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the thinned trabeculae in the proximal ends of the ribs.'" The tumor-simulating intrathoracic masses of heterotopic marrow occur characteristically either unilaterally or bilaterally in the posterior mediastinum, often below the seventh thoracic vertebra and sometimes with a segmental arrangement.ll Radiologically, they present as rounded, soft tissue opacities paravertebrally with a clear-cut outline, sometimes lobulated due to the superimposition of several densities. No calcification has been reported in these masses, nor has there been any report of bone erosion. Intrathoracic EMH appears to follow a constant pattern resulting in this uniform radiologic picture, the findings of which have been correlated with pathologic studies.s.5*15 Other diagnostic features in EMH include a history of chronic anemia, splenomegaly (or history of splenectomy) and possible radiologic bone changes characteristic of the hemopoietic disorder ( eg thalassemia) In the differential diagnosis, the following lesions should be considered: ( 1) Neurogenic tumor should be considered first, as it is the most common posterior mediastind tumor. However, in 50 percent of the cases there is evidence of sclerosis or erosion in the adjacent bone;20 lobulation is absent and there is no predilection for involvement of the lower thoracic region. (2) Hodglun's disease with mediastinal involvement usually affects the anterior and superior mediastinal regions, and pain is often a prominent symptom. (3) An abscess arising from the thoracic spine may have systemic symptoms, has no lobulation and may reveal involvement of bone structures. ( 4 ) Primary or secondary malignancies are not usually lobulated and may show bone involvement and systemic signs, with a rapidly progressive course. (5) An extrapleural cyst is single, producing a curved margin anteriorly and laterally. (6) An intrathoracic meningocele may present radiologically as a single or occasionally as bilateral circular opacities. Vertebral deformities are usually present with or without associated neurofibromatosis. Posterior mediastinal masses are commonly neoplastic and thoracotomy is invariably considered under these circumstances. A diagnosis of EMH before operation is therefore vital, as it would avoid unnecessary surgery. An awareness of the condition and a careful consideration of the diagnostic features mentioned will lead to a confident diagnosis before operation. . 1 Brannan D: Extramedullary hematopoiesis in anemias. John Hopkins Med J 41 :104, 1927 2 Gleave HH: Paravertebral heterotopia of bone marrow in case of acholuric jaundice. J Pathol42:538, 1936 3 Dawson BE: Hume Lectures on haemolytic icterus. Br Med J 1:963, 1931 4 Wintrobe MW: Clinical Hematology (ed 4). Philadelphia, Lea & Febiger, 1956, p 48 5 Hartfall SJ, Stewart MJ: Massive paravertebral heterotopia of bone marrow in a case of acholuric jaundice. J Pathol37:455, 1933 212 JOE R WISE 6 Hanford RB, Schneider GF, MacCarthy JD: Massive thoracic extramedullary hemopoiesis. N Engl J Med 203: 120, 1960 7 Ross P, Logan W: Roentgen findings in extramedullary hematopoiesis. Am J Roentgen01 Radium Ther Nucl Med 106:604,1969 8 Marinozzi V: Aspetti insoliti dell'iperplasia midollare nelle anemie emolitiche. Haematologica 43:737, 1958 9 Knoblich R: Extramedullary hematopoiesis presenting as intrathoracic tumour: report of case in patient with thalassaemia minor. Cancer 13:462, 1960 10 Malamos B, Papavasiliou C, Avramidis A: Tumour simulating intrathoracic extramedullary hemopoiesis: report of case. Acta Radio1 57227, 1962 11 Papavasiliou C, S6kakis P: Tumour-simulating intrathoracic marrow heterotopia in thalassaemia major. Thorax 19:121, 1964 12 Sorsdahl OS, Taylor PE, Noyes WD: Extramedullary hematopoiesis: Mediastinal masses and spinal cord compression. JAMA 109:343, 1964 13 Seidler RC, Becker JA: Intrathoracic extramedullary hematopoiesis. Radiology 83: 1057, 1964 14 Hanam E: Massive thoracic extramedullary haemopoiesis in a case of haemoglobin E-thalassaemia. Singapore Med J 5: 122, 1904 15 Plonskier M: Uber tumorformige (extramedullare, heterotype) subpleurale Knockenmarksherde. Virchows Arch [Pathol Anat] 277:804, 1930 16 Saleeby ER: Heterotopia of bone marrow without apparent cause. Am J Pathol 139, 1925 17 Lyall A: Massive extramedullary bone formation in case of pernicious anemia. J Pathol 41:469, 1935 18 Gray H: Anatomy of the Human Body (Lewis WH, ed), ( ed 24). Philadelphia, Lea, 1942, p 1428 19 Case records of Massachusetts General Hospital, Case 14, 1968. N Engl J Med 278:782, 1968 20 Good CA: Roentgenologic diagnosis of surgical lesions of mediastinum. Chicago Med Soc Bull 53:51, 1950 Patient-Activated Atrial Pacing. in the Treatment of Recurrent Supraventricular ~ a c h ~ c a r d i a * Joe R. Wise, Jr., M.D. A specially designed pacemaker was implanted in a patient witb recnrrent supraventricular tachycardia complicated by pulmonary edema. The unit is designed to pace the right atrium temporarily when activated by the patient, wing a hand-held magnet. All subsequent episodes of snpraventricular tachycardia have been terminated within a few seconds. R ecurrent supraventricular tachycardia can usually be prevented by suppressive antiarrhythmic drug *From the Cardiology Section, Medical Services Eastern Maine Medical Center, Bangor, Me. Reprint requests: Dr. Wise, One Fern Street, Bangor, Maine 04401 CHEST, 65: 2, FEBRUARY, 1974 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20947/ on 05/06/2017 therapy. In some patients, however, drugs alone are ineffective and other methods of control have been recommended including combinations of drugs and ventricular p a ~ i n g , ~and . ~ the use of implanted carotid sinus stim~lators.~ Recently, temporary atrial pacing has been used successfully to terminate episodes of supraventricular tachycardia.4~7In some cases, the tachycardia recurs so frequently that temporary atrial pacing is impractical and a more permanent method of control is required.sJ0 The purpose of this report is to describe the use of a specially designed permanent pacemaker which can be activated on demand by the patient to pace the right atrium and interrupt paroxysms of supraventricular tachycardia, which could not be controlled by more conventional means. The patient, a 36-year-old man, first noticed intermittent palpitation at age 19. Medical evaluation at that time disclosed no associated cardiovascular abnormality. Episodes of rapid heart action were brief, terminated spontaneously and occurred several times each year. At age 36, after two years of progressive dyspnea on exertion, he developed cardiac failure which responded promptly to treatment with digitalis and diuretics, but left ventricular hypertrophy and third and fourth heart sounds persisted. The episodes of rapid heart action, subsequently found to be supraventricular tachycardia, occurred much more frequently and often precipitated acute pulmonary edema. Electrical cardioversion was required For termination of the supraventricular tachycardia on 13 occasions in one year. Combinations of antiarrhythmic drugs including digoxin (0.25 mg, twice a day), and quinidine gluconate (450 mg every eight hours), propranolol ( U) mg four times daily), diphenylhydantoin ( 100 mg four times per day) and procainamide (250 mg every four hours) failed to reduce the frequency or duration of the attacks. There was no evidence of ventricular pre-excitation and thyroid function studies ,showed no abnormalities. Blood pressure was never elevated. On two occasions intra-atrial electrograms showed what appeared to be a reciprocating tachycardia which could be terminated by atrial stimulation at rates of 70 per minute and 100 per minute (Fig 1). Ventricular stimulation was ineff ective ( Fig 2 ) . In view of the dilliculty in c o n b b g the arrhythmia, a trial of longterm atrial pacing was elected. Attempts to position a pacing catheter within the coronary sinus were unsuccessful. On March 18, 1972, an epicardial electrode was attached to the right atrium, low near the junction of the atrium and the inferior vena cava in a region where endocardial pacing had been effective previously. The pulse generator (General Electric dual rate A207OAA) implanted in the right axilla was designed to operate at a fixed rate of 110 beats per minute only when activated by handheld magnet. Since implantation of this unit, the episodes of rapid heart action have continued to occur several times a week, but are terminated quickly, usually within 10 to U) seconds, after activation of the pacemaker. Re-entrant or reciprocal rhythm rather than a rapidly discharging ectopic focus may be the basis for the majority of supraventricular tachycardias.~Jl~l~ According to this view, an atrial premature beat occurring during the relatively refractory period of the atrioventricular node is conducted to the ventricle more slowly than normally timed sinus beats. This slowed conduction allows time for some of the fibers of the A-V node to recover so that the wave of excitation may be conducted, not RCURE 1( A ) . Intra-atrial electrogram. Continuous recording from catheter advanced slowly into right atrium from superior vena cava. Note that atrial depolarization appears within (toward end of top strip) but after onset of QRS complex. FIGURE 1( B ) . Surface electrocardiomam dur- ing atrial ;acing. Random atrial st&ation at 100 per minute. ( .) restores sinus rhythm (t) CHEST, 65: 2, FEBRUARY, 1974 :-1 - f itt-tWl ! ! ! ! !i !i !i !i i! i! i!i !i !i !i i! i! '! ! t PATIENT-ACTIVATED ATRIAL PACIN6 213 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20947/ on 05/06/2017 FIGURE2. Surface electrocardiogram. Ventricular pacing (.) produces ventricular depolarizations which fail to terminate the tachycardia. only to the ventricles, but also retrograde to the atrium there producing an atrial depolarization, which is in turn conducted to the ventricles, and a reciprocal cycle is established. For at least some of the arrhythmias, the reentry cycle seems to be entirely confined within the A-V junctional tissue.13 A single, critically timed electrical stimulus can intenupt a re-entry cycle by prematurely depolarizing a portion of the pathway. Using this principal, lowenergy direct endocardial stimulation using pacemaker devices has been used to terminate a variety of supraventricular tachycardias.4-9*14,15 In our patient, on two occasions, atrial stimulation with a standard external pacemaker (Medtronic 5880) at rates of 70 per minute and 100 per minute terminated the tachycardia. Termination of the arrhythrma by random atrial stimuli in thls manner suggests that the rhythm was a re-entrant or reciprocal type. During the temporary pacing, rates of 70 per minute and 100 per minute and stimulus strengths of less than 10 ma were selected since they were within the capability of standard available pacemaker pulse generators. No attempt was made to initiate the tachycardia. It is of interest that ventricular pacing in this case produced ventricular contractions, which did not tenninate the tachycardia (Fig 2 ) . This suggests that retrograde conduction to the reentry pathway was blocked and that ventricular pacing would have been ineffective in terminating the tachycardia. After the effectiveness of atrial pacing was established, a permanent pacing system was implanted. The pulse generator, used previously by Preston and Kirsha in a patient with Wolff-Parkinson-White pre-excitation, is capable of pacing at either of two pre-selected rates. The basic or primary pre-set rate is zero so that the pulse generator remains off until activated. A magnet held over the pulse generator activates a reed-switch which converts the unit to the second pre-set rate, in this case 110 beats per minute, and the pulse generator paces at this rate until the magnet is withdrawn and the unit reverts to the primary rate of zero. Our patient has no d&culty in recognizing the onset and termination of his episodes of tachycardia. At the onset of the tachycardia, the magnet is held over the pulse generator for a few seconds until the tachycardia is terminated. The magnet is then returned to a small case attached to the patient's belt. Battery life should be prolonged since the unit remains inactive most of the time and no sensing circuit is involved. Pacing from the atrium rather than competitive ventricular pacing avoids the danger of ventricular fibrillation. Thoracotomy can be avoided by pacing from the coronary sinus but this,too, is not without r i ~ k . l ~ - ~ s ACKNOWLEDGMENT: We thank David M. Sensenig, M.D., Eastern Maine Medical Center, for performing the thoracotomy. 1 Cheng TO: Transvenous ventricular pacing in the treat- ment of paroxysmal atrial tachyarrhythmias alternating with sinus bradycardia and standstill. Am J Cardiol 22: 874-879,1968 2 Cohen HE, Kahn M, Donoso E: Treatment of supraventricular tachycardias with catheter and permanent pacemakers. Am J Cardiol20:735-738, 1967 3 Cantwell JO, Weaver WT, Fletcher GF: Paroxysmal atrioventricular junctional tachycardia. Treatment with carotid sinus stimulation. JAMA 216: 1860-1862, 1971 4 Haft JI, Kosowsky BO, Lau SH, et al: Termination of atrial flutter by rapid electrical pacing of the atrium. Am J Cardiol20:239-244, 1967 5 Massumi RA, Kistin AD, Tawakkol AA: Termination of reciprocating tachycardia by atrial stimulation. Circulation 36:637-643, 1967 6 Hunt NC, Cobb FR, Waxman MB, et al: Conversion of supraventricular tachycardias with atrial stimulation: Evidence for re-entry mechanism. Circulation 38:10601065, 1968 7 Cohen HE, Meltzer LE, Latimer G, et al: The treatment of refractory supraventricular arrhythmias with induced permanent atrial fibrillation ( abstr ) . Circulation ( Suppl 3 ) 42:III-144, 1970 8 Zipes DP, Wdace AG, Sealy WC, et al: Artificial atrial and ventricular pacing in the treatment of arrhythmias. Ann Intern Med 70:885-896, 1969 9 Preston TA, Kirsh NM: Permanent pacing of the left atrium for treatment of WPW tachycardia. Circulation 42: 1073-1077,1970 10 Davidson RM, Wallace AG, Sealy WC, et al: Electrically induced atrial tachycardia with block. Circulation 44: 1014-1021, 1971 11 Moe GK, Preston JB, Burlington H: Physiologic evidence for a dual A-V transmission system. Circulation Res 4:357375, 1956 12 Bigger JT Jr, Goldreyer BN: The mechanism of supraventricular tachycardia. Circulation 42373-688, 1970 13 Coldreyer BN, Bigger JT Jr: Site of re-entry in paroxysmal supraventricular tachycardia in man. Circulation 43: 15-26, 1972 14 Barold SS, Linhart JW, Samet P, et al: Supraventricular 214 JOE R. WISE Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20947/ on 05/06/2017 CHEST, 65: 2, FEBRUARY, 1974 tachycardia initiated and terminated by a single electrical stimulus. Am J Cardio124:37-48, 1969 15 Kitchen JC, Goldre~erBN: Demand pacemaker for refractory supraventricular tachycardia. N Engl J Med 287:596-599,1972 16 h e r DH, Moss AJ: Permanent percutaneous atrial pacing from the coronary vein. Circulation 42427-436, 1970 17 Moss AJ, Rivers RJ, Cooper M: Long-term pervenous atrial pacing from the proximal portion of the coronary vein. JAMA 209:543-545, 1969 18 Nepodono RJ, Cannon E, Zaroff L: Two observations regarding pervenous atrial pacing from the coronary sinus. J Electrocardiol4:275-278,1971 Mycotic Aneurysm of the Ascending Aorta Secondary to Serratia Infection: Differentiation from Prosthetic Valve ~ndocarditis* Burt R. Meyers, M.D., Rashmikant Shah, M.D., and Martin Lefkowitz, M.D. Twenty-one months after prosthetic aortic and mltral valve replacement, a 64-year-oM man developed bacteremia secondary to a Serratia infection. intensive investigation failed to reveal the origin of infection and gentamicin therapy did not eradicate the organisms from the bloodstream. 'Ihe patient died. Postmortem examination revealed a large mycotic aneurysm arising from the aortotomy site but no evidence of prosthetic valve endocarditis. Late occurring bacteremia following valve replacement is discussed. Aortography may be necessary to delineate this problem. B acterial and fungal endocarditis in patients with prosthetic cardiac valves may respond to antibiotic therapy alone but generally requires surgery with valve Sande et all recently reported replacement for 22 patients with prosthetic cardiac valves who had sustained bacteremia and suggested a way of differentiating valvular involvement from other causes. We recently treated a patient with prosthetic aortic and mitral valves who developed sustained Serratia bacteremia. This was secondary to a mycotic aneurysm of the ascending aorta, which could not be clinically differentiated from bacterial endocarditis. Mycotic aneurysms in this area are uncommon and involvement with the 'From the Division of Infectious Diseases Department of e the City Medicine, The Mount Sinai School of ~ d c i n of University of New York, New York, N.Y., and the Department of Pathology, Grasslands Hospital, Valhalla, N.Y. Reprint requests: Dr. Meyers, Mount S i ~ Hospital, i 100th Street and Fifth Avenue, New York City 10029 species of the genus Serratia has not been previously reported. A 64-year-old man underwent aortic and mitral valve replacement on June 19, 1970. After operation he developed a wound infection at the lower end of the sternum which was treated by debridement, cauterization and local measures. Drainage persisted and in June, 1971, after culture revealed Enterobacter organisms, doxycycline was given orally for ten days, with some clinical improvement. In September, 1971, Enterobacter organisms were cultured again, and doxycyche therapy was reinstituted. Drainage persisted and two days prior to admission, the patient complained of cough, fever and weakness, and 1 ml of serosanguinous fluid was aspirated from the wound but was not cultured. Administration of tetracycline was resumed but the fever and symptoms persisted and the patient was readmitted on March 31, 1972. Physical examination on admission revealed an irregular pulse rate of 88/min; respirations, 16/min; blood pressure 110/60 m m Hg; and temperature, 39.4444 CO.The conjunctivae were free of petechiae. The neck veins were distended and showed a positive hepatojugular rdlex. There were rilles and rhonchi at the lung bases. Examination of the heart revealed cardiomegaly with the point of maximum intensity (PMI) in the sixth intercostal space at the anterior arillary line. There was a blowing systolic murmur heard at the apex (grade 3/6) and a short harsh systolic murmur (grade 4/6) heard over the aortic area. The liver was palpable 2 cm below the costal margin; the spleen was not enlarged. There was 2+ clubbing of the fingers. Administration of antibiotics was discontinued and blood cultures were obtained. Roentgenograms of the chest revealed an enlarged heart with prosthetic aortic and mitral valves and prominence of the pulmonary vasculature. An intravenous pyelogram showed an intrarenal mass suggestive of a cyst. Laboratory studies disclosed the following values: hematocrit, 32 percent; white blood cell count 7,50O/rnms, with 74 percent polymorphonuclear leukocytes, 20 percent lymphocytes and 6 percent monocytes; blood urea nitrogen ( BUN),16 mg/100 ml; serum protein, 6.9 gm/ml; albumin, 3.1 gm/100 ml; alkaline phosphatase, 110 international units ( IU ) ; serum glutamic oxaloacetic transaminase ( SCOT ) , 65 IU; and the urinalysis was normal. The latex-fixation test was positive in a dilution of 1/160. Daily temperature spikes to 38.8889 COoccurred, and blood cultures drawn on the sixth hospital day revealed the presence of Serratia. Intramuscular administration of gentamicin was begun and blood cultures drawn on April 13 and 14 again revealed this micro-organism. Twenty days after gentamicin therapy was begun, he became lethargic and less responsive. Blood cultures obtained on the 36th hospital day were again positive for Serratia. Repeated chest films showed cardiomegaly and congestive heart failure, without evidence of sternal osteomyelitis. On the 46th hospital day he became unresponsive, passed a tarry stool, developed hypotension and died. Autopsy findings revealed a healed midsternal incision with no evidence of infection, abscess formation, or osteomyelitis. A fibrous walled saccular false aneurysm 8 cm in its greatest diameter, was noted between ;he sternum and the anterior wall of the aorta. The inner wall had a granular fibrinous, shaggy and cobblestone appearance CHEST, 65: 2, FEBRUARY, 1974 Downloaded From: http://journal.publications.chestnet.org/pdfaccess.ashx?url=/data/journals/chest/20947/ on 05/06/2017 MYCOTIC ANEURYSM 215