Diagnosing Heart Disease Physical Diagnosis

During the mid-eighteenth century, Leopold Auen-brugger, working in Vienna, described a new diagnostic technique. By percussing the chest - that is, by striking the chest and both listening to and feeling the reverberation - he was able to tell, to some extent, what lay within. His method enabled him to ascertain the size of the heart and to determine the presence of fluid in the chest, a common manifesta tion of heart failure. However, because prevailing disease theories placed little importance on the localization of lesions in the body, Auenbrugger's technique attracted little attention. His work was to gain greater attention as a result of a political upheaval in a nearby country.

The French Revolution not only reshaped the political structure of France, but also radically changed the institutions that controlled hospitals and medical schools. Physicians practicing in these institutions changed the perception of disease. Their emphasis on the importance of specific lesions in the body stimulated a desire to correlate clinical physical findings with anatomic lesions found at autopsy. Every day, Parisian physicians in the early nineteenth century went from bedside to bedside, examining patients with all manner of diseases, and all too often they had the opportunity to correlate their physical findings with those found at autopsy. In this milieu, René Laennec invented the stethoscope for listening to sounds in the chest. Auenbrugger's technique of percussion became widely used when it was discovered that lesions could be localized in the chest with Laennec's stethoscope. Although both of these techniques were used primarily to diagnose diseases of the lung, they were also used to diagnose heart problems.

Auscultation with the stethoscope was not immediately accepted. It was a skill that took time and practical experience to learn, and one that could yield misleading results. Furthermore, it was of no help in diagnosing many cardiac diseases that did not produce physical signs and could be diagnosed only by the patient's own sensations. One of these diseases was manifested by chest pain and is now understood to be caused by occlusion of the coronary arteries of the heart.

Diagnosis by History: Coronary Heart Disease In addition to anatomic studies, eighteenth-century practitioners published descriptions of coronary heart disease based on patients' reports of characteristic symptoms. (Coronary heart disease, as we now use the term, encompasses such entities as angina pectoris and myocardial infarction, or "heart attack.") In 1768 William Heberden of London gave a lecture at the College of Physicians of London, published in 1772, in which he coined the term angina pectoris and differentiated it from other pains in the chest:

They who are afflicted with it, are seized while they are walking, (more especially if it be up hill, and soon after eating) with a painful and most disagreeable sensation in the breast, which seems as if it would extinguish life, if it were to increase or to continue; but the moment they stand still, all this uneasiness vanishes. ... In all other respects, patients are, at the beginning of this disorder, perfectly well. . . . Males are most liable to this disease, especially such as have past their fiftieth year.

Heberden focused on the clinical manifestations of the disease, not on its cause. However, others had earlier described disease of the coronary arteries. The English surgeon John Hunter, after finding this condition during an autopsy on a person who had died in a fit of anger, declared: "My life is in the hands of any rascal who chooses to annoy me." Hunter's words proved true. He collapsed and died in 1793, presumably of a myocardial infarction, soon after leaving an acrimonious meeting.

Many different manifestations of coronary heart disease were noted over the next century. Although the first diagnosis before death was probably made in 1878, recognition of coronary heart disease did not become widespread until its diagnosis by technological means became common early in the twentieth century. That new technology was derived in some ways from one of the oldest forms of diagnosis -feeling the pulse.

Mechanical Diagnosis: The Pulse and the Electrocardiogram

People have felt the pulse to diagnose disease since antiquity. Attempts to analyze the pulse have included timing its rate and noting its pattern, particularly any abnormalities in its rhythm. John Floyer, who in 1709 constructed a portable clock with which to time the pulse, noted that the natural pulse rate varied according to a person's place of residence, age, and sex.

A very slow pulse, one of the most striking abnormalities, was often associated with intermittent loss of consciousness, or syncope. This condition has come to be known as Stokes-Adams (or occasionally Adams-Stokes) disease, after two Dublin physicians, Robert Adams and William Stokes, each of whom described characteristics of the disease in the first half of the nineteenth century. Today this condition is treated with pacemakers (described later). Early attempts to understand the cause of a slow beat led to the development of mechanical devices for analyzing heartbeat.

In 1859 the French physiologist Etienne-Jules Marey drew on the earlier work of German physiologists such as Carl Ludwig, inventor of the kymograph, to devise an instrument that could produce a permanent record of the cardiac pulsations on a drum of smoked paper. Marey used this instrument to record the pressure within the heart of a horse. He also recorded pressure tracings from the arteries that could be felt on the surface of the human body. In the 1890s the English physician James Mackenzie developed the polygraph, an instrument that recorded the pulsations of the arteries and veins directly onto a continuous strip of paper. With this device he was able to describe many abnormalities of the pulse and to identify the cardiac causes of several of these. His work was advanced by the London physician Thomas Lewis, who analyzed abnormal cardiac rhythms with the electrocardiogram (EKG), a new instrument that could record the electrical signals generated by the heart. Invented in 1902 by Willem Einthoven, the EKG earned its inventor the 1924 Nobel Prize in medicine or physiology.

Because Lewis and Mackenzie were working within a social system that placed a high value on the clinical skills of the physician and a low value on the use of technology, neither thought of the EKG machine as an instrument that could replace the senses of the skilled bedside observer. However, working in a climate in which the role of the physician was not so socially important, James Herrick of Chicago saw the value of the EKG for diagnosing diseases that could not be diagnosed with the unaided senses. Coronary artery disease was one such disease. Herrick's clinicopathological description of it in 1912 received little attention; however, after his collaboration in 1918 and 1919 with Fred Smith to describe the characteristic EKG changes, Herrick's definition of the disease entity became widely recognized. This was an early example of a pattern to be repeated throughout the twentieth century - a disease first described clinically would become more widely accepted once it was defined in terms of a laboratory technique.

Hemodynamic Diagnosis: Diagnosis by Measuring Physiology

In a sense, the development of hemodynamic diagnosis was returning full circle to the issues of pressures and volumes in the heart that Harvey was working with in 1628. Harvey had been unable to measure these parameters in human hearts. Physicians' daily use of these measurements today is in large part the result of a self-experiment performed in 1929.

During the spring of 1929, while working in the relatively unsophisticated setting of a small German country hospital, Werner Forssmann became fascinated by the work of nineteenth-century French physiologists such as Marey, and particularly by a diagram showing Marey's recorded pressures from a horse's heart. Forssmann decided to perform the procedure Marey had used on himself by passing a urethral catheter from the main vein in his arm up into his heart, hoping to provide a new, more effective means of delivering medication. Despite his supervisor's refusal to grant him permission, Forssmann was determined to perform the experiment. However, he needed the cooperation of the surgical nurse who controlled access to the necessary instruments.

Forssmann was eventually so successful in convincing her of the safety and importance of the experiment that she insisted he perform the experiment on her. Forssmann, however, persuaded the nurse to lie down on a cart, where he strapped her down, claiming the action to be a "precaution against falling off." With the nurse thus immobilized, Forssmann inserted the catheter into his own arm, pushed it through the veins into his heart, and then released the nurse. She helped him walk down the stairs into the basement, where an X-ray image confirmed that the catheter was indeed within his heart. The experiment earned Forssmann some praise, but much more hostility, and as a result, he left academic medicine and did no more work on cardiac catheterization.

But others went forward with Forssmann's method. In 1932 Dickinson Richards, Jr., and André Cour-nand began collaborating on studies of the heart and circulation at New York Hospital. They started with the assumption that the heart, lungs, and circulatory system form a single system for the exchange of gases between the environment and the organism. In order to calculate the cardiac output, they needed to obtain blood samples from the right atrium, the cardiac chamber that collects blood from the body before pumping it to the lungs to receive more oxygen. After practicing Forssmann's technique on laboratory animals for four years, Cournand, Richards, and their colleagues determined that the passage of catheters into animals' hearts did not significantly interfere with cardiac functioning.

Although their first attempt to perform the procedure on a patient, in 1940, was unsuccessful, they were encouraged to continue their efforts by senior investigators studying cardiac output determined by the ballistocardiogram, an instrument that recorded the motion of the body caused by the heartbeat. Cournand was eventually able to insert a catheter into a human heart and to compare the directly measured cardiac output with that determined by the ballistocardiogram. He showed that cardiac output as measured by the ballistocardiogram was too low. More important, he showed that it was practical and safe to insert a catheter routinely into the right side of the human heart.

During the next few years, Richards, Cournand, and their colleagues designed a new catheter that was easier to maneuver and constructed a measuring device that enabled them to record simultaneously four different pressure tracings along with the EKG. In 1942 they advanced the catheter into the right ventricle, and in 1944 into the pulmonary artery, thus making it possible to measure the hemodynamic pressure and the amount of oxygen present in the blood at each stage of passage through the right side of the heart. Funded by the federal government through the Committee on Medical Research, from 1942 to 1944 this group studied more than 100 critically ill patients suffering from traumatic shock, hemorrhagic shock, burn shock, and shock caused by rupture of an internal organ. They outlined the profound effects of reduced circulating blood volume on cardiac output, particularly on the flow of blood to peripheral organs and the kidneys, and described how the condition could be reversed by replacement of the appropriate volume of blood. Later, they used the same catheterization technique to diagnose congenital cardiac defects: An abnormal opening between the cardiac chambers was detected by means of pressure and oxygen measurements made with the catheter. Similarly measuring the pressure in the cardiac chambers was found to be valuable for diagnosing acquired cardiac defects, particularly diseases of the heart valves.

Richards and Cournand shared the 1956 Nobel Prize in medicine or physiology with Forssmann. Not long after the discovery that right-sided pressures could be measured, others extended the technique to measure pressures on the left side of the heart. The procedure has greatly aided our understanding of the pathophysiology underlying various forms of congestive heart failure. The invention of electronic devices for measuring pressures has enabled physicians to analyze the pulsatile pressure tracings in various disease states. Other investigators have shown how injecting dye into the heart can aid in diagnosis. Today, the passing of diagnostic catheters into the heart is such a routine procedure that patients may not even spend a night in the hospital.

These techniques for hemodynamic monitoring have come to define and dominate places in hospitals set aside for the care of critically ill patients. Some intensive care units are designed specifically for the care of patients suffering from coronary artery dis ease. Physicians and nurses working in coronary care units, which first became widespread in the United States in the 1960s and 1970s, utilize both hemodynamic monitoring and EKG monitoring of the pulse, the latter to detect and correct life-threatening cardiac dysrhythmias. In other intensive care units, cardiac catheters are used to monitor the cardiac function of patients suffering from a wide variety of noncardiac disorders. Although they are useful for some groups of patients, whether coronary care units are necessary for all patients with myocardial infarction remains unclear.

Western ideas about what constitutes heart disease are based increasingly in technological diagnosis and on the ability to invade the thorax in order to make diagnoses and also to intervene. Along with the increased use of technology has come the unstated but generally pervasive assumption that diagnosis has finally become objective, transcultural, and reflective of some natural, inevitable underlying diagnostic system. The validity of this assumption is doubtful. Historical analysis shows that the definition of heart disease, as well as of the specific diseases and their appropriate diagnostic tests, is a product of both biology and culture.

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