Analysis and prevention of falls among community-dwelling older adults in southern Thailand

AIM

To analyse fall prevalence, risk factors and perceptions among Thai older adults to design a prevention model.

DESIGN

Quantitative and qualitative data were collected using a convergent parallel mixed-methods design.

METHODS

A cross-sectional analysis was conducted using secondary data from health screenings of older adults in 20 subdistrict hospitals in southern Thailand from January 2018 to September 2019 (n = 12,130). In-depth interviews (IDIs) and focus group discussions (FGDs) were conducted with purposively sampled participants who were representatives of older adults and stakeholders (n = 50).

RESULTS

The quantitative analysis showed that the prevalence of falls was 12.1%. The independent risk factors were female gender, employment status, cognitive impairment, semi-dependent functional ability, balance problems, vision impairment, hearing difficulties, use of medications, reliance on assistive devices and access to outdoor toilets. The qualitative analysis revealed misconceptions on falls and fall prevention measures among older adults and community stakeholders. In Thailand, healthcare providers and community nurses play a crucial role in providing primary advice and conducting interventions, yet they encounter obstacles due to lack of personnel, time constraints, limited resources, inadequate support and unclear policies. Stakeholders stress the urgency of improving practice guidelines, developing evidence-based strategies and aligning with government policies.

CONCLUSIONS

Fall risk factors and prevention challenges among older adults were identified. Effective fall prevention programmes are needed.

IMPACT

The identified fall events may guide public health agencies and local administrations in planning fall prevention programmes. For implementation in Thai communities, teamwork among leaders and stakeholders is key.

PATIENT OR PUBLIC CONTRIBUTION

IDIs and FGDs were conducted with older adults, village health volunteers, nurses, healthcare providers, local organization administrators and village headmen.

Circadian Variations and Associated Factors in Patients with Ischaemic Heart Disease

Circadian rhythms have been identified in cardiovascular diseases, and cardiovascular risk factors can modify the circadian rhythm. The purpose of this study was to describe the onset of ischaemic heart disease symptomatology in relation to the date and time, the day of the week of presentation, the season, AMI location and severity and the level of influence of individual patient characteristics in a retrospective cross-sectional study involving 244 ischaemic heart disease patients from the intensive care unit of La Ribera Hospital (Spain). The onset of pain was more frequent in the morning, the season with the highest frequency of ischaemic events was winter, and the lowest incidence was during weekends. Regarding the severity of ischaemic heart disease, the circadian rhythm variables of weekdays vs. weekends and seasons did not show a significant association. The length of hospital stay was associated with the onset of pain in the afternoon. The onset of pain at night was associated with the subendocardial location of the infarction. In conclusion, living in a Mediterranean country, the Spanish population showed a circadian pattern of AMI, where the onset of pain has an influence on AMI location and on the length of hospital stay and is the same in patients with different individual risk factors.

Evaluation of the effectiveness of breastfeeding as a factor in the prevention of breast cancer

BACKGROUND

As cancer is one of the main causes of fatal illnesses in the world, and breast cancer is responsible for an elevated number of deaths in women, it is important to implement measures to prevent this disease.

METHOD

In order to assess the influence of breastfeeding in preventing breast cancer in women, forteen prospective cohort articles are included in this study, and their methodological quality has been assessed through the Newcastle Ottawa quality assessment scale cohort studies. After determining the risk of bias for each case study, those with fewer systematic errors and therefore greater validity, have been selected to demonstrate the relationship they propose exists between breastfeeding and breast cancer.

RESULTS

50% percent of the research included found that breastfeeding does not reduce the risk of breast cancer, while the other 50% argue that it is a protective factor. However, with regards to quality, the case studies that conclude that breastfeeding is not associated with breast cancer have more evidential support.

CONCLUSION

It is difficult to establish whether or not breastfeeding prevents breast cancer given the diversity of conclusions in the literature. Nevertheless, the findings of this study reinforce the importance of developing strategies to improve long-term women's health in the field of prevention.

Psycho-Social Factors in Patients with Cardiovascular Disease Attending a Family-Centred Prevention and Rehabilitation Programme: EUROACTION Model in Spain

BACKGROUND

Coronary heart disease (CHD) persists as the leading cause of death worldwide. Cardiovascular prevention and rehabilitation (CVPR) has an interdisciplinary focus, and includes not only in physiological components, but it also addresses psycho-social factors.

METHODS

The study analysed the Spanish psycho-social data collected during the EUROACTION study. In Spain, two hospitals were randomised in the Valencia community. Coronary patients were prospectively and consecutively identified in both hospitals. The intervention hospital carried out a 16-week CVPR programme, which aimed to assess illness perceptions and establish healthy behaviours in patients and their partners.

RESULTS

Illness perceptions were significantly and inversely associated with anxiety and depression. Low levels of anxiety were associated with better self-management of total cholesterol (p = 0.004) and low-density lipoprotein-cholesterol (p = 0.004). There was concordance at one year among patients and partners who participated in the programme related to anxiety (p < 0.001), fruit consumption (p < 0.001), and vegetable consumption (p < 0.001).

CONCLUSIONS

The EUROACTION study emphasised the importance of assessing psycho-social factors in a CVPR programme and the inclusion of family as support in patients' changes in behaviour.

Lipid Profile Results after Cardiovascular Prevention Programme: Euroaction Model in Spain

BACKGROUND

Cardiovascular prevention and rehabilitation programmes (CVPRP) are an established model of care designed to improve risk factor management. They have been successfully implemented in a variety of settings, in patients with coronary heart disease (CHD).

OBJECTIVE

To assess the long term impact of a nurse-coordinated, multidisciplinary, CVPRP in patients with CHD in the reduction of lipid profile and medication prescription in clinical practice.

METHODS

The study used an analytical, experimental, population based, prospective and longitudinal design. In Spain, the study was conducted in the Valencian Community, including two randomized hospitals. Coronary patients were prospectively and consecutively identified in both hospitals. The intervention hospital carried out an 8-week CVPRP.

RESULTS

The proportion of patients achieving improved standards of preventive care increased in the intervention hospital compared with the usual care hospital, mainly regarding LDL-C concentrations. Furthermore, an increased prescription of statins was found in the intervention group. However, there were no statistically significant differences in triglycerides and glucose levels.

CONCLUSION

The EUROACTION nurse-led CVPRP enabled coronary patients to control lipid profile to the European targets. A large proportion of patients were prescribed statin therapy as cardioprotective medication with favorable changes in medication for coronary patients. To improve the potential for cardiovascular prevention, we need local preventive cardiology programmes adapted to the health policy of individual countries.

The Beneficial Effect of Physical Exercise on Inflammatory Makers in Older Individuals

Old age is associated with a loss of motor functions and a general progressive decline in cognitive functions. Physical exercise is one of the ways in which inflammatory levels in general can be reduced, and therefore physical exercise can be considered a biological aging decelerator. In this article, we examine the relationships between physical exercise and inflammatory markers reported for the different physical exercise protocols that have been used in studies with older individuals, as well as the effects of these regimens. The different types of exercises programmed, and methods used to implement them were very heterogeneous in the articles we analysed. Both, the aerobic exercise and resistance training protocols produced a decrease in plasma levels of IL-6, CRP and TNF-α, and an increase of IL-10 plasma levels as a chronic effect. However, the acute-response of physical exercise appeared to be an initial increase in IL-6 expression and plasma IL-6 levels. Continuing with these exercise programs usually subsequently achieved a chronic response in which there was a decrease in both the basal levels of IL-6, CRP and TNF-α, and the IL-6 produced as acute responses. Regardless of the type of exercise performed, it seems that the exercise parameters, intensity, duration, subject variables, fitness, and level of inflammation are key factors in achieving the expected balance between proinflammatory and anti-inflammatory cytokines.

The Effects of Exercise on IL-6 Levels and Cognitive Performance in Patients with Schizophrenia

Exercise plays an important role in brain plasticity, leading to improvements in cognitive function and delaying the cognitive deterioration of healthy people. These effects can be observed in individuals with schizophrenia through improvements in their performance in cognitive tasks and a decrease in the symptomology of the disease. In this review we examine the current evidence for the roles that exercise and the immune system play in patients with schizophrenia, and specifically analyze the interleukin-6 (IL-6) pathway as a potential mechanism resulting in these positive effects. Inflammation and high levels of IL-6 are associated with both the severity of schizophrenia and the cognitive impairment suffered throughout the disease. Performing regular exercise can modulate IL-6 by lowering its basal levels and by causing lower acute increases in the plasma levels of this cytokine in response to exercise (an anti-inflammatory response to physical exertion). Although there is evidence for the positive effects of physical exercise on schizophrenia, more studies will be required to better understand how variation in different exercise parameters affects both the acute and chronic plasma levels of IL-6.

Experimental Study of the Effects of EIPA, Losartan, and BQ-123 on Electrophysiological Changes Induced by Myocardial Stretch

INTRODUCTION AND OBJECTIVES

Mechanical response to myocardial stretch has been explained by various mechanisms, which include Na(+)/H(+) exchanger activation by autocrine-paracrine system activity. Drug-induced changes were analyzed to investigate the role of these mechanisms in the electrophysiological responses to acute myocardial stretch.

METHODS

Multiple epicardial electrodes and mapping techniques were used to analyze changes in ventricular fibrillation induced by acute myocardial stretch in isolated perfused rabbit hearts. Four series were studied: control (n = 9); during perfusion with the angiotensin receptor blocker losartan (1 μM, n = 8); during perfusion with the endothelin A receptor blocker BQ-123 (0.1 μM, n = 9), and during perfusion with the Na(+)/H(+) exchanger inhibitor EIPA (5-[N-ethyl-N-isopropyl]-amiloride) (1 μM, n = 9).

RESULTS

EIPA attenuated the increase in the dominant frequency of stretch-induced fibrillation (control=40.4%; losartan=36% [not significant]; BQ-123=46% [not significant]; and EIPA=22% [P<.001]). During stretch, the activation maps were less complex (P<.0001) and the spectral concentration of the arrhythmia was greater (greater regularity) in the EIPA series: control=18 (3%); EIPA = 26 (9%) (P < .02); losartan=18 (5%) (not significant); and BQ-123=18 (4%) (not significant).

CONCLUSIONS

The Na(+)/H(+) exchanger inhibitor EIPA attenuated the electrophysiological effects responsible for the acceleration and increased complexity of ventricular fibrillation induced by acute myocardial stretch. The angiotensin II receptor antagonist losartan and the endothelin A receptor blocker BQ-123 did not modify these effects.

Interleukin 6 and cognitive dysfunction

The interleukin-6 (IL-6) is a pleiotropic cytokine that plays a key role in interaction between immune and nervous system. Although IL-6 has neurotrophic properties and beneficial effects in the CNS, its overexpression is generally detrimental, adding to the pathophysiology associated with CNS disorders. The source of the increase in peripheral IL-6 remains to be established and varies among different pathologies, but has been found to be associated with cognitive dysfunction in several pathologies. This comprehensive review provides an update summary of the studies performed in humans concerning the role of central and peripheral IL-6 in cognitive dysfunction in dementias and in other systemic diseases accompained by cognitive dysfuction such as cardiovascular, liver disease, Behçet's disease and systemic lupus erythematosus. Further research is needed to correlate specific deficits in IL-6 and its receptors in pathologies characterized by cognitive dysfunction and to understand how systemic IL-6 affects high cerebral function in order to open new directions in pharmacological treatments that modulate IL-6 signalling.

Dynamics of serum-induced endothelial cell apoptosis in patients with myocardial infarction

BACKGROUND

In patients with ST-segment elevation myocardial infarction (STEMI) reperfused with primary coronary intervention (PCI), the dynamics of endothelial cell (EC) viability, apoptosis and necrosis and its relationship with the structural consequences on the left ventricle have not been addressed so far.

DESIGN

In 20 STEMI patients, we incubated human umbilical vein endothelial cells (HUVECs) with serum drawn before reperfusion and subsequently afterwards (24, 96 h, 30 days). Viability, apoptosis and necrosis percentages were evaluated by flow cytometry. Values were compared with 12 age- and sex-matched control subjects with normal coronary arteries. Cardiac magnetic resonance (CMR) was performed during the first week after infarction.

RESULTS

Serum from STEMI patients induced a progressive loss of EC viability, with a nadir of 67.7 ± 10.2% at 96 h (baseline: 75 ± 6% and controls: 80.2 ± 3.9%, P < 0.001 in both cases). This is due to an increase in apoptosis that peaked at 96 h after reperfusion (15.2 ± 7.1% vs. 11 ± 6 at baseline and 5.8 ± 1.6% in controls, P < 0.001 in both cases). However, no significant dynamic changes in EC necrosis were detected. Extensive myocardial oedema (> 30%, median of left ventricular mass) was the only CMR variable significantly associated with a higher percentage of EC apoptosis at 96 h (extensive vs. nonextensive oedema: 18.3 ± 6.8% vs. 12.1 ± 6.3%, P < 0.05).

CONCLUSIONS

Dynamic changes in EC viability occur in the setting of STEMI patients reperfused with PCI, these changes peak late after reperfusion, they are mainly the result of an increase of apoptosis and are associated with the presence of extensive myocardial oedema.

Ventricular fibrillation conduction through an isthmus of preserved myocardium between radiofrequency lesions

BACKGROUND

Selective local acceleration of myocardial activation during ventricular fibrillation (VF) contributes information on the interactions between neighboring zones during the arrhythmia. This study analyzes these interactions, centering the observations on an isthmus of myocardium between two radiofrequency (RF) lesions.

METHODS

In nine isolated rabbit hearts, a gap of preserved myocardium was established between two RF lesions in the anterolateral left ventricle (LV) wall. Before, during, and after increasing the spatial heterogeneity of VF by local myocardial stretching, VF epicardial recordings were obtained.

RESULTS

Local stretch in the anterior LV wall decreased the excitable window (17 ± 7 ms vs 26 ± 7 ms; P < 0.05) and increased the dominant frequency (DFr; 18.9 ± 5.0 Hz vs 15.2 ± 3.6 Hz; P < 0.05) in this zone, without changes in the non-stretched posterolateral zone (25 ± 4 ms vs 27 ± 6 ms, ns and 14.1 ± 2.7 Hz vs 14.3 ± 3.0 Hz, ns). The DFr ratio at both sides of the gap was inversely correlated to the excitable window ratio (R = -0.57; P = 0.002). Before (31% vs 26%), during (29% vs 22%), and after stretch suppression (35% vs 25%), the wavefronts passing through the gap from the posterolateral to the anterior LV wall were seen to predominate. The number of wavefronts that passed from the anterior to the posterolateral LV wall was related to the excitable window in this zone (R = 0.41; P = 0.03).

CONCLUSIONS

The VF acceleration induced in the stretched zone does not increase the flow of wavefronts toward the non-stretched zone in the adjacent gap of preserved myocardium. The absence of significant changes in the electrophysiological parameters of the non-stretched myocardium limits the arrival of wavefronts in this zone.

Modifications of mechanoelectric feedback induced by 2,3-butanedione monoxime and Blebbistatin in Langendorff-perfused rabbit hearts

AIM

Myocardial stretching is an arrhythmogenic factor. Optical techniques and mechanical uncouplers are used to study the mechanoelectric feedback. The aim of this study is to determine whether the mechanical uncouplers 2,3-butanedione monoxime and Blebbistatin hinder or modify the electrophysiological effects of acute mechanical stretch.

METHODS

The ventricular fibrillation (VF) modifications induced by acute mechanical stretch were studied in 27 Langendorff-perfused rabbit hearts using epicardial multiple electrodes and mapping techniques under control conditions (n = 9) and during the perfusion of 2,3-butanedione monoxime (15 mM) (n = 9) or Blebbistatin (10 μm) (n = 9).

RESULTS

In the control series, myocardial stretch increased the complexity of the activation maps and the dominant frequency (DF) of VF from 13.1 ± 2.0 Hz to 19.1 ± 3.1 Hz (P < 0.001, 46% increment). At baseline, the activation maps showed less complexity in both the 2,3-butanedione monoxime and Blebbistatin series, and the DF was lower in the 2,3-butanedione monoxime series (11.4 ± 1.2 Hz; P < 0.05). The accelerating effect of mechanical stretch was abolished under 2,3-butanedione monoxime (maximum DF = 11.7 ± 2.4 Hz, 5% increment, ns vs baseline, P < 0.0001 vs. control series) and reduced under Blebbistatin (maximum DF = 12.9 ± 0.7 Hz, 8% increment, P < 0.01 vs. baseline, P < 0.0001 vs. control series). The variations in complexity of the activation maps under stretch were not significant in the 2,3-butanedione monoxime series and were significantly attenuated under Blebbistatin.

CONCLUSION

The accelerating effect and increased complexity of myocardial activation during VF induced by acute mechanical stretch are abolished under the action of 2,3-butanedione monoxime and reduced under the action of Blebbistatin.

Modifications in ventricular fibrillation and capture capacity induced by a linear radiofrequency lesion

INTRODUCTION AND OBJECTIVES

An analysis was made of the effects of a radiofrequency-induced linear lesion during ventricular fibrillation and the capacity to capture myocardium through high-frequency pacing.

METHODS

Using multiple epicardial electrodes, ventricular fibrillation was recorded in 22 isolated perfused rabbit hearts, analyzing the activation maps upon applying trains of stimuli at 3 different frequencies close to that of the arrhythmia: a) at baseline; b) after radio-frequency ablation to induce a lesion of the left ventricular free wall (length=10 [1] mm), and c) after lengthening the lesion (length=23 [2] mm).

RESULTS

Following lesion induction, the regularity of the recorded signals decreased and significant variations in the direction of the activation fronts were observed. On lengthening the lesion, there was a slight increase in the episodes with at least 3 consecutive captures when pacing at cycles 10% longer than the arrhythmia (baseline: 0.6 [0.7]; initial lesion: 1 [1], no significant differences; lengthened lesion: 3 [2.8]; P<.001), while a decrease was observed in those obtained upon pacing at cycles 10% shorter than the arrhythmia.

CONCLUSIONS

The radio-frequency -induced lesion increases the heterogeneity of myocardial activation during ventricular fibrillation and modifies arrival of the activation fronts in the adjacent zones. High-frequency pacing during ventricular fibrillation produces occasional captures during at least 3 consecutive stimuli. The lengthened lesion in turn slightly increases capture capacity when using cycles slightly longer than the arrhythmia.

The sum of ST-segment elevation is the best predictor of microvascular obstruction in patients treated successfully by primary percutaneous coronary intervention. Cardiovascular magnetic resonance study

INTRODUCTION AND OBJECTIVES

The usefulness of ST-segment elevation resolution (STR) for predicting epicardial reperfusion is well established. However, it is still not clear how ST-segment changes are related to microvascular obstruction (MVO) observed by cardiovascular magnetic resonance (CMR) after primary percutaneous coronary intervention (pPCI) for ST-segment elevation myocardial infarction (STEMI).

METHODS

The study involved 85 consecutive patients admitted for a first STEMI and treated by pPCI who had a patent infarct-related artery. An ECG was recorded on admission and 90 min and 6, 24, 48 and 96 h after pPCI. Thereafter, STR and the sum of ST-segment elevation (sumSTE) in all leads were determined.

RESULTS

Overall, CMR revealed MVO in 37 patients. In infarcts with MVO, sumSTE was greater both before and after revascularization than in infarcts without MVO (P≤.001 at all times). In contrast, there was no significant difference in the magnitude of STR between infarcts with and without MVO 90 min after revascularization (P=.1), though there was after 6 h (P< .05 at all times). The area under the receiver operating characteristic curve for detecting MVO was greater for sumSTE than STR (P< .05 for all measurements). On multivariate analysis, after adjusting for clinical, angiographic and ECG characteristics, a sumSTE >3 mm 90 min after pPCI was an independent predictor of MVO on CMR, while an STR ≥70% was not (odds ratio=3.1; 95% confidence interval, 1.2-8.4; P=.02).

CONCLUSIONS

MVO was associated with a significantly increased sumSTE at all times after revascularization. The difference in the magnitude of STR between infarcts with and without MVO was significant only >6 h after revascularization. The best predictor of MVO was a sumSTE >3 mm 90 min after pPCI.

The sum of ST-segment elevation is the best predictor of microvascular obstruction in patients treated successfully by primary percutaneous coronary intervention. Cardiovascular magnetic resonance study

INTRODUCTION AND OBJECTIVES

The usefulness of ST-segment elevation resolution (STR) for predicting epicardial reperfusion is well established. However, it is still not clear how ST-segment changes are related to microvascular obstruction (MVO) observed by cardiovascular magnetic resonance (CMR) after primary percutaneous coronary intervention (pPCI) for ST-segment elevation myocardial infarction (STEMI).

METHODS

The study involved 85 consecutive patients admitted for a first STEMI and treated by pPCI who had a patent infarct-related artery. An ECG was recorded on admission and 90 min and 6, 24, 48 and 96 h after pPCI. Thereafter, STR and the sum of ST-segment elevation (sumSTE) in all leads were determined.

RESULTS

Overall, CMR revealed MVO in 37 patients. In infarcts with MVO, sumSTE was greater both before and after revascularization than in infarcts without MVO (P≤.001 at all times). In contrast, there was no significant difference in the magnitude of STR between infarcts with and without MVO 90 min after revascularization (P=.1), though there was after 6 h (P< .05 at all times). The area under the receiver operating characteristic curve for detecting MVO was greater for sumSTE than STR (P< .05 for all measurements). On multivariate analysis, after adjusting for clinical, angiographic and ECG characteristics, a sumSTE >3 mm 90 min after pPCI was an independent predictor of MVO on CMR, while an STR ≥70% was not (odds ratio=3.1; 95% confidence interval, 1.2-8.4; P=.02).

CONCLUSIONS

MVO was associated with a significantly increased sumSTE at all times after revascularization. The difference in the magnitude of STR between infarcts with and without MVO was significant only >6 h after revascularization. The best predictor of MVO was a sumSTE >3 mm 90 min after pPCI.

Pharmacological modifications of the stretch-induced effects on ventricular fibrillation in perfused rabbit hearts

Stretch induces modifications in myocardial electrical and mechanical activity. Besides the effects of substances that block the stretch-activated channels, other substances could modulate the effects of stretch through different mechanisms that affect Ca2+ handling by myocytes. Thirty-six Langendorff-perfused rabbit hearts were used to analyze the effects of the Na+/Ca2+ exchanger blocker KB-R7943, propranolol, and the adenosine A2 receptor antagonist SCH-58261 on the acceleration of ventricular fibrillation (VF) produced by acute myocardial stretching. VF recordings were obtained with two epicardial multiple electrodes before, during, and after local stretching in four experimental series: control ( n = 9), KB-R7943 (1 μM, n = 9), propranolol (1 μM, n = 9), and SCH-58261 (1 μM, n = 9). Both the Na+/Ca2+ exchanger blocker KB-R7943 and propranolol induced a significant reduction ( P < 0.001 and P < 0.05, respectively) in the dominant frequency increments produced by stretching with respect to the control and SCH-58261 series (control = 49.9%, SCH-58261 = 52.1%, KB-R7943 = 9.5%, and propranolol = 12.5%). The median of the activation intervals, the functional refractory period, and the wavelength of the activation process during VF decreased significantly under stretch in the control and SCH-58261 series, whereas no significant variations were observed in the propranolol and KB-R7943 series, with the exception of a slight but significant decrease in the median of the fibrillation intervals in the KB-R7943 series. KB-R7943 and propranolol induced a significant reduction in the activation maps complexity increment produced by stretch with respect to the control and SCH-58261 series. In conclusion, the electrophysiological effects responsible for stretch-induced VF acceleration in the rabbit heart are reduced by the Na+/Ca2+ exchanger blocker KB-R7943 and by propranolol but not by the adenosine A2 receptor antagonist SCH-58261.

Effects of chronic exercise on myocardial refractoriness: a study on isolated rabbit heart

AIM

To determine whether chronic physical training increases atrial and ventricular refractoriness in isolated rabbit heart.

METHODS

Trained rabbits were submitted to a protocol of treadmill running. The electrophysiological parameters of refractoriness investigated in an isolated heart preparation were: (1) atrial effective refractory period (AERP) and atrial functional refractory period and ventricular effective and functional refractory periods (VERP and VFRP) using the extrastimulus technique at four different pacing cycle lengths; (2) the dominant frequency (DF) of ventricular fibrillation (VF). A multi-electrode plaque containing 256 electrodes and a spectral method were used to obtain the mean, maximum and minimum DF of VF. Sinus cycle length of the isolated hearts was determined as an electrophysiological parameter of training. In vivo heart rate, myocardial heat shock proteins (HSP60) and inducible nitric oxide synthase were also determined in some animals as electrophysiological and biochemical markers of training respectively.

RESULTS

VERP and VFRP were longer in the trained group than in the control group. The mean DF of VF was lower in the trained group than in the control group. Despite the fact that training did not significantly modify the AERP, it tended to be longer in the trained group (P = 0.09).

CONCLUSION

Training seems to increase the electrical stability of ventricular myocardium. As the electrophysiological modifications were exhibited in hearts not submitted to extrinsic nervous system or humoral influences, they are, at least in part, intrinsic modifications. These electrophysiological data also suggest that training could protect against reentrant ventricular arrhythmias.

Analyzing the electrophysiological effects of local epicardial temperature in experimental studies with isolated hearts

As a result of their modulating effects upon myocardial electrophysiology, both hypo- and hyperthermia can be used to study the mechanisms that generate or sustain cardiac arrhythmias. The present study describes an original electrode developed with thick-film technology and capable of controlling regional temperature variations in the epicardium while simultaneously registering its electrical activity. In this way, it is possible to measure electrophysiological parameters of the heart at different temperatures. The results obtained with this device in a study with isolated and perfused rabbit hearts are reported. An exploration has been made of the effects of local temperature changes upon the electrophysiological parameters implicated in myocardial conduction. Likewise, an analysis has been made of the influence of local temperature upon ventricular fibrillation activation frequency. It is concluded that both regional hypo- and hyperthermia exert reversible and opposite effects upon myocardial refractoriness and conduction velocity in the altered zone. The ventricular activation wavelength determined during constant pacing at 250 ms cycles is not significantly modified, however. During ventricular fibrillation, the changes in the fibrillatory frequency do not seem to be transmitted to normal temperature zones.

[Changes in the spectral characteristics of ventricular fibrillation in lesions produced by radiofrequency ablation. An experimental study]

INTRODUCTION AND OBJECTIVES

Although electro- physiological databases contain information about changes in the time domain in lesions produced by radiofrequency ablation, very few data on changes in the frequency domain are available. The aim of this study was to investigate changes in the spectral characteristics of ventricular fibrillation in zones with radiofrequency lesions.

METHODS

Recordings of ventricular fibrillation were obtained in 11 isolated perfused rabbit heart preparations using a multiple epicardial electrode located on the left ventricular free wall. Spectral parameters derived by Fourier analysis before and after the creation of transmural radiofrequency lesions were compared.

RESULTS

In the ablated zones, significant reductions were observed in the spectral density of the dominant (0.168+/-0.113 mV(2)/Hz vs 0.025+/-0.018 mV(2)/Hz; P< .001) and mean frequencies (0.053+/-0.057 mV(2)/Hz vs 0.012+/-0.016 mV(2)/Hz; P< .001), the normalized energy around the dominant frequency (0.860+/-0.570 vs 0.128+/-0.091; P< .001), and the standard deviation of the power spectrum (0.031+/-0.020 mV(2)/Hz vs 0.004+/-0.001 mV(2)/Hz; P< .001). There was no significant change in the dominant (16.2+/-5.6 vs 14.8+/-1.8 Hz) or mean frequency (17.7+/-3.4 vs 16.6+/-1.3 Hz). The spectral parameters that could be used in a multivariate model to identify the lesion were the standard deviation of the power spectrum and the spectral density of the mean frequency.

CONCLUSIONS

During ventricular fibrillation, the spectral parameters associated with spectral power and spectral energy were significantly altered in zones with radiofrequency lesions and could be used to identify those zones. There was no significant change in either the dominant or mean frequency in these zones.

[Effect of streptomycin on stretch-induced change in myocardial activation during ventricular fibrillation]

The aim of this study was to determine whether the changes in myocardial activation pattern resulting from acute stretching during ventricular fibrillation can be counteracted by administering a compound that blocks receptors sensitive to stretch. The study involved 16 isolated rabbit hearts, in which refractoriness and activation frequency during ventricular fibrillation were measured before, during and after localized acute stretching of the left ventricular free wall, either without (series A, n=8) or with (series B, n=8) the presence of streptomycin, 200 micromol. At baseline and during and after stretching, ventricular fibrillation was slower with streptomycin perfusion in series B than in series A (dominant frequency at baseline, 13+/-2 Hz vs. 16+/-2 Hz, respectively; P< .005; dominant frequency with stretching, 14+/-2 Hz vs. 19+/-3 Hz, respectively; P< .005). Streptomycin attenuated the electrophysiological changes produced by stretching and had a direct effect on refractoriness and activation frequency during ventricular fibrillation.

Selective Myocardial Isolation and Ventricular Fibrillation

BACKGROUND

Few experimental studies have analyzed the effects of selective radiofrequency (RF) lesions upon ventricular fibrillation (VF). The RF-induced isolation of selected zones would make it possible to determine whether these zones are essential for existence of the arrhythmia.

METHODS

In 31 Langendorff-perfused rabbit hearts, the characteristics and inducibility of VF were analyzed before and after the induction of RF lesions comprising: (1) the posterior zone of the septum and of the walls of both ventricles (n = 10); (2) the anterior zone of the septum and of the walls of both ventricles (n = 11); and (3) the midseptal zone (n = 10).

RESULTS

Complete isolation of the zone encompassed by the lesions was obtained in 5, 6, and 5 experiments of series 1, 2, and 3, respectively. In these experiments, the arrhythmia was only induced from within the zone encompassed by the lesions in one experiment belonging to series 2 (P < 0.05 with respect to baseline). In contrast, in all but one of the cases in series 2, VF could be induced from outside the isolated zone (ns vs baseline). Partial isolation was obtained in five experiments of each series. In these experiments, on pacing from within the partially isolated zone, sustained VF was not induced in any experiment (P < 0.05 with respect to baseline), while in all cases VF could be induced on pacing from the external zone (ns vs baseline).

CONCLUSION

In the experimental model used, the three zones studied were not essential for maintaining VF. In most cases, their partial or total isolation avoided inducibility of the arrhythmia in those zones, though not in the remaining myocardium.

[Time-frequency analysis of ventricular fibrillation. An experimental study]

INTRODUCTION AND OBJECTIVES

The analysis of frequency variability during ventricular fibrillation has yielded inconsistent results. We used an experimental model of ventricular fibrillation, with a short timescale, to analyze variations in frequency and their associated spatial distribution.

METHODS

Epicardial recordings of ventricular fibrillation were made in 10 perfused isolated rabbit heart preparations using a multiple electrode system (i.e., 240 unipolar electrodes). Both spectral and time-frequency analysis were used to derive the dominant frequency in the anterolateral wall of the left ventricle.

RESULTS

Linear regression analysis showed that there was a good correlation between the dominant frequency obtained using the two signal analysis methods: frequency (spectral analysis) = 1.01 x frequency (time-frequency analysis) -- 0.4 (r=0.9; P< .0001; standard error of the estimate, 2.2 Hz). In all cases except one, the dominant frequency exhibited a significant temporal variation on a short timescale (time-frequency analysis); the coefficient of variation was between 0.19 (0.06) and 0.24 (0.07) (NS). In all cases, there were significant differences between regions. The location at which the frequency was highest varied according to the timepoint considered, though it was predominantly in the apical or anterior zone.

CONCLUSIONS

In the absence of external modulating factors, the frequency of ventricular fibrillation exhibits temporal and spatial variations which can be observed at short timescales. In the free wall of the left ventricle, the dominant frequency is highest in the apical and anterior zones, and the maximum frequencies are most often found in these zones.

Modification of ventricular fibrillation activation patterns induced by local stretching

INTRODUCTION

We hypothesize that local modifications in electrophysiological properties, when confined to zones of limited extent, induce few changes in the global activation process during ventricular fibrillation (VF). To test this hypothesis, we produced local electrophysiological modifications by stretching a circumscribed zone of the left ventricular wall in an experimental model of VF.

METHODS AND RESULTS

In 23 Langendorff-perfused rabbit hearts frequency, time-frequency and time-domain techniques were used to analyze the VF recordings obtained with two epicardial multiple electrodes before, during, and after local stretching produced with a left intraventricular device. Acute local stretching accelerated VF in the stretched zone reversibly and to a variable degree, depending on the magnitude of stretch and the time elapsed from its application. In the half time (5 minutes) of the analyzed period, a longitudinal lengthening of 12.1 +/- 4.5% (vertical axis) and 11.8 +/- 6.2% (horizontal axis) in the stretched zone produced an increase in the dominant frequency (DFr) (15.2 +/- 1.9 versus 18.8 +/- 2.5 Hz, P < 0.0001), a decrease in mean VV interval (63 +/- 8 versus 53 +/- 6 msec, P < 0.001), and an increase in the complexity of the activation maps-with more areas of conduction block and more breakthrough patterns (23% versus 37%, P < 0.01), without significant changes in the percentages of complete reentry patterns (9% versus 9%, ns). Simultaneously, in the nonstretched zone, no variations were observed in the DFr (15.2 +/- 2.1 versus 15.3 +/- 2.5 Hz, ns), mean VV intervals (66 +/- 8 versus 65 +/- 8 msec, ns), or types and percentages of maps with breakthrough (25% versus 20%, ns) or reentry patterns (12% versus 8%, ns). No significant correlation was observed between the DFr in the two zones (R = 0.24, P = 0.40).

CONCLUSION

Local stretching increases the electrophysiological heterogeneity of myocardium and accelerates and increases the complexity of VF in the stretched area, without significantly modifying the occurrences of the types of VF activation patterns in the nonstretched zone.