Nekton

In early 1994, a random ECG check revealed a 'left bundle branch block' in my heart. In layman's terms this meant that one of the nerve paths that control heartbeat had 'carked it'! Probably due to a dissolute diver's life lived much too fully over too many years.

A cardiologist at the time explained it as, 'having lost a redundant system, that there was another parallel system still in place and working and that at some time in the vague and indefinite future I may need a pacemaker.' I continued diving, albeit more conservatively in regards to current and exertion. But in August of that year, when John Riley and I found the wreck of the 'MYOLA' off Long Reef, in Sydney, my regular diving depths increased to 160 feet. Although I was cautious there were times when I experienced 'funny' episodes at depth.

In January, 1995, after a celebratory Christmas 'drink', the 'other system'
went down. My pulse dropped to an alarming 37 and I was diagnosed with total heart block, a term used to describe the failure of the heart's nervous sheath. A pacemaker was now a life-saving necessity and after a 50 minute, local-
anaesthetic operation one was in place.

During this period I resigned myself to the end of my thirty-plus years diving career, but enquiries elicited the knowledge that I could, in fact, continue diving. The big question, of course, was under what conditions? and, more importantly, to what depth?

Shortly after my release from hospital I called the pacemaker manufacturers in Texas and spoke with one of the company's engineers. She advised me that they had dived my model to 195 feet but that they were only able to recommend the 'normal' sports limits of 140 feet.

When you have a device implanted in you that is a life-support system device
you tend to get a bit 'twitchy' about pushing it to its limits. I really wanted to know a bit more about pacemakers and depth limits, information that was difficult to come by. My commercial diving days are long gone, so deep diving depths weren't a consideration, but I was really unhappy about being stuck at 140 feet when the 'MYOLA' was twenty feet below me.

An old friend, Murray Conlon of Southern Tasmanian Divers in Hobart told me
that he'd had a pacemaker for years and regularly dived the wreck of the
'NORD', a Tasmanian wreck lying at - 140 feet! Not much help!

My luck improved when I was put in touch with Alex Watson, who runs the
Bioengineering Unit at Sydney's Prince Henry Hospital. These are the people who handle the supply of pacemakers and who have all of the technology for
service testing and checking.

I explained my problem to Alex, a diver of longstanding, who suggested that
if I obtained a small pressure pot then he would arrange a 'test dive' of sample pacemakers. Rick Poole of Pro-Diving services provided me with an excellent small portable pressure pot and test gauge and Alex and I began our series of tests.

We first test dived a pacemaker model similar to my own ten times to 200 feet, carrying out external electrical function tests following dives one, two, three and ten. In each instance the pacemaker showed no signs of malfunctioning and the test machinery printouts were quite satisfactory.

The next, and toughest test, was two dips to 300 feet, dives that bulged the
thick perspex lid on the pot and that resulted in a measurable distortion to the pacemaker case when a straight edge was applied. Even after this abuse the pacemaker still tested OK.

Our experiments were obviously too small a sample from which to draw any firm conclusions other than: That the model I am fitted with will do all that its manufacturers claim for it: That their conservative suggested limits are quite safe; and that there's a considerable safety margin, or fudge factor, built in.

I am indebted to long time diver and all round good guy, Alex Watson for his
invaluable help in reassuring me that the small watch-sized unit implanted in my left breast can keep me ticking over at least as far down as the 'MYOLA'. It's 'heartening' to know!

Pacemakers - An Update

Since writing the above story in 1996, there have been some interesting developments in the pacemaker story, the chief of which had some serious, if not deadly, consequences.

Battery life in a pacemaker is about 5-7 years as it delivers its tiny continuous pulses down the wires embedded into the heart muscle. Checked every six months or so, when the unit's output voltage tapers to a pre-set level the device is accessed surgically under local anesthetic, separated from its wires by pop-out terminals and a new unit is implanted. All routine thus far.

However, in 2000, when my unit's voltage dropped to the replacement level things started to go quite wrong and the story becomes a cautionary tale. Routine replacement took place without difficulty and I quizzed the surgeon as to the suitability of the unit for scuba diving. I was assured it was fine. WRONG! It was only my caution and scepticism that saved my life.

While I was waiting for the minor surgery to heal, I did a routine check by calling the pacemaker manufacturers in the USA, a conglomerate which had meanwhile absorbed the Texas outfit which had manufactured by old unit. I got evasive replies and a lab technician who had offered - as a fellow diver - to find some test data for me was gagged and prevented from telling me anything other than that the unit was suitable for hyperbaric treatment depths of 45 feet/ 12 odd metres.

I stopped talking to America and contacted the local distributor, fortunately encountering another technician who was a diver. He offered to make a unit available for testing, which we duly did, diving it in the medical lock of Rick Poole's, Pro Diving Services, chamber. Dived and tested to 100 feet/30 metres the unit was ok except for slight case buckling, but a dive to 170 feet crushed the case. It would have been 'goodnight McGuinness' for me had I dived the unit to my usual 50 plus metres depths.

I then set about finding the whys and how to get a suitable diving-capable pacemaker. I drew blanks at NSW's Prince Henry Hyperbaric unit and the same at Royal Adelaide. I put out feelers on the world-wide-web. No joy. I figured out the why though. Case design, an electronically welded titanium container, helium immersed and tested in a vacuum post-welding for any molecular leaks, (the ingress of bodily fluid into a unit would be potentially fatal in many cases) had not changed over the years but battery technology had improved radically. Whereas a pacemaker's volume had been almost totally taken up by battery bulk in the past, now there was a considerable gas gap as battery size shrank.

My astute occasional diving lady companion suggested I check with Dr Simon Mitchell, who was at the time running the Wesley Hyperbaric facility, in Brisbane. Simon was brilliant. He had a table of efficacy of pacemakers from various manufacturers, ranging from the very best to the mediocre in pressure-
resistant terms.

The best, a model from St Jude Medical in California, was rated to 230 feet (the Yanks are delightfully non-metric!) so I arranged a meeting with the cardiologist, assured him I wasn't going to sue his tits off, and asked for a good one. Wiping imaginary sweat from his brow he asked when? As soon as possible, I replied, and duly got a good one implanted in January 2001; one that has safely taken me to nearly 55 metres on the Aaron Ward, in the Solomons, and back and which has done many 50 metre dives in the interval.

The caution in the cautionary tale? Should you, or any of your diving acquaintances need to be fitted with a pacemaker, do your homework; understand that diving and pressure effects are not widely or well understood in the medical profession and the manufacturers have been slow in disseminating adequate information, and question closely and persistently until you see the relevant data. Remember, it's your life at stake. Well-meaning assurances are of little value if they result in your being laid out on a slab.

Born in New Zealand, Peter Fields began diving in 1961 with the inverted twin-
cylinder, 'Porpoise', single hose regulator set. Certified as a CMAS Instructor in 1969, he co-founded New Zealand's first, 'pay for tuition' dive school and worked as a commercial diver and partner in Diving Services NZ Ltd, during the early 'seventies, before joining two companions in a sailing voyage to the Southern Ocean and South America, searching for, and diving, shipwrecks. Moving to Australia in 1978, he managed the Moray-Dacor distributorship before establishing his own company, Fields Henry Pty Ltd, in 1981. The sole Australian distributor for Scubapro through until 1990, he subsequently became a partner in Pacific Commercial Diving Supply; equipment supplier to the Commercial and Military. Co-discoverer, (with John Riley) of Sydney's last big shipwreck, the 'Myola', missing since 1919. He still searches for other minor wrecks on a regular weekly basis and is, he says twinkingly, "burdened with a collection of old friends."

(The account that follows first appeared in 'Professional Diver Journal', in 1996, and is reproduced here in order to set the scene for the cautionary advice in Peter's, 'Pacemakers - An Update', that appears further down the page. - Ed.)