Marc W. Deyell, MD, FRCPC, Stanley Tung, MD, FRCPC, Andrew Ignaszewski, MD, FRCPC

The implantable cardioverter- defibrillator: From Mirowski to its current use

Sudden cardiac death can be prevented in two broad categories of patients—those who have survived a life-threatening ventricular or who have sustained ventricular tachycardia, and those who have not experienced sudden cardiac arrest but are known to be at increased risk.

ABSTRACT: Sudden cardiac death y the mid-20th century it Michel Mirowski is the initial presentation for many was well known that ven- Mieczyslaw (Michel) Mirowski was patients with cardiac disease. Dr tricular were born 14 October 1924 in Warsaw, Michel Mirowski was a pioneering Bthe mechanism of death in a .4 The story of his early life is cardiologist who recognized the large proportion of patients with car- nothing short of incredible. He grew public health importance of this diac disease. The 1960s brought with up in a middle-class family among the fact. In the 1970s his efforts led to them the advent of electronic moni- large Jewish population of Warsaw at the development of the implantable toring, cardiopulmonary resuscita- that time, but his relatively comfort- cardioverter-defibrillator that has tion, and synchronized cardiover- able life changed dramatically with revolutionized the ability to prevent sion.1-3 Once clinicians had tools at the outbreak of the Second World War. and treat sudden cardiac arrest. their disposal for the treatment of ven- With the invasion of Poland by the However, in the first decade of the tricular arrhythmias, it was not sur- Nazis in 1939, Michel knew he could 2000s these devices remain under- prising to see the first coronary care not stay in Poland, but he was deter- utilized in British Columbia and units opened in 1962.2 mined to continue his education. There- Canada. Increased physician aware- While considerable attention was fore, at the age of 15, he made the deci- ness is needed regarding which being paid to the treatment of arrhyth- sion to leave his family and flee to patients are at high risk of sudden mias among hospitalized patients, lit- Russia along with a friend. He would cardiac death and would benefit from tle attention was being paid to the be the only member of his family to this potentially lifesaving therapy. major public health problem of sud- survive the Second World War. den cardiac death (SCD) outside the Mirowski spent the following 5 coronary care unit.4 SCD is the initial years of the war in the Soviet Union, presentation of cardiac disease in 15% fleeing the advancing Germans. Des- of patients5 and more than 50% of all pite long odds, he continually evaded such deaths occur out of hospital.6 Michel Mirowski was one of the few Dr Deyell is an electrophysiology fellow at clinicians in the 1960s to recognize the University of British Columbia and is the scope of the problem of SCD. It based at St. Paul’s Hospital. Dr Tung is an was his perseverance that ultimately electrophysiologist at St. Paul’s Hospital led to the development of the first suc- and a clinical assistant professor at UBC. cessful therapy for out-of-hospital Dr Ignaszewski is a clinical professor of cardiac arrest—the implantable car- medicine and head of the UBC Division of dioverter-defibrillator (ICD). .

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Russian authorities who were intent nal defibrillator paddle, on a dog.9 Mower were involved in many of the on sending refugees to labor camps in The paper describing their work was early refinements, including the devel- Siberia. Somehow, he always man- eventually published after initial opment of the capacity of synchro- aged to find enough work to feed him- rejections,10 but there remained con- nized cardioversion for ventricular self and to stave off the malnutrition siderable antagonism in the cardiolo- tachycardia.9 True to Mirowski’s orig- and disease that was rampant in the gy community toward the concept of inal vision, a catheter-electrode-based Soviet Union at that time. the ICD. The antagonism also meant model developed in the late 1980s After the war ended, Mirowski that they faced significant difficulty in could be implanted without a thoraco- briefly returned to Poland and began securing funding for their research. tomy, in a similar manner to the stan- medical school in Gdansk before leav- Mirowski and Mower eventually dard pacemaker. ing to pursue his medical education in obtained support from a major pace- In the late 1980s Mirowski was Western Europe. He eventually enter - maker company in 1970 to further diagnosed with multiple myeloma and ed medical school in Lyon, France, in develop the ICD, but after 2 years the he succumbed to the disease in 1990. 1947, despite knowing almost no company decided there was no mar- While his invention of the ICD was an French or English. It was in Lyon ket for the device. In 1972 Mirowski enormous advance for cardiac medi- where Mirowski was first attracted to was introduced to Stephen Heilman, cine, perhaps his greatest legacy was cardiology and also where he met and a physician and engineer who had the attention he drew to the problem fell in love with his wife, Anna. formed a small medical equipment of SCD as a whole. Upon graduation from medical company called Medrad. Heilman was school in 1954, he worked initially in excited by the concept of the ICD and ICDs in 2010 , , as a registrar and then immediately put the company’s engi- Unlike the early prototypes, modern pursued further training in Mexico neers at Mirowski and Mower’s dis- devices are much smaller, with the City, , and Staten Island. He posal. The partnership was fruitful and newest models weighing as little as returned to Israel in 1963 to set up a resulted in the production of the first 90 g and measuring less than a cen- private practice in a small community ICD prototype small enough to be timetre thick. In addition to having hospital. His new boss, Professor completely implanted in a dog in full pacemaker capabilities, all mod- Harry Heller, unwittingly became the 1975. A film of the first successful ern ICDs are capable of overdrive pac- inspiration for Mirowski’s research. of a dog implanted with ing (antitachycardia pacing), which In 1966 Heller began having episodes the prototype ICD was released and can often terminate ventricular tachy- of ventricular tachycardia and died the now-famous footage catapulted cardia without resorting to shock soon after. It was with Heller’s death the ICD from relative obscurity to the therapy. ICDs are also available with that Mirowski first conceived the idea forefront of cardiac research overnight. biventri cular pacing (cardiac resyn- of an implantable defibrillator. Mirowski and the group at Medrad chronization therapy) to improve symp- further refined the prototype to make toms in selected patients with ad - Development of the ICD it suitable for human implantation and vanced heart failure. In 1968 Mirowski was recruited to the eventually received approval for such The use of ICDs in Canada and Sinai Hospital in Baltimore, where he an implant from the FDA. After Mirow- around the world has grown consider- became the director of the hospital’s ski and Mower enlisted the aid of col- ably since 1980. In 2008, 593 ICDs new coronary care unit and was given leagues at , were implanted in British Columbia protected time for research. Fortu- cardiac surgeon Myron Weisfeldt and and 5811 were implanted across Cana- nately for this research, the hospital electrophysiologist Philip Reed, the da. Although these numbers are ex- had a division of biomedical engi- first successful human implant of an pected to rise in the years to come, neering and an animal laboratory.7 At ICD was performed in February 1980.11 ICDs currently remain underutilized the Sinai, Mirowski joined with Mor- Though the first ICD model was a in Canada, even among survivors of ton Mower, a junior cardiologist on success, it weighed 225 g, required a cardiac arrest.12 staff with extensive animal research thoracotomy for implantation of the experience, to begin work on an ICD electrode patches, and was only capa- Patient selection in July 1969.8 Only a month later they ble of defibrillation. In the years that Whether to implant an ICD in a par- successfully tested their first crude followed, numerous advances in ICD ticular patient is a complex decision prototype, made from a broken exter- design have been made. Mirowski and and involves careful discussion among

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the health care providers and the pa- vs 16% for ICD vs placebo). The num- complex. Implantation is not without tient. The ultimate decision to implant ber needed to treat to prevent one risk, including inappropriate shocks, an ICD rests with the cardiac electro- death over 2 years was 12 patients and device recall or malfunction, and in - physiologist, who will be responsible the cost per life-year saved by an ICD creased hospitalization. Devices also for appropriate programming and was estimated at US$66 677 in 2002.16 remain expensive and require long- long-term follow-up of the device. It Based on these trials, the 2005 Cana- term follow-up at specialized centres is important for the other treating dian Cardiovascular Society/Canadian experienced in their management. physicians to know which patients Heart Rhythm Society guidelines17 Considerable research has therefore should be referred to a cardiologist or and the more recent 2008 American centred on attempting to identify electrophysiologist and considered College of Cardiology/American Heart patients at highest risk for SCD and for an ICD. Association/Heart Rhythm Society cases where the potential benefits of There are two broad categories of guidelines18 give their strongest level ICD use outweigh the risks and the patients who can benefit from an ICD. of support for ICD use in these groups. cost. First are patients who have survived a It is important to note that patients The most important risk factor for life-threatening ventricular arrhyth- with potentially reversible causes of SCD in the primary prevention popu- mia or who have sustained ventricular their VT or VF were excluded from lation is an impaired left ventricular tachycardia (VT). In this instance, the these trials. EF, with the risk of VT and VF increas- ICD would be implanted for the sec- A less clear-cut situation arises ing markedly as the EF drops below ondary prevention of sudden cardiac when a patient who is at high risk for 30% to 35%.20 The risk of SCD is also arrest (SCA). The definition of “sus- ventricular arrhythmias, usually be- dependent on the cause of the reduced tained” VT differs greatly in the liter- cause of an impaired left ventricular ejection fraction. Patients with ische- ature, but is usually defined as VT ejection fraction (EF), presents with mic heart disease due to a previous MI resulting in hemodynamic symptoms syncope of unknown cause. Here, an or severe coronary artery disease are (syncope, pre-syncope, chest pain) or electrophysiology study can be of at greater risk than those with non- lasting greater than 30 seconds. Sec- value in deciding which patients ischemic cardiomyopathies. ond are patients who have not yet might benefit from an ICD. If sus- The major clinical trials of ICDs experienced SCA but are at increased tained VT or VF is induced during the for primary prevention in patients with risk. Here an ICD would be implanted study, implantation of an ICD should ischemic heart disease and low EF for primary prevention of SCA. be considered.15 were almost uniformly positive, with Less commonly, patients present relative reductions of overall mortali- ICDs for secondary with sustained VT but have no evi- ty of 30% to 50% at over 2 years of prevention dence of structural heart disease on follow-up.21-23 The majority of benefit Not surprisingly, patients who have evaluation. An ICD should be strong- was seen in patients with ejection frac- survived SCA due to ventricular fib- ly considered in this population, par- tions less than 30%. In the SCD-HeFT rillation (VF) or hemodynamically ticularly if the VT is associated with trial of patients with EF less than 30%, unstable VT have the highest rate of severe symptoms (pre-syncope, angi- the number needed to treat to save one recurrence and would therefore stand na, or heart failure). However, some life over almost 4 years of follow-up to benefit most from an ICD. Similar- individuals with better-tolerated VT was 14 patients,24 and the cost per ly, patients who have sustained VT may be amenable to antiarrhythmic quality-adjusted life-year saved by an and are highly symptomatic or have therapy or to ablation without the need ICD has ranged between US$34 000 underlying structural heart disease are for an ICD.19 and US$70 200.25 Certain patients with also at high risk of recurrence. The recommendations for ICD use ejection fractions between 30% and It was precisely these groups that for secondary prevention are present- 35% also appeared to benefit in some were studied in the earliest random- ed inTable 1 . trials, but only if they had other high- ized trials of ICD use.13-15 The largest risk markers of either nonsustained of these trials was the AVID trial, where ICDs for primary VT on monitoring or inducible VT or the ICD was compared with amioda- prevention VF.21,23 These findings form the basis rone or sotalol. There was a significant The issue of which patients should of the recommendations for ICD reduction in mortality over 18 months receive an ICD for the primary pre- implantation in the ischemic heart dis- of follow-up favoring the device (24% vention of SCD is considerably more ease population.

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Importantly, most of these trials Table 1. Who should receive an ICD* for secondary prevention? enrolled patients at least 1 month after MI in an effort to exclude any patient Patient category Remarks whose ejection fraction was likely to Should definitely receive an ICD improve with recovery of stunned Survivors of cardiac arrest due to VF or This excludes patients with a transient or myocardium. In fact, implantation of hemodynamically unstable VT reversible cause, including • Recent acute MI (within 48 hours) an ICD immediately after MI in those • Drug use with depressed ejection fractions con- • Electrolyte abnormalities ferred no benefit in two recent tri- Patients with known structural heart disease Ablation may be an alternative in some patients als.26,27 Similarly, EF can improve sig- and sustained VT nificantly after coronary artery bypass Patients with syncope of uncertain origin but EPS can be especially helpful in evaluating grafting (CABG), thereby reducing inducible VF or hemodynamically significant syncope in patients with structural heart disease VT at EPS the risk of SCD. Routine implantation of ICDs at the time of surgery con- Should be strongly considered for an ICD ferred no benefit to patients with EF Patients with no structural heart disease but Treatment with pharmacotherapy or ablation sustained VT may be more appropriate initial therapy less than 35% in the CABG-PATCH trial.28 Therefore, any consideration * See box for abbreviations used in table for an ICD should be delayed until Table 2. Who should receive an ICD* for primary prevention? 1 to 3 months after surgery. The trials of ICD for primary pre- Patient category Remarks vention in patients with nonischemic Should definitely receive an ICD cardiomyopathies were less conclu- Patients with ischemic heart disease and Must be at least sive. The two earliest trials showed no EF ≤ 30% • 1 month since MI benefit with ICD use, but they were • 3 months since revascularization (CABG or PCI) small and likely underpowered.29,30 Should be strongly considered for an ICD Two larger subsequent trials showed a Patients with nonischemic cardiomyopathy Should be NYHA class II or III reduction in SCD and overall mortal- and EF ≤ 30% (little evidence of benefit in NYHA class I) ity, albeit a smaller reduction than that Patients with ischemic heart disease and Must be at least seen in the ischemic heart disease pop- EF 31%–35% with inducible VT/VF at EPS • 1 month since MI • 3 months since revascularization (CABG or PCI) ulation.24,31 Again, those with ejection Patients with inherited or acquired Including (but not exclusive to) HCM, Brugada fractions less than 30% were most conditions predisposing them to ventricular syndrome, long QT syndrome, and ARVC likely to benefit. arrhythmias with high-risk features Some patients with recently diag- May be considered for an ICD nosed nonischemic cardiomyopathy Patients with ischemic heart disease and EF An EPS is useful in risk stratifying patients with will be expected to have significant 31%–35% without inducible VT/VF at EPS ischemic heart disease and EF 31%–35% recovery of their EF with medical Patients with nonischemic cardiomyopathy Should be NYHA class II or III therapy. Therefore, it is recommended and EF 31%–35% that these patients be on maximal * See box for abbreviations used in table medical therapy for at least 9 months Abbreviations before assessing their candidacy for an electrophysiologist is essential for ARVC: arrhythmogenic right ventricular cardiomyopathy an ICD. identifying high-risk patients who CABG: coronary artery bypass grafting There is also a role for ICDs in would benefit from an ICD. CHF: congestive heart failure the primary prevention of SCD in The recommendations for ICD use EF: ejection fraction EPS: electrophysiology study patients who have preserved ejection for primary prevention of SCD are HCM: hypertrophic cardiomyopathy fractions but conditions that predis- summarized inTable 2 . The Canadi- ICD: implantable cardioverter-defibrillator pose them to ventricular arrhythmias an and American guidelines differ MI: myocardial infarction NYHA: New York Heart Association (such as hypertrophic cardiomyopathy, somewhat in their recommendations PCI: percutaneous coronary intervention long QT syndrome, arrhythmogenic and we have emphasized the Canadi- VF: ventricular fibrillation right ventricular cardiomyopathy, or an recommendations where conflicts VT: ventricular tachycardia Brugada syndrome). An evaluation by arise.17,18

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When not to implant As well as knowing who might bene- The most important risk factor for fit from ICD therapy, it is important SCD in the primary prevention for treating physicians to know who is not an appropriate candidate (see population is an impaired left Table 3 ). Patients with VT or VF due ventricular EF, with the risk of VT and to reversible causes should not receive an ICD. This includes patients with VF increasing markedly as the EF VT or VF within the first 48 hours of drops below 30% to 35%. an acute MI due to electrolyte abnor- malities or due to the effects of drug use or intoxication. Patients with incessant VT or VF are also not can- didates for an ICD until their arrhyth- mia is brought under control with Thanks to the pioneering work of 2. Lee TH, Goldman L. The coronary care antiarrhythmic or ablation therapies. Michel Mirowski and colleagues, unit turns 25: Historical trends and future Severe psychiatric conditions are also patients at high risk for SCD can directions. Ann Intern Med 1988;108: relative contraindications for an ICD, be treated effectively with an ICD. 887-894. especially if follow-up will be dif- Increasing physician awareness in 3. Lown B, Fakhro AM, Hood WB Jr, et al. ficult or if ICD discharges would British Columbia regarding the ap- The coronary care unit. New perspec- exacerbate the psychiatric condition. propriate indications for device im - tives and directions. JAMA 1967;199: Patients with severe symptomatic plantation will enhance the delivery 188-198. heart failure (NYHA class IV) or with of this potentially lifesaving therapy 4. Kastor JA. Michel Mirowski and the auto- frequent hospitalizations are more to those patients who need it most. matic implantable defibrillator. Am J Car- likely to die from cardiac pump fail- diol 1989;63:977-982 contd. ure than VT or VF and should not have Competing interests 5. Kannel WB, Doyle JT, McNamara PM, et an ICD implanted unless their clinical Dr Tung has received research funding al. Precursors of sudden coronary death. status improves.32 Similarly, patients from Medtronic Canada. He has also Factors related to the incidence of sud- whose life expectancy is less than 1 received speaking fees from Boston Sci- den death. Circulation 1975;51:606 - 613. year due to cardiac or noncardiac dis- entific Canada and St. Jude Medical Cana- 6. Gillum RF. Sudden coronary death in the ease are not likely to survive to bene- da. United States: 1980–1985. Circulation fit from an ICD. 1989;79:756-765. References 7. Mendeloff AI. Michel Mirowski and the Summary 1. Kouwenhoven WB, Jude JR, Knicker- Department of Medicine at the Sinai Hos- Sudden cardiac death remains an im- bocker GG. Closed-chest cardiac mas- pital of Baltimore. Pacing Clin Electro- portant public health problem today. sage. JAMA 1960;173:1064-1067. physiol 1991;14(5 Pt 2):873-874.

Table 3. Who should not be considered for ICD* therapy? Abbreviations Patients with VT/VF with a reversible cause ARVC: arrhythmogenic right ventricular cardiomyopathy CABG: coronary artery bypass grafting Patients with incessant VT/VF CHF: congestive heart failure EF: ejection fraction Patients not expected to survive for at least 1 year EPS: electrophysiology study Patients with severely symptomatic CHF HCM: hypertrophic cardiomyopathy • Symptoms at rest (NYHA class IV) or ICD: implantable cardioverter-defibrillator • Multiple hospitalizations MI: myocardial infarction NYHA: New York Heart Association Patients with severe psychiatric illness where PCI: percutaneous coronary intervention • ICD implantation would aggravate the illness/symptoms or VF: ventricular fibrillation • ICD follow-up would be compromised VT: ventricular tachycardia

* See box for abbreviations used in table

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8. Mower MM. Building the AICD with 17. Tang AS, Ross H, Simpson CS, et al. Med 1996;335:1933-1940. Michel Mirowski. Pacing Clin Electro- Canadian Cardiovascular Society/ 24. Bardy GH, Lee KL, Mark DB, et al. Amio- physiol 1991;14(5 Pt 2):928-934. Canadian Heart Rhythm Society position darone or an implantable cardioverter- 9. Kastor JA. Michel Mirowski and the auto- paper on implantable cardioverter defib- defibrillator for congestive heart failure. matic implantable defibrillator. Am J Car- rillator use in Canada. Can J Cardiol N Engl J Med 2005;352:225-237. diol 1989;63:1121-1126. 2005;21(suppl A):11A-18A. 25. Sanders GD, Hlatky MA, Owens DK. 10. Mirowski M, Mower MM, Staewen WS, 18. Epstein AE, DiMarco JP, Ellenbogen KA, Cost-effectiveness of implantable car- et al. Standby automatic defibrillator. An et al. ACC/AHA/HRS 2008 Guidelines dioverter-defibrillators. N Engl J Med approach to prevention of sudden coro- for Device-Based Therapy of Cardiac 2005;353:1471-1480. nary death. 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