527

Preliminary Communications

AN OPERATION FOR FACILITATING

EXTERNAL PACING OF THE HEART IN

THE LONG-TERM TREATMENT OF

HEART-BLOCK

THE earliest attempts to pace the heart artificially incases of complete heart-block were made with electrodesapplied directly to the skin over the precordium. Elec-trical stimulation of the heart was achieved through theintact chest wall and the voltage required was of the orderof 100 V. As far as pacing was concerned this method wassatisfactory. The main objection arose from the fact thatthe pectoral muscles lay between the electrodes and theheart; with each stimulus the pectoral muscles gave aviolent jerking contraction, which was intolerable to thepatient. Indeed the field of stimulation spread beyond thepectoral muscles to include other muscles of the pectoralgirdle and the abdominal wall.A later method involved the application of electrodes

directly to the heart itself, with the lead wires passingthrough the chest wall to an external pacemaker. Stimuliof only a few volts were sufficient, and the patient was notconscious of the stimulation. Unfortunately infection

inevitably tracked along the lead wires from the pointwhere they pierced the skin, and this led to sepsis at themyocardium.

In the past ten years special efforts have been made todesign a satisfactory implantable pacemaker. The manydifferent approaches to this problem have been sum-marised by Siddons,2 who points out the many difficultiesand disappointments of existing methods.

Since an external pacemaker with external electrodeshas obvious advantages I have re-examined the problemof its use. It seemed that an alternative approach wouldbe to modify the chest wall in such a way that externalelectrodes did not cause contraction of the pectoralmuscles.

METHOD

ExperimentalIn dogs a window was excised from the chest wall over the

heart, so that in this area the heart, covered only by peri-cardium, was in direct contact with the overlying skin. Thedog’s heart could then be paced through a pair of smallelectrodes placed on this skin area using electrode jelly for thecontact. The electrodes, leads, and pacemaker itself were, ofcourse, entirely external to the animal. Since the muscles andnerves had been excised there was no contraction of pectoralmuscles from direct or reflex stimulation. The animal showedno signs of being aware of the stimuli from the pacemaker. Thestimulus required to pace the dog’s heart by this method wasapproximately 15 V for 3 milliseconds. The actual thresholdvaried a little with the positioning of the electrodes.Clinical

Following these successful experiments the operation wascarried out on one patient in February, 1965, at St. Mary’sHospital, London.The patient had been in complete heart-block for three years.

At operation a disc of the chest wall, including muscle andcostal cartilages and approximately 2 in. in diameter, wasexcised over the region of the ventricles down to the peri-cardium. Soft tissues, which included the internal mammaryartery and a portion of the anterior margin of the pleura, wereremoved or displaced laterally, and a Thiersch graft was laidinto the circular depression.

Recovery was complicated by a pneumothorax and surgicalemphysema but these conditions responded to treatment.

1. Zoll, P. M. New Engl. J. Med. 1952, 247, 768.2. Siddons, A. H. M. Triangle, 1964, 5, 182.

From the time of operation pacing was commenced throughtwo electrodes placed on the Thiersch graft. Initially thestimulation threshold was 6 V for 4 milliseconds, although thisrose to 18 V for 4 milliseconds. This rise in threshold was notconsidered to be a significant objection to the method as therewas no evidence of any contraction of skeletal muscles and the

patient was completely free of any sensation from the pace-maker stimuli. Moreover in the experiments with dogs a

similar rise in threshold had been observed initially, but later,when the cedema had subsided and healing was complete, thethreshold fell again.

RESULTS AND DISCUSSION

The patient was satisfactorily paced for three weeks bythis external route, but at the end of this period the grafthad not healed over. To assist healing, the external pacingwas replaced by pacing via an endocardial electrode

passed down the jugular vein. During this period ofendocardial pacing the patient developed sudden cardiacarrest and died. A Thiersch graft was used in preferenceto a skin flap in the hope of reducing the threshold, butin retrospect this was an error.The purpose of this communication is to describe a new

technique in pacing the heart. The basic principleinvolved is that of modifying, by operation, the precordialchest wall so that the intensity of stimulus required toexcite the myocardium from the exterior is reduced, andthere is no excitation of sensory receptors or of themuscles in that region.With further development this should make possible

the long-term pacing of the heart using external electrodeswith an external pacemaker.

SUMMARY

A technique has been developed for avoiding thestimulation of pectoral muscles from external pacing byelectrodes placed over the precordium. A 2-in. disc ofchest wall, including muscle and costal cartilages, wasexcised over the ventricles; a Thiersch graft was appliedand electrodes were placed on the graft. A patient waspaced for 3 weeks by this method.

I am grateful to the council of the Royal College of Surgeons for thefacilities made available in the department of physiology, and par-ticularly to Prof. David Slome for advice and encouragement in theexperimental aspects of this research. Dr. Dennis Hill, of the

department of anxsthetics, cooperated in the experimental work andgave invaluable help with instrumentation. The clinical work is beingdone in conjunction with Mr. Lance Bromley and Dr. EdwinBesterman at St. Mary’s Hospital, London.

PETER H. LORDM.CHIR. Cantab., F.R.C.S.

Lately H. N. SmithResearch Fellow*

* Present appointment: Consultant Surgeon, High Wycombe.

Department of Physiology,Royal College of Surgeons of England,

Lincoln’s Inn Fields,London, W.C.2

PREVENTION BY ISOPROPANOLAMINE

OF KWASHIORKOR-TYPE FATTY LIVERIN THREONINE-DEFICIENT RATS

A FATTY liver, microscopically similar to that found inkwashiorkor, can be produced by feeding weanling rats adiet containing 9°o casein, 5% fat, and 81% sucrose,supplemented with salts, vitamins, choline, methionine,cystine, and tryptophan. This diet has a low content ofthreonine. The formation of the fatty liver can be pre-vented by the addition to the diet of 0-36° L-threonine,but not by addition of D-threonine, or other essentialaminoacids.l 2 The degree of fatty infiltration can be

1. Arata, D., Harper, A. E., Svenneby, G., Williams, J. N., Jr., Elvehjem,C. A. Proc. Soc. exp. Biol. Med. 1954, 87, 544.

2. Singal, S. A., Hazan, S. J., Sydenstricker, V. P., Littlejohn, J. M.J. biol. Chem. 1953, 200, 883.