See Also: Biography of Howard Burchell
Early Days of Pacing
Indications for and Results of Implanting Cardiac Pacemakers
Cardiac pacing intrigued Burchell, offering, as it did, a clinical equivalent of the rhythms modification he used in the experimental laboratory. In 1964 he, Connolly and Ellis reported on the first 38 patients who had completely implantable units (Electrodyne and Medtronic) placed at the Mayo Clinic during 1962-1964. Prior to that time (1961-1962) it appears that external generators were used in 2 patients at Mayo, connected to implanted leads, one myocardial and one transvenous. It is remarkable that so early in the experience of cardiac pacing Burchell clearly recognized the hemodynamic benefit of maintaining AV synchrony and the potential of using AV ablation for PAT. He also included, for comparison, a contemporaneous control group of complete heart block patients who did not receive a pacemaker. Interestingly the majority of these admittedly less symptomatic patients did quite well on thiazides or sublingual Isuprel.
Burchell HB, Connolly DC, Ellis, FH. Indications for and Results of Implanting Cardiac Pacemakers. Am J Med, 1964;37:764-777.
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Management of Cardiac Tachyarrhythmias with Cardiac Pacemakers 
By the late 1960s it was known that pacemakers could be therapeutic in cases of ventricular tachycardia. Burchell and Merideth presented clear illustrations of successful overdrive pacing and also discussed the notion of anti-tachycardia pacing using random extra stimuli from a fixed rate mode, non-invasive function changes newly available at that time. Just as carefully portrayed was the inconsistency of such approaches with arguments made for continued growth in the sophistication of pacemaker technology.
Burchell HB, Merideth J. Management of Cardiac Tachyarrhythmias with Cardiac Pacemakers. Ann New York Acad Sci, 1969; 167:546-556. Back to Top
Pre-Excitation: Recognition and Intervention Ventricular Pre-Excitation in the Isolated Perfused Heart 
In 1939 Burchell spent six months at the National Heart Hospital in London under the guidance of Dr (later Sir) John Parkinson, the P in WPW. Thereafter he maintained a strong interest in the hypotheses used to explain WPW ECG patterns. Around 1951, still early days of cardiac catheterization, he made intracardiac recordings in a WPW case as had been reported by his friend Charles Kossmann in 1950. Interestingly, when poring over electrical recordings, he occasionally noticed the WPW phenomenon in his isolated perfused dog heart preparation. Because early septal activation still occurred after the ventricular free walls had been removed, he postulated the existence of a conducting pathway from the atrium to the right side of the septum.
Burchell HB. Ventricular Pre-Excitation in the Isolated Perfused Heart. Am J Physiol, 1952;169:721-725. Back to Top
Atrioventricular and Ventriculoatrial Excitation in Wolff-Parkinson-White Syndrome (Type B) 
For some years Burchell had talked with his friend. Dirk Durrer in Amsterdam, about interrupting the bundle of Kent at surgery. The ideal case to try this on would be a patient who had WPW and was coming to open-heart surgery for some other reason. It was not until 1966 that he and surgeon Dwight McGoon had the opportunity of testing this idea. The 43 year old man had an ASD, paroxysmal tachycardia, and WPW Type B. At operation early activation was found at the base of the right ventricle near the AV groove. Injection of procaine into the base of the right ventricle temporarily abolished the pre- excitation of the ventricle. Burchell HB, Frye RL, Anderson MW, McGoon DC. Atrioventricular and Ventriculoatrial Excitation in Wolff-Parkinson-White Syndrome (Type B): Temporary Ablation at Surgery. Circulation, 1967; 36:663-672 Back to Top
Studies on the Spread of Excitation through the Ventricular Myocardium 
Burchell was introduced to experimental medicine by Arlie Barnes, at the Mayo Clinic, in the late 1930s. Together they studied the ECG effects of chromic catgut-induced localized pericardial injury, comparing it with the changes seen after ligating a coronary artery (Am Heart J 1939, 18: 133-144). He also put together a detailed analysis of the heart's movements seen in ultra high-speed (1,200 frames/sec) cines made by Maurice Visscher and his colleagues at the University of Minnesota (Am Heart J, 1941, 22: 794-803). When he returned to the Mayo Clinic after war service, in 1946, he subjected many of his clinical ideas to testing in the experimental lab. In the realm of electrophysiology his most active interest was in the spread of excitation.
He and his long-time collaborator. Ray Pruitt, wanted to better understand the sequence of activation of the septal and free wall myocardium. In a series of studies published in the then new journal, Circulation, in the early 1950s, they mapped activation delays at multiple sites in the Langendorff-perfused dog heart. By removing sections of the heart or by making judicious incisions they deduced the pathways of impulse propagation.
They found that the mean pathway in the muscular mass of the dog's ventricular septum is from apex to base. The left side of the septum is activated before the right side, and the apical part of the right side is activated before its base. Incisions in either side of the septum usually produced on the homolateral side delays in excitation of the septal surface above the injury as well as below it. The incision on the left side of the septum usually resulted in an increased duration of the P-R interval (Circulation, 1952, 6:161-171).
Burchell HB, Essex HY, Pruitt RD. Studies on the Spread of Excitation through the Ventricular Myocardium: II. The Ventricular Septum. Circulation, 1952, 6:161-171. Back to Top
Action Potentials Supporting the Presence of Specialized Conduction Pathways in the Dog's Ventricle
In a second report, in Circulation Research the next year, and using the same model, Burchell described early potentials of short duration preceding the main muscle excitatory potentials. These were frequently encountered on the upper left surface of the septum and preceded the main muscle potentials by 5-20 milliseconds. He attributed these early potentials to specialized conducting tissues or to activation of bundle branch fibers. Burchell HB, Essex HE, Lambert EH. Action Potentials Supporting the Presence of Specialized Conduction Pathways in the Dog's Ventricle. Research in Progress, 1952; : 186-188.
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The Value of Esophageal Electrocardiogram in the Elucidation of Postinfarction Intraventricular Block
These laboratory investigations naturally led to efforts to better map the sequence of ventricular activation in man. His earliest efforts used an esophageal electrode, an approach he had earlier evaluated for detecting healed posterior infarcts, where information from the standard leads was equivocal (Am J Med Sc, 1948, 216:492-500). Mapping with the esophageal lead was the basis of a 1951 paper where late posterior LV activation was attributed to peri-infarction block complicating prior posterior (inferior) myocardial infarction. Burchell recognized similar, but not identical, findings made earlier by Frank Wilson and S.R. First. Burchell HB, Pruitt RD. The Value of Esophageal Electrocardiogram in the Elucidation of Postinfarction Intraventricular Block. Amer Heart J, 1941; 42:81-87.
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