Everything you should know about a defibrillator tester
A defibrillator tester is a medical device used to assess and verify the accuracy and functionality of an implantable cardioverter-defibrillator (ICD). It is a means to confirm the efficacy (and to some extent, safety) of an ICD in terminating life-threatening ventricular tachycardia and ventricular fibrillation. Fibrillations are the irregular heartbeat of more than 350 beats/minute. ICDs are used by patients with a high risk of severe tachyarrhythmias, cardiac arrest, and recent survivors of sudden cardiac death (SCD). Testing of ICDs and the shock lead integrity using a defibrillator analyzer or tester is one longstanding practice.
The testing can be done immediately after implantation or before the discharge of the patient. Severe ventricular tachyarrhythmias are arguably the most delicate and typical emergency in cardiology. There have been significant technological advancements in the design of ICDs, and the compulsion to use a defibrillator analyzer has witnessed some decline.
It is worthy to note that ‘defibrillator tester’ and ‘defibrillator analyzer’ are used interchangeably to mean the same medical equipment.
History of the defibrillator tester
The defibrillation history dates back to the invention of its machine by an electrical engineer, William Kouwenhoven, in 1930. Implantable cardioverter-defibrillators were introduced in the 1980s, notably in the USA, in 1985, and the defibrillator testing began shortly after the development of ICDs. Initially, defibrillator analyzers would require a lot of alterations to carry out their function. However, newer ICD models have more stable and consistent thresholds, and such modifications are no longer needed.
Defibrillator testing systems utilize a safety margin of 10 J of energy, which is very typical of an ICD with maximum output energy of 25 J. Higher mortality was noticed amongst patients with inadequate or uncaptured safety margins. Hence, the newest defibrillator testers have reduced energy thresholds making it difficult for a patient’s safety margin to be out of that accounted for by the defibrillator tester.
Indications to use a defibrillator tester
Defibrillators are simply medical devices that send an electrical shock to the heart to stop severe tachyarrhythmias and restore normal heart rhythms. External and portable defibrillators are known as implantable cardioverter-defibrillators. They are generally needed to treat the appropriate arrhythmias. The indications to use an ICD are more specific. A defibrillator analyzer confirms the ability of an ICD to do what is intended.
Indications for defibrillation include ventricular fibrillation, ventricular tachycardia without a pulse, and cardiac arrest arising from or causing ventricular fibrillation. The indications for cardioversion, which is a specific form of defibrillation, are atrial fibrillation, atrial flutters, supraventricular tachycardia, and ventricular tachycardia with a pulse.
The primary prevention of arrhythmias in a high-risk population (Prior myocardial infarction, coronary artery disease, and so on) and secondary prevention for cardiac arrest or death survivors are the significant indications to use an ICD. However, a highlight of uncommon indications is presented below:
- Acquired diseases such as myocarditis, acquired valvular disorders, and many infiltrative disorders.
- Congenital diseases, such as valvular diseases. There is also an increased risk of future arrhythmias after correction surgeries on many congenital anomalies.
- Inherited disorders such as catecholaminergic ventricular tachycardia, hypertrophic cardiomyopathy, long QT syndromes, right ventricular dysplasia, Brugada syndrome, and so on.
The indications and benefits of using a tester are:
- Defibrillator testers provide useful information about the functional state of an ICD. The integrity of the system and shock circuit must be intact at the point of use/action to prevent a fatal malfunction. Some technicians have reported ways to maneuver this compliance check, but an analyzer remains the foolproof device to confirm a defibrillation system's integrity.
- Defibrillator testers are used to check the shock efficacy of an ICD. This is related to the effectiveness of the ICD in terminating fibrillation. Patients with higher defibrillation thresholds will require modifications to prevent any malfunction. This helps to offer preventive measures further as higher thresholds have been linked to specific cardiac issues. Hence, all these checks are quite vital.
- Defibrillator testers are used to confirm the sensing (ability to detect) capacity of an ICD. The effectiveness of an ICD in sensing ventricular defibrillations is very related to its effectiveness in terminating it. The R wave is exploited in checking this sensitivity. Many research papers confirm a significant number of their ICD samples have inadequate sensing capacity. This shows the importance of monitoring these parameters.
Complications of using a defibrillator analyzer
Defibrillator testing requires additional resources and is time-consuming too. However, this is not a problem considering the benefits of performing the test and other potential complications that may be worrisome. A handful of complications can arise from the anesthesia used, induction of fibrillation, circulatory problems during ventricular fibrillation or shocks. General anesthesia must use a defibrillator tester, and common risks of central nervous system dysfunction, breathing problems, and so on remain valid.
Also, the induction of ventricular tachycardia or ventricular fibrillation can cause stroke and death. There is a hemodynamic compromise, and systemic perfusion is reduced enough to cause ischemia during ventricular fibrillation. The central nervous system is not left out as the cerebral blood flow is reduced, and the general hypotension after fibrillations can result in other complications. There may be a need to use inotropic drugs. The risk of arterial thromboembolism is also significant due to the shock impulses.
With all these possibilities in mind, defibrillator testers are still safe as research shows an infrequent rate of occurrence (and total observations in only about 0.4% of cases) of the complications.
General specifications of an analyzer
The specifications of a defibrillator analyzer may vary slightly amongst brands. This is the reason some of the highlighted specifications are in a narrow range.
- Energy output load – 50 Ohm ± 1%
- Resolution- 0.1 J (low) and 1 J (high)
- The energy range is 0 – 100 J (low), and up to 400 J (high) or 900 J for some brands, accuracy is ± 2% + 0.5-1 J
- The maximum current is 100 amp, 35 amp (low)
- The maximum voltage is 5200-5500 V, 1750 V (low)
- Discharge waveform viewable through ECG output, paddles and scope output
- Sync. time of 0-250 milliseconds
- Operating temperature is 15-30 ℃, can withstand 0-40 ℃
- Storage temperature is 0 – 55 ℃, the maximum relative humidity of 90>#/p###
How defibrillator testers work
The use of a defibrillator analyzer is the last procedure in the implantation of an ICD. The most common technique of defibrillator testing is the step-down defibrillation protocol. General anesthesia using a short-acting agent like etomidate can be used. Ventricular fibrillation is induced electrically through the pacing electrodes using different modes such as shock on T wave, burst mode, etc. The method of testing involves delivering sufficient shock energy, like 15 J, to effect defibrillation. If defibrillation fails, a maximum rescue shock energy can be given. This energy is successively stepped down, with each subtraction of 3 J. There are about 3 minutes designated for hemodynamic recovery. If the initial energy failed to cause defibrillation, the gradual addition of 3 J is applicable, helping to determine the defibrillation threshold (DFT) or lowest effective defibrillation (LED). This is the lowest energy that was able to achieve defibrillation.
For an ICD to satisfy this test, the LED must be less than or equal to the device's maximum defibrillation energy minus a safety margin (typically 10 J).
DFT/LED ≤ Maximum defibrillation energy of ICD – Safety margin
Factors that can influence elevated DFT include hypertrophic cardiomyopathy, left ventricular hypertrophy, low left ventricular ejection fraction, large body surface area, and the male gender. Drugs like amiodarone and sotalol also have a significant impact on the DFT.
The top reputable brands of defibrillator analyzers are:
- FLUKE- This is a great brand called Fluke Biomedical LLC. Prominent defibrillator tester models are the Impulse 7000DP, Impulse 7010, etc. They offer a topnotch accuracy of ± 1% and the ability to test external transcutaneous pacemakers, amongst others.
- RIGEL – Rigel from seaward is another great brand of defibrillator analyzer. They are very portable and efficient, with long-lasting rechargeable batteries.
- BC Marketplace- This is another good brand with all the common features of the other brands. They also have a printer output.
- DATREND- A great brand from a Canadian giant, Datrend Systems Inc. They offer defibrillator testers of premium quality.
- GOSSEN METRAWATT- One cannot go wrong choosing Gossen Metrawatt too.
Over the years, defibrillation testing has proven useful in confirming that an ICD can deliver the individualized defibrillation energy. Some arguments from recent years have scrutinized the necessity of defibrillator testers, while others reinforced it.
Doubts about the necessity of defibrillator analyzer initially arose from academic papers that claimed the probability of a very high DFT and failed ICD use is very low. Other arguments show that the energy required for the cardioversion of ventricular tachycardia, which is the most encountered tachyarrhythmias among patients, is insignificant, and all commercial ICDs can take care of it.
However, all this information could not invalidate the importance of defibrillator analyzers. The population of patients that receive better care due to defibrillation testing performed is overwhelming. In many instances, an unrelated case of inability to defibrillate has been detected. Also, defibrillation testing often reveals more clinical information about patients before discharge. In the long run, there has been a significant reduction in the mortality rate. Patients have been able to receive optimal care, all thanks to defibrillator testers.