Modifiable and Non-Modifiable Risk Factors for Premature Coronary Heart Disease (PCHD): Systematic Review and Meta-Analysis.

AIM: We aimed to compare the prevalence of modifiable and non-modifiable coronary heart disease (CHD) risk factors among those with premature CHD and healthy individuals. METHODS: PubMed, CINAHL, Embase, and Web of Science databases were searched (review protocol is registered in PROSPERO CRD42020173216). The quality of studies was assessed using the National Heart, Lung and Blood Institute tool for cross-sectional, cohort and case-control studies. Meta-analyses were performed using Review Manager 5.3. Effect sizes for categorical and continuous variables, odds ratio (OR) and mean differences (MD)/standardised mean differences (SMD) with 95% confidence intervals (CI) were reported. RESULTS: A total of n=208 primary studies were included in this review. Individuals presenting with premature CHD (PCHD, age ≤65 years) had higher mean body mass index (MD 0.54 kg/m2, 95% CI 0.24, 0.83), total cholesterol (SMD 0.27, 95% CI 0.17, 0.38), triglycerides (SMD 0.50, 95% CI 0.41, 0.60) and lower high-density lipoprotein cholesterol (SMD 0.79, 95% CI: -0.91, -0.68) compared with healthy individuals. Individuals presenting with PCHD were more likely to be smokers (OR 2.88, 95% CI 2.51, 3.31), consumed excessive alcohol (OR 1.40, 95% CI 1.05, 1.86), had higher mean lipoprotein (a) levels (SMD 0.41, 95% CI 0.28, 0.54), and had a positive family history of CHD (OR 3.65, 95% CI 2.87, 4.66) compared with healthy individuals. Also, they were more likely to be obese (OR 1.59, 95% CI 1.32, 1.91), and to have had dyslipidaemia (OR 2.74, 95% CI 2.18, 3.45), hypertension (OR 2.80, 95% CI 2.28, 3.45), and type 2 diabetes mellitus (OR 2.93, 95% CI 2.50, 3.45) compared with healthy individuals. CONCLUSION: This meta-analysis confirms current knowledge of risk factors for PCHD, and identifying these early may reduce CHD in young adults.

Risk Factors for Early-Onset Versus Late-Onset Coronary Heart Disease (CHD): Systematic Review and Meta-Analysis.

AIM: We aimed to systematically compare literature on prevalence of modifiable and non-modifiable risk factors for early compared to late-onset coronary heart disease (CHD). METHODS: PubMed, CINAHL, Embase, and Web of Science databases were searched (review protocol registered in PROSPERO CRD42020173216). Study quality was assessed using the National Heart, Lung and Blood Institute tool for observational and case-control studies. Review Manager 5.3 was used for meta-analysis. Effect sizes were expressed as odds ratio (OR) and mean differences (MD)/standardised MD (SMD) with 95% confidence intervals (CI) for categorical and continuous variables. RESULTS: Individuals presenting with early-onset CHD (age <65 years) compared to late-onset CHD had higher mean body mass index (MD 1.07 kg/m2; 95% CI 0.31-1.83), total cholesterol (SMD 0.43; 95% CI 0.23-0.62), low-density lipoprotein (SMD 0.26; 95% CI 0.15-0.36) and triglycerides (SMD 0.50; 95% CI 0.22-0.68) with lower high-density lipoprotein-cholesterol (SMD 0.26; 95% CI -0.42--0.11). They were more likely to be smokers (OR 1.76, 95% CI 1.39-2.22) and have a positive family history of CHD (OR 2.08, 95% CI 1.74-2.48). They had lower mean systolic blood pressure (MD 4.07 mmHg; 95% CI -7.36--0.78) and were less likely to have hypertension (OR 0.47, 95% CI 0.39-0.57), diabetes mellitus (OR 0.56, 95% CI 0.51-0.61) or stroke (OR 0.31, 95% CI 0.24-0.42). CONCLUSION: A focus on weight management and smoking cessation and aggressive management of dyslipidaemia in young adults may reduce the risk of early-onset CHD.

Risk Factors for Premature Coronary Heart Disease in Women Compared to Men: Systematic Review and Meta-Analysis.

Background: We aimed to systematically examine literature on the prevalence of known modifiable and nonmodifiable risk factors for premature coronary heart disease (PCHD) in women compared with men. Materials and Methods: PubMed, CINAHL, Embase, and Web of Science databases were searched. Review protocol is registered in PROSPERO (CRD42020173216). Quality was assessed using the National Heart, Lung, and Blood Institute tool. Review Manager 5.3 was used for meta-analysis. Effect sizes were expressed as odds ratio (OR) and mean differences/standardized mean differences (SMD) with 95% confidence intervals (CIs) for categorical and continuous variables. Results: In this PCHD cohort (age <65 years), the mean age of presentation in women was 3 years older than men. Women had higher total cholesterol (SMD 0.11; 95% CI 0.00 to 0.23) and higher high-density lipoprotein cholesterol (SMD 0.49; 95% CI 0.29 to 0.69). Women were more likely to have hypertension (OR 1.51, 95% CI 1.42 to 1.60), diabetes mellitus (OR 1.78, 95% CI 1.55 to 2.04), obesity (OR 1.33, 95% CI 1.24 to 1.42), metabolic syndrome (OR 3.73, 95% CI 1.60 to 8.69), stroke (OR 1.63, 95% CI 1.51 to 1.77), peripheral vascular disorder (OR 1.67, 95% CI 1.43 to 1.96), and depression (OR 2.29, 95% CI 1.96 to 2.67). Women were less likely to be smokers (OR 0.60, 95% CI 0.55 to 0.66), have reported alcohol intake (OR 0.36, 95% CI 0.33 to 0.40), and reported use of illicit drug (OR 0.32, 95% CI 0.16 to 0.62). Conclusions: Risk factor profile in PCHD has a clear sex difference that supports early, aggressive, holistic, but sex-specific, approach to prevention.

Early pregnancy cardio metabolic risk factors and the prevalence of metabolic syndrome 10 years after the first pregnancy.

BACKGROUND: We aimed to compare risk factors for CVD 10 years postpartum among women who had ≥ 1 compared to no cardio metabolic risk factor in early first pregnancy. METHODS: Women of the SCOPE (Screening fOr Pregnancy Endpoints) study from Adelaide, South Australia were invited to participate in a cardiovascular risk assessment 10 years after the delivery of the first child. Data from 141 women who completed all the assessments are included in the analyses. RESULT: Compared to women who did not have any cardio metabolic risk factor at 15 ± 1 weeks' gestation during the first pregnancy, those who had ≥ 1 risk factor were 5.5 times more likely to have metabolic syndrome 10 years postpartum (aOR = 5.5, 95% CI 1.8-17.3, p = 0.004). Women who had ≥ 1cardio metabolic risk factor during the first pregnancy were more likely to be obese (p = 0.001), have high total cholesterol levels (p <0.001) or have increased insulin resistance (p <0.001) 10 years later compared to women who had no risk factor during the first pregnancy. 63.5% of the women with no cardio metabolic risk factor compared to 39% of women who had ≥ 1 risk factor in first pregnancy, had neither a complicated first pregnancy nor was diagnosed with MetS 10 years postpartum (p = 0.023). CONCLUSION: Cardio metabolic risk factors at the booking visit in the first pregnancy may be useful in identifying young women at risk of future CVD.

Women's awareness of cardiovascular disease risk after complications of pregnancy.

BACKGROUND: Certain maternal complications of pregnancy, including hypertensive disorders of pregnancy, gestational diabetes mellitus, birth of a growth restricted infant, idiopathic preterm labour, and placental abruption, are associated with a significantly increased risk of future maternal cardiovascular disease. In Australia, it is relatively unknown how many women with a history of complicated pregnancies are aware of their future cardiovascular disease risk. AIM: The aim of this study was to determine what percentage of women attending a cardiovascular disease prevention clinic in South Australia soon after a complicated pregnancy were aware of their increased risk of cardiovascular disease. METHODS: This prospective observational study included 188 women attending a postpartum prevention clinic between 7th August 2018 and 10th February 2021. These women had experienced a serious maternal complication of pregnancy approximately seven months earlier. Women completed a self-administered health awareness survey immediately prior to their first clinic appointment to assess their awareness of their increased cardiovascular risk. FINDINGS: Over two-thirds (69.1 %) of the women were unaware of the association between pregnancy complications and cardiovascular disease, and 6.4 % of the cohort did not realise they had experienced a complicated pregnancy. Almost 10 % of the cohort did not correctly identify the complication/s they had been diagnosed with during pregnancy. CONCLUSION: Awareness of the association between complications of pregnancy and future cardiovascular disease was low in our cohort of women who had experienced a complication of pregnancy only seven months earlier. This emphasises the need for improved education for and communication with women to assist in implementing preventative care strategies.

Effectiveness of a nurse practitioner-led cardiovascular prevention clinic at reduction of metabolic syndrome following maternal complications of pregnancy: a preliminary analysis.

AIM: Maternal complications of pregnancy, including hypertensive disorders of pregnancy, gestational diabetes mellitus, intrauterine growth restriction, preterm labour, and placental abruption, are associated with increased risk of future cardiometabolic disease. Lifestyle interventions that focus on preventative strategies for this young, high-risk population of women may assist in cardiometabolic disease risk reduction. The aim of this preliminary registry analysis was to observe the change in maternal metabolic syndrome status after receiving a nurse practitioner-led lifestyle intervention delivered soon after a complicated pregnancy. METHOD: This preliminary analysis included 64 eligible women who had attended both baseline (approximately 6 months postpartum) and review (approximately eighteen months postpartum) appointments at the postpartum lifestyle clinic after an index pregnancy complicated by at least one maternal complication of pregnancy. Metabolic syndrome status at both appointments was assessed. RESULTS: At the baseline appointment, 22 (34.4%) women met the criteria for metabolic syndrome. This number reduced at the review appointment to 19 (29.7%). This difference was not statistically significant. There were some modest improvements in the individual cardiometabolic risk factors, as well as marked improvements in the women who had recovered from metabolic syndrome over twelve months. CONCLUSION: There was a high percentage of metabolic syndrome present early in the postpartum period. The results of this preliminary analysis highlight the importance of continuing preventative care and ongoing research for this group of high-risk women.

Prevalence of Metabolic Syndrome in Women After Maternal Complications of Pregnancy: An Observational Cohort Analysis.

Introduction: Certain complications of pregnancy, including hypertensive disorders of pregnancy, gestational diabetes mellitus, intrauterine growth restriction, spontaneous preterm birth, and placental abruption, are established independent risk factors for premature cardiovascular disease in women. Metabolic syndrome, which is associated with an increased risk of cardiovascular disease, may be a suitable alternative to traditional cardiovascular risk calculators that underestimate risk in young women. This study aimed to investigate the prevalence of metabolic syndrome in women who experienced a complicated pregnancy 6 months earlier. Methods: This observational study investigated the prevalence of metabolic syndrome as defined by the International Diabetes Federation in all eligible participants (n = 247) attending a postpartum lifestyle intervention clinic from August 2018 to June 2021 at the Lyell McEwin Hospital in Adelaide, South Australia. Results: A total of 89 (36%) participants met the criteria for metabolic syndrome at a mean follow up time of 7 months postpartum. Almost 90% of the cohort were abdominally obese, and over two thirds of the total cohort met at least two of the criteria for metabolic syndrome. Conclusions: Women with a prior history of one of the common major pregnancy complications are at high risk of future cardiovascular and metabolic disease, with many showing either metabolic syndrome or multiple risk factors at only 7 months postpartum. The results indicate that follow-up within 1 year postpartum is an appropriate time to commence preventative strategies, as many women are already showing early signs of disease.

In-hospital mode of death after out-of-hospital cardiac arrest.

Introduction: Factors associated with in-hospital mortality after out-of-hospital cardiac arrest (OHCA), such as mode of death and withdrawal of life-sustaining treatment (WLST), are not well established. This study aimed to compare clinical characteristics, timing of WLST and death, and precipitating aetiology between modes of death for OHCAs treated at hospital within a local health network. Methods: Retrospective cohort study of adult non-traumatic OHCAs included in a hospital based OHCA registry between 2011 and 2016 and deceased at hospital discharge, excluding cases retrieved to external hospitals. Mode of death was defined as (1) cardiovascular instability, (2) non-neurological WLST, (3) neurological WLST, and (4) formal brain death. Relevant data were extracted from the registry and stratified according to mode of death and timing of death as early (within the emergency department) or late (after admission). Results: Mode of death data was available for 69 early and 144 late deaths. Cardiovascular instability was the primary mode for 75% of early deaths, while 72% of late deaths were attributed to neurological injury (47% neurological WLST and 24% brain death, combined). Cardiovascular instability was associated with cardiac aetiology, brain death was associated with younger age and highest rates of organ donation, and neurological WLST was associated with highest rates of targeted temperature management, and longest time from arrest to death (p < 0.05). Conclusions: This is the first study to compare clinical characteristics of adult patients resuscitated from OHCA according to in-hospital mode of death. A consensus on the definition of mode of death with standardised classification is needed.

Sex Differences in Incidence and Outcome of Out-of-Hospital Cardiac Arrest Within a Local Health Network.

Introduction: Sex and gender differences in presentation and characteristics of out-of-hospital cardiac arrest (OHCA) are established in cohorts with presumed cardiac aetiology but not non-cardiac etiology. This study investigated the effect of sex on incidence and outcome of OHCA according to presumed and adjudicated aetiology within a local health network. Methods: Population-based observational cohort study of emergency medical services (EMS) attended OHCAs within an Australian local health network. Cases identified from an EMS registry between 2012-2016 were linked to a hospital registry. Age-standardised incidence and baseline characteristics were stratified by sex for EMS-treated OHCA, non-EMS witnessed presumed cardiac and obvious non-cardiac sub-cohorts, and hospitalised cases. Logistic regression was used to explore the primary outcome of survival to hospital discharge. Results: We identified 2,024 EMS-attended and 780 EMS-treated OHCAs. The non-EMS witnessed sub-cohorts comprised 504 presumed cardiac and 168 obvious non-cardiac OHCAs. Adjudicated aetiology was recorded in 123 hospitalised cases. Age-standardised incidence for women was almost half that of men across all groups. Across cohorts, women were generally older and arrested with a non-shockable initial rhythm in an area of low socioeconomic status. There was no sex difference in the primary outcome for the main EMS-treated cohort or in the non-cardiac sub-cohorts. The sex difference in outcome in the presumed cardiac sub-cohort was not present after multivariable adjustment. Conclusions: There are sex differences in incidence and outcome of EMS-treated OHCA that appear to be driven by differences in susceptibility to cardiac arrhythmias and underlying etiology, rather than treatment delays or disparities.

Overcoming challenges of establishing a hospital-based out-of-hospital cardiac arrest registry: accuracy of case identification using administrative data and clinical registries.

INTRODUCTION: Comprehensive identification of out-of-hospital cardiac arrest (OHCA) cases for inclusion in registries remains challenging due to the inherent diversity of OHCA aetiology, presentation, and management. The Northern Adelaide Local Health Network (NALHN) OHCA registry identifies OHCAs presenting to NALHN hospitals using existing data sources to monitor in-hospital treatment and survival. This study aimed to investigate the accuracy of hospital-based data sources for identifying OHCA cases treated at hospital. METHODS: Retrospective analysis of all OHCAs aged >18 years included in the NALHN OHCA registry between 2011-16. Registry cases are identified from an emergency medical service (EMS) OHCA registry, Emergency Department (ED) and ICD-10 coding datasets, and key-word searches of two in-hospital clinical registries. Sensitivity and positive predictive values (PPV) of each hospital-based data source were analysed with respect to (a) the number of cases expected to be identified by that source, (b) total OHCA. Non-OHCAs yielded by each source were explored and a sub-analysis of ICD-10 codes was performed. RESULTS: Between 2011-16, the four hospital-based sources yielded 992 cases, of which 383 were confirmed as OHCA. The ED coding dataset was the most accurate with a sensitivity and PPV of 78%. The ICD-10 coding dataset had good sensitivity but low PPV (33%). The ED coding dataset, combined with the two in-hospital clinical registries, identified 93% of OHCAs. CONCLUSIONS: No single dataset identified all OHCAs presenting to NALHN hospitals. Combined hospital-based data sources provide a valid method of identifying OHCAs treated at hospital that may be adapted to augment EMS-based data.

Risk factors for premature coronary artery disease (PCAD) in adults: a systematic review protocol.

PCAD possesses a public health challenge resulting in years of productive life lost and an escalating burden on health systems. Objective of this review is to compare modifiable and non-modifiable risk factors for PCAD compared to those without PCAD. This review will include all comparative observational studies conducted in adults aged >18 years with confirmed diagnosis of PCAD (on angiography) compared to those without PCAD. Databases to be searched include; PubMed, CINAHL, Embase, Web of Science, and grey literature (Google Scholar). All identified studies will be screened for title and abstract and full-text against the inclusion criteria on Covidence software. Data relevant to exposures and outcomes will be extracted from all included studies. All studies selected for data extraction will be critically appraised for methodological quality. Meta-analysis using random-effects model will be performed using Review Manager 5.3. Effect sizes for categorical risk factors will be expressed as odds ratios with 95% confidence intervals. For risk factors measured in continuous form, mean difference (if units are consistent) otherwise standardized mean difference (if units are different across studies) will be reported. Heterogeneity between studies will be assessed using I 2 test statistics. GRADE will be used to assess the certainty of the findings. Systematic review registration number:PROSPERO Registration # CRD42020173216.

Hypertensive disorders of pregnancy and later cardiovascular disease risk in mothers and children.

Preeclampsia (PE) and gestational hypertension (GH) are pregnancy-specific diseases that occur in around 10% of pregnancies worldwide. Increasing evidence suggests that women whose pregnancies were complicated by PE or GH, and their offspring, are at increased risk of cardiovascular disease (CVD) later in life. We hypothesised that PE and GH would associate with CVD risk factors 8-10 years after the first pregnancy in the mother and child and that differences in cardiovascular risk profile would be seen between 8- and 10-year-old male and female children. This is a follow-up study of the Adelaide SCOPE pregnancy cohort where 1164 nulliparous women and their babies were recruited between 2005 and 2008. Haemodynamic function was assessed using non-invasive USCOMBP+ and USCOM1A devices. Microvascular function was assessed by post-occlusive reactive hyperaemia. Of the 273 mother-child pairs followed up, 38 women had PE and 20 had GH during pregnancy. Augmentation index (Aix) and suprasystolic pulse pressure (ssPP) were increased, whereas measures of microvascular function were decreased in children who were born to PE compared to uncomplicated pregnancies. Female children had decreased Aix and ssPP compared to male children after in utero exposure to PE. Women who developed GH during their first pregnancy had increased systolic, diastolic and mean arterial pressures compared to women who had uncomplicated pregnancy. Our data suggest that GH is associated with increased cardiovascular risk in women 8-10 years after first pregnancy and PE is associated with increased offspring risk at 8-10 years of age, highlighting differences between these two hypertensive disorders of pregnancy.

The impact of maternal asthma during pregnancy on offspring retinal microvascular structure and its relationship to placental growth factor production in utero.

Asthma is a common chronic disease in pregnancy that affects placental function and fetal growth and associated with cardio-metabolic disorders in the offspring but the mechanisms are unknown. This study explored whether maternal asthma in pregnancy is associated with the development of offspring microvascular structure and whether it was related to biomarkers of angiogenesis in utero. Children aged 4 to 6 years, born to either asthmatic mothers (n = 38) or healthy controls (n = 25), had their retinal microvascular structure examined. Maternal plasma PlGF concentrations at 18 and 36 weeks' gestation were measured. There was a significant global difference in all retinal microvascular measures between children of asthmatic mothers relative to controls and increased retinal venular tortuosity in children born to asthmatic mothers (7.1 (95% CI 0.7-13.5); P = .031). A rise in plasma PlGF from 18 to 36 weeks' gestation was observed in the control population which was significantly lower in the asthma group by 190.9 pg/mL. PlGF concentrations were correlated with microvascular structure including arteriolar branching and venular tortuosity. These exploratory findings indicate that exposure to maternal asthma during pregnancy is associated with persistent changes in microvascular structure in childhood that may be driven by alterations to angiogenic mechanisms in utero.

Cardiologists appropriately exclude resuscitated out-of-hospital cardiac arrests from emergency coronary angiography.

OBJECTIVE: Emergency coronary angiography after resuscitated out-of-hospital cardiac arrest as a selective or non-selective diagnostic procedure with or without intervention continues to be the subject of debate. This study sought to determine if cardiologists reliably select patients using clinical judgement for emergency coronary angiography without missing acutely ischemic cases requiring revascularization. METHODS: Presenting clinical details and ECGs (within 2 hours) from 52 consecutive out-of-hospital cardiac arrest patients who underwent non-selective coronary angiography were compiled retrospectively. Three out-of-hospital cardiac arrest-experienced interventional cardiologists, blinded to patient outcome, independently determined working diagnosis, and decision for emergency coronary angiography using clinical judgement. Sensitivity of the cardiologists' decision was assessed with respect to the outcome of acute revascularization. Inter-rater differences, consensus in clinical assessment, and influence of working diagnosis were also investigated. RESULTS: Sensitivity of individual cardiologist's decision for emergency coronary angiography with respect to acute revascularization was very high (adjusted overall sensitivity = 95.8%, 95% CI = 89-100, cardiologist range = 93%-100%), and perfect for the consensus of 2 or more cardiologists (100%, 95% CI = 79.4-100). There was no statistical difference in the sensitivity of this decision between cardiologists (P < 0.05), and inter-rater agreement was moderate (78% overall agreement, Κ = 0.56). CONCLUSIONS: Experienced cardiologists recommend emergency coronary angiography in all resuscitated out-of-hospital cardiac arrest requiring acute revascularization and appropriately excluded one-third of patients. Rather than advocating a non-selective, or conversely, a restrictive strategy with respect to coronary angiography after out-of-hospital cardiac arrest, the findings support an individualized approach by a multidisciplinary emergency team that includes experienced cardiologists. The results should be confirmed in a larger prospective study.

Agreement of aneroid and oscillometric blood pressure devices used in pregnancy.

OBJECTIVES: The objective of this study was to compare three automated blood pressure devices (Microlife VSA, Uscom BP+ and Tensiomed Arteriograph) with an aneroid device in an Australian antenatal population to determine an accurate and reliable alternative method of measuring blood pressure in pregnant women. STUDY DESIGN: This observational, prospective study recruited a random sample of 200 pregnant women of any gestation attending an antenatal clinic in an Australian hospital. Each participant had two peripheral blood pressure measurements per instrument performed, resulting in eight measurements per participant. MAIN OUTCOME MEASUREMENTS: Intra- and inter-device reliability of peripheral blood pressure measurements made by the aneroid device and the three automated brachial-cuff oscillometric devices were assessed. The agreement between devices was graded according to standardised criteria. RESULTS: Both intra- and inter-device reliability of blood pressure measurements of the four devices in this study were found to be 'excellent' (ICCs > 0.75). Microlife VSA and Uscom BP+ showed acceptable levels of agreement (±5mmHg) when compared to the aneroid device. Arteriograph did not show an acceptable level of agreement with the aneroid device for systolic blood pressure, but did for diastolic blood pressure. CONCLUSION: Accurate automated devices may ensure consistent assessment of blood pressure in the antenatal setting. Our results suggest that Microlife VSA and Uscom BP+ may be suitable alternatives to the aneroid device for use in the antenatal setting. Further studies assessing both auscultatory and oscillometric blood pressure devices in pregnancy, and especially in hypertensive cohorts, are required.

A South Australian registry of biphasic cardioversions of atrial arrhythmias: efficacy and predictors of success.

BACKGROUND: Restoration of sinus rhythm by biphasic cardioversion is an established strategy for patients in atrial arrhythmias. This study aimed to investigate the real-life practice of cardioversions throughout a local hospital to determine frequency and predictors of success and use of high energy (> 200 joules). METHODS: Prospective analysis of consecutive biphasic cardioversions from 2009-2013. Patient demographics, medical history and cardioversion data were collected. RESULTS: 484 cardioversions from 379 patients were included in the final analysis. The majority (73%) of cardioversions were immediately successful after a single shock; overall success was 88% (1-5 shocks). Exploratory analyses revealed that single-shock success was significantly associated with lighter weight (OR 1.19, 95% CI 1.0-1.4, p<0.05). If a second shock was required, energy escalation was significantly associated with success (OR 3.11, 95% CI 1.43-6.77, p<0.05). Increasing weight was the strongest predictor of receiving high energy (10kg increase OR 1.43, 95% CI 1.13-1.81, p<0.05). CONCLUSIONS: This prospective analysis reflects the real-life heterogeneous practice of biphasic cardioversions of atrial arrhythmias throughout a local hospital. These findings highlight the importance of first shock energy selection with careful consideration of patient weight. We emphasise the recommendation to escalate energy, highlighting the need for high-energy defibrillators in 'hard-to-cardiovert' patients.