Fighting "the big one": ICD’s prolong life

Last summer, in the midst of a Major League baseball game broadcast on North American TV, the home plate umpire was called out. Permanently. Pulling off his mask, he walked away from the batter’s box, staggered, and dropped in his tracks. He was dead before he could be taken to hospital. Most people watching that day — and the majority of those who heard about the incident afterward — probably assumed the umpire fell victim to “the big one”. . . a massive heart attack. In fact, he succumbed to the most common cause of death in the Western world: sudden cardiac death (SCD). Sadly, if the umpire’d had an ICD – an Implantable Cardioverter Defibrillator – he’d probably be alive today. In fact, based on the results of a study published in The New England Journal of Medicine in November, thousands of the 40,000 Canadians who died last year of sudden cardiac death would still be alive today if they’d had access to an ICD. Sponsored by the U.S. National Institutes of Health, the Antiarrhythmics Versus Implantable Defibrillators Study [AVID] found that ICDs reduced death by 39 per cent in the first year (26 per cent in Year 2, 30 per cent in Year 3) compared to the mortality rate of peopltreated with antiarrhythmic drugs. The study followed 1,016 patients in 56 clinical sites in the U.S. and Canada with a history of ventricular fibrillation (VF) or serious ventricular tachycardia (VT) from 1993 to April 1997, when it was halted by an independent monitoring board – 16 months early. The results were simply so clear cut it wasn’t necessary to continue.

“We’ve known for some time that ICDs are effective at restoring normal rhythms in patients with life threatening rapid heart rhythms, but now we have solid proof that they also prevent deaths,” says Dr. Paul Dorian, one of the study’s authors. Dorian is a cardiologist and head of the Cardiac Electrophysiology Program at St. Michael’s Hospital in Toronto.

Ventricular fibrillation is the cause of sudden death in most individuals who die suddenly, Dorian explains. “It’s an extremely rapid – over 400 beats per minute – uncoordinated beating of the heart. When the heart is in fibrillation, it quivers, basically. It doesn’t really beat. This is only treatable with an electrical shock to the heart. It virtually never stops by itself. And if you have this rhythm, unless you get this electrical shock to the heart, you’re dead within five to 10 minutes. So, it’s an immediately lethal heart rhythm disturbance.”

Ventricular tachycardia is also an abnormal and potentially dangerous rhythm but it’s not as bad as ventricular fibrillation. VT is a more coordinated but still very rapid heartbeat. It can cause dizziness or loss of consciousness, but it may stop on its own. It doesn’t cause death in seconds to minutes like ventricular fibrillation, but it can cause death within a period of minutes to hours if it’s not treated. “It’s still very dangerous,” Dorian says, “but it doesn’t kill you instantly.”

Most instances of VF or VT are the result of a previous heart attack that’s left a patch of scar tissue in the heart, though scarring can also be caused by other forms of heart disease. (Heart attacks are the leading cause of scarring in North America, but, in South America, the most common cause is a parasite that invades the heart. In Asia, where heart attacks are less common, high blood pressure’s the No. 1 cause; in the Indian subcontinent, it’s rheumatic fever.) VF or VT leading to sudden cardiac death can arise secondary to a heart attack, but not immediately afterward. “This is not like somebody’s had a heart attack an hour or a day ago,” Dorian says. “These are people who’ve had heart attacks in the remote past – months or years or even decades ago. So the majority of people who die suddenly have a remote history of heart attack, but in the minutes or hours or days preceding their death, they were in their usual state of health, just doing their usual thing – nothing unusual happening.”

The problem is, it’s almost impossible to tell who’s likely to suffer what Dorian calls “a short circuit in the heart. Whenever you have a scar in the heart, from any cause, whether it’s a heart attack or an infection or whatever other problem, some scars that develop in the heart may go on to become short circuits. Why some do and some don’t is not understood. When they do, they’re latent, if you like. The short circuits are present in the heart, but they’re activated by some stimulus, and we don’t understand what that is. It’s like turning on a light switch. The electrical circuitry is there, and the potential for light is there, but it doesn’t actually happen until you turn the switch.”

The solution is an ICD, a battery operated (batteries last nine years and are easily replaced), titanium encased mini computer that not only senses but actually corrects tachyarrhythmias (abnormally fast heartbeats). The device is implanted under the skin in the upper chest, and titanium and silicone wires are threaded through a vein and into the right ventricle of the heart. The implantation procedure (which takes about an hour under local anesthetic) and technology is similar to that of pacemakers (which sense and correct abnormally slow heartbeats).

At 5 1/2 oz. and about the size of a small pager, an ICD is of course noticeable. “It’s a bit of a lump in the chest,” Dorian admits, but after six months or so, “most patients basically have forgotten it’s there. The most common complaint is that, when they roll over in bed and lie on their left side, they can feel it, because it is a lump under the skin. But during everyday life, especially when you’re upright, you don’t notice it. We have patients who play golf, windsurf, ski, who do all kinds of physical activities without much impediment.”

Yes, an ICD will set off metal detectors in airports, but there are no limitations in terms of computers, microwave ovens and so on. Electronic surgical instruments and MRI scanners can interfere with an ICD, but doctors can work around both problems – they just have to know the unit’s there. There are also some industrial settings to beware of – such as using an arc welder – but there are very few situations where these devices will malfunction, Dorian says. “They’re very well shielded. We tell our patients to lead normal lives. Go anywhere they want. Do anything they want.”

Nonetheless, it isn’t always easy convincing people they should have an ICD implanted. If they’ve already suffered a heart attack or another heart problem, they might be an easier sell, and if they’ve ever gone into VT or VF – and they’re still around – they might need even less convincing. The point is, once you’ve had an episode of VT or VF (and been resuscitated by paramedics or bystanders doing CPR, then transported to hospital, where you may have been given cardioversion or defibrillation with paddles to your chest), you’ve identified yourself as being at risk: The risk of recurrence is now as high as 50 per cent. Another high risk group are those who’ve had a previous heart attack or other heart problems, but again, there’s no way of knowing whose number will come up. All Dorian can do is add up his patient’s risk factors and make an educated guess – for now: Ongoing research should eventually answer that question, though results are still years away.

In the meantime, Canadians have some catching up to do: Currently we implant about 18 ICDs each year per million people, compared to some 36 per million in Germany and 100 per million in the States. “There are obviously many and complicated reasons why things are done in the States and not in Canada, some of which relate to easier access to technologies. Some of it relates to the difference in healthcare delivery systems, differences in the way they’re paid for and reimbursed, and some of it relates to the fact that Canadian physicians and the Canadian public are inherently more conservative than American physicians and the American public,” Dorian says. “But, if you asked me for a purely personal opinion – I have no scientific basis for saying this, but I’m willing to be quoted: We should be doing more ICD implants than we are, and the United States should be doing fewer.

“We now have proof for the first time that for particular patients with heart disease, with a prior history of very serious rhythm disturbances, that these devices appear to be better treatment than the best available medication. This is not necessarily true for every patient, but true for many with these disturbances.

“There are very few people who are ignorant of the fact that they’re at risk for SCD,” Dorian says, “because most of those I’m talking about have already had heart trouble, had fainting spells or a cardiac arrest. These are people who know they have cardiac rhythm disturbances. My advice is, if they have a history of this, they may want to discuss with their family doctor or their cardiologist whether they may or may not receive benefit from these devices.”