Tachycardia detection by antitachycardia devices: present limitations and future strategies

Early experience with three generations of implantable devices has demonstrated the need to further refine the accuracy of automated rhythm analysis. Although initial experience with commercially utilized morphological waveform analysis has been disappointing, other time and frequency domain electrogram features have been developed and show potential promise for future devices. While single chamber algorithms for rate and rate variations have theoretical appeal because of their limited power demands, practical experience has demonstrated that inaccurate arrhythmia diagnosis continues to occur by antitachycardia devices that utilize them. Technological advancement in hardware manufacturing and the design of increasingly more efficient software algorithms for tachycardia detection will continue to yield lower power digital circuitry, to increase device battery power and life, and to permit more and more accurate automated arrhythmia diagnosis and treatment by antitachycardia devices. Two chamber sensing has been available for decades in dual chamber antibradycardia pacemakers. The introduction of this technology into antitachycardia devices is not only inevitable but should dramatically improve the precision of diagnosis in future generation devices.

The value of rate regularity and multiplicity measures to detect ventricular tachycardia in the presence of atrial fibrillation or flutter

The predominant cause of inappropriate therapy by implantable antitachycardia devices with pacing and nonpacing cardioverter defibrillators, is mistaking a fast ventricular response during atrial fibrillation or flutter with true ventricular tachycardia (VT). The distinction between these arrhythmias is an important consideration in addressing the problem of reducing false-positives in detection mechanisms for implantable devices. Dual chamber analysis that examines atrial and ventricular event ratios has been proposed as a solution to this problem, but would still fail in distinguishing paroxysmal VT requiring treatment from a fast but otherwise benign ventricular response during atrial fibrillation or flutter. In this study, two methods for discriminating these tachyarrhythmias were evaluated. Method 1 examined ventricular rate and rate regularity as a method for VT detection. Method 2 combined rate and regularity as well as an additional multiplicity criterion for recognition of atrial flutter with a fast ventricular response. In 20 patients, Method 1 had 100% sensitivity of VT detection and 80% specificity for detection of atrial fibrillation or flutter. Method 2 had 90% sensitivity and 90% specificity. These results suggest that use of these algorithms in future implantable devices would result in a decrease in false-positive device therapies.

Case management in cerebral revascularization

PURPOSE

We examined the clinical and financial outcomes of case management coupled with the initiation of selective use of the intensive care unit (ICU) in all cerebral revascularization procedures.

METHODS

Three hundred eighty-four procedures in 331 patients were retrospectively reviewed. Morbidity and mortality rates, hospital length of stay, cost, and ICU or hospital readmissions were examined. Hypertension was examined as an independent variable for its effect on patient outcome.

RESULTS

Cerebral revascularization, including carotid endarterectomy, vertebral-carotid artery transposition, and subclavian-carotid artery transposition, yielded a 0.78% stroke rate and 0.26% perioperative death rate in this series. ICU admission was necessary in nine patients (2.3%) for cardiac or respiratory instability. Three patients (0.78%) required transfer to the ICU for management of hypertension or hypotension. The mean hospital length of stay after institution of case management was reduced by 2.1 days, and the mean cost was decreased by $1987, a savings of 28.9% of total hospital cost.

CONCLUSION

The dual approach of case management and selective use of the ICU promotes quality patient care, conserves financial resources without adversely affecting morbidity or mortality rates, enhances physician/nurse collaboration, and improves patient satisfaction.

Digital signal processing chip implementation for detection and analysis of intracardiac electrograms

The adoption of digital signal processing (DSP) microchips for detection and analysis of electrocardiographic signals offers a means for increased computational speed and the opportunity for design of customized architecture to address real-time requirements. A system using the Motorola 56001 DSP chip has been designed to realize cycle-by-cycle detection (triggering) and waveform analysis using a time-domain template matching technique, correlation waveform analysis (CWA). The system digitally samples an electrocardiographic signal at 1000 Hz, incorporates an adaptive trigger for detection of cardiac events, and classifies each waveform as normal or abnormal. Ten paired sets of single-chamber bipolar intracardiac electrograms (1-500 Hz) were processed with each pair containing a sinus rhythm (SR) passage and a corresponding arrhythmia segment from the same patient. Four of ten paired sets contained intraatrial electrograms that exhibited retrograde atrial conduction during ventricular pacing; the remaining six paired sets of intraventricular electrograms consisted of either ventricular tachycardia (4) or paced ventricular rhythm (2). Of 2,978 depolarizations in the test set, the adaptive trigger failed to detect 6 (99.8% detection sensitivity) and had 11 false triggers (99.6% specificity). Using patient dependent thresholds for CWA to classify waveforms, the program correctly identified 1,175 of 1,197 (98.2% specificity) sinus rhythm depolarizations and 1,771 of 1,781 (99.4% sensitivity) abnormal depolarizations. From the results, the algorithm appears to hold potential for applications such as real-time monitoring of electrophysiology studies or detection and classification of tachycardias in implantable antitachycardia devices.

Effects of stents on lithotripsy of ureteral calculi: treatment results with 18,825 calculi using the Lithostar lithotriptor

Between November 14, 1988 and August 1, 1993, 18,825 ureteral calculi were treated in the United States using 25 different mobile and 2 fixed base Siemens Lithostar lithotriptors. Lithotripsy was performed by 1,012 urologists using the modified Puigvert technique. The overall stone-free rate was 83.8% with a retreatment rate of 10.8%. The stone-free rate varied from 85.8% with stones of 10 mm. or smaller to 67.9% for stones larger than 20 mm. A ureteral stent or catheter was placed before lithotripsy in 19.3% of all treatments and 80.7% had in situ treatment without instrumentation. For calculi of any size, the use of ureteral stents or catheters had no effect on treatment outcome at any ureteral location.

Subclavian revascularization. A quarter century experience

OBJECTIVE

Twenty-five years of experience with subclavian revascularizations were reviewed to determine the long-term patency rates of different extrathoracic approaches.

SUMMARY BACKGROUND DATA

Although it is generally agreed that proximal subclavian stenosis should be treated by an extrathoracic route whenever possible, the optimum procedure is debated. Alternatives include subclavian carotid bypass, subclavian-to-subclavian or axillo-axillary bypasses, and the authors' preferred technique of subclavian carotid transposition (SCT).

METHODS

Records were researched for the past 25 years in a single specialty surgical clinic for extrathoracic subclavian revascularizations. One hundred ninety such procedures were identified, and hospital charts and office medical records were reviewed for procedure, preoperative symptoms, blood pressure differentials, and postoperative complications. Patency was determined by physical examination, differential blood pressures, Doppler spectral analysis, duplex examinations, and arteriography.

RESULTS

Bypass procedures were used infrequently, and although the results are reported, they are excluded from any analysis. Subclavian carotid transposition was used in 178 procedures. All anastomoses were found to be patient at follow-up, except for one, which failed at 26 months. Mean follow-up was 46 months, with five patients lost to follow-up. Overall mortality rate was 2.2%, with the mortality falling to 1.1% if only subclavian carotid transposition patients are included.

CONCLUSIONS

Subclavian carotid transposition should be the treatment of choice for routine subclavian carotid occlusive disease because of its exceptional long-term patency and low morbidity.

Cryopreserved saphenous vein allografts for below-knee lower extremity revascularization

OBJECTIVE

Cryopreserved saphenous vein allografts have been offered as an alternative conduit for bypass in ischemic limbs. The authors examined the efficacy of this conduit for arterial bypass to the distal popliteal and tibial arteries in patients in whom autogenous vein was not available.

SUMMARY BACKGROUND DATA

Previous experience with arterial and venous allografts has been unsatisfactory because of aneurysmal degeneration and poor patency. Endothelial loss and host rejection have been suggested as mechanisms of graft failure. Cryopreservation by modern techniques with rate controlled freezing, dimethyl sulfoxide (DMSO), and other cryopreservants, has addressed these issues and rekindled interest in vein allografts.

METHODS

Over a period of more than 5 years, 115 cryopreserved vein allografts were implanted in 87 limbs to the distal popliteal (14) or tibial (101) arteries. The indication for surgery was rest pain in 56 procedures (49%), gangrene in 36 (31%), claudication in 21 (18%), and replacement of aneurysmal allografts in 2. Follow-up was 1 to 61 months (mean 25 months).

RESULTS

There was no significant difference in patency related to site of proximal or distal anastomosis, patency of runoff vessels, use of anticoagulation, age, sex, diabetes, hypertension, smoking, indication, source of graft, or use of multiple segments. Revision was required in six grafts for aneurysmal dilatation. Histologic examination of explanted sections of allografts showed no immune response, and immunosuppressive drugs were not used.

CONCLUSIONS

Although limb salvage has been satisfactory, long-term patency rates for cryopreserved vein allografts are poor when compared with autogenous vein. The cost of cryopreserved allografts far exceeds that of prosthetic grafts, for which comparable and superior results have been reported. Use of cryopreserved vein allografts should be reserved for situations in which adequate lengths of autogenous vein do not exist and the risk of infection of prosthetic grafts is high.

Persistent elevation of serum oestradiol levels by functional ovarian cysts despite effective pituitary desensitization with GnRH agonists

OBJECTIVE

This study assessed whether functional ovarian cysts may prevent suppression of serum oestradiol levels even after pituitary desensitization had been achieved with buserelin.

PATIENTS

Of 288 in-vitro fertilization (IVF) cycles studied 10 patients were found to have cysts with serum oestradiol levels > 200 pmol/l despite 3 weeks of buserelin.

DESIGN AND MEASUREMENTS

The 10 patients with cysts were given 0.1 mg GnRH and serum gonadotrophins were measured at time 0, 30 and 60 minutes subsequently. Immediately following the GnRH stimulation test the cysts were aspirated transvaginally under ultrasound guidance. Serum oestradiol levels were again measured 3 days after cyst aspiration.

RESULTS

Basal LH and FSH levels were < 3 U/l and there was no significant rise in response to GnRH. On the day of cyst aspiration serum oestradiol levels varied between 244 and 1127 pmol/l, and in all cases serum oestradiol levels fell to < 200 pmol/l within 3 days of cyst aspiration.

CONCLUSION

In the presence of a functional ovarian cyst, failure to suppress the serum oestradiol level does not necessarily imply a failure of pituitary desensitization with a GnRH agonist.

Recurrent aortic occlusion

In a review of 134 aortic occlusions in 123 patients, there were 10 patients that suffered recurrent aortic occlusions (RAO). These patients developed RAO after revascularization for primary aortic occlusion and presented with signs and symptoms of acute lower extremity ischemia. The recurrent occlusions occurred in one native aorta and in 10 aortobifemoral grafts. The etiology of the primary aortic occlusion included chronic aortic occlusion in eight patients and acute aortic occlusion and aortic graft occlusion in one patient each. Original primary operations performed included aortoiliac thromboendarterectomy with Dacron patch aortoplasty (1 patient), AF bypass (8 patients), and aortofemoral graft thrombectomy (1 patient). All of the grafts had end-to-end proximal anastomoses, the diameter of which ranged from 12 to 16 mm. Secondary operations performed for RAO included six axillofemoral bypasses, four redo aortobifemoral bypasses, and one graft thrombectomy. All patients were managed with immediate anticoagulation, expeditious arteriography, and revascularization. There were no perioperative deaths, and no limbs were lost. No patient was lost to follow-up (mean 10 years). Extra-anatomic bypass has proved durable. Redo aortobifemoral bypass is useful in selected patients with surgically correctable lesions.

Cloning and characterisation of genes for tetrapyrrole biosynthesis from the cyanobacterium Anacystis nidulans R2

The genes for 5-aminolevulinic acid dehydratase (ALAD) and uroporphyrinogen III synthase (UROS), two enzymes in the biosynthetic pathway for tetrapyrroles, were independently isolated from a plasmid-based genomic library of Anacystis nidulans R2 (also called Synechococcus sp. PCC7942), by their ability to complement Escherichia coli strains carrying mutations in the equivalent genes (hemB and hemD respectively). The identity of the genes was confirmed by comparing the appropriate enzyme activities in complemented and mutant strains. Subclones of the original plasmids that were also capable of complementing the mutants were sequenced. The inferred amino acid sequence of the cyanobacterial HemB protein indicates a significant difference in the metal cofactor requirement from the higher-plant enzymes, which was confirmed by overexpression and biochemical analysis. The organisation of the cyanobacterial hemD locus differs markedly from other prokaryotes. Two open reading frames were found immediately upstream of hemD. The product of one shows considerable similarity to published sequences from other organisms for uroporphyrinogen III methylase (UROM), an enzyme involved in the production of sirohaem and cobalamins (including vitamin B-12). The product of the other shows motifs which are similar to those found in proteins responsible for metabolic regulation in yeast and indicates that this family of transcription control proteins, which has previously been reported only from eukaryotes, is also represented in prokaryotes.

Automated analysis of spontaneously occurring arrhythmias by implantable devices. Limitations of using rate and timing features alone

Real-time automated systems for arrhythmia analysis by implantable antitachycardia devices have been designed to incorporate two-channel rate criteria with intracavitary atrial and ventricular electrogram morphology. Because the power requirements for morphologic analysis substantially limit antitachycardia device longevity, the authors sought to develop an alternative algorithm that relies solely on rate and three newly developed timing features: onset (median ventricular rate filtering to detect abrupt onset), loss of atrioventricular (AV) sequency (premature ventricular depolarizations), and regularity-multiplicity (minimal median cycle length variation concurrent with integral [n:1] AV periodicity). This system was assessed using spontaneously occurring arrhythmias in patients undergoing electrophysiology studies. Electrograms were captured on FM tape (1-500 Hz) using biopolar catheters in the high right atrium and the left ventricular apex. In 11 patients, 25 distinct arrhythmias were analyzed, which included sinus tachycardia (ST) (1 passage), supraventricular tachycardia (SVT) (6 passages), ventricular tachycardia (VT) with concurrent sinus rhythm (16 passages), VT with concurrent atrial flutter (VT/AFl) (2 passages), and ventricular fibrillation (VF) (1 passage). The algorithm correctly diagnosed 1 of 1 episode of ST, 4 of 6 episodes of SVT, 15 of 16 episodes of VT with concurrent sinus rhythm, 0 of 2 episodes of VT/AFl, and 1 of 1 episode of VF. Ventricular tachycardia episodes were misdiagnosed as SVT because of absence of loss of AV sequency in VT onset (1 episode), presence of multiplicity between VT and AFl (1 episode), and absence of VT regularity during AFl (1 episode).(ABSTRACT TRUNCATED AT 250 WORDS)

The development of functional ovarian cysts during pituitary down-regulation

This study investigated the development of functional ovarian cysts during pituitary down-regulation prior to in-vitro fertilization (IVF), and identified 16 cases of cysts in 288 IVF cycles studied. Comparing the patients with functional ovarian cysts to the other 272 IVF cycles, there was no significant difference in age or incidence of endometriosis but significantly (P < 0.01) more patients with cysts had ovulatory dysfunction. The serum progesterone was < 5.7 nmol/l in all 16 patients with cysts on day 4 of the IVF cycle, and in eight of these patients the serum progesterone was < 5.7 nmol/l on the day buserelin was commenced. In 10 of the 16 patients with cysts, serum oestradiol concentrations remained elevated despite the prolonged use of buserelin, and the cysts were aspirated. The aspirate in all cases was clear without any suggestion of endometriosis. The cyst aspirates had significantly lower progesterone (P < 0.001), higher androstenedione (P < 0.01) and similar oestradiol concentrations to 10 follicular fluid samples collected at the time of oocyte retrieval. This study suggests that functional ovarian cysts may develop during pituitary down-regulation, and these cysts are follicular cysts rather than persistent corpora lutea or endometriomata.

Cefamandole versus cefazolin in vascular surgical wound infection prophylaxis: cost-effectiveness and risk factors

PURPOSE

Recent studies of perioperative antimicrobial prophylaxis have indicated an improved efficacy of beta-lactamase-stable cephalosporins compared with cefazolin, the most commonly used prophylactic agent. Previous studies in our institution have revealed a superiority of cefamandole to cefazolin in patients undergoing heart surgery, although there was no difference between cefazolin and cefuroxime in patients undergoing peripheral vascular surgery. This study was therefore designed to compare cefamandole with cefazolin in wound infection prophylaxis in clean vascular surgery.

METHODS

The study was conducted from August 1990 through May 1992 and consisted of 893 patients with aortic or infrainguinal arterial procedures randomized to receive either cefamandole or cefazolin.

RESULTS

The difference in infection rates associated with cefamandole versus cefazolin prophylaxis (3.2% vs 1.9%, respectively) was not significant (p = 0.42). A cost savings of approximately $95,000 per year at our institution favors the continued use of cefazolin over cefamandole. Risk factor analysis was carried out for preoperative and postoperative events that might have predisposed to infection. Only preoperative use of aspirin and the postoperative finding of a lymphocele correlated with a higher infection rate.

CONCLUSIONS

Cefazolin continues to be the most cost-effective antibiotic for prophylaxis in clean vascular surgical procedures.

A stochastic network model of the interaction between cardiac rhythm and artificial pacemaker

The electrical interaction between the heart and an artificial pacemaker is often complex. Because of the sophistication and diversity of dual-chamber device algorithms, even experienced cardiologists can have difficulty interpreting paced electrocardiograms (ECG's). In order to study heart-pacemaker interaction (HPI), a computer model of the cardiac conduction system has been developed which includes the effects of artificial pacemaker function and failure. The stochastic network model of cardiac conduction consists of five vertices, each representing a functional electrophysiologic element. Electrophysiologic multidimensional conditional probability functions determine the depolarization status of each vertex. The atrioventricular (AV) node is emulated using a mathematical model which includes the influence of past cycle lengths on AV nodal conduction time. Twenty-three classes of arrhythmias may be simulated and, for pacing simulation, one of 12 antibradycardia pacing modes may be chosen. Random effects of pacemaker malfunction including oversensing, undersensing, or failure-to-capture may be simulated through the use of probability distribution functions. This model should prove useful in the development of pacemaker algorithms, determining patient-specific pacemaker therapy, and predicting causes for apparent pacemaker malfunction. The model has been used in the development of an expert system to analyze paced ECG's for pacemaker function and malfunction.

Low energy lithotripsy with the Lithostar: treatment results with 19,962 renal and ureteral calculi

Between November 1988 and January 1992, 19,962 renal and ureteral calculi were treated in the United States using 18 different mobile and 2 fixed base Lithostar lithotriptors. Lithotripsy was performed on 11,516 renal and 8,446 ureteral calculi by 750 urologists using the same technique. The success rate (asymptomatic with stone fragments of 4 mm. or less) for renal stones was 87.9%, the stone-free rate was 68.9% and the retreatment rate was 16.5%. Auxiliary procedures were performed in 32.2% of the renal calculi. The success rate for ureteral calculi was 89.5%, the stone-free rate was 83.5% and the retreatment rate was 10.7%. Auxiliary procedures were performed in 25.5% of the ureteral calculi. The overall success rate was 88.4% stone-free rate 75.5%, retreatment rate 14.0% and auxiliary procedure rate 29.4%. Anesthesia personnel were used in 1.9% of the cases. Low energy extracorporeal shock wave lithotripsy was found to be safe and effective.

Real-time arrhythmia identification from automated analysis of intraatrial and intraventricular electrograms

Implantable cardioverter defibrillators have dramatically improved survival rates for patients at risk of sudden cardiac death, but the occurrence of inappropriate shocks remains an unresolved problem. Various means for better tachycardia detection, chiefly morphological analysis, have been proposed to address this problem. A new computerized scheme entitled Two-Channel Rate-Morphology (2CRM) was introduced. It is a real-time arrhythmia detection algorithm that combines timing and morphology information from intraatrial and intraventricular electrograms for arrhythmia diagnosis. The program 2CRM applies an initial cycle-by-cycle coding scheme followed by contextual diagnosis of underlying rhythm. The program was tested on 36 distinct passages of two-channel intracardiac signals from 30 patients. The distribution of the arrhythmias are as follows: 4 atrial fibrillation, 6 atrial flutter, 6 supraventricular tachycardia, 10 ventricular tachycardia, and 10 ventricular flutter-fibrillation. Of the analyzed 3,417 individual cardiac cycles 3,135 (91.7%) were correctly identified. Contextual diagnosis reversed 123 single-cycle errors to obtain a performance of 3,258 correct out of 3,417 (95.3%). Utilizing an uninterrupted continuous correct contextual diagnosis as indicator of successful arrhythmia detection, 2CRM obtained an accuracy of 34 out of 36 passages (94.4%).

Automated interpretation of cardiac arrhythmias. Design and evaluation of a computerized model

Historically, the development of computerized models that utilize the deductive methods used by clinicians for the interpretation of cardiac arrhythmias have been limited by the absence of a consistently reliable means of detecting atrial activation. In this study, a theoretical model was developed with a hierarchical organization of problem-solving strategies utilizing automated analysis of atrial activation from a commercially available esophageal pill electrode and ventricular activation from a simultaneously recorded surface electrocardiographic lead. The theoretical model was then tested in 21 patients with 1 or more of 28 distinct supraventricular and ventricular arrhythmias. Of the 641 individual cardiac cycles analyzed, 636 (99.2%) were correctly identified. The accuracy of a contextual, that is, more comprehensive, interpretation of consecutive cardiac cycles was 638/641 (99.5%). The following cardiac arrhythmias were identified: sinus rhythm, sinus bradycardia, atrial premature depolarizations, atrial flutter, and supraventricular tachycardias with normal and aberrant ventricular conduction, first-degree and second-degree heart block; junctional escape, junctional rhythm, idioventricular rhythm, ventricular premature depolarization, and ventricular tachycardia with and without retrograde activation; atrial bigeminy, atrial trigeminy, atrial couplets, ventricular bigeminy, ventricular trigeminy, and ventricular couplets. This study represents the first computerized model ever developed to incorporate the morphology and timing of atrial activation with the morphology and timing of ventricular activation for arrhythmia diagnosis. Such modeling appears to be capable of achieving accurate interpretation of spontaneous, complex clinical cardiac arrhythmias and atrioventricular relationships.

Cystadenoma of the pancreas in a newborn

Cystadenoma of the pancreas is a rare entity. In the pediatric population, three cases have been reported. We present a case of cystadenoma of the pancreas in a newborn. The tumor involved the head and body of the pancreas. Subtotal pancreatectomy with preservation of the duodenum, common bile duct, and pancreatic tail was performed.

Ventricular tachycardia detection using bipolar electrogram analysis is site specific

While algorithms for bipolar intraventricular electrogram analysis have potential use in complementing rate criteria for ventricular tachycardia (VT) detection by implantable antitachycardia devices, the sensitivity of such algorithms to the intracavitary site of electrogram detection has not been determined. In this study, unfiltered (1-500 Hz) electrograms were recorded from a bipolar electrode catheter initially positioned at the right ventricular (RV) apex (site 1) of 12 patients during sinus rhythm (SR1) and during induced monomorphic VT (VT1). Sinus rhythm (SR2) and the identical VT (VT2) were recorded a second time after repositioning the same electrode catheter within the RV apex (site 2) 7-44 mm (mean +/- SD = 15 +/- 10) from its original site. The data were digitized at 1,000 Hz. Templates from SR1 and SR2, respectively, were compared subsequently with individual intraventricular electrograms from 15-25 sec passages of SR1 and VT1 and SR2 and VT2, respectively, using correlation waveform analysis. At site 1, the mean patient correlation coefficient ranged from 0.982-0.998 during SR1 and 0.062-0.975 during VT1. At site 2, the mean patient correlation coefficient ranged from 0.995-0.998 during SR2 and 0.113-0.983 during VT2. Using a correlation threshold of 0.9, VT was differentiated from SR in 11/12 patients (91%) overall: 8/12 patients (67%) at site 1, 9/12 patients (75%) at site 2, and 6/12 patients (50%) at both sites. Thus, while discrimination of VT from SR is feasible with morphological analysis of bipolar right ventricular intracavitary electrograms, the accuracy of bipolar intraventricular electrogram analysis may depend upon intracavitary electrode location in selected patients.

In search of a perfect partnership

There's no question that our partnership is a natural, given the technological emphasis in modern medicine. My comments are not intended as criticism, but offered in the spirit of broadening our mutual understanding. I believe that open communication will enhance our continued collaboration in this interdisciplinary effort and yield significant advances in medical science.

The evolving surgical management of recurrent carotid stenosis

The traditional approach to recurrent carotid stenosis has been repeat endarterectomy or patch angioplasty. Concern with the durability of repeat carotid endarterectomy has resulted in our use of carotid resection with autogenous graft interposition. This study was designed to determine the outcome and efficacy of carotid resection compared with repeat carotid endarterectomy in the management of recurrent carotid stenosis. From 1974 to 1991, 162 operations (repeat carotid endarterectomy 105, carotid resection 57) were performed for recurrent carotid stenosis. Indication for operation was hemispheric symptoms in 63% of patients, nonlateralizing symptoms in 25%, asymptomatic stenosis in 7%, and previous stroke in 5%. Ninety-one percent of patients had stenosis greater than 90% on arteriography. The perioperative stroke rate for carotid resection was 3.5%, with a subsequent rate of 0.0064 strokes per year. For repeat carotid endarterectomy, the perioperative stroke rate was 1.9% with a subsequent rate of 0.011 strokes per year. Graft patency after carotid resection was 93% (mean follow-up, 35 months). Four patients treated with carotid resection had graft thrombosis, and two of the four remained asymptomatic. After repeat carotid endarterectomy, one patient had carotid thrombosis, and recurrent stenosis greater than 50% developed in 23 patients (mean follow-up, 64 months). Twenty patients treated with repeat carotid endarterectomy underwent an additional operation for further symptomatic recurrent carotid stenosis. We conclude carotid resection is a safe and effective alternative to repeat carotid endarterectomy for patients undergoing operation for recurrent carotid stenosis.

A review of the literature on the use of ultrasonography in schistosomiasis with special reference to its use in field studies. 3. Schistosoma japonicum

This paper gives a brief description of the pathology resulting from Schistosoma japonicum infection, and ways in which it can be investigated. It then reviews reports of the application of ultrasound in investigating lesions in schistosomiasis japonica, including papers published in Chinese and Japanese. Ultrasonography has been widely used for the diagnosis of schistosomiasis and for the investigation of pathological changes resulting from the infection. Marked and characteristic changes are observed in the structure of the liver parenchyma in advanced disease. Chronic pathology may be seen as a result of past infection. Animal studies have been used to compare ultrasound images with actual pathological changes. Ultrasonography can also be used to detect early changes, for example periportal fibrosis, which can indicate the development of portal hypertension. The problem of differential diagnosis is discussed.