Treatment of myocardial infarction in a coronary care unit

Treatment

of Myocardial Coronary

A Two Year THOMASKILLIP

Care

Experience III, M.D., New

York,

N 1963 Day’ and Brown et a1.2 reported their initial experiences with the clustering of patients with acute myocardial infarction in special care areas designed for continuous monitoring of the electrocardiogram. Early recognition of cardiac arrest with prompt initiation of resuscitative measures was emphasized. A decrease in mortality of the monitored patients was attributed to improved treatment of serious arrhythmias and cardiac arrest during the first three to five days after acute infarction. As a result of these encouraging reports, in January 1965 a study of specialized care for myocardial infarction was begun at The New York Hospital-Cornell Medical Center.3 This communication details a two year experience with 250 patients with objectively proved acute myocardial infarction treated in a specially designed, equipped and staffed coronary care unit in a voluntary teaching hospital.4 OF CORONARY

CARE

UNIT

DESIGN AND EQUIPMENT A four bed coronary care unit (CCU) was constructed in a 39 by 19 ft. room on a general medical The equipment includes narrow, stretcherward. type beds, central oxygen and suction outlets, multiple electrical outlets with appropriate grounding, a cardiac arrest alarm system and four bedside units suitable for monitoring the electrocardiogram and arterial or venous pressure. Only the electrocardiogram has been monitored routinely. Each bedside oscilloscope is connected to a central console in the nursing station and consists of four oscilloscopes and an alarm system sensitive to changes in heart rate. Four patients and their individual electrocardiographic patterns are under observation simul-

in a

Unit

with 250 Patients* and JOHN T.

F.A.C.C.

I

DESCRIPTION

Infarction

New

KIMBALL,

M.D.

York

taneously. gency

A defibrillator

drugs,

ventilators

equipment

for

cardiac

Emer-

pacemaking,

and a direct writer electrocardiograph

immediately

available.

autonomous,

self-sufficient

teaching

is at each bedside.

The

CCU

functions

unit in a general

are as an

medical

pavilion.

STAFFING

The Nursing Staff: At least one specially trained registered nurse is present in the unit at all times. Each has completed a 40 hour training course presented by the physicians of the Division of Cardiology prior to working alone in the unit. The course emphasizes recognition and treatment of arrhythmias, heart failure and cardiac arrest. Continued education of the nursing staff is maintained by periodic review sessions and frequent analysis of experiences in the unit. Practical experience in the administration of precordial shock is provided by experiments in the dog laboratory and by having the nurses assist during elective “cardioversions.” Physicians: At least one member of the pavilion house staff, consisting of two interns and one assistant resident physician, is present in the unit or on the adjacent medical floor at all times without exception. Daily rounds in the CCU are made by the house officers under the direct supervision of a senior member of the cardiology staff who is also available for consultation at other times. Each new group of house officers rotating through the CCU receives special lectures and demonstrations on recognition of arrhythmias, therapy of common complications and all aspects of cardiac resuscitation. The private doctor of a patient in the CCU reHe attends his patient mains the physician of record. However, only as he would on private patient floors. Complihouse officers are permitted to write orders. cations are managed by the house officers and cardiology staff according to established therapeutic routines. In practice, management of all patients in the

* From the Department of Medicine, Cornell University Medical College, New York, N. Y. This study was supPorted by Contract No. PH 108-65-09 with the U. S. Public Health Service, Department of Health, Education, and Welfare. VOLUME

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458

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TABLE I Final Diagnosis in 434 Patients Admitted to the Coronary Care Unit with Suspicion of Acute Myocardial Infarction During a Two Year Period

Total admissions Definite acute myocardial infarction Possible acute myocardial infarction No acute myocardial infarction Angina pectoris Arrhythmias Other diagnoses

No.

%

434

100

265

62

68 101

15 23

31 35 35

Kimball in the CCU five days after complete control of serious arrhythmias, severe cardiac decompensation, cardiogenic shock, or cardiac arrest. Transfers are not made earlier than planned to make room for more critically ill patients. Autopsies have been obtained on 62 per cent of the patients who died in the unit. CLASSIFICATION OF CASES Interpretation

of clinical

tion of objective It is important, criteria

therefore,

rigidly

Following careful

to define

in presenting

discharge

review

events and

evalua-

tests may vary among observers. diagnostic

a clinical

from the hospital,

of the clinical

study.

and after

record,

each

pa-

tient has been classified into one of the following groups CCU is controlled by the medical house staff under supervision of the Division of Cardiology.

Dejinite Acute Myocardial Infarction. Criteria for diagnosis include a compatible clinical history, the development of diagnostic Q waves, or evolution of S-T segment and T wave abnormalities on electrocardiograms with characteristic changes in SGOT, SGPT and LDH activity in serial blood samples. Possible Acute Myocardial Infarction. Patients so classified have had chest pain suggesting acute infarction, nonspecific alterations of S-T segments and T waves in the initial electrocardiograms, which during hospitalization progress toward normal, and normal or nondiagnostic variations in blood enzyme activity. No Acute Myocardial Infarction. This category includes patients whose symptoms on admission are subsequently diagnosed as having been due to angina pectoris, arrhythmia, heart failure, or abnormalities of other organ systems such as the gastrointestinal tract and musculoskeletal system.

A.

GENERAL POLICIES Any patient suspected of having acute myocardial infarction by his personal physician (whether the latter is a house officer or a private attending physician) is eligible for admission to the CCU if a bed is available. Decisions regarding admission are the responsibility of the resident physician in the CCU. Evaluation of the severity of the illness is not a factor in determining admission. Routine evaluation includes a detailed history, thorough physical examination, complete blood count, urinalysis, electrocardiograms and chest roentgenograms. Blood analyses include assay for enzyme activity [serum glutamic oxalacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), a-hydroxybutyrate dehydrogenase and lactic dehydrogenase (LDH)], urea nitrogen, glucose and cholesterol. Special studies (arterial pH, ~0s and pCO2, carbon dioxide combining power, lactate, and cardiac output or direct arterial pressure) are performed as indicated. Oxygen is administered routinely by nasal cannulas or mask for 24 to 48 hours. An intravenous polyethylene catheter is inserted and 5% dextrose in water administered continuously to keep the cannula patent during the entire CCU stay. Patients are kept at bed rest; however, use of a bedside commode is allowed. Most patients are moderately sedated. Every effort is made to maintain a quiet atmosphere. Rectal temperatures are recorded. Mild cathartics are used routinely. All patients are treated with warfarin sodium in the absence of specific contraindications. Patients remain in the CCU a minimum of three If the diagdays following resolution of symptoms. nosis of acute myocardial infarction is not confirmed, the patient is transferred to regular care. Patients with uncomplicated acute infarction are transferred on the sixth day. Those with complications remain

:

B.

C.

Thejnal CCU

diagnoses

with

an

of 434fiatients

initial

acute

myocardial

Table

I;

infarction

are

in

was conit could

neither

be established

proximately no evidence

15 per

nor

ruled

cent

In

out.

25 per cent of the group

ap-

there was

of infarction.

OBSERVATIONS IN MYOCARDIAL Of the 265 patients infarction

been excluded their admission

with

treated

INFARCTION

definite

acute myo-

in the CCU,

15 have

from further study, since prior to to the CCU

and was controlled

of success.

of

tabulated

In

established.

curred

to the

diagnosis

in 62 per cent this diagnosis

sidered

cardial

admitted

presumptive

The remaining

a cardiac with varying

arrest ocdegrees

250 patients are the

subject of this report. These

patients

years with

ranged

an average

in age from

age of 64.

28 to 94

Average

age

THE AMERICANJOURNAL OF CARDIOLOGY

Treatment

of Myocardial

for women was 67 and for men, 63. There were 180 men (720/‘) and 70 women (28%). CLASSIFICATION

~VOheart failure.

No clinical signs of cardiac de-

compensation.

R. c. D.

Heart failure. Diagnostic criteria include rales, S3 gallop and venous hypertension. Severeheart failure. Frank pulmonary edema. Cardiogenic shock. Signs include hypotension (systolic pressure of 90 mm. Hg or less) and evidence of peripheral vasoconstriction such as oliguria, cyanosis and diaphoresis. Heart failure, often with pulmonary edema, has also been present in the majority of these patients.

The distribution according to clinical severity of 250 patients admitted consecutively to the CCU with proved myocardial infarction is shown in Table II. Approximately a third of the patients had no evidence of heart failure, a third had mild to moderate heart failure, and the remainder had either pulmonary edema or shock. INCIDENCE

OF ARRHYTHMIA

l’he electrocardiograms displayed on the oscilloscopic monitors of all patients in the unit were carefully observed for the occurrence of abnormal rhythms. Arrhythmia was defined as the presence of any of the following: atrial, nodal, or ventricular premature complexes; sinus tachycardia or bradycardia; atria1 or nodal tachycardia; atria1 flutter or fibrillation; sinus arrest with nodal or ventricular escape rhythm; first, second, or third degree atrioventricular block; atrioventricular dissociation; and ventricular tachycardia, fibrillation, or asystole. Arrhythmias were observed in 226 (9Oyc) of the patients (Table III). The incidence of arrhythmia varied with the clinical severity of the infarction: The more severe the functional insult, the higher the incidence of arrhythmia. In all patients with pulmonary edema or cardiogenie shock arrhythmia developed. Some arrhythmias are relatively benign and some potentially or actually life-threatening. We consider that the recognition of a life-threatening arrhythmia should impel immediate consideration of definitive therapy by the observing physician or nurse. Five potentially life-threatening arrhythmias VOI.UME

20,

459 TABLE

Distribution

11

of Severity According Signs in 250 Patients

to C:linicxl

OF SEVERITY

To provide a clinical estimate of the severity of the myocardial derangement, each patient was classified into one of the following groups: A.

Infarction

OCTOBER

1967

Cardiac

Compensation

No heart failure Heart faiiure Pulmonary edema Cardiogenic shock Total

Incidence

Cardiac

No.

I” !<

81 96 26 47 250

33 38 10 19 100

TABLE III of Arrhythmia and Functional in 250 Patients

Compensation

No congestive heart failure Congestive heart failure Pulmonary edema Cardiogenic shock Total

Severity

Cases of Arrhythmia (7 No. /C .-

Total Cases

81 96 26 47 250

83 90 100 100 90

67 86 26 47 226

TABLE IV Relation of Presence or Absence of Shock to Incidence Life-threatening Arrhythmias in 250 Patients

Life-Threatening Arrhythmia

Sinus arrest or bradycardia 2nd or 3rd degree A-V block Ventricular tachycardia Ventricular fibrillation Ventricular asystole

Shock Absent 203 %

Cases

17 23 59 5 4

8 11 29 2 2

of

Shock Present 47 ‘;

C;,ses

s 14 17 4 14

11 30 36 9 30

are (1) sinus bradycardia or arrest, (2) second or third degree A-V block, (3) frequent ventricular premature complexes and ventricular tachycardia, (4) ventricular fibrillation and (5) ventricular asystole. The development of life-threatening arrhythmia was influenced by the presence or absence of shock (Table IV). Of 203 patients in whom shock did not develop, serious arrhythmia was observed in 91 (45%). Of 47 patients in whom shock appeared, 44 (94Q/,) had a life-threatening arrhythmia. Ventricular tachycardia was the most common in both groups. A-V block was approximately three times more frequent in patients who had shock than in those who did not. Ventricular fibrillation as the primary arrhythmia was uncommon in the absence of shock. Ventricular asystole occurred in 30 per cent of patients

460

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TABLE v Comparison of Morbidity and Mortality in Two Groups of Patients Treated Consecutively in a Coronary Care Unit Bkfore and After Certain Changes in Policy of Management

Cases

Patients Life-threatening mia Cardiac

,--Group BCases 101-250 Shock Shock Absent Present

No. %

87 87

13 13

116 77

34 23

No. % NO. % No. %* NO. %

44 51 19 22 2 11 23 26

12 92 11 85 2 18 9 69

47 41 11 9 6 55 8 7

32 94 25 74 1 4 29 85

arrhyth-

arrest

Survivors Mortality

*Per

r-Group ACases l-100 Shock Shock Absent Present

cent of patients

who had cardiac

arrest.

with shock, usually as a terminal event, but was rare in the patients who were not in shock. MORTALITY

Grouping patients together in a special facility with trained personnel and appropriate equipment is an expensive departure from the usual mode of hospital management. To determine whether the concept of a CCU was applicable to a university teaching hospital, we compared morbidity and mortality rates in the CCU with those for patients admitted to regular care. Since the unit accommodates about 40 per cent of the patients admitted to the hospital with acute myocardial infarction, there is ample clinical material for a comparative analysis. Patients treated consecutively on regular care were selected for study after review of their the same diagnostic criteria medical records; outlined earlier for the patients in the CCU were utilized. After eight months of operation, the data from 100 patients with confirmed acute myocardial infarction admitted consecutively to the CCU were compared with those from 100 patients admitted to regular care during the same period. It is probably impossible to eliminate all sources We beof potential bias in such a comparison. lieve that the two populations are similar since (1) admission to the CCU was on a bed-availability basis without selection for severity of illness, (2) the age distributions for the two groups were similar, (3) the sex ratios were identical and (4) the distribution based on the presence or absence of shock was the same. The results of the comparison were discouraging. Mortality in the hospital in the two groups was

Kimball essentially similar: 30 per cent for patients on regular care and 32 per cent for those in the CCU. Life-threatening arrhythmias occurred in 36 per cent of the patients on regular care. A higher incidence in the CCU, 54 per cent, probably reflects greater recognition consequent to monitoring and close medical supervision. On regular care 2 patients survived cardiac arrest and were discharged from the hospital. In the CCU 7 patients survived cardiac arrest and were transferred to regular care, but only 4 were discharged from the hospital alive. When it was realized that the CCU was not accomplishing its objective, several policy changes were instituted. In order to emphasize the principle of immediate defibrillation for cardiac arrest due to ventricular tachycardia or ventricular fibrillation, the nurses were authorized to apply precordial shock if a physician was not available within 60 seconds. Friendly rivalry developed between nurses and house officers. In the 18 months after initiation of the new policy, defibrillation has been applied within 60 seconds or less in every instance of cardiac arrest due to ectopic ventricular arrhythmia. Following the comparative analysis, rather rigid routines were established in application of the principle of prompt and vigorous treatment of life-threatening arrhythmias, hypotension, or heart failure. During the early experience with the CCU, house officers had considerable authority to determine the treatment of complications. Early signs of heart failure, premature ventricular complexes, ventricular tachycardia and other problems had been managed with a variety of therapeutic programs. The range of choices open to the house officer was proscribed, and the cardiology staff outlined the treatment to be used for each problem. Thus, three major changes were instituted after 100 patients (group A) had been treated in the CCU: (1) Immediate defibrillation by the available trained professional, nurse, or physician. (2) Prompt treatment was initiated for life-threatening arrhythmia, failure and hypotension. (3) The range of therapeutic programs for the physician-in-training were proscribed by the formulation of standard treatments by the senior cardiology staff. The improvement in morbidity and mortality in the management of the subsequent 750 patients (group B) in the CCU has been most gratifying. The data are analyzed according to the presence or absence of shock (Table v). In the patients who did not have shock, the incidence of lifeTHE

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threatening arrhythmias fell from 51 per cent in group A to 41 per cent in group B; the incidence of cardiac arrest fell from 22 per cent in group A to 9 per cent in group B; and the mortality fell from 26 per cent in group A to 7 per cent in group B. Only 2 (11%) of the patients in group A who suffered cardiac arrest without In group shock survived to leave the hospital. B, 6 patients (55%) of those with cardiac arrest were discharged from the hospital alive. In the last 14 months, during the accumulation of group B, not a single death due to primary arCauses of the rhythmia occurred in the CCU. 8 deaths in patients without shock were distributed as follows: 2 were due to intractable cardiac failure, and 2 were due to cardiac rupture; 4 patients were found dead in bed after transfer to regular care. Although the number of patients is not large, there has been no improvement in mortality of the patients with shock in group B compared to group A. Indeed, the morbidity and mortality from myocardial infarction complicated by shock is the same in the CCU as on regular care. The comparison of coronary unit care and regular care will be reported in detail elsewhere.5 The failure of intensive care to improve the mortality rate from shock presents a continuing challenge to current therapeutic concepts. FUNCTIONAL

SEVERITY

OF

INFARCTION

The usefulness of a clinical assessment of left ventricular function in analyzing morbidity and mortality in acute myocardial infarction is illustrated in Table VI. It is reasonable to assume that heart failure, pulmonary edema and shock represent increasing degrees of myocardial dysfunction secondary to infarction. The data from 250 patients consecutively treated in the CCU demonstrate that the average age, the incidence of life-threatening arrhythmias, the occurrence of cardiac arrest and the mortality increase as the clinical signs of myocardial abnormality are more severe. Particularly striking is the mortality of 81 per cent in patients with shock. Since 19 per cent of our patients suffered from shock, this inordinately high death rate adversely influences the mortality for the entire series. Comparison of results among different institutions should be enhanced by an analysis of clinical material based on the functional severity of the infarction. LATE

DEATHS

Unexpected death myocardial infarction

of the patient with acute after transfer from a spe-

VOLUME20, OCTOBER1967

461

Infarction

TABLE VI Morbidity and Mortality Related to Clinical .\ssessment of Ventricular Function in 250 Patients

Distribution (y?) Average age (yr. Incidence life-threatening mia (%) Incidence cardiac arrest Hospital mortality (%)

)

CHF

=

congestive

33 58

38 65

111 0 ‘)

19 67

36 5 6

46 15 17

73 4h 3x

94 77 81

arrhyth(%)

heart

failure;

Pulm.

=

pulmonary.

cialized care facility has been reported by a number of workers.6x7 Of our first 100 patients, 10 potentially long term survivors died from 4 hours to 65 days after transfer to regular care. Each had suffered a cardiac arrest or life-threatening They had usuarrhythmia while in the CCU. ally been transferred two or three days after the In complication had been adequately treated. the management of the subsequent series of 150 patients, those individuals who suffered lifethreatening arrhythmias or cardiac arrest were kept under surveillance in the unit an additional five days after the complication was successfully Following the initiation of this policy, treated. there were 11 late deaths in 1.50 consecutive admissions. Only 4 died unexpectedly. Seven These obdied from intractable heart failure. servations suggest that unexpected late deaths are more likely to occur in patients who have life-threatening arrhythmias or cardiac arrest early in the course of acute myocardial infarction. The incidence of late death appears to be reduced when patients at risk are monitored several additional days. POSSIBLE INFARCTION Sixty-eight patients in the entire series admitted to the CCU were classified as having possible myocardial infarction. Each had chest pain suggesting acute infarction. The electrocardiogram was abnormal but not diagnostic. Daily analysis of serum transaminase and lactic dehydrogenous activity did not confirm the presence of infarction. Hence, although infarction could not be disproved, there was no objective Patients in confirmation of the initial diagnosis. this group were usually transferred to regular care after three days in the CCU, and the length of hospitalization averaged about 21 days. Only 2 patients with a diagnosis of possible infarction died in the hospital, for a mortality rate Both patients were found dead in of 3 per cent. bed after transfer. Unfortunately, permission

Killip

and

for autopsy was not obtained for either. This low mortality rate suggests that a patient with chest pain which subsides and does not recur and who has nondiagnostic serial serum enzyme determinations and a stable nondiagnostic electrocardiogram may be transferred from a monitoring unit after a few days with very low risk. DISCUSSION The development of the coronary care unit represents one of the most significant advances in the hospital practice of medicine in the past An inordinate mortality and risk of decade. sudden death in patients suffering from acute myocardial infarction has been recognized for many years.2.8 Following the introduction of technics for cardiac massage and transthoracic defibrillation, sporadic applications of resuscitative measures to patients with myocardial inCardiac arrest farction were reported.gJo teams were developed and emergency measures The reapplied throughout hospital services. sults were disappointing.” ,12 Analysis of experience in resuscitation indicated that success was most likely if trained personnel with appropriate equipment were immediately available when cardiac arrest occurred.” Unfortunately, this cannot be accomplished in all instances on a busy hospital service. With delay in application of definitive therapy when the patient was remote from available services, survival was rare. It remained for Day13 to formulate the next logical step. He segregated patients with myocardial infarction in a specially designed unit, monitored the heart rate and rhythm, and trained nurses to administer precordial shock for defibrillation or transthoracic pacemaking. He reported striking improvement in the mortality rate compared to previous experience in a nonteaching hospital. Other reports6 3’ ,14of the application of the coronary care unit concept have appeared. As experience in managing patients in these units has accumulated, the emphasis has shifted from treatment of cardiac arrest to prevention of this potentially catastrophic complication. Such a policy has been highly successful in our own institution. Although frequently sudden, and hence often “unexpected,” the cessation of adequate circulatory function is usually preceded by warning signals. If the cardiac rate and rhythm are being closely monitored, early prodromata may be recognized and treatment instituted to prevent cardiac arrest. For exam-

Kimball ple, rapid atria1 fibrillation or flutter is usually preceded by the onset of atria1 premature complexes. Complete heart block is usually preceded by conduction disturbances manifesting as first or second degree block. Sudden, complete heart block or asystole is uncommon in the absence of intractable cardiogenic shock. Frequent ventricular premature contractions with close coupling intervals are the harbinger of ventricular tachycardia or fibrillation. The relation of the coupling interval of an ectopic impulse to the subsequent development of fibrillation in the atrium or ventricle has been emphasized.15 Thus, the emphasis in management of myocardial infarction in a special care unit, based on sound clinical and physiologic experience, has shifted. The coronary care unit remains an area where the professional personnel must retain constant vigilance and a high degree of expertise for treating the emergent cardiovascular crisis. It is now apparent, however, that the prime function of the coronary care unit is prevention. Recognition and prompt treatment of the potentially life-threatening complications, especially arrhythmias, appears to have significantly reduced the mortality of patients with myocardial infarction. Experience at the New York Hospital, however, suggests that to accomplish this aim a number of modifications in traditional policies of medical care are required. The coronary care unit in this institution was developed in an attempt to evaluate its impact An expensive, specially on medical care. equipped unit which alters the usual role of the nurse and physician in patient management can be justified only if it significantly decreases morbidity and mortality. We have carefully defined the diagnostic criteria for infarction so that the data from patients treated in different parts of the hospital can be compared. Our data can thus be compared with those of other workers. Unfortunately, diagnostic criteria are conspicuously absent from many reports, making comparison difficult if not impossible. The group of patients with possible infarction, separated according to our criteria, represent an important population among the patients admitted. Our data indicate that when objective evidence of infarction is not forthcoming, despite a very suggestive history, the risk of death is exceedingly low. Such patients can be moved to regular care with relative safety. Obviously, if this group of patients is included in statistics describing the fate of those with established inTHE

AMERICAN

JOURNAL

OF

CARDIOLOGY

Treatment

of Myocardial

farcts, the mortality rate would be considerably reduced. If this were done in our own series, the mortality would fall from 28 to 22 per cent for the entire series, and from 24 to 21 per cent for the last 150 patients. A reasonable assumption is that prognosis in myocardial infarction will be influenced by the degree of altered myocardial mechanical performance. Utilizing the presence of heart failure, pulmonary edema, or shock as rough clinical guides to myocardial function, we have found a good correlation with mortality. Patients without evidence of heart failure have had a low mortality. Patients with pulmonary edema, and especially shock, have had a high mortality. Since hospital populations differ, this functional classification should be helpful in comparing results from one institution to those of another. PRINCIPLES

OF CORONARY

UNIT

CARE

Guides for design and instrumentation are available from many sources. If the guiding principles of simple yet adequate “hotel” facilities (it is usually stated firmly but without overwhelming proof that privacy is important), reliable monitoring instruments for heart rate and rhythm, immediate availability of resuscitation equipment and constant attendance by trained personnel are borne in mind, a variety of worthwhile designs and arrangements is possible. Instrumentation: Engineering and technical advances have made available devices to monitor a wide range of body functions. Indeed, the creation of a new device to monitor a physiologic variable seems to require only the combination of ingenuity and money. At present, however, the only body function it is essential to monitor with electronic devices, in the management of the majority of patients with acute myocardial infarction, is the rate and rhythm of the heart as revealed by a continuously displayed electrocardiogram. Appropriate alarms may be activated by changes in rate above or below It is important to have the elecpreset limits. trocardiogram displayed both at the bedside and A manual or autoin a nearby nurse’s station. matic strip recorder at the central station is helpful. Whether or not instruments for monitoring other body functions are useful or should be available depends upon local situations. We have not found monitoring the temperature, respiration, or the electroencephalogram helpful. We have routinely utilized direct measurement of arterial pressure by cannulation of a VOLUME 20, OCTOBER 1967

Infarction

463

peripheral artery in hypotensive or shock states. This technic has been of considerable aid in adjusting pressor therapy and determining central aortic pressure when indirect peripheral technics measurement of blood pressure were for unreliable.

Future progress in instrumentation will probably occur in two areas: (1) improved arrhythmia detection and (2) serial analysis of left ventricular function. Although apparatus currently available can detect changes in ventricular rate, the diagnosis of arrhythmia is accomplished by Automation with trained nurses or physicians. on-line data analysis will vastly extend the clinical applicability of monitoring, now limited by a Such an analysis shortage of trained personnel. program faces many difficulties, but several groups are working on computer technics for diagnostic electrocardiography.i6 .I7 Of great value would be the perfection of devices for “nondestructive,” continuous measurement of some index of ventricular contractility It is and the distribution of cardiac output. likely that heart failure, hypotension and shock are gradually occurring events, rather than precipitant, as they SO often appear to the cliniEfforts to reduce mortality in myocardial cian. infarction as well as many other conditions will be greatly enhanced by the abilit!. to follow myocardial performance. Personnel: Successful medical care in a hospital requires the cooperation of individuals with varied skills. Too often, physicians have overlooked the important role played by the nursing profession. In the coronary care imit, close cooperation between the nurse and phy-sician is In our opinion, optimal treatment in essential. a unit designed and equipped for patients with myocardial infarction cannot be attained unless certain prerogatives hitherto reserved for the physician are delegated to the nurse. The overriding fact is that the nurse is frequently the only medically trained professional at the bedside during important clinical events. If resuscitation is to have a reasonable chance of success, it must be initiated promptly with onset of cardiac arrest. The nurse must be trained and given the authority to treat cardiac arrest, Seriincluding application of precordial shock. ous morbidity and mortality can be prevented by treatment of life-threatening arrhythmias. It is therefore imperative to train nurses to recognize these complications and to give them authority to initiate treatment while awaiting arrival of the physician.

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and

The delegation of medical authority is a departure from usual medical practices. It is a Yet challenge to physicians and nurses alike. the lesson seems clear: Special treatment by trained personnel in a coronary care unit saves lives. However, the physician, who traditionally initiates treatment, is frequently occupied with other tasks during the unexpected emergency and is not immediately available. It seems certain that the next few years will witness a number of bold and necessary experiments in the delegation of medical responsibility from the physician to trained nurses and medical assistants as we attempt to provide high quality medical care to all our citizens. SUMMARY

The results of treatment of 250 patients with established acute myocardial infarction in a coronary care unit in a university hospital are described. The criteria for diagnosis have been carefully defined. In 62 per cent of patients admitted with a tentative diagnosis of acute infarction, the initial impression was confirmed. Fifteen per cent of patients admitted to the unit were classified as having possible infarction; in this group, the mortality rate was 3 per cent. A classification of functional severity based on clinical evidence of heart failure or shock is presented. Morbidity and mortality in acute myocardial infarction are related to the functional severity of the illness. Although arrhythmia is common, the overriding importance of five life-threatening arrhythmias is emphasized. Mortality of patients in the coronary care unit was not improved in comparison to those treated under regular care until strong central direction of therapeutic programs, immediate treatment of arrhythmia in cardiac arrest, and delegation of some medical authority to trained nurses was accomplished. The change in concept of the purposes and practices of special coronary care from resuscitation to prevention of arrhythmia is emphasized. The mortality in myocardial infarction complicated by shock remains high. In the absence of shock, aggressive medical treatment in the coronary care unit reduced mortality from 26 to 7 per cent. The implications of these data in the management of patients admitted to a hospital with a diagnosis of acute myocardial infarction are discussed. ACKNOWLEDGMENT This study would not have been possible without the advice, criticism and cooperation of the nurses who have

Kimball devoted themselves to the development of specialized care for patients with acute myocardial infarction. We are especially indebted to the Misses Mary Fordham, R.N., and Christine Haas, R.N., and Mrs. Ruth Boland Mullaly, R.N. REFERENCES 1. DAY, H. W. An intensive coronary care area. Die. Chest, 44: 423, 1963. 2. BROWN, K. W. G., MACMILLAN, R. L., FORBATH, N., MEL’GRANO, F. and SCOTT, J. W. Coronary unit, an intensive care centre for acute myocardial infarction. Lancet, 2: 349, 1963. 3. KILLIP, T. and KIMBALL, J. T. Experience with monitoring myocardial infarction of the New York Hospital-Cornell Medical Center: Comparison of regular hospital care and coronary unit care. Pmt. New England Cardiovas. Sot., 24: 27, 1965-1966. 4. KIMBALL, J. T., KLEIN, S. W., STRINGFELLOW,C. A. and KILLIP, T. Comparison of coronary unit and regular hospital care in acute myocardial infarction. Circulation, 34 (Suppl. III): 143, 1966. 5. KIMBALL, J. T. and KILLIP, T. Unpublished data. 6. LOWN, B., FAKHRO, A. M., HOOD, W. B. and THORN, G. W. The coronary care unit, new perspectives and directions. J.A:M.A., 199: 188, i96f’. 7. GOBLE. A. J.. SLOMAN. G. and ROBINSON. J. S. Mortality reduction ‘in a coronary care unit. &it. M. J., 1: 1005, 1966. 8. STEPHEN, S. A. Discussion. In: SNOW, P. J. D. Treatment of myocardial infarction with propranolol. Am. J. Cardiol., 18: 460, 1966. 9. BLOOMFIELD,D. K. and MANNICK,J. A. Successful resuscitation in acute myocardial infarction with ventricular fibrillation: Report of a case. New England J. Med., 258: 1244, 1958. 10. Moss, A. J. et al. Closed-chest cardiac massage in the treatment of ventricular fibrillation complicating acute myocardial infarction. Report of three cases with survival. New England J. Med., 267: 679, 1962. 11. MINOGUE, W. F., SMESSART, A. A. and GRACE, W. J. External cardiac massage for cardiac arrest due to myocardial infarction. A changing concept. Am. .I. Cardiol., 13: 25, 1964. 12. KLASSEN, G. A., BROADHURST,C., PERETZ, D. I. and JOHNSON,A. L. Cardiac resuscitation in 126 medical patients using external cardiac massage. Lancet, 1: 1290, 1963. 13. DAY, H. W. Effectiveness of an intensive coronary care unit. Am. J. Cardiol., 15 : 51, 1965. 14. The Current Status of Intensive Coronary Care. American College of Cardiology-University of Pennsylvania Medical Center Symposium. Edited by MELTZER, L. E. and KITCHELL, J. R. New York, 1966. Charles Press. 15. KILLIP, T. and LAMBREW, C. T. Electrical control of cardiac rhythm. Ann. Rev. Med., 17: 477, 1966. 16. POROY, L. et al. Computer analysis of the electrocardiogram. J. Mt. Sinai Hosp., 34: 69, 1967. 17. WORTZMAN,D., GILMORE, W., SCHWETMAN,H. and HIRSCH, J. I. A hybrid computer system for the measurement and interpretation of electrocardiograms. Ann. New York Acad. SC., 128: 876, 1966. THE AMERICANJOURNAL OF CARDIOLOGY