Syphilis tests in diagnostic and therapeutic decision making

Predictive value calculations were used to derive diagnostic guidelines for syphilis. Specificity of the VDRL (Venereal Disease Research Laboratory) and treponemal tests is high in healthy persons but less in elderly and ill persons. Sensitivity of the VDRL test is high in secondary and early latent syphilis but reduced in primary and late syphilis or in cerebrospinal fluid evaluations. Primary syphilis should be diagnosed by darkfield microscopy, with VDRL confirmation for atypical lesions. Screening of asymptomatic persons with the VDRL test, followed by treponemal test confirmation on positive sera, is recommended for all pregnant women, contacts of persons with infectious syphilis, and other high-risk groups. Quantitative VDRL assessment at 3, 6, and 12 months after treatment should be used to assess the adequacy of treatment for both late latent and early syphilis. Cerebrospinal fluid VDRL assessment and cell count should be restricted to seropositive persons with a high risk of neurosyphilis.

An update and guidance on narrowband ultraviolet B phototherapy: a British Photodermatology Group Workshop Report

Summary These guidelines for use of narrowband (TL-01) ultraviolet B have been prepared for dermatologists by the British Photodermatology Group on behalf of the British Association of Dermatologists. They present evidence-based guidance for treatment of patients with a variety of dermatoses and photodermatoses, with identification of the strength of evidence available at the time of preparation of the guidelines, and a brief overview of background photobiology.

Qualitative analysis of psychosocial impact of diagnosis of Chlamydia trachomatis: implications for screening

OBJECTIVES

To investigate the psychosocial impact for women of a diagnosis of Chlamydia trachomatis and discuss the implications for the proposed UK chlamydia screening programme.

DESIGN

Qualitative study with semistructured interviews. Interview transcripts analysed to identify recurrent themes.

PARTICIPANTS

Seventeen women with a current or recent diagnosis of chlamydia.

SETTING

A family planning clinic and a genitourinary medicine clinic in Glasgow.

RESULTS

Three themes were identified: perceptions of stigma associated with sexually transmitted infection, uncertainty about reproductive health after diagnosis, and anxieties regarding partner's reaction to diagnosis. Most women had not previously perceived sexually transmitted infections as personally relevant; this was a function of stereotypical beliefs about who was "at risk" of sexually transmitted infection. These beliefs were pervasive and negatively affected reactions to diagnosis and produced anxiety about disclosure of the condition to others (particularly sexual partners) and future reproductive morbidity. This anxiety, given the uncertain natural history of chlamydia, may prove difficult to dispel.

CONCLUSIONS

There are three primary areas of concern for women after a diagnosis of chlamydia which need to be examined in the proposed screening programme. Information provided should normalise and destigmatise chlamydial infection and positively promote genitourinary medicine services. Support services should be available because notification of partner can cause anxiety. Uncertainty about future reproductive morbidity may be inevitable; staff providing screening will require guidance in providing advice under such conditions.

Illiteracy among Medicaid recipients and its relationship to health care costs

Poor literacy is associated with poor health status, but whether illiteracy is also linked to higher medical care costs is unclear. We characterized the literacy skills of 402 randomly selected adult Medicaid enrollees to determine if there was an association between literacy skills and health care costs. Each subject's literacy skills were measured with a bilingual (English/Spanish) reading-assessment instrument. We also reviewed each subject's health care costs over the same one-year period. The mean reading level of this Medicaid population was at grade 5.6. Mean annual health care costs were $4,574 per person. There was no significant relationship between literacy and health care costs. While there are compelling reasons to improve poor reading skills among Medicaid enrollees, illiteracy in this population does not appear to contribute to the high cost of providing government-sponsored care.

Early and intensive continuous hemofiltration for severe renal failure after cardiac surgery

BACKGROUND

The aim of this study was to test whether early and intensive use of continuous venovenous hemofiltration (CVVH) achieved a better than predicted outcome in patients with severe acute renal failure undergoing cardiac operations, and whether a simple and yet accurate model could be developed to predict their outcome before starting CVVH.

METHODS

Medical record analysis with collection of demographic, clinical, and outcome information was used.

RESULTS

Sixty-five consecutive patients were treated with early and intensive CVVH (mean operation to CVVH time, 2.38 days; pump-controlled ultrafiltration rate, 2 L/h) after coronary artery bypass grafting (56.9%), single valve procedure (16.9%), or combined operations (26.2%). In 32.3% of patients, intraaortic balloon counterpulsation was required and 20% of patients were emergencies. Sustained hypotension despite inotropic and vasopressor support occurred in 40% of patients and prolonged mechanical ventilation in 58.5%. Using an outcome prediction score specific for acute renal failure, the predicted risk of death was 66%. Actual mortality was 40% (p = 0.003). Using multivariate logistic regression analysis and neural network analysis, patient outcome could be predicted with good levels of accuracy (receiver operating characteristic 0.89 and 0.9, respectively).

CONCLUSIONS

Early and aggressive CVVH is associated with better than predicted survival in severe acute renal failure after cardiac operations. Using readily available clinical data, the outcome of such patients can be predicted before the implementation of CVVH.

An extracorporeal membrane oxygenation-based approach to cardiogenic shock in an older population

BACKGROUND

We investigated the efficacy of an integrated system of advanced supportive care based on extracorporeal membrane oxygenation (ECMO) in older patients with an estimated mortality of more than 90% to establish whether its use is justifiable.

METHODS

Treatment was provided by cardiac surgeons and critical care physicians and included the following key elements: (1) ECMO, (2) early application of continuous venovenous hemofiltration, (3) inhaled nitric oxide, (4) maintenance of perfusion pressure with norepinephrine, (5) maintenance of pulmonary blood flow by ventricular filling with intravenous colloids, (6) avoidance of early postoperative anticoagulation, (7) frequent use of transesophageal echocardiography, and (8) low tidal volume ventilation. Demographic features, intraoperative details, postoperative course, ECMO weaning rate, morbidity, survival to hospital discharge, and the quality of life of survivors were recorded.

RESULTS

Seventeen consecutive patients (median age, 69 years) with refractory cardiogenic shock were studied. The median duration of ECMO was 86 hours (20 to 201 hours). Eleven patients (65%) were successfully weaned from ECMO. Seven patients (41%) survived to discharge. The major causes of morbidity were bleeding and leg ischemia. All patients who survived to discharge were alive and well at follow-up (median, 21 months) and reported a satisfactory quality of life.

CONCLUSIONS

An ECMO-based approach can be used with acceptable results in the treatment of refractory cardiogenic shock, even in older patients.

QT interval dispersion in chronic heart failure and left ventricular hypertrophy: relation to autonomic nervous system and Holter tape abnormalities

OBJECTIVE

To study QT dispersion in left ventricular hypertrophy and chronic heart failure and to determine the relation to ventricular arrhythmias.

SETTING

Investigational laboratory of a tertiary referral centre.

STUDY DESIGN

Patients with left ventricular hypertrophy and normal systolic function (n = 14) and patients with chronic heart failure (n = 18) were matched with controls (n = 17). The QT dispersion was examined in relation to abnormalities in resting mechanical and autonomic function and to the findings of 24 hour Holter monitoring.

MAIN OUTCOME MEASURES

QT dispersion is the difference between the maximum and the minimum QT values from the 12 lead electrocardiogram. Mean(SD) QT dispersion from the 10 lead electrocardiogram was also examined once the 12 lead minimum and maximum values had been removed. The QT distribution is the curve describing the distance from the mean for all QT intervals (ms).

RESULTS

All measures of QT dispersion were increased significantly in left ventricular hypertrophy and tended to increase in those with heart failure. The QT distribution was abnormal in both heart failure and left ventricular hypertrophy. There was no relation between the degree of change in QT dispersion and the incidence of ventricular arrhythmia on 24 hour Holter monitoring. Also there was no relation between QT dispersion and autonomic or mechanical abnormalities. The QT dispersion was related to QRS duration.

CONCLUSION

Though QT dispersion and distribution are abnormal in left ventricular hypertrophy these findings do not support the hypothesis that QT dispersion reflects arrhythmic risk in either hypertrophy or heart failure.

Regional differences in the delayed rectifier current (IKr and IKs) contribute to the differences in action potential duration in basal left ventricular myocytes in guinea-pig

OBJECTIVE

To compare the properties of single myocytes isolated from different layers of the basal region of the left ventricle and to test the hypothesis that differences in the delayed rectifier current (IK) contribute to regional differences in action potential duration.

METHODS

Myocytes were isolated from basal sub-endocardial, mid-myocardial and sub-epicardial layers of the guinea-pig left ventricle. Membrane voltage and current were measured using the switch-clamp technique.

RESULTS

Mean action potential duration measured at 90% repolarisation (APD90) was longer in sub-endocardial myocytes than in mid-myocardial and sub-epicardial myocytes [APD90 ms at 0.2 Hz: sub-endocardial 292 +/- 12 (n = 40), mid-myocardial 243 +/- 8 (n = 42) and sub-epicardial 227 +/- 9 (n = 36), P < 0.001, analysis of variance (ANOVA)]. The APD-rate relationship (stimulation frequencies 2, 1, 0.2 and 0.017 Hz) was steeper in sub-endocardial than in mid-myocardial or sub-epicardial myocytes (P < 0.001, ANOVA). The density of IK was greater in mid-myocardial (4.05 +/- 0.09 pA pF-1) and sub-epicardial (3.90 +/- 0.41 pA pF-1) than in sub-endocardial myocytes (2.74 +/- 0.27 pA pF-1, P < 0.01 ANOVA). The rapidly-activating (IKr) and slowly-activating (IKs) components of IK were significantly smaller in sub-endocardial than in mid-myocardial or sub-epicardial myocytes. D,L-Sotalol-induced prolongation of APD90 was similar in the three regions studied.

CONCLUSIONS

There are significant transmural gradients in the electrophysiological properties of myocytes isolated from the base of the left ventricular free wall in guinea-pig. Sub-endocardial myocytes had a longer APD90 attributable in part to a significantly smaller IK density. We have been unable to identify M cells in the guinea-pig left ventricular free wall.

The value of postoperative radiotherapy as an adjuvant to radical neck dissection

In this study the results of combined radiotherapy and surgery are compared with the results of surgery alone in patients with neck node metastases from squamous cell carcinomas of the head and neck region. Postoperative radiotherapy decreases the recurrence rate in the neck, especially in cases with histologically established extranodal spread. Results of preoperative radiotherapy were similar to those of irradiation after surgery. Postoperative radiotherapy is favored, because it allows a selection of patients for extra treatment on the base of prognostic information, provided by the histologic characteristics of the neck dissection specimen.

Use of gay Internet sites and views about online health promotion among men who have sex with men

In May-June 2002, 4,974 men who have sex with men (MSM), average age 31 years, completed a self-administered questionnaire online accessed through two popular gay Internet sites in the UK (gaydar and gay.com UK). Most men were white (95%), employed (83%), lived in the UK (91%) and self-identified as gay (85%). Nearly half (46%) had not been tested for HIV, while 6% said they were HIV-positive. One-third (31%) reported high-risk sexual behaviour in the previous three months, i.e. unprotected anal intercourse with a partner of unknown or discordant HIV status. Nearly all the men (82%) had looked for a sexual partner on the Internet and three-quarters had been doing so for more than a year. Almost half the men (47%) said they preferred to meet men through the Internet rather than in bars or other 'offline' venues. Although nearly 40% of men said the most important reason for using these Internet sites was to find sexual partners, a further 17% said they primarily used them to have contact with other men, 16% because they were bored, 12% for entertainment, 4% because they were lonely and 3% because they were addicted to it. The majority of men in this survey had favourable attitudes towards online health promotion. Most men thought that Internet sites should allow health workers into chat-rooms (75%); would click on a banner to find out about sexual health (78%); and said if they met a health worker in a chat-room they would find out what they had to say (84%). In multivariate analysis, being HIV-positive, older age and high-risk sexual behaviour were all independently associated with an increased frequency of using the Internet to look for sex (p<0.05). The Internet has emerged as an important meeting place for men who have sex with men. As online HIV prevention initiatives are developed it will be important to monitor the extent to which the favourable attitudes seen here are reflected in preventive behaviours.

Impact of a theoretically based sex education programme (SHARE) delivered by teachers on NHS registered conceptions and terminations: final results of cluster randomised trial

OBJECTIVE

To assess the impact of a theoretically based sex education programme (SHARE) delivered by teachers compared with conventional education in terms of conceptions and terminations registered by the NHS.

DESIGN

Follow-up of cluster randomised trial 4.5 years after intervention.

SETTING

NHS records of women who had attended 25 secondary schools in east Scotland.

PARTICIPANTS

4196 women (99.5% of those eligible).

INTERVENTION

SHARE programme (intervention group) v existing sex education (control group).

MAIN OUTCOME MEASURE

NHS recorded conceptions and terminations for the achieved sample linked at age 20.

RESULTS

In an "intention to treat" analysis there were no significant differences between the groups in registered conceptions per 1000 pupils (300 SHARE v 274 control; difference 26, 95% confidence interval -33 to 86) and terminations per 1000 pupils (127 v 112; difference 15, -13 to 42) between ages 16 and 20.

CONCLUSIONS

This specially designed sex education programme did not reduce conceptions or terminations by age 20 compared with conventional provision. The lack of effect was not due to quality of delivery. Enhancing teacher led school sex education beyond conventional provision in eastern Scotland is unlikely to reduce terminations in teenagers.

TRIAL REGISTRATION

ISRCTN48719575 [controlled-trials.com].

Trends in sexual behaviour among London homosexual men 1998-2003: implications for HIV prevention and sexual health promotion

OBJECTIVES

To examine changes in sexual behaviour among London homosexual men between 1998 and 2003 by type and HIV status of partner.

METHODS

Homosexual men (n=4264) using London gyms were surveyed annually between 1998 and 2003 (range 498-834 per year). Information was collected on HIV status, unprotected anal intercourse (UAI) in the previous 3 months, and type of partner for UAI. High risk sexual behaviour was defined as UAI with a partner of unknown or discordant HIV status.

RESULTS

Between 1998 and 2003, the percentage of men reporting high risk sexual behaviour with a casual partner increased from 6.7% to 16.1% (adjusted odds ratio (AOR) 1.36 per year, 95% confidence interval (CI) 1.26 to 1.46, p <0.001). There was no significant change in the percentage of men reporting high risk sexual behaviour with a main partner alone (7.8%, 5.6%, p=0.7). These patterns were seen for HIV positive, negative and never tested men alike regardless of age. The percentage of HIV positive men reporting UAI with a casual partner who was also HIV positive increased from 6.8% to 10.3% (AOR 1.27, 95% CI 1.01 to 1.58, p <0.05).

CONCLUSION

The increase in high risk sexual behaviour among London homosexual men between 1998 and 2003 was seen only with casual and not with main partners. STI/HIV prevention campaigns among London homosexual men should target high risk practices with casual partners since these appear to account entirely for the recent increase in high risk behaviour.

Adjuvant chemo- and hormonal therapy in locally advanced breast cancer: a randomized clinical study

Between 1977 and 1980, 118 breast cancer patients with locally advanced disease, T3B-4, any N, M0 or T1-3, tumor positive axillary apex biopsy, were randomized to one of three arms: I: radiotherapy (RT) to the breast and adjacent lymph node areas; II: RT followed by 12 cycles of cyclophosphamide, methotrexate, 5 fluorouracil (CMF) and tamoxifen during the chemotherapy period; III: 2 cycles of adriamycin and vincristine (AV), alternated with 2 cycles of CMF, then RT, followed by another 4 cycles of AV, alternated with 4 CMF; tamoxifen during the entire treatment period. The median follow-up period was 5 1/2 years. The adjuvant chemo- and hormonal therapy did not improve the overall survival; the 5-year survival was 37% for all three treatment arms. There was no statistically significant difference in RFS between the three modalities, nor when arm I was compared to arm II and III together, p = 0.11. Local recurrence (LR) was observed in 24 of the 86 patients (28%) who had reached complete remission (CR). LR was not statistically different over the three treatment arms. In 18 of the 24 patients with LR, distant metastases appeared within a few months from the local recurrence. In arm III, the CR rate after 4 cycles AV plus CMF and RT hardly changed after another 8 cycles of chemotherapy. The menopausal status did not influence the treatment results. Dose reduction in more than 4 cycles of chemotherapy was accompanied by better results, p = 0.04.

IN CONCLUSION

adjuvant chemo- and hormonal therapy did not improve RFS and overall survival. These findings do not support the routine use of adjuvant chemo- and endocrine therapy for inoperable breast cancer.

Effects of hypertrophy on regional action potential characteristics in the rat left ventricle: a cellular basis for T-wave inversion?

BACKGROUND

In cardiac hypertrophy, ECG T-wave changes imply an abnormal sequence of ventricular repolarization. We investigated the hypothesis that this is due to changes in the normal regional differences in action potential duration. We assessed the contribution of potassium- and calcium-dependent currents to these differences. Both the altered sequence of ventricular repolarization and the underlying cellular mechanisms may contribute to the increased incidence of ventricular arrhythmias in hypertrophy.

METHODS AND RESULTS

Rats received daily isoproterenol injections for 7 days. Myocytes were isolated from basal subendocardial (endo), basal midmyocardial (mid), and apical subepicardial (epi) regions of the left ventricular free wall. Action potentials were stimulated with patch pipettes at 37 degrees C. The ratio of heart weight to body weight and mean cell capacitance are increased by 22% and 18%, respectively, in hypertrophy compared with controls (P<.001). Normal regional differences in action potential duration at 25% repolarization (APD25) are reduced in hypertrophy (control: endo, 11.4+/-0.9 ms; mid, 8.2+/-0.9 ms; epi, 5.1+/-0.4 ms; hypertrophy: endo, 11.6+/-0.9 ms; mid, 10.4+/-0.8 ms; epi, 7.8+/-0.6 ms). The regional differences in APD25 are still present in 3 mmol/L 4-aminopyridine. Hypertrophy affects APD75 differently, depending on the region of origin of myocytes (ANOVA P<.05). APD75 is shortened in subendocardial myocytes but is prolonged in subepicardial myocytes (control: endo, 126+/-7 ms; epi, 96+/-10 ms; hypertrophy: endo, 91+/-6 ms; epi, 108+/-7 ms). These changes in APD75 are altered by intracellular calcium buffering.

CONCLUSIONS

Normal regional differences in APD and the changes observed in hypertrophy are only partially explained by differences in I(tol). In hypertrophy, the normal endocardial/epicardial gradient in APD75 appears to be reversed. This may explain the T-wave inversion observed and will have implications for arrhythmogenesis.

The relationship between literacy and health

In non-industrialized countries, populations with the lowest literacy rates have the poorest health status. In the United States, however, there is no published research on whether illiteracy, independently of other sociodemographic factors, is related to health status. There are numerous plausible mechanisms by which such a relationship could occur. For example, published reports indicate that most information handouts, consent forms, and other materials for patients are written at reading levels too difficult for most American adults. These and other findings may have important implications in the health care of underserved populations. Research is needed to determine the health effects of impaired literacy skills among Americans, and to develop non-literacy-dependent methods for providing patient education, obtaining informed consent, and administering diagnostic tests.

Heterosexism and homophobia in Scottish school sex education: exploring the nature of the problem

This paper focuses on instances of heterosexism and homophobia, as well as examples of good practice in sex education, observed in 25 Scottish schools. Possible reasons for why good practice is not more widespread are explored. Qualitative and quantitative data are presented. Various constraints to good practice are identified by teachers, and are discussed in the context of survey data on pupil attitudes towards same-sex sexual relationships, and on teacher confidence in teaching about homosexuality.

Regular partners and risky behaviour: why do gay men have unprotected intercourse?

Studies in both the UK and the USA continue to show that gay and bisexual men put themselves at risk of exposure to HIV through unprotected intercourse, most often with regular partners. As part of a larger study of homosexually active men, 310 men who had had unprotected anal intercourse with a man in the previous year were asked to describe the last occasion on which this had happened. The majority of men had had unprotected intercourse with a regular partner and did not perceived it as risky, although most did not know the HIV status of their partner. Regular and non-regular partners were perceived differently. Men were more likely to be emotionally involved in regular partners and to perceive unprotected penetrative sex with a regular partner as not risky. Future health education initiatives must take into account men's emotional involvement in regular partners and their perception of unprotected intercourse with such partners as not risky.

Regional differences in electrical and mechanical properties of myocytes from guinea-pig hearts with mild left ventricular hypertrophy

OBJECTIVE

To investigate electrical and mechanical properties of single myocytes isolated from different regions of the left ventricle in control and hypertrophied hearts.

METHODS

Mild cardiac hypertrophy was induced in guinea-pigs by aortic constriction. Myocytes were isolated from basal sub-endocardial, basal mid-myocardial and apical sub-epicardial layers of the left ventricle. Action potentials were stimulated at 1 Hz. Membrane currents were measured using the switch-clamp technique. Cell shortening was measured using a photodiode array.

RESULTS

In control hearts mean action potential duration (APD) was longer in sub-endocardial myocytes than in sub-epicardial myocytes. In hypertrophy APD was prolonged in sub-epicardial and mid-myocardial myocytes and unchanged in sub-endocardial myocytes (APD90 ms, control: sub-endocardial 273 +/- 12, mid-myocardial 254 +/- 14, sub-epicardial 229 +/- 9; hypertrophy: sub-endocardial 259 +/- 13, mid-myocardial 291 +/- 9, sub-epicardial 268 +/- 11, P < 0.005, ANOVA). There was no significant regional difference in APD in hypertrophied hearts. In control hearts L-type calcium current (ICa) was similar in all regions. In hypertrophy ICa was increased in sub-epicardial and mid-myocardial myocytes and reduced in sub-endocardial myocytes. Calcium-activated tail currents were not regionally different in control or hypertrophied hearts, but were increased in hypertrophy.

CONCLUSIONS

Changes in electrical and mechanical properties associated with hypertrophy are not homogeneous throughout the left ventricle. The difference in APD between sub-endocardial and sub-epicardial myocytes seen in control hearts is lost in hypertrophy. These results may favour the propagation of re-entry arrhythmias in hypertrophied hearts.

After-hours discharge from intensive care increases the risk of readmission and death

Despite reports showing night discharge from an intensive care unit (ICU) is associated with increased mortality, it is unknown if this has resulted in changes in practice in recent years. Our aim was to determine prevalence, trends and effect on patient outcome of discharge timing from ICU throughout Australia and New Zealand. Two datasets from the Australian and New Zealand Intensive Care Society Adult Patient Database (ANZICS APD) were examined: (1) All submissions to the APD from 1.1.2003 to 31.12.2004 to determine contemporary practices. (2) Forty hospitals which had submitted continuous data between 1.1.2000 and 31.12.2004 to determine trends in practice over time. Outcomes investigated were hospital mortality and ICU readmission rate. Between 1.1.2003 and 31.12.2004, the ANZICS APD reported 76,690 patients discharged alive from ICU; 13,968 (18.2%) were discharged after-hours (between 1800 and 0559 hours). After-hours discharges had a higher readmission rate (6.3% vs. 5.1%; P < or = 0.0001) and higher mortality (8.0% vs. 5.3%; P = < 0.0001). Peak readmission (8.6%) and mortality rates (9.7%) were seen in patients discharged between 0300 and 0400 hours. After-hours discharge was a predictor of mortality (odds ratio 1.42, 95% confidence interval 1.32-1.52; P= < 0.0001) in multivariate analysis. Between 2000 and 2004, after-hours discharges increased (P = 0.0015) with seasonal peaks during winter The risk of death increased as the proportion of patients discharged after-hours rose. After-hours discharge from ICU is associated with increased risk of death and readmission to ICU. It has become more frequent. The risk of death increases as more after-hours discharges occur.

Effect of exercise-induced ischemia on QT interval dispersion

An increased spatial dispersion of ventricular repolarization duration (QT dispersion) is associated with an increased vulnerability to arrhythmias. This study was designed to examine the effect of exercise on QT dispersion in ischemic heart disease (IHD). QT dispersion, corrected QT dispersion, and percentage change in uncorrected and corrected QT dispersion between rest and peak exercise were examined in 14 members of a control group, 17 patients with IHD, and 14 patients with IHD who were receiving beta-blockers (IHD-B). All subjects had undergone a standard Bruce protocol exercise test, and QT intervals were measured at rest and peak exercise with a digitizing tablet interfaced to a personal computer. QT dispersion at rest was markedly increased in the IHD group compared with that in the control and IHD-B groups, respectively (corrected QT dispersion in milliseconds), 74 +/- 7, 40 +/- 4, 49 +/- 5, p < 0.03). The corrected QT dispersion at peak exercise was greater in the IHD group compared with that in the control group (57 +/- 5 vs 26 +/- 3 msec, p < 0.03). The percentage change in QT dispersion with exercise was significantly higher in the IHD group (52% +/- 5%) compared with that in both the control group (28% +/- 4%, p < 0.002) and the IHD-B group (30% +/- 3%, p < 0.01). A larger mean QT dispersion at peak exercise and an increased percentage change in QT dispersion with exercise may help explain the increased susceptibility of the IHD group for arrhythmias. The cardioprotective action of beta-blockers may be explained by their blunting effect on exercise-related changes in QT dispersion.

Membrane current changes in left ventricular myocytes isolated from guinea pigs after abdominal aortic coarctation

OBJECTIVE

The aim was to look for membrane current changes as a basis for the prolongation of action potential duration in left ventricular myocytes following abdominal aortic coarctation.

METHODS

Immature female guinea pigs underwent laparotomy and an aortic coarctation was fashioned immediately distal to the renal arteries. After 20 weeks the hearts were removed and single myocytes were isolated from the left ventricles by standard enzymatic techniques. The switch-clamp technique was used.

RESULTS

Heart weight:body weight ratio was increased by 7% in the coarctation group (p < 0.01). Systolic left ventricular pressure was 59(SEM 4) mm Hg in control and 76(7) mm Hg in coarctation animals (p < 0.05). Cell capacity was increased by 21% in the coarctation group (p < 0.05), and mean resting potential was 4.6 mV more negative in this group (p < 0.001). Action potential duration at 90% repolarisation was 310(17) ms in the control group (n = 22) and 358(13) ms in the coarctation group (n = 34, p < 0.05). Peak density of L-type calcium current was -8.6(0.4) pA.pF-1 in control and -11.1(0.7) pA.pF-1 in coarctation cells (p < 0.01). The regression line for calcium current versus cell capacity was shifted to higher calcium currents in the coarctation group. The half inactivation potential for this current was shifted by 11.5 mV (p < 0.01). Calcium-activated tail currents were larger and the envelope of tail currents was prolonged in the coarctation cells. No significant differences were found in the amplitude of IK or of IKl.

CONCLUSIONS

After infrarenal aortic coarctation, action potential duration of left ventricular myocytes is prolonged. This prolongation may be attributed to an increase in calcium current density and a shift of its inactivation variable, together with an increased magnitude and prolonged time course of sodium-calcium exchange current. These current changes are potentially arrhythmogenic.