here.

First approved by the FDA in the fall of 2016, Medtronic brought it to market in spring of 2017.  The launch has been so successful it has brought on growing pains for the company in terms of production and customer service (more on that later). It was aimed at Type I diabetics who cannot create any insulin on their own. It’s now being used by some Type II’s on full insulin replacement. I’m one of them. I’ve been living with it for a couple of months now and the reality is that it’s an incredible system, but as with any first-generation technology, it still has its warts. But on balance it has made things much easier to control my blood glucose levels than using the traditional meter, finger stick, and sliding insulin dosage methods.

How Does It Work?

The Medtronic MiniMed 670G is the first system in which a CGM can talk to an insulin pump. But notice carefully that its called a Continuous Glucose Monitor and not a Continuous Blood Glucose Monitor. That’s because, unlike the traditional finger stick that draws blood, this measures glucose in the interstitial fluid that lies just under your skin. And so the readings will almost never match those from the finger stick, but they do come close. These two devices can talk to each other. Specifically, the information from the CGM is fed to the pump which has a smart chip and determines the correct insulin dosage on almost a minute by minute basis based on the patient’s programmable targets. To handle mealtime, the user can set the pump to deliver a before or after meal bolus based on expected carbohydrate intake.

The first component is the insulin pump. Initially, your Medtronic trainer will work with your diabetes professional to program the device. It begins with a reservoir of insulin which can hold roughly a three to four day supply. Medtronic’s system comes with two consumables: a reservoir with a built-in needle to draw the insulin from a vial (you’ll need to order the insulin from your pharmacy or mail order provider), and an infusion set which you attach to the reservoir after you fill it. Medtronic MiniMed 670GThe infusion set includes tubing and a plastic needle that you insert into your body with a device Medtronic calls a “serter.” There’s also a waterproof adhesive patch so you can detach the tube to suspend insulin delivery, take a shower, then reattach the tube. There are a number of options in the programming to best handle the individual needs of the patient, even more options when it’s hooked to the CGM. The two devices should be positioned to be able to communicate, but not too close together.

Medtronic MiniMed 670G
Guardian 3 Transmitter and Sensor

The second component is really two pieces, the CGM which consists of a rechargeable transmitter and a sensor that’s supposedly good for about 6 to 7 days. While using the infusion set for the pump is a relatively straightforward affair, attaching the transmitter and sensor is a bit more complex (the instruction book lays out about a 20 step process). But it really only takes a short time to get used to it.

When you start up the transmitter and new sensor, it takes a little time to find the pump, then almost two hours to “warm up.” After that, you need to do a finger stick to calibrate the CGM, a process you’ll repeat every 12 hours at a minimum, but sometimes more often depending on quirks in the algorithm and your own blood sugar trends.

Medtronic MiniMed 670G
670g in Auto Mode

The system provides a base level of insulin (basal) throughout the day, based on your settings and the readings from the CGM. Your health care professional will program the best settings for you when you get started. And you augment that before meals with a bolus (the equivalent of a short-term shot) just as you did before using the system. When things are working well, the system is in Auto Mode and a blue shield displays your current glucose value.



Medtronic MiniMed 670G
670g in Safe Mode

When the system is not quite happy with what’s going on, say you need to calibrate the sensor, or the algorithm wants a new blood glucose reading, you’ll see the Safe Mode screen until you put things right again.





It’s important to remember that this is still first generation technology. So you shouldn’t be surprised when it does some peculiar things. Like waking you up in the middle of the night to check your blood glucose levels for no apparent reason. It happened to me at 5:30 one morning even though my blood glucose had been stable for hours at a respectable 109 and the next calibration wasn’t due for another five hours. The Medtronic folks attribute it to the algorithm and the conversation between the CGM and the pump. I will also say this now happens less frequently than it did when I started using the system.

There are other alerts, some of which you can control, others you can’t, like an alarm before you hit a low or a high. The system can be very demanding, with increasingly loud beeps when you delay calibrating it. Sometimes they are useful. But if you’re in a theater, or driving your car, they can be infuriating.

The people at the 24/7 MiniMed 670G hotline are generally quite knowledgeable, though the wait times can be long, and the questions they ask to get you started can be tedious, especially if you are on the third or fourth call to resolve the same problem. I ran into one problem the customer support folks called the Auto-Mode Loop. When this happens, the system will ask you for a fresh finger stick within minutes after you’ve already done one and will do it ad nauseam. One tech told me to take it out of Auto mode for ten minutes. Another said for thirty minutes, another for three hours. In frustration, I took it out of Auto Mode for 12 hours and a month later the problem has yet to return.

You have to have some sympathy for Medtronic. Because of the way the FDA approves devices, once it’s on the market, you cannot alter it without starting a whole new application process. That means no over-the-air software or firmware fixes, only workarounds.

User Hostile Software

In order track how you are doing, Medtronic has created CareLink software. When it works it will take the data from your blood glucose monitor and your pump and give you a comprehensive report on how you are doing, which you can share with your healthcare team. The problem, at least based on my experience, is that the software is the absolute antithesis of “user-friendly.”

Carelink does not support many of the major browsers, including Google Chrome and some flavors of Microsoft Internet Explorer. It took me more than an hour with their tech support folks to get it up and running. And even then, they had me install a special version of Firefox. And I had to change my screen resolution, which totally screwed up everything else displayed on my computer. Medtronic claims the problem is that CareLink was written in the Java programming language, which is now unsupported by those other browsers. After all that work, I was able to upload the data. But to do it again, I have to again change my screen resolution and browser. Not fun. But if you can get it working, it does generate great reports. Many diabetes professionals also have the software, so you can bring your pump and meter to them and get this whole thing done in minutes instead of hours.

The Raw Deal for Medicare Patients

Many private insurance plans will cover the MiniMed 670G. That includes the pump, meter, transmitter, sensors, and consumables such as infusion sets and reservoirs. But not Medicare. Even though the whole system has been approved by the Food and Drug Administration, that’s still not good enough for Medicare, which claims that because of the requirements for finger sticks, it is not as good as other CGMs such as those from Dexcom and Libra. I spoke with a Medicare official who basically did not understand the difference between what the MiniMed system can do and what a conventional CGM can do.

Fundamentally, other CGMs are measurement devices. That’s all they do. The Medtronic Guardian Link transmitter and sensor is a communications device that instructs the pump on how much insulin to deliver. That’s a huge difference. And so far Medicare either doesn’t get it, or doesn’t care, or just doesn’t want to deal with the cost. And the costs are big. Medtronic says it is pursuing updated labeling for the Guardian Sensor 3, which the company believes will enable reimbursement to Medicare patients under the recent CMS ruling that will pay for some CGM’s. But Medtronic is not providing any prediction as to when that might happen. And in the meantime, the system remains financially out of reach to thousands, perhaps hundreds of thousands. of Medicare patients who can really use it to better control this horrific chronic disease. .

Here’s an example of the out-of-pocket costs if you were to buy this without insurance. We’ve seen the pump priced at $7249. We’ve seen the Guardian Link 3 Transmitter priced at $990. The sensors that go with it cost $50 apiece and last for 6 to 7 days (though there are hacks that will double that). So, for a Medicare patient who has to pay for the pump, transmitter, and sensors, that’s about $11,000 to get going. Fortunately, the infusion sets, reservoirs, and meters are covered. For someone on a fixed income, like the majority of Medicare patients, that puts the MiniMed 670G out of reach for the thousands or tens of thousands of diabetics for whom this breakthrough technology could enable far better diabetes control.

Does It Work?

The bottom line is that with the MiniMed 670G Hybrid Closed Loop System, I am better able to manage my diabetes than ever before, with a lowering of my AIC levels as well. And that makes it worth all the hassles. For me, it puts an end to the guesswork of just where I stand at any given moment. Did I eat too many carbs? Am I about to hit a low? The peace of mind alone is worth plenty. Though I’m not sure it’s worth $11-grand out-of-pocket.

There are two Facebook user groups just for the MiniMed 670G, the Medtronic 670G Support Group, and the Medtronic 670G Users Group. Here you will find tips and experiences from other users, including the hacks to extend sensor life. Medtronic has its own blog, the Loop Blog, but it’s quite corporate. If you search the Internet, you will find other blogs as well.

Here’s Medtronic’s introductory video:



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