AMAZONE: prevention of persistent pain after breast cancer treatment by online cognitive behavioral therapy-study protocol of a randomized controlled multicenter trial

Background

Surviving breast cancer does not necessarily mean complete recovery to a premorbid state of health. Among the multiple psychological and somatic symptoms that reduce the quality of life of breast cancer survivors, persistent pain after breast cancer treatment (PPBCT) with a prevalence of 15–65% is probably the most invalidating. Once chronic, PPBCT is difficult to treat and requires an individualized multidisciplinary approach. In the past decades, several somatic and psychological risk factors for PPBCT have been identified. Studies aiming to prevent PPBCT by reducing perioperative pain intensity have not yet shown a significant reduction of PPBCT prevalence. Only few studies have been performed to modify psychological distress around breast cancer surgery. The AMAZONE study aims to investigate the effect of online cognitive behavioral therapy (e-CBT) on the prevalence of PPBCT.

Methods

The AMAZONE study is a multicenter randomized controlled trial, with an additional control arm. Patients (n=138) scheduled for unilateral breast cancer surgery scoring high for surgical or cancer-related fears, general anxiety or pain catastrophizing are randomized to receive either five sessions of e-CBT or online education consisting of information about surgery and a healthy lifestyle (EDU). The first session is scheduled before surgery. In addition to the online sessions, patients have three online appointments with a psychotherapist. Patients with low anxiety or catastrophizing scores (n=322) receive treatment as usual (TAU, additional control arm).

Primary endpoint is PPBCT prevalence 6 months after surgery.

Secondary endpoints are PPBCT intensity, the intensity of acute postoperative pain during the first week after surgery, cessation of postoperative opioid use, PPBCT prevalence at 12 months, pain interference, the sensitivity of the nociceptive and non-nociceptive somatosensory system as measured by quantitative sensory testing (QST), the efficiency of endogenous pain modulation assessed by conditioned pain modulation (CPM) and quality of life, anxiety, depression, catastrophizing, and fear of recurrence until 12 months post-surgery.

Discussion

With perioperative e-CBT targeting preoperative anxiety and pain catastrophizing, we expect to reduce the prevalence and intensity of PPBCT. By means of QST and CPM, we aim to unravel underlying pathophysiological mechanisms. The online application facilitates accessibility and feasibility in a for breast cancer patients emotionally and physically burdened time period.

Trial registration

NTR NL9132, registered December 16 2020.

The relationship of weather with daily physical activity and the time spent out of home in older adults from Germany – the ActiFE study

Background

There is a need for a comprehensive evaluation of the associations between varieties of weather conditions on the time spent out-of-home (TOH) and on walking duration (WD) among older adults. We aim to investigate the extent to which various weather parameters (temperature, solar radiation, sunshine duration, humidity, windspeed, and rain) determine daily WD the TOH in older adults.

Methods

The ActiFE (Activity and Function in Older People in Ulm) study is a prospective study of participants aged 65 years or older who wore an accelerometer and kept a movement diary in up to three temporally separated waves from 2009 to 2018 for a duration up to seven days per wave (up to three weeks in summary). We used weather data from a weather station near the participants‘ homes. Age-adjusted and gender-stratified generalized mixed models were used to predict WD and TOH (with 95% confidence interval (CI)) within and between weather categories. Generalized additive models were computed for the single predictions at the weather quartile boundaries. Cubic splines (with 95% pointwise confidence bands (CB)) visualized the continuous course of the weather values.

Results

Higher temperatures, solar radiation and more hours of sunshine, led to an increase in WD and TOH, while higher precipitation, humidities and windspeeds led to a decrease. Women had in general higher WD and TOH times than men.

Conclusions

Our data suggest that weather parameters have a considerable influence on PA and TOH. Future analyses and interpretation of PA data should therefore account for weather parameters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11556-022-00286-0.

[Challenges of discharge management in geriatric traumatology : Example of an integrated orthogeriatric service]

BACKGROUND

Geriatric patients are currently responsible for almost one third of all emergency hospital admissions. An increase of 50% is expected in the next decade. This age redistribution poses new challenges for inpatient care and discharge management. The requirements of an orthopedic trauma surgery clinic in the care of this patient group can be clarified with the help of this first collaboratively created geriatric orthopedic trauma surgery complex treatment unit of a university hospital.

OBJECTIVE

What influence do age and delirium have on discharge management, length of inpatient stay and discharge destination in a geriatric cohort?

MATERIAL AND METHODS

All patients who received inpatient treatment as part of the orthopedic trauma surgery geriatric complex treatment (GKB) between May 2017 and December 2019 were evaluated. An analysis of the demographics, length of inpatient stay, discharge destinations and evaluation of the Barthel index collected on admission and discharge, the mini-mental state examination (MMSE) and the geriatric depression scale (GDS) were carried out.

RESULTS

Out of 312 patients, 110 men and 193 women with a median age of 81 years, 77 patients (24.6%) showed delirium when enrolled in the GKB and 39 (12.5%) dementia. Older patients presented more often with delirium than younger people (p = 0.013), especially those aged 70-79 years (p = 0.037). Dementia patients suffered more frequently from postoperative delirium (p < 0.01). The mean hospital stay was 17.79 days (±4.6 days). The GKB was regularly completed in 60.7% of all cases and 39.3% patients dropped out early. Patients with delirium were discharged significantly less often into their own home but into short-term care or nursing homes (p = 0.038). A general correlation between delirium development and the discharge destination was noticeable (p = 0.004).

CONCLUSION

Patients with dementia are more likely to develop delirium postoperatively, which leads to an increase in the length of inpatient stay, an increase in treatment costs and more work for the discharge management team. In addition, the discharge to the patients' home is impaired by delirium, which means that the growing need for places in short-term care and nursing homes also creates socioeconomic burdens.

Self- and proxy report for the assessment of pain in patients with and without cognitive impairment: experiences gained in a geriatric hospital

BACKGROUND

Pain assessment is a complex procedure in patients with different degrees of cognitive impairment. The challenge is to determine whether self-reporting tools are adequate and to identify the cases in which proxy ratings are necessary.

PATIENTS AND METHODS

As part of an open, prospective observational study, 178 patients underwent a comprehensive pain assessment consisting of the Numeric Rating Scale (NRS), the Verbal Rating Scale with four and five items (VRS4 and VRS5) and the Pain Assessment in Advanced Dementia Scale (PAINAD).

RESULTS

Even without prior knowledge of a patient's cognitive impairment, this toolkit can be used to reliably identify cases where self-rating is appropriate and where proxy rating becomes necessary. Inter-rater reliability: "good" agreement [Cohen's κ = 74.2% (p < 0.001) (95%CI, 54.6-93.8%)], test-retest reliability: "moderate" agreement [κ = 55.3% (p < 0.001) (95%CI, 28.5-82.1%)]. Furthermore, movement resulted in a higher correlation between the selected assessments. Self-report assessments are appropriate up to a mini-mental state examination (MMSE) value greater than ten. In comparison to NRS, VRS4 and VRS5 remain more stable as the degree of cognitive impairment increases.

CONCLUSIONS

In the majority of the cases, our approach enables reliable appropriate pain assessment without the strict prerequisite of an upstream cognitive assessment.

Observer-rated pain assessment instruments improve both the detection of pain and the evaluation of pain intensity in people with dementia

BACKGROUND

Observer-rated pain assessment instruments for people with dementia have proliferated in recent years and are mainly effective in identifying the presence of pain. The objective of this study was to determine whether these tools can also be used to evaluate intensity of pain.

METHOD

Quasi-experimental design. Cognitively intact [Mini Mental State Examination (MMSE) ≥ 24, n = 60] and impaired people (MMSE < 20, n = 65) in nursing home facilities took part in the study. Participants were observed at rest and during a movement protocol. Directly afterwards, the observer, blinded to cognitive status, completed three behavioural pain assessment instruments (Abbey Pain Scale, Pain Assessment in Advanced Dementia Scale (PAINAD), Non-communicative Patient's Pain Assessment Instrument (NOPPAIN) ], before interviewing the resident about pain self-report.

RESULTS

Significant correlations were found between observer-rated and self-rated measures of pain and were stronger in persons with dementia than in cognitively intact adults. Discriminant function analysis (DFA) revealed: (1) that the use of observer-rated instruments improved recognition of the presence or absence of pain by up to 25.4% (in dementia) and 28.3% (in cognitively intact adults) above chance; and (2) the same instruments improved the classification of residents into the correct self-reported level of pain intensity by up to 42.5% (in dementia) and 34.1% (in cognitively intact adults) above chance. However, DFA also reveals a considerable rate of 'false alarms' for pain in cognitively intact and 'misses' in cognitively impaired people.

CONCLUSIONS

The use of the Abbey Pain Scale, PAINAD or NOPPAIN improves both the recognition of pain presence/absence as well as rating pain severity in older people with impaired cognition.

The grapes of war. Somatoform pain disorder and history of early war traumatization in older people

Persistent pain is not a normal part of aging. Nevertheless, many older patients have long-lasting, more or less medically unexplained pain symptoms and, consequently, are often severely disabled, incur high health care costs, and have high comorbidity rates. Moreover, the effects of early traumatization, especially due to wars, and even below the level of posttraumatic stress disorder (PTSD) are apparent. However, the developmental and neurobiological underpinnings of somatoform pain disorder, especially in pain-prone elderly patients, and its correlations with a history of war traumatization even decades after the incident remain unclear. Furthermore, a management strategy for this disorder tailored to older people and their special needs is lacking. Adequate therapeutic regimens such as adjusted psychotherapeutic procedures for elderly patients can only be promoted through a better understanding of the neurobiological and biographical underpinnings of this still controversial disorder.

[Maintenance of health and relief for caregivers of elderly with dementia by using "initial case management": experiences from the Lighthouse Project on Dementia, Ulm, ULTDEM-study]

BACKGROUND

When facing the well-known demographic development with an increasing number of people suffering from dementia, there is a need of programmes to support nursing relatives and care at home. Many support services have been established in the past few years but they are rarely used by the relatives and the patients. The purpose of the Lighthouse Project Ulm (ULTDEM Study) was to prove the effectiveness of a single advisory approach in order to provide support services after care level classification and to relieve the burden placed on relatives caring for family members suffering from dementia ("initial case management").

METHODS

The ULTDEM Study is a prospective, open, randomized, controlled, interventional study with different parallel outcome measures (burden of caring, quality of life and mood). After the randomization, the interventional group was given comprehensive, individual advice about available treatment possibilities for dementia patients. Control group participants received standard treatment. Inclusion criteria were application of a care level (0 or 1) as well as dementia diagnosis. All participants (patients/relatives) underwent an initial and a 6 month comprehensive assessment.

RESULTS

Our results show that a single advisory approach does not lead to a significant difference in outcome measures in interventional and control groups. Those tendencies described have to be interpreted as clinically not relevant. Although utilization of support services increases, it remains similar in both study groups. A confirmatory interpretation has not been possible due to a lack of adjustment to the findings regarding multiple testing and an insufficient degree of recruitment. Possible causes will be discussed such as premature intervention during the course of the disease, a lack of intervention blinding, recruitment bias and lack of an influence on adherence with regard to the use of support services.

IMPLICATIONS

The study demonstrates that there is a substantial information deficit for persons affected by dementia and their relatives. Innovative ways still have to be developed to ensure that this information actually reaches the target audience.

Physical activity and other health-related factors predict health care utilisation in older adults: the ActiFE Ulm study

BACKGROUND

Health care utilisation (HCU) can be a useful outcome for estimating costs and patient needs. It can also be used as a surrogate parameter for healthy ageing. The aim of this study was to analyse the associations of formerly described and potentially new parameters influencing health care utilisation in older adults in Germany.

PATIENTS AND METHODS

The ActiFE Ulm (Activity and Function in the Elderly in Ulm) study is a population-based study in 1,506 community dwelling older adults aged 65-90 years in Ulm and surrounding areas in southwestern Germany. Between March 2009 and April 2010 a full geriatric assessment was performed including accelerometer-based average daily walking duration, comorbidity, medication, physical and psychological functioning, health care utilisation, sociodemographic factors etc. The association between above named measures and health care utilisation, represented by the number of drugs, the days in hospital and the number of physician contacts over one year was calculated in multiple regression models. Analysis was conducted among subjects with complete information (n = 1,059, mean age 76 years, 55% male).

RESULTS

The average number of drugs was 4.5 and over 95% of participants visited a physician at least once a year while still more than 65% contacted their physician more than twice a year. Reduced physical activity, BMI, self-rated health and/or comorbidity and male sex were the best predictors of health care utilisation in community dwelling older adults when looking at both the number of drugs and the number of physician contacts over 12 months together. With regard to single diseases entities the best predictors of both the number of drugs and the number of physician contacts were asthma, chronic obstructive pulmonary disease (COPD)/chronic bronchitis and chronic neurological diseases (mostly Parkinson's disease). The number of drugs was most strongly associated with coronary heart disease, diabetes, and high blood pressure.

CONCLUSION

Reduced walking activity, self-rated health and/or comorbidity and male sex are the best predictors of health care utilisation as measured by the number of drugs and number of physician contacts over 12 months. Walking activity could be regarded as the most promising modifiable predictor of HCU in older adults.

[Implementation of a palliative care concept in a geriatric acute care hospital]

To integrate palliative care patients into an acute geriatric ward requires extensive and continuous education and preparation of all participating professionals. It can be a lengthy process to integrate palliative care concepts despite cooperation of the hospital administration. The group of patients to be integrated differs from the patients of regular geriatric wards because of a higher percentage of relatively young oncologic patients and they differ from a regular palliative ward because about 50% are non-oncologic patients, while the average age is much higher than in normal palliative care. It is possible to integrate specialized palliative care into a regular geriatric ward. Patients admitted without palliative intention will benefit the most from ward-integrated palliative care if the treatment aim turns this way. Ward-integrated palliative care can be an integral part of treating geriatric patients in addition to acute geriatric medicine, rehabilitation, and prevention. It can also provide caretakers and patients with the benefits from continuity of treatment and care.

The primary care physician and Alzheimer's disease: an international position paper

This paper aims to define the role of the primary care physician (PCP) in the management of Alzheimer's disease (AD) and to propose a model for a work plan. The proposals in this position paper stem from a collaborative work of experts involved in the care of AD patients. It combines evidence from a literature review and expert's opinions who met in Paris, France, on July 2009 during the International Association of Geriatrics and Gerontology (IAGG) World Congress. The PCP's intervention appears essential at many levels: detection of the onset of dementia, diagnostic management, treatment and follow-up. The key role of the PCP in the management of AD, as care providers and care planners, is consolidated by the family caregiver's confidence in their skills. In primary care practice the first step is to identify dementia. The group proposes a "case finding" strategy, in target situations in which dementia should be detected to allow, secondarily, a diagnosis of AD, in certain cases. We propose that the PCP identifies 'typical' cases. In typical cases, among older subjects, the diagnosis of "probable AD" can be done by the PCP and then confirm by the specialist. While under-diagnosis of AD exists, so does under-disclosure. Disclosure to patient and family should be done by both specialist and PCP. Then, the PCP has a central role in management of the disease with the general objectives to detect, prevent and treat, when possible, the complications of the disease (falls, malnutrition, behavioural and psychological symptoms of dementia). The PCP needs to give basic information to the caregiver on respite care and home support services in order to prevent crisis situations such as unplanned institutionalisation and "emergency" hospital admission. Finally, therapeutic research must be integrated in the daily practice of PCP. It is a matter of patients' right to benefit from access to innovation and clinical research whatever his age or diseases, while of course fully respecting the rules and protective measures that are in force.

[Control of symptoms during the final stage of the patient's life]

Nursing homes have taken on more and more the character of a hospice where palliative competence has significantly become more important. The aim of palliative treatment is not to heal but to control the symptoms during the final stage. The treatment of pain is definitely the main priority. Diagnosing and estimating the severity of the pain are basic requirements of an effective analgesic treatment. In addition to the pain, there are other symptoms such as nausea and emesis, dyspnoea, death rattle,fear, delirium and obstipation in the final stages of a disease which should be controlled very carefully. Not only patients suffering from cancer, but also very sick multimorbide patients and those suffering from dementia in geriatric environments will profit from palliative care.

Effects of dietary flaxseed on vascular contractile function and atherosclerosis during prolonged hypercholesterolemia in rabbits

Dietary flaxseed has significant anti-atherogenic effects. However, the limits of this action and its effects on vascular contractile function are not known. We evaluated the effects of flaxseed supplementation on atherosclerosis and vascular function under prolonged hypercholesterolemic conditions in New Zealand White rabbits assigned to one of four groups for 6, 8, or 16 wk of feeding: regular diet (RG), 10% flaxseed-supplemented diet (FX), 0.5% cholesterol-supplemented diet (CH), and 0.5% cholesterol- and 10% flaxseed-supplemented diet (CF). Cholesterol feeding resulted in elevated plasma cholesterol levels and the development of atherosclerosis. The CF group had significantly less atherosclerotic lesions in the aorta and carotid arteries after 6 and 8 wk than the CH animals. However, the anti-atherogenic effect of flaxseed supplementation was completely attenuated by 16 wk. Maximal tension induced in aortic rings either by KCl or norepinephrine was not impaired by dietary cholesterol until 16 wk. This functional impairment was not prevented by including flaxseed in the high-cholesterol diet. Aortic rings from the cholesterol-fed rabbits exhibited an impaired relaxation response to acetylcholine at all time points examined. Including flaxseed in the high-cholesterol diet completely normalized the relaxation response at 6 and 8 wk and partially restored it at 16 wk. No significant changes in the relaxation response induced by sodium nitroprusside were observed in any of the groups. In summary, dietary flaxseed is a valuable strategy to limit cholesterol-induced atherogenesis as well as abnormalities in endothelial-dependent vasorelaxation. However, these beneficial effects were attenuated during prolonged hypercholesterolemic conditions.

Protein biomarkers associated with acute renal failure and chronic kidney disease

Acute renal failure (ARF) as well as chronic kidney disease (CKD) are currently categorized according to serum creatinine concentrations. Serum creatinine, however, has shortcomings because of its low predictive values. The need for novel markers for the early diagnosis and prognosis of renal diseases is imminent, particularly for markers reflecting intrinsic organ injury in stages when glomerular filtration is not impaired. This review summarizes protein markers discussed in the context of ARF as well as CKD, and provides an overview on currently available discovery results following 'omics' techniques. The identified set of candidate marker proteins is discussed in their cellular and functional context. The systematic review of proteomics and genomics studies revealed 56 genes to be associated with acute or chronic kidney disease. Context analysis, i.e. correlation of biological processes and molecular functions of reported kidney markers, revealed that 15 genes on the candidate list were assigned to the most significant ontology groups: immunity and defence. Other significantly enriched groups were cell communication (14 genes), signal transduction (22 genes) and apoptosis (seven genes). Among 24 candidate protein markers, nine proteins were also identified by gene expression studies. Next generation candidate marker proteins with improved diagnostic and prognostic values for kidney diseases will be derived from whole genome scans and protemics approaches. Prospective validation still remains elusive for all proposed candidates.

Beurteilung von Schmerz bei Demenz (BESD)

BACKGROUND

The observation scale PAINAD (pain assessment in advanced dementia) is composed of five behavioral categories: breathing, vocalization, facial expression, body language, and consolability. The present study investigates the construct validity of the German version.

PATIENTS AND METHODS

We conducted a prospective one-dimensional observation study with repeated measurements (t(1)=pretreatment, t(2)=2 h posttreatment, t(3)=24 h posttreatment). The sample consisted of 12 verbally noncommunicative demented inpatients with severe comorbidity treated in three geriatric clinics. Their age was M=84.3 years (SD=4.4) on the average. Ten of them were female. Inclusion criteria were pain-related physical illness and observed pain behavior. Every patient was treated with analgesics after t(1). After t(2) the medication was discontinued in five patients until t(3). Nurses documented the PAINAD scores after an observation period of 2 min during routine care.

RESULTS

Pain behavior at t(2) diminished considerably displaying a large effect size. Scores continued to be low at t(3) only in the sample with continued medication. Scores in the other part of the sample returned to initial values.

CONCLUSION

The data demonstrate that pain medication strongly impacts the pain behavior of demented patients. The outcome supports the assumption that PAINAD really measures pain.

The effects of dietary hempseed on cardiac ischemia/reperfusion injury in hypercholesterolemic rabbits

BACKGROUND

Hempseed is a novel functional food that contains several health-promoting polyunsaturated fatty acids (PUFAs). PUFAs, such as those found in flaxseed and fish, have been shown to protect the heart against arrhythmias following ischemia/reperfusion.

OBJECTIVE

TO INVESTIGATE THE POTENTIAL OF DIETARY HEMPSEED AS A CARDIOPROTECTIVE AGENT AGAINST GLOBAL ISCHEMIA AND SUBSEQUENT REPERFUSION BY ASSESSING SEVERAL MEASUREMENTS OF CARDIAC PERFORMANCE: QT interval duration, left ventricular pressure, arrhythmia incidence and arrhythmia duration.

METHODS

MALE NEW ZEALAND WHITE RABBITS WERE FED ONE OF SIX DIETS: a control diet; or one supplemented with 10% hempseed, 10% delipidated hempseed, 0.5% cholesterol, 0.5% cholesterol plus 10% hempseed or 5% coconut oil. After eight weeks on their respective diets, the hearts were excised and subjected to 30 min of global ischemia and 45 min of reperfusion. Electrocardiogram traces were recorded throughout the experiment and were subsequently analyzed for QT interval duration, left ventricular pressure, arrhythmia incidence and arrhythmia duration. Plasma and cardiac tissue were analyzed for fatty acid content and composition.

RESULTS

Cholesterol-fed animals exhibited significantly higher PUFA levels in their plasma, but this did not directly translate into higher PUFA levels in their cardiac fractions. There were no significant differences among the groups in the incidence or duration of ischemia-derived arrhythmias. During reperfusion, there was a significant decrease in the incidence of fibrillation in the hearts obtained from cholesterol-fed and hempseed- plus cholesterol-fed rabbits compared with the hearts from delipidated hempseed-fed rabbits.

CONCLUSIONS

Dietary hempseed induced limited beneficial effects on cardiac function during ischemia/reperfusion challenge. The present study does not support the use of dietary hempseed to protect the heart during ischemic insult in this experimental model.

Effect of celecoxib and dexamethasone on postoperative pain after lumbar disc surgery

OBJECTIVE

This study was designed to assess the efficacy of perioperative administration of celecoxib (Celebrex; Pharmacia GmbH, Erlangen, Germany) in reducing pain and opioid requirements after single-level lumbar microdiscectomy.

METHODS

We studied 34 patients (mean age, 44.26 yr; standard deviation [SD], 13.09 yr) allocated randomly to receive celecoxib 200 mg twice a day for 72 hours starting on the evening before surgery or placebo capsules in a double-blind study. Fourteen patients received 20 to 80 mg dexamethasone intravenously during surgery (mean, 40 mg; SD, 19.22 mg) because of visible signs of compression of the affected nerve root. After lumbar disc surgery, patients were monitored for visual analog scores for pain at rest and on movement, patient-controlled analgesia (PCA) piritramide requirements, and von Frey thresholds in the wound area.

RESULTS

Pain scores decreased and wound von Frey thresholds increased continuously until discharge, with no intergroup differences. Mean 24-hour PCA piritramide requirements were 22.63 mg (SD, 23.72 mg) and 26.14 mg (SD, 22.57 mg) in the celecoxib and placebo groups, respectively (P = not significant). However, patients with intraoperative dexamethasone (n = 14) required only 10.29 mg (SD, 8.55 mg) 24-hour PCA piritramide, in contrast to the 34.25 mg (SD, 24.69 mg) needed in those who did not receive intraoperative dexamethasone (P = 0.001). In addition, 24 hours after the operation, pain scores on movement were significantly lower in the dexamethasone subgroup (P = 0.003).

CONCLUSION

Celecoxib has no effect on postoperative pain scores and PCA piritramide requirements. The intraoperative use of 20 to 80 mg dexamethasone is able to significantly decrease postoperative piritramide consumption and pain scores on the first day after surgery.

Inhibition of Na+/Ca2+ exchange by KB-R7943: transport mode selectivity and antiarrhythmic consequences

The Na+/Ca2+ exchanger plays a prominent role in regulating intracellular Ca2+ levels in cardiac myocytes and can serve as both a Ca2+ influx and efflux pathway. A novel inhibitor, KB-R7943, has been reported to selectively inhibit the reverse mode (i.e., Ca2+ entry) of Na+/Ca2+ exchange transport, although many aspects of its inhibitory properties remain controversial. We evaluated the inhibitory effects of KB-R7943 on Na+/Ca2+ exchange currents using the giant excised patch-clamp technique. Membrane patches were obtained from Xenopus laevis oocytes expressing the cloned cardiac Na+/Ca2+ exchanger NCX1.1, and outward, inward, and combined inward-outward currents were studied. KB-R7943 preferentially inhibited outward (i.e., reverse) Na+/Ca2+ exchange currents. The inhibitory mechanism consists of direct effects on the transport machinery of the exchanger, with additional influences on ionic regulatory properties. Competitive interactions between KB-R7943 and the transported ions were not observed. The antiarrhythmic effects of KB-R7943 were then evaluated in an ischemia-reperfusion model of cardiac injury in Langendorff-perfused whole rabbit hearts using electrocardiography and measurements of left ventricular pressure. When 3 microM KB-R7943 was applied for 10 min before a 30-min global ischemic period, ventricular arrhythmias (tachycardia and fibrillation) associated with both ischemia and reperfusion were almost completely suppressed. The observed electrophysiological profile of KB-R7943 and its protective effects on ischemia-reperfusion-induced ventricular arrhythmias support the notion of a prominent role of Ca2+ entry via reverse Na+/Ca2+ exchange in this process.

Changes in the expression of cardiac Na+-K+ ATPase subunits in the UM-X7.1 cardiomyopathic hamster

Previous studies have shown that cardiac Na+ -K+ ATPase activity in the UM-X7.1 hamster strain is decreased at an early stage of genetic cardiomyopathy and remains depressed; however, the mechanism for this decrease is unknown. The objective of the present study was to assess whether changes in the expression of cardiac Na+-K+ ATPase subunits in control and UM-X7.1 cardiomyopathic hamsters are associated with alterations in the enzyme activity. Accordingly, we examined sarcolemmal Na+-K+ ATPase activity as well as protein content and mRNA levels for the alpha1, alpha2, alpha3 and beta1-subunit of the Na+-K+ ATPase in 250-day-old UM-X7.1 and age-matched, control Syrian hamsters; this age corresponds to the severe stage of heart failure in the UM-X7.1 hamster. Na+-K+ ATPase activity in UM-X7.1 hearts was decreased compared to controls (9.0 +/- 0.8 versus 5.6 +/- 0.8 micromol Pi/mg protein/hr). Western blot analysis revealed that the protein content of Na+-K+ ATPase alpha1- and beta1-subunits were increased to 164 +/- 27% and 146 +/- 22% in UM-X7.1 hearts respectively, whereas that of the alpha2- and alpha3-subunits were decreased to 82 +/- 5% and 69 +/- 11% of control values. The results of Northern blot analysis for mRNA levels were consistent with the protein levels; mRNA levels for the alpha1- and beta1-subunits in UM-X7.1 hearts were elevated to 165 +/- 14% and 151 +/- 10%, but the alpha2-subunit was decreased to 60 +/- 8% of the control value. We were unable to detect mRNA for the alpha3-subunit in either UM-X7. 1 or control hearts. These data suggest that the marked depression of Na+-K+ ATPase activity in UM-X7.1 cardiomyopathic hearts may be due to changes in the expression of subunits for this enzyme.

Predictors of torsades de pointes in rabbit ventricles perfused with sedating and nonsedating histamine H1-receptor antagonists

Several nonsedating histamine H1-receptor antagonists are associated with torsades de pointes ventricular tachycardia. The objectives of this study were to: (i) compare electrocardiographic, monophasic action potential, and arrhythmogenic effects of sedating and nonsedating H1-receptor antagonists, and (ii) identify correlates of drug-induced torsades de pointes in an isolated ventricle model. Isolated, electrically paced (1-3 Hz) rabbit ventricles were Langendorff-perfused with either drug-free Tyrode's solution or one of the following: (i) the sedating H1-receptor antagonist hydroxyzine (0.1-30 microM), (ii) cetirizine, a nonsedating metabolite of hydroxyzine (1-300 microM), and (iii) the nonsedating, putatively arrhythmogenic H1-receptor antagonist astemizole (0.1-30 microM). Volume conducted electrocardiographic signals and monophasic action potentials from the periapical left ventricular endocardium and epicardium were recorded. There were no apparent changes in control (n = 15) or hydroxyzine-perfused (n = 7) hearts. Cetirizine (n = 13) produced a mild biphasic electrocardiographic QT interval prolongation and was associated with early afterdepolarizations, but not with torsades de pointes. Astemizole (n = 11) lengthened QT intervals, and at high concentration (30 microM) induced torsades de pointes in 10 of 11 hearts (P < 0.001 vs. all other groups). These findings are consistent with previously reported repolarizing current inhibition by cetirizine, but may additionally indicate "compensatory" inhibition of inward currents at higher concentrations. By contrast, astemizole-induced changes are consistent with unopposed repolarizing current inhibition.

Modification of heart sarcolemmal Na+/K+-ATPase activity during development of the calcium paradox

This study examined the status of sarcolemmal Na+/K+-ATPase activity in rat heart under conditions of Ca2+-paradox to explore the existence of a relationship between changes in Na+/K+-pump function and myocardial Na+ as well as K+ content. One min of reperfusion with Ca2+ after 5 min of Ca2+-free perfusion reduced Na+/K+-ATPase activity in the isolated heart by 53% while Mg2+-ATPase, another sarcolemmal bound enzyme, retained 74% of its control activity. These changes in sarcolemmal ATPase activities were dependent on the duration and Ca2+ concentration of the initial perfusion and subsequent reperfusion periods; however, the Na+/K+-ATPase activity was consistently more depressed than Mg2+-ATPase activity under all conditions. The depression in both enzyme activities was associated with a reduction in Vmax without any changes in Km values. Low Na+ perfusion and hypothermia, which protect the isolated heart from the Ca2+-paradox, also prevented reperfusion-induced enzyme alterations. A significant relationship emerged upon comparison of the changes in myocardial Na+ and K+ content to Na+/K+-ATPase activity under identical conditions. At least 60% of the control enzyme activity was necessary to maintain normal cation gradients. Depression of the Na+/K+-ATPase activity by 60-65% resulted in a marked increase and decrease in intracellular Na+ and K+ content, respectively. These results suggest that changes in myocardial Na+ and K+ content during Ca2+-paradox are related to activity of the Na+/K+-pump; the impaired Na+/K+-ATPase activity may lead to augmentation of Ca2+-overload via an enhancement of the Na+/Ca2+-exchange system.

Functional role of ionic regulation of Na+/Ca2+ exchange assessed in transgenic mouse hearts

Na+/Ca2+ exchange is the primary mechanism mediating Ca2+ efflux from cardiac myocytes during diastole and, thus, can prominently influence contractile force. In addition to transporting Na+ and Ca2+, the exchanger is also regulated by these ions. Although structure-function studies have identified protein regions of the exchanger subserving these regulatory processes, their physiological importance is unknown. In this study, we examined the electrophysiological and mechanical consequences of cardiospecific overexpression of the canine cardiac exchanger NCX1.1 and a deletion mutant of NCX1.1 (Delta680-685), devoid of intracellular Na+ (Na+i)- and Ca2+ (Ca2+i)- dependent regulatory properties, in transgenic mice. Using the giant excised patch-clamp technique, normal ionic regulation was observed in membrane patches from cardiomyocytes isolated from control and transgenic mice overexpressing NCX1.1. In contrast, ionic regulation was nearly abolished in mice overexpressing Delta680-685, indicating that the native regulatory processes could be overwhelmed by expression of the transgene. To address the physiological consequences of ionic regulation of the Na+/Ca2+ exchanger, we examined postrest force development in papillary muscles from NCX1.1 and Delta680-685 transgenic mice. Postrest potentiation was found to be substantially greater in Delta680-685 than in NCX1.1 transgenic mice, supporting the notion that ionic regulation of Na+/Ca2+ exchange plays a significant functional role in cardiac contractile properties.

The reversible enolization and hydration of pyruvate: possible roles of keto, enol, and hydrated pyruvate in lactate dehydrogenase catalysis

The reversible enolization and hydration of pyruvic acid and pyruvate anion were monitored using spectrophotometric methods at several temperatures. Widely varying values for the equilibrium constant for the enolization of pyruvic acid and pyruvate ion appear in the literature. To accurately determine the position of equilibrium for the enolization reaction, we have developed a method that gives consistent results in which purified samples of sodium pyruvate are first "titrated" with triiodide ion to remove any triiodide-scavenging impurities such as those resulting from aldol condensation reactions. After reequilibration to allow the regeneration of enol pyruvate, the addition of small quantities of triiodide result in an initial burst in the decrease of absorbance at 353 nm, followed by the much slower zero-order decrease due to the formation of new enol pyvuvate molecules. The absorbance change during the burst phase of the reaction is proportional to the enol concentration plus that of any triiodide-scavenging impurity which may be present in the original pyruvate solution. Thus, as the quantity of triiodide used in the pretreatment stage of the experiments is increased, these burst absorbance changes, ΔA, decrease until a constant value of ΔA is reached. Accordingly, this final ΔA value is proportional to enol pyruvate (or enol pyruvic acid) in the absence of triiodide-scavenging impurity, allowing the accurate and reproducible determinations of Kenol. The equilibrium constants for both pyruvate and pyruvic acid are relatively temperature insensitive and, typically, Kenol (pyruvate anion) = 2.6 × 10-5 and Kenol (pyruvic acid) = 7.8 × 10-5 at 25.0°C. The zero-order phase of the reaction of triiodide ion may be used to calculate rate constants for enolization. The hydration and dehydration of pyruvic acid were followed directly by following absorbance changes in the peak at 340 nm due to the keto group. The thermodynamic and kinetic results reported in this paper are used to help determine whether the observed "substrate" inhibition of the lactate dehydrogenase catalyzed reduction of pyruvate is actually caused by keto, hydrated, or enol pyruvate.Key words: pyruvate, enolization, hydration, lactate dehydrogenase.

Alterations of heart function and Na+-K+-ATPase activity by etomoxir in diabetic rats

To examine the role of changes in myocardial metabolism in cardiac dysfunction in diabetes mellitus, rats were injected with streptozotocin (65 mg/kg body wt) to induce diabetes and were treated 2 wk later with the carnitine palmitoyltransferase inhibitor (carnitine palmitoyltransferase I) etomoxir (8 mg/kg body wt) for 4 wk. Untreated diabetic rats exhibited a reduction in heart rate, left ventricular systolic pressure, and positive and negative rate of pressure development and an increase in end-diastolic pressure. The sarcolemmal Na+-K+-ATPase activity was depressed and was associated with a decrease in maximal density of binding sites (Bmax) value for high-affinity sites for [3H]ouabain, whereas Bmax for low-affinity sites was unaffected. Treatment of diabetic animals with etomoxir partially reversed the depressed cardiac function with the exception of heart rate. The high serum triglyceride and free fatty acid levels were reduced, whereas the levels of glucose, insulin, and 3,3',-5-triiodo-L-thyronine were not affected by etomoxir in diabetic animals. The activity of Na+-K+-ATPase expressed per gram heart weight, but not per milligram sarcolemmal protein, was increased by etomoxir in diabetic animals. Furthermore, Bmax (per g heart wt) for both low-affinity and high-affinity binding sites in control and diabetic animals was increased by etomoxir treatment. Etomoxir treatment also increased the depressed left ventricular weight of diabetic rats and appeared to increase the density of the sarcolemma and transverse tubular system to normalize Na+-K+-ATPase activity. Therefore, a shift in myocardial substrate utilization may represent an important signal for improving the depressed cardiac function and Na+-K+-ATPase activity in diabetic rat hearts with impaired glucose utilization.

Cardiac sarcolemmal Na(+)-Ca2+ exchange and Na(+)-K+ ATPase activities and gene expression in alloxan-induced diabetes in rats

To determine the sequence of alterations in cardiac sarcolemmal (SL) Na(+)-Ca2+ exchange, Na(+)-K+ ATPase and Ca(2+)-transport activities during the development of diabetes, rats were made diabetic by an intravenous injection of 65 mg/kg alloxan. SL membranes were prepared from control and experimental hearts 1-12 weeks after induction of diabetes. A separate group of 4 week diabetic animals were injected with insulin (3 U/day) for an additional 4 weeks. Both Na(+)-K+ ATPase and Ca(2+)-stimulated ATPase activities were depressed as early as 10 days after alloxan administration; Mg2+ ATPase activity was not depressed throughout the experimental periods. Both Na(+)-Ca2+ exchange and ATP-dependent Ca(2+)-uptake activities were depressed in diabetic hearts 2 weeks after diabetes induction. These defects in SL Na(+)-K+ ATPase and Ca-transport activities were normalized upon treatment of diabetic animals with insulin. Northern blot analysis was employed to compare the relative mRNA abundances of alpha 1-subunit of Na(+)-K+ ATPase and Na(+)-Ca2+ exchanger in diabetic ventricular tissue vs. control samples. At 6 weeks after alloxan administration, a significant depression of the Na(+)-K+ ATPase alpha 1-subunit mRNA was noted in diabetic heart. A significant increase in the Na(+)-Ca2+ exchanger mRNA abundance was observed at 3 weeks which returned to control by 5 weeks. The results from the alloxan-rat model of diabetes support the view that SL membrane abnormalities in Na(+)-K+ ATPase, Na+Ca2+ exchange and Ca(2+)-pump activities may lead to the occurrence of intracellular Ca2+ overload during the development of diabetic cardiomyopathy but these defects may not be the consequence of depressed expression of genes specific for those SL proteins.

Ischemic preconditioning and arrhythmogenesis in the rabbit heart: effects on epicardium versus endocardium

The goals of this study were: (1) to determine if preconditioning protects against arrhythmias and contractile dysfunction, and if protection for these two endpoints occurs in parallel; and (2) to investigate the anti-arrhythmic action of preconditioning by examining its effect on electrical activity in epicardium v endocardium. We monitored ECGs, epicardial and endocardial monophasic action potentials (MAP), left-ventricular developed presssure (LVDP) and end-diastolic pressure (EDP) in isolated rabbit hearts. Hearts were subjected to a 30-min test ischemia and 45 min of reperfusion. Preconditioning cycles (PC) consisted of 1-4 ischemic episodes (5 min each separated by 10 min of reperfusion) administered 30 min before the test protocol. The test ischemia caused ventricular fibrillation (VF) in 42% of non-PC hearts. One PC totally suppressed VF (0%). The incidence of VF was 30% in 2 PC, 72% in 3 PC and 47% in 4 PC hearts. A large rise in EDP occurred in non-PC and 1 PC hearts, and this rise was prevented by 2, 3 or 4 PC. None of the protocols improved post-ischemic recovery of LVDP or EDP. The test ischemia generated a large dispersion in MAP duration between epicardium and endocardium (39ms), but this dispersion was markedly reduced after 1 PC (14ms). In conclusion, our results demonstrate that 1 PC completely protects against ischemia-induced VF in rabbit hearts, whereas 2 or more PC are required to prevent the ischemia-induced rise in EDP. Thus, preconditioning against arrhythmias and contractile dysfunction does not occur in parallel. Our data also suggest that 1 PC may exert its anti-arrhythmic effect through reduction of the substrate for reentrant arrhythmias during ischemia (dispersion of repolarization) via effects on MAP changes in endocardium.

Mechanism of depression in cardiac sarcolemmal Na+-K+-ATPase by hypochlorous acid

Oxidative stress during pathological conditions such as ischemia-reperfusion is known to promote the formation of hypochlorous acid (HOCl) in the heart and to result in depression of cardiac sarcolemmal (SL) Na+-K+-ATPase activity. In this study, we examined the direct effects of HOCl on SL Na+-K+-ATPase from porcine heart. HOCl decreased SL Na+-K+-ATPase activity in a concentration- and time-dependent manner. Characterization of Na+-K+-ATPase activity in the presence of different concentrations of MgATP revealed a decrease in the maximal velocity (Vmax) value, without a change in affinity for MgATP on treatment of SL membranes with 0.1 mM HOCl. The Vmax value of Na+-K+-ATPase, when determined in the presence of different concentrations of Na+, was also decreased, but affinity for Na+ was increased when treated with HOCl. Formation of acylphosphate by SL Na+-K+-ATPase was not affected by HOCl. Scatchard plot analysis of [3H]ouabain binding data indicated no significant change in the affinity or maximum binding capacity value for ouabain binding following treatment of SL membranes with HOCl. Western blot analysis of Na+-K+-ATPase subunits in HOCl-treated SL membranes showed a decrease (34 +/- 9% of control) in the beta1-subunit without any change in the alpha1- or alpha2-subunits. These data suggest that the HOCl-induced decrease in SL Na+-K+-ATPase activity may be due to a depression in the beta1-subunit of the enzyme.

Electrocardiographic Changes and Mortality Due to Myocardial Infarction in Rats With or Without Imidapril Treatment

BACKGROUND: Various angiotensin-converting enzyme inhibitors are known to improve heart function and prolong survival in patients and animals after myocardial infarction. Because myocardial infarction is known to induce arrhythmias, this study tested the hypothesis that early treatment with the angiotensin converting enzyme inhibitor imidapril reduces mortality during acute myocardial infarction because of protective effects against arrhythmogenesis. METHODS AND RESULTS: Rats were randomly divided into four groups: sham control, myocardial infarction, sham plus imidapril, and myocardial infarction plus imidapril. Myocardial infarction was produced by ligation of the left anterior descending coronary artery. Treated rats received imidapril (1 mg/kg/day) through a gastric tube beginning 1 hour after coronary occlusion; control rats received tap water. Electrocardiogram (ECGs) were recorded 1, 3, 7, and 21 days postocclusion. Infarct size and scar weight were determined at 21 days in the myocardial infarction groups with and without imidapril treatment. ECGs of untreated rats showed ST-segment changes, abnormal Q waves, premature ventricular complexes, and QT(c) prolongation 1-21 days after coronary occlusion. Total mortality in 21 days averaged 35% in untreated rats; mortality within 48 hours was 30%. On the other hand, imidapril-treated rats showed fewer ST-segment changes, fewer abnormal Q waves, and a decreased incidence of premature ventricular complexes after coronary occlusion; the ST-segment and QT(c) interval returned to basal values within 1 week after occlusion. Imidapril treatment did not affect the ECG pattern in sham-treated control animals. Total mortality in the imidapril-treated group in 21 days after infarction was 22.5%; mortality within 48 hours was 20% (P <.05 compared with the untreated infarction group). Infarct size and scar weight caused by coronary occlusion did not differ in the untreated and imidapril-treated groups. CONCLUSIONS: Early treatment with imidapril markedly decreases mortality in rats after acute myocardial infarction. The lower mortality is not associated with a decrease in infarct size but is consistent with a protective effect of the drug against arrhythmogenesis.

Cardioprotection induced by ischemic preconditioning in the mammalian heart: effects on arrhythmogenesis

Ischemic preconditioning (PC) describes the protection that occurs when a brief period of ischemia increases the tolerance of the heart to a future ischemic episode of longer duration. This protection is typically measured as a reduction in myocardial infarct size or improved recovery of contractile function. Few studies have tested whether PC also prevents the occurrence of severe arrhythmias, such as ventricular tachycardia (VT) and fibrillation (VF). We studied the effects of preconditioning on arrhythmias in Langendorff-perfused rabbit hearts. All hearts were subjected to a 30-min test ischemia followed by reperfusion. Preconditioned hearts underwent one to four ischemic periods (5 min each, separated by 10 min of reperfusion) 30 min prior to the test ischemia. VF occurred in 42% of non-PC hearts during ischemia. One PC period totally suppressed VF (0%; p < 0.05) and two PC periods provided partial protection (VF = 17%). In contrast, 64 and 50% of hearts receiving three or four PC periods fibrillated during ischemia, respectively. The test ischemia induced an ischemic contracture that was prevented by two or three PC periods, but not one or four PC periods. None of the PC protocols improved postischemic contractile recovery. In conclusion, our data show that a single PC period completely protects against ischemia-induced VF in rabbit hearts. Preconditioning also prevents development of an ischemic contracture. However, the optimal preconditioning "dose" that prevents arrhythmias is not the same as that which protects against contractile dysfunction.

Electrophysiology of Myocardial Cells in the Epicardial, Midmyocardial, and Endocardial Layers of the Ventricle

The recent discovery of multiple myocardial cell types in the ventricular wall of most species has prompted a reevaluation of several electrophysiologic and electrocardiographic findings. This review briefly presents the salient electrophysiologic features of myocardial cells in the epicardial, midmyocardial and endocardial regions of the ventricle. The epicardial action potential exhibits a prominent notch between phase 1 and phase 2 that results in a spike and dome configuration. The notch is smaller in midmyocardial cells and absent in endocardial cells. The action potential notch is due to the presence of a transient outward current (I(to)), which diminishes in amplitude from the epicardial to endocardial surfaces. Midmyocardial or "M cells" exhibit electrophysiologic features intermediate between those of myocardial and conducting cells. M cells differ from epicardial and endocardial cells primarily in their response to slowing of the stimulation rate. These cells display an exaggerated prolongation of action potential duration at moderate to slow rates of stimulation. The atypical response in M cells reflects decreased levels of the delayed rectifier K(+) current (I(K)) in this cell type (dV/dt) compared to epicardial or endocardial cells. These electrophysiologic distinctions contribute to differences in the responsiveness of the various cell types to pharmacologic agents and disease. Also, the dispersion of repolarization created between epicardium and endocardium in the early phases of the action potential, and between M cells and other ventricular layers during late repolarization, may explain the J wave and U wave of the electrocardiogram, respectively.

Phase 2 reentry as a mechanism of initiation of circus movement reentry in canine epicardium exposed to simulated ischemia

OBJECTIVES

Myocardial ischemia results in an early phase of arrhythmias that primarily involves reentrant mechanisms. However, the trigger that initiates reentry remains unknown. We studied the initiation of reentry attending the development of electrical heterogeneity during simulated ischemia in isolated canine right ventricular subepicardium.

METHODS

Preparations consisted of thin epicardial sheets in which action potentials were recorded at 4 sites with intracellular microelectrodes. Tissues were superfused with a hyperkalemic, hypoxic and acidotic 'ischemic' solution.

RESULTS

Simulated ischemia produced a 40-70% abbreviation of the action potential at some epicardial sites but not others, primarily by suppressing development of the action potential plateau (or dome). This typically created a marked dispersion of repolarization within the preparation. Local re-excitation ensued when the action potential dome propagated from sites where it was maintained to sites where it was abolished. This mechanism, termed 'phase 2 reentry', produced an extrasystole which then initiated one or more cycles of circus movement reentry. Tachycardias consisting of repetitive reentry occurred in larger tissues. The window for reentry occurred over a range of stimulation rates that shifted to faster rates as ischemia progressed. The transient outward current blocker, 4-aminopyridine, restored the dome at all sites by reversing the ischemia-induced abbreviation of the action potential. Thus, block of the transient outward current restored electrical homogeneity and abolished all reentrant activity within the epicardial preparations.

CONCLUSION

Our results implicate phase 2 reentry as a new mechanism for genesis of extrasystoles during simulated ischemia and identify this mechanism as a trigger of circus movement reentry. Validation of this hypothesis awaits the results of future studies using high-resolution recording techniques.

Differences in the electrophysiological response of canine ventricular epicardium and endocardium to ischemia. Role of the transient outward current

BACKGROUND

Acute ischemia is known to produce more severe electrophysiological disturbances in canine ventricular epicardium than endocardium, although the mechanism for the differential sensitivity is still unresolved. Recent studies have demonstrated the presence of a prominent transient outward current (Ito) in ventricular epicardium but not endocardium. The present study was designed to test the hypothesis that the differential sensitivity of these two tissues to ischemia results, at least in part, from a more prominent Ito in epicardium than in endocardium.

METHODS AND RESULTS

Isolated canine ventricular epicardial and endocardial tissues and myocytes were studied by standard microelectrode techniques. Simulated ischemia (hyperkalemia, hypoxia, and acidosis) abolished the action potential plateau and caused a 50% to 60% shortening of action potential duration in epicardium but only a 10% to 20% shortening in endocardium. 4-Aminopyridine, an Ito inhibitor, restored the plateau in epicardium and reduced the dispersion of action potential duration between epicardium and endocardium. Stimulation protocols that minimized the contribution of Ito, such as acceleration of the stimulation rate or introduction of early premature beats, produced a paradoxical prolongation of the epicardial response caused by restoration of the action potential dome. Thus, ischemia-induced dispersion of repolarization was greatly diminished at rapid rates and after premature beats. Similar results were obtained in tissues and myocytes obtained from the same myocardial layers, suggesting that the differential sensitivities of epicardium and endocardium to ischemia are largely a result of inherent differences in cellular properties.

CONCLUSIONS

Our data suggest that the presence of a prominent Ito in epicardium but not endocardium contributes importantly to the selective electrical depression of epicardium by simulated ischemia. The repolarizing influence of Ito serves to amplify the ischemia-induced changes in inward (ICa and INa) and outward (calcium-activated) currents. By facilitating loss of the dome in epicardium, Ito contributes to the development of a marked dispersion of repolarization between normal and ischemic epicardium and between epicardium and endocardium, thereby providing the electrophysiological substrate for the genesis of reentrant arrhythmias.

Reflected reentry, delayed conduction, and electrotonic inhibition in segmentally depressed atrial tissues

Reflection is a subclass of reentrant cardiac arrhythmias in which reexcitation of the heart occurs as a result of to and fro electrotonically mediated transmission of impulses across a narrow zone of impaired conductivity. Although relatively well characterized in ventricular tissues, the reflection mechanism has not been studied in atrial tissues. In this study we examine the possibility of reflected reentry in segmentally depressed atrial tissues and evaluate conduction characteristics in these preparations. Narrow strips of atrial pectinate muscle or crista terminalis (canine and calf) were placed in a three-chambered bath and the central segment was superfused with an isotonic sucrose solution or an "ischemic" Tyrode's solution. Proximal to distal conduction across the 1.0- to 1.2-mm wide ischemic gap showed step delays as long as 210 ms. Reflected reentry was readily demonstrable when prominent step delays occurred during anterograde conduction of the impulse across the gap. Progressive acceleration of the stimulation rate resulted in progressively greater impairment of anterograde conduction until complete block occurred. The incidence and patterns of reflected reentry were therefore a sensitive function of the stimulation rate. Other features exhibited by these preparations include a slow recovery of excitability following the action potential, postrepolarization refractoriness, and electrotonic inhibition and summation. Our data suggest that the characteristics of conduction and reflection in segmentally depressed atrial tissues are qualitatively similar to those in ventricular tissues. The presence of electrotonic inhibition in atrial may also help to explain the functionally inexcitable zone seen in the vortex of the leading circle model of atrial flutter.

Arrhythmic effects of norepinephrine in a model of cardiac ischemia and reperfusion

The aim of this study was to assess the direct effects of norepinephrine on mechanisms of arrhythmia induced by conditions of ischemia followed by reperfusion. Isolated canine Purkinje fiber-papillary muscle preparations were studied using standard microelectrode techniques. Tissues were superfused for 40 min with a solution simulating "ischemia" (i.e., hypoxic, acidotic, elevated lactate, and zero substrate) and then "reperfused" for 60 min. Ischemia produced a moderate loss of membrane potential in both tissues. Reperfusion resulted in rapid polarization of the tissues, which was accompanied by oscillatory afterpotentials and aftercontractions in 6 of 12 and 4 of 12 Purkinje fibers, respectively. This was followed by a progressive loss of membrane potential and inexcitability in Purkinje fibers. Recovery was associated with activity resembling depolarization-induced automaticity in 4 of 12 fibers. Addition of norepinephrine (0.5 microM) to the ischemic and reperfusion solutions altered primarily the reperfusion responses. Oscillatory afterpotentials and aftercontractions were larger and occurred in 8 of 8 and 6 of 8 Purkinje fibers, respectively. Norepinephrine also prevented or blunted the progressive depolarization to inexcitability in Purkinje tissues and increased automaticity occurring at low (depolarization-induced automaticity) and more polarized membrane potentials (enhanced normal pacemaker activity). This study demonstrates that norepinephrine exacerbates several potential mechanisms of arrhythmia elicited by reperfusion in canine Purkinje tissues.

Electrophysiological effects of amrinone and milrinone in an isolated canine cardiac tissue model of ischemia and reperfusion

The purpose of this study was to determine if amrinone or milrinone after the electrophysiological responses of canine ventricular tissues to "ischemia" or reperfusion. Isolated canine Purkinje tissue-papillary muscle preparations were studied using standard microelectrode techniques. Tissues were superfused for 10 min with a solution that mimicked ischemia (hypoxia, acidosis, elevated lactate levels and zero substrate). Reperfusion with normal Tyrode's solution was then instituted for 60 min. Next, tissues were equilibrated with amrinone (5.3 X 10(-4) M) or milrinone (2.5 X 10(-4) M) for 15 min and the protocol was repeated with drug in all solutions. Without drug, ischemic conditions resulted in moderate depolarization of Purkinje and muscle tissues. Reperfusion caused a rapid hyperpolarization in Purkinje tissue. This was followed by a phase of mild depolarization associated with enhanced pacemaker activity. All preparations recovered by 45 min of reperfusion. With amrinone or milrinone present, the changes in membrane potential induced by conditions of ischemia and reperfusion were not different from control. However, an early phase of very rapid ectopic activity was seen during reperfusion with amrinone or milrinone. This ectopic activity had a constant cycle length during the pauses in stimulation. However, irregular patterns of spontaneous and driven beats were observed when electrical stimulation was superimposed on the ectopic activity. Amrinone and milrinone also increased pacemaker activity in Purkinje tissue but this occurred later in reperfusion. This study demonstrates that amrinone and milrinone sensitize isolated canine ventricular tissues to the arrhythmogenic effects of reperfusion. The mechanism underlying the arrhythmic activity elicited by the bipyridines is not clear, but may involve re-entry or abnormal automaticity.

Mechanisms of frequency-induced potentiation of contractions in isolated rat atria

Mechanisms underlying the potentiation of contractions after periods of high frequency stimulation (post-stimulation potentiation; PSP) and periods of rest (rest potentiation; RP) were investigated in isolated rat atria. Transmembrane action potentials were not changed during PSP and RP and were superimposable upon the pre-test action potentials. However, the 45Ca content of atrial strips was significantly increased during PSP, which indicates a net gain in intracellular Ca. 45Ca content was not changed during RP. PSP and RP were increased in magnitude in atria pre-treated with gallopamil (2.5 mumol/l). This effect was due to a greater depression by gallopamil of the pre-test contractions than the potentiated post-test contractions. In contrast, PSP was abolished in atria exposed to 7.5 mmol/l [Ca]o and a transient depression of the post-test contractions was seen. RP was also abolished by high Ca medium, but contractions were not depressed after periods of rest. RP, but not PSP, was unmasked when gallopamil was added to high Ca medium to decrease the size of the basal contractions. Conversely, ryanodine (100 mmol/l) abolished RP but did not affect PSP. With ryanodine present, PSP was greatly increased when the extracellular Ca concentration was increased to 5 mmol/l, whereas RP remained abolished. These results suggest that PSP may reflect an increased transsarcolemmal influx of extracellular Ca, possibly mediated through Na-Ca exchange. In contrast, the mechanism suggested for RP is a transient increase in contractile Ca resulting from an intracellular redistribution of Ca to release sites in the sarcoplasmic reticulum.

Interaction of ischemia and reperfusion with subtoxic concentrations of acetylstrophanthidin in isolated cardiac ventricular tissues: effects on mechanisms of arrhythmia

The aim of this study was to determine if "ischemia" and/or reperfusion potentiate digitalis toxicity through effects on oscillatory afterpotentials. Isolated canine Purkinje tissue-papillary muscle preparations were studied using standard microelectrode techniques. Tissues were superfused for 10 min with an "ischemic" solution that mimicked hypoxia, acidosis, elevated lactate, zero substrate and normo- or hyperkalemia. Reperfusion with "normal" Tyrode's solution was then reinstated for 60 min. Next, subthreshold oscillatory after potentials were induced with acetylstrophanthidin (ACS) and the protocol was repeated with ACS in all solutions. Without ACS, ischemic conditions with 4 mM KCl caused depolarization of Purkinje and muscle tissues. Reperfusion resulted in hyperpolarization of Purkinje tissue followed by mild depolarization, and then recovery. Purkinje tissue exposed to ischemic conditions with hyperkalemia responded similarly, except that hyperpolarization upon reperfusion was absent. In the presence of ACS, ischemic conditions with 4 mM KCl abolished oscillatory afterpotentials and caused marked depolarization of Purkinje tissue. Reperfusion decreased the coupling intervals and increased the amplitude of oscillatory afterpotentials relative to pre-ischemic levels, and frequently elicited arrhythmic activity. Arrhythmias ceased and tissues recovered by 60 min of reperfusion. Ischemic conditions incorporating hyperkalemia also abolished ACS-induced oscillatory afterpotentials and delayed their reappearance upon reperfusion. All other reperfusion responses were similar. This study demonstrates that "ischemic" suppresses oscillatory afterpotential-mediated effects of digitalis in canine Purkinje tissue, whereas reperfusion potentiates oscillatory afterpotential-induced arrhythmias.