As its name suggests, Sudden Cardiac Arrest (SCA) is abrupt and often fatal. While heart attacks are caused by blockages in the arteries of the heart, SCA is caused by disruption in the electrical function of the heart, which causes its natural rhythm to be lost. Unlike heart attacks, SCA is little understood.
"It is best thought of as electrical chaos in the ventricles of the heart and a related cessation of effective mechanical functioning," explains Dwight Reynolds, MD, chief of cardiology at the OU Medical Center in Oklahoma City, USA. "The upshot is that the vital organs are not sufficiently supplied with blood."
In most cases, SCA is fatal, as it requires immediate treatment
to restore correct heart function. Indeed, it is sometimes referred to as sudden cardiac death. It occurs largely in patients at risk from or manifesting cardiac disease of some kind, and is the largest cause of death among such patients.
Reynolds, who is also a representative of the Heart Rhythm Society (HRS), estimates that, in the USA, SCA accounts for around two-thirds of cardiac deaths and as much as 20% of all deaths.
SCA claims the lives of around 325,000 Americans each year – more than breast cancer, stroke and AIDS combined.
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"In the majority of cases the ventricular fibrillation resulting in SCA is related to underlying coronary artery disease," says Reynolds. "So, SCA has the same substrate as for heart attack, which is caused by an obstruction in the arteries in the heart. However, even if there is no coronary disease, there are other heart conditions that are also causative."
Hypertension, for example, and the resulting malfunctions associated with long-term high blood pressure can be a sufficient platform for SCA, even in the absence of coronary disease. However, the vast majority of SCA incidents occur in the setting of heart failure, when the mechanism of the heart is not pumping sufficient volumes of blood.
"We discovered that patients with heart failure or reduced left ventricular ejection fraction have a higher propensity for sudden death," says Reynolds. "Some 40%–60% of all deaths in patients with heart failure were as a result of SCA."
Despite being so widespread and intrinsically linked to so many deaths, SCA has never received the publicity that has grown around other health concerns, such as HIV or breast cancer. The reason is that the technology to treat and prevent SCA was not sufficiently mature to make a great difference to the mortality rate. Now, it
A number of independent studies have shown that the mechanisms
for the prevention and treatment now available can significantly reduce the incidence of SCA. Over the last 20 years, two kinds of technology have developed that can treat SCA in different settings.
The maturation of these technologies – Implantable Cardioverter Defibrillators (ICD) and Automatic External Defibrillators (AED) – means that high-risk patients can be fitted with devices to regulate heartbeat, and automatic devices can be made accessible in public areas where large populations congregate. Implantable devices have been shown – in numerous studies over the last ten years looking at high risk populations and comparing outcomes against other best therapies – to be capable of dramatically reducing the number of SCA events and resulting deaths.
Some devices implanted under the skin include wires to the heart, although the latest generation do not. Each device monitors heart activity and automatically restores cardiac rhythm with a shock if the right conditions are evident.
These implantable defibrillators can be used not only in patients with a history of SCA, but with patients who are in high-risk populations. They, therefore, offer a preventative measure against SCA.
"The technology can be implanted in people with no prior history of ventricular arrhythmia or SCA, so we can use it in primary prevention populations, and without the fear that the treatment will be worse than the disease," says Reynolds.
Identifying high-risk populations is part of the motive behind the educational activities of the HRS, which is encouraging the wider population to become aware of cardiac health issues. Just as we might know our cholesterol count or blood pressure, HRS is suggesting people should know their ejection fraction.
The ejection fraction measures the pumping capability of the heart by looking at the proportion of blood it ejects with each beat. A volume of 55% or more is normal, while people with a score of 35% or less have a higher risk of SCA, which could be reduced with an implantable device.
Measuring the ejection fraction sometimes still involves the nuclear imaging of the heart, which requires the injection of a benign radioisotope. More commonly, however, a measure can be taken using cardiac ultrasound, which is a non-invasive test taking only 20–30 minutes.
The second technology to emerge in recent years is the automatic external defibrillator, which is targeted for widespread use in the community. For those struck down by SCA, rapid treatment is vital and can only be achieved if the right equipment is at hand.
Reynolds says: "We know that a shock to the chest can be life saving, but the problem is that the technical expertise to operate defibrillator equipment is often missing. People with ventricular arrhythmia need attention within four minutes to save their life or prevent brain damage."
The advent of automatic external defibrillators, however, means that the operator of the technology does not have to make any crucial decisions, and requires no training. The equipment has evolved rapidly in the last ten years to the point where an operator need only apply the patches to the patient’s chest and press the activation button. The machine then delivers the shock. This means that the operator can be an unqualified bystander.
"If we can disseminate this technology and raise awareness in the wider community, many more people will be saved," says Reynolds. "One focus of the HRS is to get this equipment into schools, where there is a high concentration of people."
These devices could also become essential equipment in areas where high-risk populations congregate, so HRS is hoping to target such locations for early use of the technology as well as encourage people to be more aware of their own cardiac health.
SURMOUNTING THE CHALLENGES
Although the technology available to prevent SCA now warrants a much greater public awareness of SCA, there are still some hurdles to overcome before implantable or automatic external devices become widespread.
For implantable devices in particular, cost is a major issue. Reynolds says: "As a result of the studies that have been concluded, there has been a rapid adoption of these devices in the USA. However, one challenge has been persuading third-party insurance carriers that these devices are life saving. Adoption has still been slower than it should be, and in Europe it is very slow. It is an expensive technology at the moment, and that is partly the reason."
For automatic external defibrillators, cost is an issue, with each device costing up to $2,000, including training. The main challenge, however, is public awareness. The OU Medical Centre where Reynolds works has recently launched a drive to promote awareness in the local community. It highlights the fact that around 6,600 Oklahomans – or 18 a day – will die from SCA this year. It is aiming to save at least 1,000 of those lives by alerting the public and healthcare providers to the dangers of SCA.
The Heart Rhythm Society is also just starting broad-based, nationwide campaigns in the USA, and is purely focused on tackling the country’s number one killer. "We believe that we can reduce mortality by 5%–10%, which would be a dramatic improvement in survival, but it is a modest estimate; much more is possible," says Reynolds.
SCA IN THE FUTURE
The ongoing development of the technology, which has already enabled the accurate detection of harmful arrhythmias and their distinction from less harmful ones, will no doubt ensure that the performance of the devices will improve, as will their cost profile.
Combined with greater awareness and access to the technology, this could lead to a vast number of lives being saved that once would have been lost.
"We were debating whether to call it sudden cardiac arrest or sudden cardiac death, but we hope that they will not be synonymous," says Reynolds.
"As therapeutic measures develop, we hope that SCA won’t mean death. The technology and our knowledge of the disease warrants us saying that we can and need to do something about SCA."
With a number of large, multicentre trials currently underway, it seems that the case for promoting the use of ICD and AED technology is gaining momentum. If those pushing the message about SCA can catch the public’s attention, then treatment and prevention could be revolutionised, with a dramatic impact on mortality.