the 1960s. in 1958, a team of researchers at johns hopkins university (who were unaware of maass' experience and publication) made an accidental discovery while studying cardiac defibrillation in dogs. the team — which included william kouwenhoven, guy knickerbocker, and james jude — noticed that by forcefully applying the paddles to the chest of the canine test subject, they could achieve a pulse in the femoral artery. further experimentation on dogs addressed such questions as the ideal location, rate, and force of chest compressions. armed with this information, the group began human trials. the first person successfully resuscitated using this technique was recalled by jude: "she was rather an obese female who … went into cardiac arrest as a result of flurothane anesthetic. this woman had no blood pressure, no pulse, and ordinarily, we would have opened up her chest. instead, since we weren’t in the operating room, we applied external cardiac massage. her blood pressure and pulse came back at once. we didn’t have to open her chest. they went ahead and did the operation on her, and she recovered completely." in a 1960 landmark article in the journal of the american medical association, the johns hopkins team reported their findings on 20 cases of in-hospital cardiac arrest. many of these patients had experienced cardiac arrest as a result of general anesthesia, and three patients were documented to be in ventricular fibrillation. the duration of chest compressions varied from less than 1 minute to 65 minutes. fourteen of the 20 patients (70%) survived and were discharged from the hospital. the authors concluded that chest compression can be useful as a bridge therapy until an external defibrillator can be brought to the scene. the combined use of ventilation and chest compressions 1964 illustration of the abcs of cpr. note that even at that time, therapeutic hypothermia was recommended within 30 minutes for victims that show signs of cerebral hypoxia. cpr as it is practiced today (the combination of mouth-to-mouth ventilation with chest compressions) made its debut in september 1960, when the two teams of researchers (kouwenhoven/jude/knickerbocker, and safar/elam/escarraga) presented their findings at the annual meeting of the maryland medical society in ocean city, maryland. they presented convincing data to show that chest compression alone did not provide effective ventilation; it was necessary to include mouth-to-mouth ventilation. the use of mouth-to-mouth ventilation (rescue breathing) had been taught to laypeople as early as 1958, but many physicians felt that closed-chest cardiac resuscitation (chest compressions) should only be taught to physicians, dentists, nurses and emergency rescue squads. in 1962, cpr was formally endorsed by the american heart association, american red cross, and the industrial medical association, but with the caveat that it should be applied only by carefully trained personnel, and training should not at that time be extended to the general public. in 1965, these organizations issued a revised statement reaffirming this view. the kouwenhoven/jude/knickerbocker team however believed that not only rescue breathing but also closed-chest cardiac resuscitation could and should be taught to laypeople. they produced an 11-minute training film called life in your hands in 1961, in which they demonstrated the new technique of cpr in various settings and stressed the importance of "air and circulation". the following year, archer gordon and david adams produced a 26-minute training film called the pulse of life. for the film, gordon and adams devised the easy-to-remember mnemonic of a, b & c, which represented the sequence of steps in cpr: airway, breathing, and circulation. these films were used in cpr classes and viewed by millions of students, many of whom were laypeople. by 1964, safar had expanded the "a-b-c" mnemonic to include: phase i a—airway (open the airway) b—breathing (provide rescue breathing) c—circulation (administer chest compressions) phase ii d—drugs (administer epinephrine, sodium bicarbonate, calcium chloride, and/or norepinephrine as necessary) e—ekg (administer external defibrillation if necessary) f—fluids (administer intravenous fluids as necessary) phase iii g—gauge (evaluate and treat the underlying cause of the cardiac arrest) h—hypothermia (begin therapeutic hypothermia within 30 minutes for victims that show signs of cerebral hypoxia) i—intensive care unit (administer chest compressions) by 1966, cpr was being taught to laypeople as well as professionals, but with disappointing results. fewer than 50% of people were able to pass a cpr performance evaluation three months after receiving standardized training in cpr, and the results of cardiac resuscitation attempts initiated outside of hospitals were dismal. in response to requests from the american red cross for the establishment of better training methods for cpr, the national research council of the national academy of sciences convened another ad hoc conference on cpr in 1966. over 30 national organizations were represented at this conference. the 1966 conference resulted in the formulation of the first national guidelines for the implementation of cpr. safar's mnemonic was trimmed back to "a-b-c-d", with "d" representing "definitive therapy". other recommendations that emerged from this conference encouraged practice with training mannequins, but continued to discourage the teaching of cpr to laypeople. of interest, both silvester's and holger nielsen's methods were still recommended as alternatives to mouth-to-mouth ventilation. defibrillation main article: defibrillation defibrillator used by claude beck in 1947 as early as the 1930s, it was known that small electric shocks could induce fibrillation in the ventricles of the heart, and that more powerful shocks could reverse this fibrillation. in 1947, claude beck (1894 – 1971) reported the first successful internal defibrillation of the human heart. to accomplish this, the chest had to be surgically opened and the defibrillator paddles placed directly on the heart. beck's groundbreaking work was eclipsed in 1955, with the development by paul zoll (1911 – 1999) of the external defibrillator — a device that could externally defibrillate the heart through the closed chest. zoll published a report of his experience in the new england journal of medicine in 1956, in which his external defibrillator was employed to successfully stop ventricular fibrillation eleven times in four different patients. since direct current batteries and capacitor technology both powerful enough to do the job and portable enough for practical use did not exist at that time, the earliest external defibrillators utilized alternating current and were run from line voltage. these ac defibrillators were very large and heavy, primarily because they contained a transformer to step up the line voltage from 110 volts to 500 or 1000 volts. they were mounted on wheels and pushed down the hallway from one part of the hospital to another. the portability problem was solved by bernard lown (1921 – 2021). lown devised a defibrillator that utilized direct current instead of alternating current. a capacitor stored the energy until it was released in one massive jolt to the chest wall. the availability of new, small capacitors considerably reduced the size and weight of external defibrillators, which could now be easily brought to victims in a wide range of environments. by 1963, hospitals were beginning to design mobile resuscitation carts equipped with these portable external defibrillators. the idea for an automated external defibrillator was first advanced in the 1970s by archibald diack (1907 – 1993), a surgeon in portland, oregon. diack and his team developed a portable unit that could diagnose an abnormal heart rhythm and deliver either a defibrillatory current or a pacing pulse, as indicated by the internal logic circuit. the device was produced by the cardiac resuscitator corporation and marketed as the "heart-aid". it was designed for temporary use by laypeople in emergency situations before professional care could be administered. the heart-aid utilized a plastic airway with an embedded electrode. an electrical current was transmitted from the capacitor, through the plastic airway device, to an electrode placed over the sternum. there was also a breath detector, which was a safeguard to prevent shocking people who were breathing. it included printed instructions and diagrams for the rescuer to properly apply the electrodes, as well as a speech synthesis chip to give verbal instructions to the rescuer. by the late 1980s, the small company had been purchased by emerson radio corporation, and other manufacturers soon entered the field. current models use electrode pads attached to the chest. recent developments in cpr in 1965, frank pantridge turned his attention to this vexing problem of heart attacks and sudden cardiac death. he believed the problem of death from acute myocardial infarction had to be solved outside the hospital, not in the emergency room or the coronary care unit. pantridge's solution was to develop the world's first mobile coronary care unit, or mccu. he staffed it with an ambulance driver, a physician, and a nurse. the team reported the initial results of their program in the august 5, 1967 issue of the lancet; their findings on 312 patients covered a 15-month period. half the patients had myocardial infarction and there were no deaths during transportation. of ground-breaking importance was the information on 10 patients who had cardiac arrest. all had ventricular fibrillation; six arrests occurred after the arrival of the mccu, and four occurred shortly before arrival of the ambulance. all 10 patients were resuscitated and admitted to the hospital. five were subsequently discharged alive. the article has historical importance because it served to stimulate pre-hospital emergency cardiac care programs throughout the world. by the early 1970s cpr, defibrillation, and a rapid means to provide prehospital care were all in place. the structure to resuscitate sudden death victims had been built and was proving successful. that most of the world did not have this structure in place in the 1970s was largely due to lack of diffusion and spread of the ideas, rather than the impossibility of carrying them out. however, the story of resuscitation does not stop in the early 1970s. major advances have continued. in 1980 the first program to train emts to perform defibrillation began in king county, washington, and similar programs spread throughout the united states. this training required 10 hours, and in the first demonstration project, survival from ventricular fibrillation increased from 7% to 26%. in 1984 the first program with fire fighter emts using automated external defibrillators (aeds) also began in king county, washington. the use of aeds simplified the training of emts and thus allowed the procedure to spread more rapidly throughout communities. automated external defibrillators require considerably less training time compared to manual defibrillators since the emt does not have to interpret the cardiac rhythm. in 1981 a program to provide telephone instructions in cpr began in king county, washington. this program used the emergency dispatchers to give instant directions while the fire department emt personnel were in route to the scene. this demonstration project increased the rate of bystander-provided cpr by 50%. dispatcher-assisted cpr is now standard care for dispatcher centers throughout the united states and in other countries such as israel, great britain, sweden, and norway. the american heart association uses a metaphor of four links in a chain to describe the elements of successful resuscitation. these links are early access (recognizing cardiac arrest and calling 911), early cpr, early defibrillation, and early advanced care (such as medications, endotracheal intubation) the early paramedic programs were all designed to provide cpr, defibrillation, and advanced care quickly enough to resuscitate patients in cardiac arrest. further advanced technologies to supplement cpr are being tested. these include the use of drones to deliver defibrillators to patients undergoing cpr outside hospital, as well as placing patients in whom cpr is ongoing but cardiac rhythm cannot be restored onto heart-lung bypass (ecmo) machines. this then allows them to be transported to specialist centres where the cause of their cardiac arrest (a blocked coronary artery for example) can be addressed. so called 'ecmo-cpr' may yet further revolutionize the way in which cpr is delivered. trials of pre-hospital ecmo-cpr in france and australia have been promising.