A novel system for the rapid generation of precise DNA deletions.

To generate DNA deletions, a tandem array of class IIS restriction enzyme recognition sites was cloned into a plasmid. The recognition sites were arranged so that each enzyme cleaves at a different site within an adjacent target sequence. Digestion with both enzymes followed by end repair and ligation resulted in the deletion of DNA between the two sites of cleavage. Because both recognition sites are preserved following deletion, it was found that sequential deletions could be generated using cycles of restriction enzyme digestion, end repair and ligation. Therefore, this system represents a valuable tool in the definition of functional DNA sequences.

Isolation and characterization of glycogen synthase in Dictyostelium discoideum.

We have partially purified the protein and isolated the glcS gene for glycogen synthase in Dictyostelium. glcS mRNA is present throughout development and is the product of a single gene coding for 775 amino acids, with a predicted molecular mass of 87 kD. The sequence is highly similar to glycogen synthase from human muscle, yeast, and rat liver, diverging significantly only at the amino and carboxy termini. Phosphorylation and UDPG binding sites are conserved, with K(m) values for UDPG being comparable to those determined for other organisms, but in vitro phosphorylation failing to convert between the G6P-dependent (D) and -independent (I) forms. Enzyme activity is relatively constant throughout the life cycle: the I form of the enzyme isolates with the soluble fraction in amoebae, switches to the D form, becomes pellet-associated during early development, and finally reverts during late development to the I form, which again localizes to the soluble fraction. Deletion analysis of the promoter reveals a GC-rich element which, when deleted, abolishes expression of glcS.

Success of surf lifesaving resuscitations in Queensland, 1973-1992.

OBJECTIVE: To determine the success of resuscitations performed by Queensland surf lifesavers and the factors associated with successful resuscitation. DESIGN: Retrospective case survey, using data from Surf Life Saving Association of Australia resuscitation report forms. SETTING: 54 Queensland beaches patrolled by surf lifesavers, and nearby areas, between 1973 and 1992. OUTCOME MEASURES: Reasons and success rates for resuscitation, distance from surf clubhouse, whether inside patrolled area, victim's age, sex, facial colour on presentation, occurrence of vomiting, airway difficulties and involvement of alcohol. RESULTS: 171 resuscitations were reported (80% involving males and 20% females), with a success rate of 67%. Seventy-two per cent were performed during patrol hours, 17% within patrolled areas (95% successful) and 55% outside patrolled areas (only 62% successful) (P = 0.004 for difference in success rates); resuscitation success rates fell with increasing distance from the surf clubhouse (P = 0.009). Reasons for resuscitation were: immersion, 70% (success rate, 68%); collapse, 22% (success rate, 47%); and surf or beach injury, 7% and 1%, respectively (success rate, 100% for each). Resuscitation was more likely to be successful if the victim's facial colour on presentation was normal, pale or blue, but not if grey, and if the victim did not vomit or regurgitate. CONCLUSIONS: Resuscitation by surf lifesavers was highly successful when the victim was close to the surf patrol, indicating a need for funding to expand patrol areas. Public awareness of the greater safety of "bathing between the flags" (in the delineated patrol area) should be increased.

Comparison of atrial-His intervals during tachycardia and atrial pacing in patients with long RP tachycardia.

INTRODUCTION: The purpose of this study is to describe a simple and reliable diagnostic maneuver that allows for the rapid differentiation of atypical AV nodal reentrant tachycardia (AVNRT) from other causes of long RP tachycardia. Long RP tachycardias may be caused by atypical AVNRT, orthodromic reciprocating tachycardia (ORT) involving a slowly conducting retrograde accessory pathway, or atrial tachycardia. The differentiation of atypical AVNRT from ORT or atrial tachycardia may be difficult, especially when the differential diagnosis includes a posteroseptal accessory pathway or an atrial tachycardia arising in the posteroseptal right atrium. METHODS AND RESULTS: Twelve patients with atypical AVNRT, 21 with ORT, and 12 with an atrial tachycardia diagnosed using conventional criteria were enrolled in this study. The atrial-His (AH) interval was measured at the His-bundle position during the tachycardia and during atrial pacing from the high right atrium at the tachycardia cycle length in the setting of sinus rhythm. In patients with atypical AVNRT, the mean AH interval was 69 69 msec +/- 50 msec (+/- SD) longer during high right atrial pacing than during the tachycardia (P < 0.001). In 10 of 12 patients with atypical AVNRT, the AH interval during atrial pacing was more than 40 msec longer than the AH interval measured during the tachycardia. In contrast, in patients with ORT or atrial tachycardia, the differences in AH interval between atrial pacing and tachycardia were never more than 20 and 10 msec, respectively. CONCLUSION: The difference in the AH interval between atrial pacing and the tachycardia allows a simple and rapid means of differentiating atypical AVNRT from other types of long RP tachycardias.

Comparison of implantation of nonthoracotomy defibrillators in the operating room versus the electrophysiology laboratory.

Implantable cardioverter-defibrillators (ICDs) with nonthoracotomy lead systems are widely available, and are implanted either in the electrophysiology laboratory or the operating room. The purpose of this study was to prospectively evaluate the safety and efficacy of nonthoracotomy ICD implantation in an electrophysiology laboratory versus an operating room. During a 7-month period, 62 consecutive ICDs with nonthoracotomy lead systems were implanted in patients in an electrophysiology laboratory. During the next 10 months, 110 consecutive ICDs were implanted in patients in a surgical operating room. All ICD implantations were performed under general anesthesia by electrophysiologists. There were no differences in age (58 +/- 14 vs 62 +/- 12 years, p = 0.06), gender distribution (p = 0.3), frequency of structural heart disease (97% vs 97%, p = 0.9), ejection fraction (0.31 +/- 0.15 vs 0.29 +/- 0.13, p = 0.3), or presentation with cardiac arrest (65% vs 53%, p = 0.2) between patients undergoing ICD implantation in the electrophysiology laboratory and operating room, respectively. The rate of successful implantation and of complications for systems implanted in the electrophysiology laboratory (95% and 13%, respectively) and in the operating room (98% and 14%, respectively) were similar (p = 0.4 and p = 0.8, respectively). Specifically, the rate of infection (0% vs 4%, p = 0.3) and hematoma formation (2% vs 4%, p = 0.8) were not statistically significantly different. Three patients who had undergone ICD implantation in an operating room died within 30 days. ICDs with nonthoracotomy lead systems can be implanted with a similarly high rate of success and acceptable complication rate in the electrophysiology laboratory and in the operating room.

Analysis of junctional ectopy during radiofrequency ablation of the slow pathway in patients with atrioventricular nodal reentrant tachycardia.

BACKGROUND: Junctional ectopy may occur during radiofrequency (RF) catheter ablation of the slow pathway in patients with atrioventricular nodal reentrant tachycardia (AVNRT). The purpose of the present study was to characterize this junctional ectopy quantitatively. METHODS AND RESULTS: The subjects of this study were 52 consecutive patients with AVNRT who underwent slow pathway ablation and 5 additional patients included retrospectively because they had developed high-degree atrioventricular (AV) block during the procedure. A combined anatomic and electrogram mapping approach was used for slow pathway ablation, and AVNRT was successfully eliminated in all patients. In the group of 52 consecutive patients, the incidence of junctional ectopy was significantly higher during 52 effective applications of RF energy than during 366 ineffective applications (100% versus 65%, P < .001). Compared with ineffective RF energy applications, successful RF energy applications had a significantly longer duration of individual bursts of junctional ectopy (7.1 +/- 7.1 versus 5.0 +/- 7.0 seconds [+/- SD], P < .05), a greater total number of junctional beats during the applications (24 +/- 16 versus 15 +/- 8, P < .01), and a greater total span of time during which junctional ectopy occurred (19 +/- 15 versus 11 +/- 12 seconds, P < .01). Four of the 52 patients plus an additional 5 patients developed transient AV block lasting 34 +/- 37 seconds. In 1 of the 9 patients who had transient AV block, third-degree AV nodal block requiring a permanent pacemaker recurred 2 weeks later. In each of the 9 patients who developed AV block, there was ventriculoatrial (VA) block in association with junctional ectopy during the RF energy application immediately preceding the AV block. Among 48 patients who did not develop AV block, 17 patients had at least one episode of VA block during junctional ectopy. The positive predictive value of VA block during junctional ectopy for the development of AV block was 19% in the consecutive series of 52 patients. Among 31 patients who always had 1:1 VA conduction in association with junctional ectopy, 12 had poor VA conduction in the baseline state, with a VA block cycle length of at least 500 milliseconds during ventricular pacing. CONCLUSIONS: In patients with AVNRT undergoing slow pathway ablation, junctional ectopy during the application of RF energy is a sensitive but nonspecific marker of successful ablation. The bursts of junctional ectopy are significantly longer at effective target sites than at ineffective sites. VA conduction should be expected during the junctional ectopy that accompanies slow pathway ablation, even when there is poor VA conduction during baseline ventricular pacing. VA block during junctional ectopy is a harbinger of AV block in patients undergoing RF ablation of the slow pathway. If energy applications are discontinued as soon as VA block occurs, the risk of AV block may be markedly reduced.

Results and efficiency of programmed ventricular stimulation with four extrastimuli compared with one, two, and three extrastimuli.

BACKGROUND: Conventional programmed ventricular stimulation protocols are inefficient compared with more recently proposed protocols. The purpose of the present study was to determine if additional efficiency could be derived from a 6-step programmed ventricular stimulation protocol that exclusively uses four extrastimuli. METHODS AND RESULTS: The subjects were 209 consecutive patients with coronary artery disease and documented sustained monomorphic ventricular tachycardia, nonsustained ventricular tachycardia, aborted sudden death, or syncope. These patients underwent 159 electrophysiological tests in the absence of antiarrhythmic drug therapy and 105 electrophysiological tests in the presence of antiarrhythmic therapy. Programmed stimulation was performed with two protocols in random order in each patient. Both protocols used an eight-beat drive train, 4-s intertrain pause, and basic drive cycle lengths of 350, 400, and 600 ms. The 6-step protocol started with coupling intervals of 290, 280, 270, and 260 ms, which were shortened simultaneously in 10-ms steps until S2 was refractory. The 18-step protocol used one, two and three extrastimuli in conventional sequential fashion. The end points were 30 s of sustained monomorphic ventricular tachycardia, two episodes of polymorphic ventricular tachycardia requiring cardioversion, or completion of the protocol at two right ventricular sites. There was no significant difference in the yield of sustained monomorphic ventricular tachycardia using the two protocols, regardless of the clinical presentation or treatment with antiarrhythmic drugs. Polymorphic ventricular tachycardia occurred with the 18-step protocol twice as frequently as with the 6-step protocol (6% versus 3%, P < .001). The duration of the 18-step protocol was significantly longer than that of the 6-step protocol in patients with inducible ventricular tachycardia (5.5 +/- 7 versus 2.3 +/- 2 minutes, P < .001), as well as in patients without inducible ventricular tachycardia (25.4 +/- 7 versus 6.9 +/- 2 minutes, P < .001). CONCLUSION: A stimulation protocol that exclusively uses four extrastimuli improves the specificity and efficiency of programmed ventricular stimulation without compromising the yield of monomorphic ventricular tachycardia in patients with coronary artery disease.

Electrophysiologic effects of sotalol and amiodarone in patients with sustained monomorphic ventricular tachycardia.

No prospective studies have compared sotalol and amiodarone during electropharmacologic testing. The purpose of this prospective, randomized study was to compare the electrophysiologic effects of sotalol and amiodarone in patients with coronary artery disease and sustained monomorphic ventricular tachycardia (VT). Patients with coronary artery disease and sustained monomorphic VT inducible by programmed stimulation were randomly assigned to receive either sotalol (n = 17) or amiodarone (n = 17). The sotalol dose was titrated to 240 mg twice daily over 7 days. Amiodarone dosing consisted of 600 mg 3 times daily for 10 days. An electrophysiologic test was performed in the baseline state and at the end of the loading regimen. An adequate response was defined as the inability to induce VT or the ability to induce only relatively slow hemodynamically stable VT. During the follow-up electrophysiologic test, 24% of patients taking sotalol and 41% of those taking amiodarone had an adequate response to therapy (p = 0.30). Amiodarone lengthened the mean VT cycle length to a greater degree than sotalol (28% vs 12%, p < 0.01). There were no significant differences in the effects of sotalol and amiodarone on the ventricular effective refractory period. In patients with coronary artery disease, amiodarone and sotalol are similar in efficacy in the treatment of VT as assessed by electropharmacologic testing. The effects of the 2 drugs on ventricular refractoriness are similar, but amiodarone slows VT to a greater extent than sotalol.

An autonomously propagating luciferase-encoding vector for Dictyostelium discoideum.

We have constructed a luc reporter vector for Dictyostelium discoideum using a 626-bp fragment from the nuclear-associated plasmid Ddp2. The ori from Ddp2 is localized within this fragment and was used to provide an autonomous replication sequence for the reporter vector. This reporter vector was stably retained in D. discoideum AX3K cells without alteration. The vector molecule was also found to exist in relatively low copy number compared to other Dictyostelium vectors in the transformed cells. We demonstrated the utility of this vector as a reporter vector with glycogen synthase promoter/luc fusions of varying sizes.

The efficacy of K-edge filters in diagnostic radiology.

The application of K-edge filters in diagnostic radiology has been investigated by many workers for over twenty years. These investigations have analysed the effects of such filters on image quality and radiation dose as well as the practicalities of their application. This paper presents a synopsis of the published works and concludes that K-edge filters do not perceptibly improve image quality and make only limited reductions in patient dose. K-edge filters are also costly to purchase and potentially result in a reduction in the cost effectiveness of x-ray examinations by increasing the x-ray tube loading. Equivalent contrast enhancement and dose reductions can be achieved by the assiduous choice of non-selective filters.

The economic impact of transvenous defibrillation lead systems.

The purpose of this study was to compare implant charges and convalescence for transvenous and epicardial defibrillation systems. Hospital stay, intensive care utilization, professional fees, and hospital bills were compared in 44 patients who underwent implantation of a cardiac defibrillator between September 1991 and May 1993. Twenty-five consecutive patients received an epicardial lead system, while 19 consecutive patients underwent implantation of the entire transvenous defibrillation system in the electrophysiology laboratory. There were no significant differences between the two groups in mean age or left ventricular ejection fraction. There was a significant reduction in postoperative hospital convalescence from 7.2 +/- 2.0 days with epicardial systems to 3.1 +/- 1.5 days with transvenous systems (P < 0.001). Postoperative intensive care unit stay was significantly reduced with transvenous systems compared with epicardial systems (0.1 +/- 0.2 vs 1.5 +/- 0.9 days; P < 0.001). Hospital charges were also significantly reduced with the transvenous lead system implants. Mean implant charges were lower with transvenous systems: $32,090 +/- $2,620 vs $38,307 +/- $2,701 (P < 0.001); convalescence charges were lower: $5,861 +/- $5,010 $12,447 +/- $4,969 (P < 0.001); the total hospital bill was also significantly lower with transvenous systems: $53,459 +/- $12,588 vs $71,981 +/- $16,172 (P < 0.001). Professional fees for implantation ($4,131 +/- $1,724 vs $6,100 +/- 0, P < 0.001), convalescence care ($1,258 +/- $960 vs $2,846 +/- $1,770; P < 0.001), and total professional fees ($12,925 +/- $4,772 vs $15,731 +/- $4,055, P < 0.05) were lower in the transvenous defibrillation group.(ABSTRACT TRUNCATED AT 250 WORDS)

Radiofrequency catheter modification of atrioventricular conduction to control the ventricular rate during atrial fibrillation.

BACKGROUND: In some patients with atrial fibrillation, the ventricular rate may be difficult to control with medications. We evaluated a radiofrequency catheter technique to modify atrioventricular conduction in atrial fibrillation in order to control the ventricular rate without creating pathologic atrioventricular block. METHODS: We studied 19 consecutive patients with atrial fibrillation and uncontrolled ventricular rates refractory to drug therapy. They had had atrial fibrillation for a mean (+/- SD) of 5.5 +/- 4.9 years, had had 4.9 +/- 0.9 unsuccessful drug trials, and were 62 +/- 15 years old. Before the procedure, the maximal ventricular rate during exercise was 180 +/- 39 beats per minute. A total of 11 +/- 5 radiofrequency-energy applications were delivered to the posterior septal or midseptal right atrium, near the ostium of the coronary sinus. RESULTS: Successful control of the ventricular rate without pathologic atrioventricular block was achieved in 14 of the 19 patients (74 percent). Persistent third-degree atrioventricular block requiring a permanent pacemaker occurred inadvertently in four patients (21 percent). Atrioventricular conduction was intentionally ablated in one patient. The 14 patients who had successful modification of conduction had persistent reductions in maximal ventricular rate during exercise (rate at three months, 126 +/- 24 beats per minute; P < 0.01). These patients had resolution of symptoms related to rapid rates during 8 +/- 2 months of follow-up. One patient had a recurrence of a rapid ventricular rate but was again asymptomatic after a second modification procedure. One patient with dilated cardiomyopathy died suddenly, five months after a successful procedure. CONCLUSIONS: A catheter technique to modify atrioventricular conduction without creating pathologic atrioventricular block is feasible in the majority of patients with symptomatic atrial fibrillation and a rapid ventricular rate refractory to drug therapy.

Effect of shock polarity on ventricular defibrillation threshold using a transvenous lead system.

OBJECTIVES: The purpose of this study was to determine whether the polarity of a monophasic shock used with a transvenous lead system affects the defibrillation threshold. BACKGROUND: The ability to implant an automatic defibrillator depends on achieving an adequate defibrillation threshold. METHODS: A transvenous defibrillation lead with distal and proximal shocking electrodes was used in this study. In 29 consecutive patients, the defibrillation threshold, using a stepdown protocol was determined twice in random order: 1) with the distal coil as the anode, and 2) with the polarity reversed. Only the 20 patients in whom an adequate defibrillation threshold could be obtained with the transvenous lead alone were included in this study. These patients were 61 +/- 14 years old (mean +/- SD) and had a mean ejection fraction of 28 +/- 12%. RESULTS: The mean defibrillation threshold was 11.5 +/- 5.0 J with the distal coil as the anode versus 16.9 +/- 7.7 J with the distal coil as the cathode (p = 0.04). The defibrillation threshold was lower by a mean of 9 +/- 7 J with the former configuration in 14 patients and was lower by a mean of 7 +/- 6 J with the latter configuration in 3 patients; in 3 patients it was the same with both configurations. Use of a subcutaneous patch was avoided in five patients by utilizing the distal electrode as the anode. CONCLUSIONS: Defibrillation thresholds with monophasic shocks are approximately 30% lower with the distal electrode as the anode. The use of anodal shocks may obviate the need for a subcutaneous patch and allow more frequent implantation of a transvenous lead system.

Implantation by electrophysiologists of 100 consecutive cardioverter defibrillators with nonthoracotomy lead systems.

BACKGROUND: Traditional lead systems for implantable cardioverter defibrillators (ICDs) require a thoracotomy for placement. Nonthoracotomy lead systems are available and are usually implanted by an electrophysiologist and a surgeon. The purpose of this study was to prospectively evaluate the safety and efficacy of ICD implantation with a nonthoracotomy lead system by electrophysiologists. METHODS AND RESULTS: A consecutive series of 100 patients (mean age, 61 +/- 13 years, +/- SD) underwent ICD implantation with a nonthoracotomy lead system while intubated and under general anesthesia. Seventy-seven patients had coronary artery disease, 15 had idiopathic cardiomyopathy, 6 had miscellaneous heart disease, and 2 had structurally normal hearts. The mean ejection fraction was 0.29 +/- 0.13. Sixty-eight patients had suffered a cardiac arrest, and 32 had had ventricular tachycardia or syncope. All patients except 9 underwent electrophysiological testing and had failed 1 +/- 1 drug trials before ICD implantation. Three types of nonthoracotomy lead systems were used. The nonthoracotomy lead with an ICD was successfully implanted in 96 patients (96%). Of the unsuccessful implants, 1 patient did not have venous access, the passive fixation lead in 1 would not remain lodged, 1 had elevated defibrillation thresholds, and 1 developed a hemopneumothorax while venous access was being obtained. The mean defibrillation threshold was 17 +/- 6 J. The mean procedure duration was 161 +/- 57 minutes. When a subcutaneous patch was used (n = 58), the procedure duration was 189 +/- 5 minutes, and when a subcutaneous patch was not required (n = 40), the procedure lasted 123 +/- 37 minutes (P < .0001). Patients remained in the hospital 4.5 +/- 4.1 days after implantation, with no procedure-related deaths. Acute complications occurred in 10 patients; 2 had lead dislodgments, 1 with previous abdominal surgery had his abdominal cavity entered (without other complications) while the ICD pocket was being made, 1 had postoperative heart failure, 1 developed a large hematoma when anticoagulation therapy was initiated, 3 required reintubation because of excessive anesthesia, 1 developed superficial cellulitis, and 1 developed a hemopneumothorax secondary to a lacerated subclavian vein. During 6 +/- 3 months of follow-up, 2 patients developed lead fractures. CONCLUSIONS: (1) Electrophysiologists can implant an ICD with a nonthoracotomy lead system safely and with a high success rate; (2) use of a subcutaneous patch correlates with longer procedure durations; and (3) special precautions should be taken in patients with previous abdominal surgery.

Relation between impedance and endocardial contact during radiofrequency catheter ablation.

Lesion size during radiofrequency catheter ablation in patients with paroxysmal supraventricular tachycardia (PSVT) is thought to be related to multiple factors, including contact pressure at the catheter-endocardial interface. Therefore a predictor of contact pressure at a potential target site for ablation might be useful. In this study 25 patients underwent duplicate 2 W applications of radiofrequency energy with the catheter in poor and firm contact with the right ventricular endocardium after successful ablation treatment for PSVT. The mean age of the patients was 44 +/- 15 years. Fifteen patients underwent slow pathway ablation for atrioventricular nodal reentrant tachycardia, and 10 patients underwent ablation for an accessory pathway. The mean impedance for low-energy applications in firm contact (139 +/- 24 ohms) was 22% +/- 13% greater (p 0.0001) than in poor contact with the right ventricle (113 +/- 16 ohms). The maximum impedance was 27% greater when the catheter was in firm (147 +/- 28 ohms) rather than poor contact (116 +/- 16 ohms), with the endocardium (p 0.0001). These results suggest that higher impedance measurements may be obtained with low-energy applications of 2 W when the ablation catheter is in firm contact with the endocardium.

Effects of partial and complete ablation of the slow pathway on fast pathway properties in patients with atrioventricular nodal reentrant tachycardia.

INTRODUCTION: The purpose of this study was to prospectively compare the effects of complete and partial ablation of slow pathway function on the fast pathway effective refractory period (ERP). METHODS AND RESULTS: The subjects were 20 patients (mean age 43 +/- 13 years) with atrioventricular nodal reentrant tachycardia (AVNRT), no structural heart disease, and easily inducible AVNRT. Autonomic blockade was achieved with propranolol (0.2 mg/kg) and atropine (0.04 mg/kg). After elimination of AVNRT and during autonomic blockade, the presence of residual slow pathway function was determined by the presence of a single AV nodal echo and/or dual AV nodal physiology. After autonomic blockade and before ablation, the mean fast pathway ERP was 319 +/- 44 msec and the mean slow pathway ERP was 251 +/- 31 msec. After slow pathway ablation and during autonomic blockade, 7 patients had residual slow pathway function and 13 did not. Complete loss of slow pathway function was associated with a shortening of the fast pathway ERP from 334 +/- 35 msec to 300 +/- 62 msec (P < 0.01), while the fast pathway ERP did not change significantly in patients with residual slow pathway function (291 +/- 29 msec vs 303 +/- 38 msec, respectively; P = 0.08). A shortening of 30 msec or more in the fast pathway ERP was observed in 11 of 13 patients who did not have residual slow pathway function, compared to 0 of 7 patients with residual slow pathway function (P < 0.001). CONCLUSION: Shortening of the fast pathway ERP after successful ablation of AVNRT is dependent upon complete loss of slow pathway function. This observation is consistent with electrotonic inhibition of the fast pathway by the slow pathway.