Sudden cardiac death: the major challenge confronting contemporary cardiology

OUP accepted manuscript

Proper management of patients affected by genetic disorders causing life-threatening arrhythmias is important for several reasons, including even societal ones, given the predominantly young age of those affected. Incorrect management often has dire consequences, ranging from unnecessary psychologic damage for the patients whose life becomes too limited by the fear of sudden death to equally avoidable tragedies when the entire armamentarium of effective therapies is not fully utilized. In this review, we focus primarily on long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT) and deal specifically with the clinical impact of the most commonly used cardiac sympathetic denervation (CSD), namely left cardiac sympathetic denervation (LCSD). The two of us have used LCSD in the management of our patients with either LQTS or CPVT for a very long time and have been involved in ∼500 such interventions. It is on the basis of this personal and direct experience that we wish to share our views with clinical cardiologists and electrophysiologists, adult and paediatric, and with genetic cardiologists. We will begin by reviewing the history and rationale underlying sympathetic denervation therapy and will continue with a disease-specific intensification of therapy, and then with a discussion on how the impressive efficacy of LCSD should translate into guideline-directed therapy in both current and future guidelines, in order to upgrade the quality of care in the era of precision medicine.

How to Assess the Epistemic Wrongness of Sponsorship Bias? The Case of Manufactured Certainty

Although the impact of so-called “sponsorship bias” has been the subject of increased attention in the philosophy of science, what exactly constitutes its epistemic wrongness is still debated. In this paper, I will argue that neither evidential accounts nor social–epistemological accounts can fully account for the epistemic wrongness of sponsorship bias, but there are good reasons to prefer social–epistemological to evidential accounts. I will defend this claim by examining how both accounts deal with a paradigm case from medical epistemology, recently discussed in a paper by Bennett Holman. I will argue that evidential accounts cannot adequately capture cases of sponsorship bias that involve the manufacturing of certainty because of their neutrality with respect to the role of non-epistemic values in scientific practice. If my argument holds, it further highlights the importance of integrating social and ethical concerns into epistemological analysis, especially in applied contexts. One can only properly grasp sponsorship bias as an epistemological problem if one resists the methodological tendency to analyze social, ethical, and epistemological issues in isolation from each other.

NAD+ Metabolism as an Emerging Therapeutic Target for Cardiovascular Diseases Associated With Sudden Cardiac Death

In addition to its central role in mediating oxidation reduction in fuel metabolism and bioenergetics, nicotinamide adenine dinucleotide (NAD+) has emerged as a vital co-substrate for a number of proteins involved in diverse cellular processes, including sirtuins, poly(ADP-ribose) polymerases and cyclic ADP-ribose synthetases. The connection with aging and age-associated diseases has led to a new wave of research in the cardiovascular field. Here, we review the basics of NAD+ homeostasis, the molecular physiology and new advances in ischemic-reperfusion injury, heart failure, and arrhythmias, all of which are associated with increased risks for sudden cardiac death. Finally, we summarize the progress of NAD+-boosting therapy in human cardiovascular diseases and the challenges for future studies.

Sudden Cardiac Death in Children and Adolescents

Sudden cardiac death (SCD) is a rare but devastating event in children and adolescents. Etiologies include congenital heart disease, cardiomyopathies, primary arrhythmia syndromes, and miscellaneous conditions. Challenges in the diagnosis and prevention of SCD in the young are reviewed.

Acute Stress Decreases but Chronic Stress Increases Myocardial Sensitivity to Ischemic Injury in Rodents

Cardiovascular disease (CVD) is the largest cause of mortality worldwide, and stress is a significant contributor to the development of CVD. The relationship between acute and chronic stress and CVD is well evidenced. Acute stress can lead to arrhythmias and ischemic injury. However, recent evidence in rodent models suggests that acute stress can decrease sensitivity to myocardial ischemia-reperfusion injury (IRI). Conversely, chronic stress is arrhythmogenic and increases sensitivity to myocardial IRI. Few studies have examined the impact of validated animal models of stress-related psychological disorders on the ischemic heart. This review examines the work that has been completed using rat models to study the effects of stress on myocardial sensitivity to ischemic injury. Utilization of animal models of stress-related psychological disorders is critical in the prevention and treatment of cardiovascular disorders in patients experiencing stress-related psychiatric conditions.

Caffeine delays autonomic recovery following acute exercise

BACKGROUND

Impaired autonomic recovery of heart rate (HR) following exercise is associated with an increased risk of sudden death. Caffeine, a potent stimulator of catecholamine release, has been shown to augment blood pressure (BP) and sympathetic nerve activity; however, whether caffeine alters autonomic function after a bout of exercise bout remains unclear.

METHODS

In a randomized, crossover study, 18 healthy individuals (26 ± 1 years; 23.9 ± 0.8 kg·m(-2)) ingested caffeine (400 mg) or placebo pills, followed by a maximal treadmill test to exhaustion. Autonomic function and ventricular depolarization/repolarization were determined using heart rate variability (HRV) and corrected QT interval (QTc), respectively, at baseline, 5, 15, and 30 minutes post-exercise.

RESULTS

Maximal HR (HRmax) was greater with caffeine (192 ± 2 vs. 190 ± 2 beat·min(-1), p < 0.05). During recovery, HR, mean arterial pressure (MAP), and diastolic blood pressure (DBP) remained elevated with caffeine (p < 0.05). Natural log transformation of low-to-high frequency ratio (LnLF/LnHF) of HRV was increased compared with baseline at all time points in both trials (p < 0.05), with less of an increase during 5 and 15 minutes post-exercise in the caffeine trial (p < 0.05). QTc increased from baseline at all time points in both trials, with greater increases in the caffeine trial (p < 0.05).

CONCLUSIONS

Caffeine ingestion disrupts post-exercise autonomic recovery because of increased sympathetic nerve activity. The prolonged sympathetic recovery time could subsequently hinder baroreflex function during recovery and disrupt the stability of autonomic function, potentiating a pro-arrhythmogenic state in young adults.

Spatial repolarization heterogeneity detected by magnetocardiography correlates with cardiac iron overload and adverse cardiac events in beta-thalassemia major

Background

Patients with transfusion-dependent beta-thalassemia major (TM) are at risk for myocardial iron overload and cardiac complications. Spatial repolarization heterogeneity is known to be elevated in patients with certain cardiac diseases, but little is known in TM patients. The purpose of this study was to evaluate spatial repolarization heterogeneity in patients with TM, and to investigate the relationships between spatial repolarization heterogeneity, cardiac iron load, and adverse cardiac events.

Methods and Results

Fifty patients with TM and 55 control subjects received 64-channel magnetocardiography (MCG) to determine spatial repolarization heterogeneity, which was evaluated by a smoothness index of QT_c (SI-QT_c), a standard deviation of QT_c (SD-QT_c), and a QT_c dispersion. Left ventricular function and myocardial T2* values were assessed by cardiac magnetic resonance. Patients with TM had significantly greater SI-QT_c, SD-QT_c, and QT_c dispersion compared to the control subjects (all p values<0.001). Spatial repolarization heterogeneity was even more pronounced in patients with significant iron overload (T2*<20 ms, n = 20) compared to those with normal T2* (all p values<0.001). Log_e cardiac T2* correlated with SI-QT_c (r = −0.609, p<0.001), SD-QT_c (r = −0.572, p<0.001), and QT_c dispersion (r = −0.622, p<0.001), while all these indices had no relationship with measurements of the left ventricular geometry or function. At the time of study, 10 patients had either heart failure or arrhythmia. All 3 indices of repolarization heterogeneity were related to the presence of adverse cardiac events, with areas under the receiver operating characteristic curves (ranged between 0.79 and 0.86), similar to that of cardiac T2*.

Conclusions

Multichannel MCG demonstrated that patients with TM had increased spatial repolarization heterogeneity, which is related to myocardial iron load and adverse cardiac events.

Incidence of ventricular arrhythmia and associated patient outcomes in hospitalized acute coronary syndrome patients in Saudi Arabia: findings from the registry of the Saudi Project for Assessment of Acute Coronary Syndrome (SPACE)

BACKGROUND AND OBJECTIVES

Mortality in acute coronary syndrome (ACS) patients with ventricular arrhythmia (VA) has been shown to be higher than those without VA. However, there is a paucity of data on VA among ACS patients in the Middle Eastern countries.

DESIGN AND SETTING

Prospective study of patients admitted in 17 government hospitals with ACS between December 2005 and December 2007.

PATIENTS AND METHODS

Patients were categorized as having VA if they experienced either ventricular fibrillation (VF) or sustained ventricular tachycardia (VT) or both.

RESULTS

Of 5055 patients with ACS enrolled in the SPACE registry, 168 (3.3%) were diagnosed with VA and 151 (98.8%) occurred in-hospital. The vast majority (74.4%) occurred in patients with ST-segment elevation myocardial infarction. In addition, males were twice as likely to develop VA than females (OR 1.7; 95% CI 1.13). Killip class >I (OR 2.0; 95% CI 1.3-3.1); and systolic blood pressure <90 mm Hg (OR 6.4; 95% CI 3.5-11.8) were positively associated with VA. Those admitted with hyperlipidemia (OR 0.49; 95% CI 0.3-0.7) had a lower risk of developing VA. Adverse in-hospital outcomes including re-myocardial infarction, cardiogenic shock, congestive heart failure, major bleeding, and stroke were higher for patients with VA (P≤.01 for all variables) and signified a poor prognosis. The in-hospital mortality rate was significantly higher in VA patients compared with non-VA patients (27% vs 2.2%; P=.001).

CONCLUSIONS

In-hospital VA in Saudi patients with ACS was associated with remarkably high rates of adverse events and increased in-hospital mortality. Using a well-developed registry data with a large number of patients, our study documented for the first time the prevalence and risk factors of VA in unselected population of ACS.

Specific characteristics of sudden death in a mediterranean Spanish population

Most of the data reported on sudden cardiac death has been from studies of Anglo-Saxon patients. We conducted a study to ascertain the relation between sudden death (SD) and some epidemiologic, clinical, and biochemical parameters and to assess the coronary histopathologic aspects of subjects in a Spanish population who had died suddenly. A total of 204 subjects (86% men), aged 12 to 80 years (mean 54 ± 15), who had died from out-of-hospital natural SD were evaluated. Only 15% of subjects had been previously diagnosed with heart disease. Pathologic evidence of underlying cardiovascular disease was found in 90% of cases, with coronary heart disease (CHD) the most frequent (58%). The CHD was acute coronary thrombosis in 41% and a stable plaque with luminal narrowing of ≥75% in 59%. An old myocardial infarction was found in 31% of the SD victims. Cardiac hypertrophy was found in 48%, with no relation between the presence of cardiac hypertrophy and CHD. Patients with stable plaques had a greater heart weight than did those with acute coronary thrombosis (p = 0.02). Male gender, older age, smoking, and low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio of ≥3 were associated with CHD. A greater percentage of patients with an eroded and/or ruptured plaque than patients with a stable plaque were smokers. Only smoking and a low-density lipoprotein/high-density lipoprotein cholesterol ratio of ≥3 were associated with an eroded and/or ruptured plaque. In conclusion, compared with the findings from studies of Anglo-Saxon patients, a lower incidence of CHD and acute coronary thrombosis and a greater incidence of cardiac hypertrophy were found in SD victims of a Mediterranean Spanish population.

Relation of atrial and/or ventricular premature complexes on a two-minute rhythm strip to the risk of sudden cardiac death (the Atherosclerosis Risk in Communities [ARIC] study)

Ventricular premature complexes (VPCs) and atrial premature complexes (APCs) are common findings on routinely obtained electrocardiograms. Despite their common occurrence, the significance of these irregular beats is unclear, especially with regard to risk of sudden cardiac death (SCD). In this study, we examined the prospective relation between baseline VPCs or APCs and SCD, myocardial infarction, and fatal coronary heart disease (CHD) in a population-based sample of subjects from the Atherosclerosis Risk in Communities (ARIC) study excluding participants with known history of CHD or stroke. Baseline examination was conducted from 1987 to 1989, with follow-up data regarding clinical cardiac events collected until December 2002. The total study population was 14,574 subjects. Kaplan-Meier curves and computed univariate and multivariate Cox proportional hazard models were employed to estimate the effect of VPC and APC occurrences on incident cardiac events. During the follow-up period, there were 130 incident cases of SCD, 1,657 incident cases of CHD cases, and 288 cases of fatal CHD. Participants with VPC were 2 times as likely to have SCD (hazard ratio [HR] 2.09, 95% confidence interval [CI] 1.22 to 3.56) compared to those without VPC. Presence of APC was not significantly associated with SCD (HR 1.15, 95% CI 0.56 to 2.39). Compared to subjects without VPC and APC, risk of SCD in subjects with VPC and APC was significantly increased (HR 6.39, 95% CI 2.58 to 15.84). In conclusion, our study shows that subjects with VPCs are significantly more likely to die from SCD, despite not having any known history of cardiovascular disease. This effect appears to be additive when APCs occur concurrently.

Prognostic value of somatosensory evoked potentials in comatose children: a systematic literature review

PURPOSE

To review the predictive powers of SEPs in comatose children after acute brain injury.

METHODS

MEDLINE, EMBASE, OVID, ISI Web of Knowledge, BIOMED Central and the Cochrane Library (1981-2007) were searched. First, predictive values were calculated for each primary study. Second, we analysed effects of different factors on the SEP diagnostic odds ratio by meta-regression. Third, we compared SEP predictive values in children and in adults.

RESULTS

We selected 14 studies covering 732 patients; analysis was conducted in 11, while the other 3 were used for simple qualitative examination. In individual papers, the presence of SEP predicted favourable outcomes as shown by the area under both sROC curves being 0.958. The same value was shown by SEP absence for predicting unfavourable outcomes. All covariates showed no significant effects on diagnostic accuracy, but only a slight non-significant trend. For SEP grading, a simple sub-group analysis showed a high predictive value for non-awakening for absence of SEPs (PPV 97.0%) and a high prognostic power to predict awakening for normal SEPs (PPV 92.2%). Pathological SEPs did not show reliable predictivity. In children, the presence of SEPs showed a high prognostic power similar to that in adults.

CONCLUSION

This study supports the use of SEPs in the integrated process of outcome prediction after acute brain injury in children. Caution is recommended in predicting unfavourable outcomes in patients with an absence of SEPs in both TBI and HIE comas. Future studies are needed to resolve the issue of the effect of aetiology and age on SEP's predictive power.

Excessive heart rate increase during mild mental stress in preparation for exercise predicts sudden death in the general population

AIMS

The aim of this study involves the early identification, among apparently healthy individuals, of those at high risk for sudden cardiac death. We tested the hypothesis that individuals who respond to mild mental stress in preparation for exercise test with the largest heart rate increases might be at highest risk.

METHODS AND RESULTS

Data from 7746 civil servants participating in the Paris Prospective Study I, followed-up for 23 years, allowed to compare heart rate changes between rest and mild mental stress (preparation prior to an exercise test) between subjects who suffered sudden cardiac death (n = 81), non-sudden (n = 129) coronary death, or death from any cause (n = 1306). The mean heart rate increase during mild mental stress was 8.9 +/- 10.8 b.p.m. Risk of sudden cardiac death increased progressively with heart rate increase during mental stress and the relative risk of the third vs. the first tertile was 2.09 (95% confidence interval, 1.13-3.86) after adjustment for confounders. This relationship was not observed for non-sudden coronary death.

CONCLUSION

An important heart rate increase produced by a mild mental stress predicts long-term risk for sudden cardiac death. Heart rate changes before an exercise test may provide a simple tool for risk stratification.

Magnitude and prognosis associated with ventricular arrhythmias in patients hospitalized with acute coronary syndromes (from the GRACE Registry)

The incidence, prognosis, and factors associated with ventricular arrhythmia (VA) in acute coronary syndrome are unknown. We sought to examine the magnitude, predictors, and outcomes of in-hospital VA in patients with acute coronary syndrome. The population comprised 52,380 patients enrolled in the Global Registry of Acute Coronary Events from 1999 to 2005. The proportion who developed VA during hospitalization was 6.9% (1.8% with ventricular tachycardia, 5.1% with ventricular fibrillation or cardiac arrest). The incidence of in-hospital VA decreased over time (8.0% in 1999, 7.0% in 2002, 5.8% in 2005, p <0.001). In-hospital case-fatality rates were higher in patients with versus those without VA (52% vs 1.6%). Several demographic and clinical variables were associated with the occurrence of VA including ST deviation, Killip class, age, initial cardiac markers, serum creatinine and heart rate, and history of selected co-morbidities. Six-month postdischarge mortality was higher in survivors of in-hospital VA versus those who did not develop VA during hospitalization (odds ratio 1.57, 95% confidence interval 1.27 to 1.95). In conclusion, development of VA during hospitalization for acute coronary syndrome was associated with higher in-hospital and 6-month mortalities.

Complex temporal patterns of spontaneous initiation and termination of reentry in a loop of cardiac tissue

A two-component model is developed consisting of a discrete loop of cardiac cells that circulates action potentials as well as a pacing mechanism. Physiological properties of cells such as restitutions of refractoriness and of conduction velocity are given via experimentally measured functions. The dynamics of circulating pulses and the pacer's action are regulated by two threshold relations. Patterns of spontaneous initiations and terminations of reentry (SITR) generated by this system are studied through numerical simulations and analytical observations. These patterns can be regular or irregular; causes of irregularities are identified as the threshold bistability (T-bistability) of reentrant circulation and in some cases, also phase-resetting interactions with the pacer.

Alimentary lipemia enhances procoagulatory effects of inflammation in patients with a history of acute myocardial infarction complicated by ventricular fibrillation

INTRODUCTION

Acute myocardial infarction, often occurring postprandially, can be complicated by ventricular fibrillation. The role of acute alimentary lipemia and inflammation in the occurrence of ventricular arrhythmias in acute myocardial infarction has not been described yet.

METHODS AND RESULTS

Before and 2 h after consumption of a defined fatty meal, blood samples of 27 patients with a history of acute myocardial infarction (AMI) were incubated with lipopolysaccharide (LPS). In 10 patients, AMI was complicated by ventricular fibrillation (VF), in 17 patients, AMI occurred without VF. CD40-ligand and CD62P expression on platelets, tissue-factor binding on monocytes and platelet-monocyte aggregates were measured with flow cytometry. Soluble CD40-ligand plasma levels were measured with an ELISA. With the meal, serum triglyceride levels increased from 211.85+/-94.60 mg/dl to 273.59+/-122.52 mg/dl (p=0.0002). LPS stimulation before the meal showed a non-significant tendency to increase platelet-monocyte aggregates and tissue factor on monocytes in both patient groups. LPS stimulation in acute alimentary lipemia significantly increased tissue-factor expression on monocytes in both patient groups and platelet-monocyte aggregates in patients with VF. Baseline plasma levels of soluble CD40L did not differ significantly between both groups. Acute alimentary lipemia significantly decreased total plasma levels of sCD40L, leading to a significantly lower level of sCD40L in patients with a history of VF.

CONCLUSIONS

Alimentary lipemia enhances procoagulatory effects of inflammatory stimulation in patients with a history of AMI complicated by ventricular fibrillation. These observations might reveal a mechanism for an increased risk of VF in acute coronary syndromes in a postprandial state.

Stress and sudden death

Cardiac patients, psychiatric patients, and certain ethnic groups experiencing acute stressful circumstances are at risk for unexpected sudden death. Although stress is associated with changes in autonomic neural function, its role as a potential risk factor for sudden unexpected death in epilepsy (SUDEP) is not known. The association of epilepsy with cardiac abnormalities, such as neurogenic arrhythmias and microscopic perivascular and interstitial fibrosis, and with depression and anxiety indicates that emotional stress should be evaluated as a potential risk factor for SUDEP. The impact of adverse emotional states on the autonomic control of cardiac rhythm is a known important factor leading to cardiac dysrhythmias in humans and other species. The interaction between emotional factors and the arrythmogenic potential of epileptiform discharges and the possibility of benefit from stress management intervention need to be investigated.

Enhanced expression of platelet CD40-ligand by in vitro lipopolysaccharide-challenge in patients with ventricular fibrillation complicating acute myocardial infarction

BACKGROUND

Acute myocardial infarction can be complicated by ventricular arrhythmias due to electrophysiological changes in the ischemic myocardium, but the exact predisposing factors causing ventricular fibrillation during myocardial infarction still remain unclear. A role of inflammatory stimulation on platelets as a potential risk factor for ventricular fibrillation during acute myocardial infarction has not been described yet.

METHODS AND RESULTS

Whole blood samples of 21 patients with a history of acute myocardial infarction (AMI) and ventricular fibrillation (VF) were incubated with lipopolysaccharide (LPS). As a control group, we studied 19 patients without VF during AMI. CD40-ligand and CD62P expression on platelets and tissue factor binding on monocytes were measured by flow cytometry. Platelet-monocyte aggregates were measured by CD41 expression on platelets adherent to monocytes. Soluble CD40-ligand plasma levels were measured with an ELISA. Without LPS, no significant difference between the patient groups concerning CD40L expression on platelets was observed, but plasma levels of soluble CD40L were significantly higher in patients with a history of AMI with VF. After LPS stimulation, patients with a history of VF showed a significantly increased expression of CD40L in comparison to the patients without ventricular fibrillation, based on a significantly higher increase of CD40L expression. CD62P expression on platelets was significantly increased in patients with a history of VF.

CONCLUSIONS

Patients with a history of VF complicating AMI show an enhanced expression of CD40L on platelets after in vitro lipopolysaccharide-challenge with an enhanced platelet activation.

Out-of-hospital cardiac deaths in adolescents and young adults in the United States, 1989 to 1998

BACKGROUND

Out-of-hospital cardiac death (OHCD), often occurring suddenly and unexpectedly, is a major public health problem. The purpose of this study is to assess the epidemiologic pattern and secular trend of OHCD in adolescents and young adults aged 15-34 years in the United States.

METHODS

United States national vital statistics mortality data from 1989 to 1998 were analyzed. OHCD was defined as death that occurred either at a pre-transport location, or in the emergency room, or was classified as "dead on arrival" in the emergency room, with an underlying cause of death as a cardiac disease (ICD-9 codes 390-398, 402, 404-429, 745, or 746).

RESULTS

Of the 48,573 cardiac deaths occurring during 1989 to 1998, 31,827 (66%) were out of hospital. Of all OHCD victims from 1989 to 1998, 70% were men, and 76% were aged 25-34 years. The leading underlying causes of OHCD were coronary heart disease (29%), cardiomyopathy (18%), and arrhythmias (14%). The OHCD rates (per million population) were twice as high in men as in women (57.0 vs. 26.7 in 1997 and 1998), in African Americans as in whites (84.9 vs. 35.9 in 1997 and 1998), and increased with age. From 1989-1990 to 1997-1998, the age-adjusted OHCD death rates increased in both men (11%) and women (33%), and in African Americans (11%) and whites (19%).

CONCLUSIONS

Although cardiac death remains rare in U.S. adolescents and young adults, the increased trend in OHCD rates in this age group warrants further investigation of etiology and prevention strategies.

Sudden cardiac death in athletes: a guide for emergency physicians

A conditioned athlete is usually regarded as a member of the healthiest segment of society, and exercise itself is looked upon as a means to improve health. Although extremely uncommon, sudden cardiac death (SCD) in young athletes is a devastating medical event to all involved (patient, family, community, team, and caregivers). Most etiologies of SCD in athletes result in the same final common denominator (cardiac arrest) on presentation to an emergency physician. There are, however, certain historic, physical examination, and electrocardiographic features of many of these disease processes that emergency physicians should have a working knowledge of to try to identify them before they result in SCD. This review examines the clinical presentation, diagnostic techniques, and management options applicable to emergency practitioners.

Enhanced Coagulation Activation by In Vitro Lipopolysaccharide Challenge in Patients with Ventricular Fibrillation Complicating Acute Myocardial Infarction

BACKGROUND

Indicators of coagulation and inflammation are elevated in patients with coronary heart disease. A role of coagulation activation in ventricular fibrillation during acute myocardial infarction has not been described.

METHODS AND RESULTS

Whole blood samples of 21 patients with a history of acute myocardial infarction complicated by ventricular fibrillation and whole blood samples of 18 patients without ventricular fibrillation were incubated with lipopolysaccharide (LPS). In both groups, the in vitro blood coagulation time was measured with the ReoRox, a viscometric whole blood coagulometer. CD62P expression on platelets, tissue-factor binding on monocytes, and platelet-monocyte aggregates were measured with flow cytometry. Without LPS, no difference in the coagulation times were observed in both patient groups. After incubation with LPS, patients with a history of ventricular fibrillation showed a significantly decreased coagulation time compared to patients without ventricular fibrillation. The decrease of coagulation time after incubation with LPS also differed significantly in both groups. Expression of CD62P on platelets was significantly higher in patients with a history of ventricular fibrillation after incubation with LPS. Although in each patient group incubation with LPS induced a significantly increased amount of tissue factor on monocytes and a significantly increased the number of platelet-monocyte aggregates, the two groups did not differ significantly concerning tissue factor binding on monocytes and the amount of platelet-monocyte aggregates.

CONCLUSIONS

After in vitro LPS challenge, patients with a history of ventricular fibrillation during myocardial infarction show an enhanced coagulation activation, which may partly be due to an enhanced platelet activation.

Heart rate variability: measurement and clinical utility

Electrocardiographic RR intervals fluctuate cyclically, modulated by ventilation, baroreflexes, and other genetic and environmental factors that are mediated through the autonomic nervous system. Short term electrocardiographic recordings (5 to 15 minutes), made under controlled conditions, e.g., lying supine or standing or tilted upright can elucidate physiologic, pharmacologic, or pathologic changes in autonomic nervous system function. Long-term, usually 24-hour recordings, can be used to assess autonomic nervous responses during normal daily activities in health, disease, and in response to therapeutic interventions, e.g., exercise or drugs. RR interval variability is useful for assessing risk of cardiovascular death or arrhythmic events, especially when combined with other tests, e.g., left ventricular ejection fraction or ventricular arrhythmias.

Hemodynamic Observations on a Yogic Breathing Technique Claimed to Help Eliminate and Prevent Heart Attacks: A Pilot Study

OBJECTIVE

This pilot study investigated the hemodynamics of a yogic breathing technique claimed "to help eliminate and prevent heart attacks due to abnormal electrical events to the heart," and to generally "enhance performance of the central nervous system (CNS) and to help eliminate the effects of traumatic shock and stress to the CNS."

DESIGN

Parameters for (4) subjects were recorded during a preexercise resting period, a 31-minute exercise period, and a postexercise resting period.

SETTINGS/LOCATION

Parameters for subjects were recorded in a laboratory at the University of California, San Diego.

SUBJECTS

Parameters for 3 males (ages 44, 45, 67) and 1 female (age 41) were recorded. One (1) subject (male age 45) had extensive training in this technique.

INTERVENTIONS

This yogic technique is a 1 breath per minute (BPM) respiratory exercise with slow inspiration for 20 seconds, breath retention for 20 seconds, and slow expiration for 20 seconds, for 31 consecutive minutes.

OUTCOME MEASURES

Fourteen beat-to-beat parameters were measured noninvasively and calculated for body surface area to yield: stroke index (SI), heart rate (HR), cardiac index, end diastolic index, peak flow, ejection fraction, thoracic fluid index, index of contractility, ejection ratio, systolic time ratio, acceleration index, and systolic, diastolic, and mean arterial pressures (MAPs). Left stroke work index (LSWI) and stroke systemic vascular resistance index (SSVRI) were calculated.

RESULTS

We report on SI, HR, MAP, LSWI, and SSVRI and how they can help to describe hemodynamicstate changes. This technique induces dramatic shifts in all hemodynamic variables during the 1 BPM exercise and can produce unique changes in the postexercise resting period after long-term practice that appears to have a unique effect on the brain stem cardiorespiratory center regulating the Mayer wave (0.1-0.01 Hz) patterns of the cardiovascular system.

CONCLUSIONS

Preclinical studies are warranted to examine the possible long-term effects of this technique that appear to reset a cardiorespiratory brain-stem pacemaker. We postulate that this effect may be the basis for the purported yogic health claim.

A brief history of sudden cardiac death and its therapy

At the end of the 19th century, there was both experimental and clinical evidence that coronary artery obstruction causes ventricular fibrillation and sudden death and that fibrillation could be terminated by electric shocks. The dominant figure at that time was McWilliam, who in 1923 complained that "little attention was given to the new view for many years." This remained so for many decades. It was not until the 1960s that the medical profession became aware of the magnitude of the problem of sudden death and began to install coronary care units where arrhythmias could be monitored and prompt defibrillation could be delivered. This approach was pioneered by Julian in 1961. Milestones that allowed this development were open-chest defibrillation by Beck, closed-chest defibrillation by Zoll, cardiac massage by Kouwenhoven et al., and development of the DC defibrillator by Lown. In 1980, Mirowski et al. implanted the first implantable cardioverter defibrillator (ICD) in a patient. Thereafter, the use of the ICD increased exponentially. Several randomized trials, largely in patients with coronary artery disease and left ventricular dysfunction or in patients with documented lethal arrhythmias, showed beyond doubt that the ICD is superior to antiarrhythmic drug therapy in preventing sudden death, although a number of trials showed no effect. Trials on antiarrhythmic drugs were disappointing. Sodium channel blockers and "pure" potassium channel blockers actually increase mortality, calcium channel blockers have no effect, and, although amiodarone reduces arrhythmic death, it had no effect on total mortality in the 2 largest trials. Only the beta-blockers have been proven to reduce the incidence of sudden death, but their effect appears not to be related to the suppression of arrhythmias but rather to the reduction in sinus rate. Drugs that prevent ischemic events, or lessen their impact, such as anticoagulants, statins, angiotensin-converting enzyme inhibitors, and aldosteron antagonists, all reduce the incidence of sudden death.

Central sympathetic blockade ameliorates brain death-induced cardiotoxicity and associated changes in myocardial gene expression

OBJECTIVE

Brain death results in cardiac injury and hemodynamic instability. After brain death, catecholamine levels surge in concert with increased expression of select myocardial gene products. Sympathetic blockade was used to investigate the effects of the adrenergic nervous system on myocardial gene expression in a rabbit model of brain death.

METHODS

A balloon expansion model of brain death in rabbits (n = 42) was used with and without sympathetic blockade (xylazine, acetylpromazine, and ketamine). Sham-operated and naive rabbits served as control animals. Over 4 hours, mean arterial pressure, heart rate, electrocardiographic results, catecholamine levels, myocardial histology, and messenger RNA levels were assessed.

RESULTS

Sympathetic blockade decreased basal catecholamine levels and blocked the catecholamine surge accompanying brain death. The typical hemodynamic instability, adverse electrocardiographic changes, and myocellular injury associated with brain death were all significantly decreased. Sympathetic blockade not only suppressed the previously reported increases in myocardial gene expression (cardiac and skeletal alpha-actin, egr-1, and heat shock protein 70) but also suppressed the expression of multiple other genes (alpha and beta myosin heavy chain, calcium ATPase [sarcoplasmic reticulum Ca(2+)-adenosine triphosphatase pump, SERCA-2a], phospholamban [ryanodine receptor], and c-jun).

CONCLUSION

Central sympathetic blockade minimizes the hemodynamic instability associated with brain death and neutralizes the increased expression of multiple myocardial gene products associated with brain death.

Altered sympathetic and parasympathetic activity in lung transplantation patients at rest and following autonomic perturbation

STUDY OBJECTIVES

To investigate the nature and extent of the alteration in autonomic function following heterotopic lung transplantation.

DESIGN

Measures of cardiac parasympathetic nervous system activity (PNSA) and systemic sympathetic nervous system activity (SNSA) were compared in lung transplant patients and age-matched healthy subjects, both at rest and following autonomic perturbation.

SETTING

Lung transplantation service of a university teaching hospital.

PATIENTS AND PARTICIPANTS

Twenty-two lung transplant patients (mean [+/- SEM] age, 50.5 +/- 2.4 years) and 13 healthy subjects (mean age, 48.2 +/- 3.7 years).

MEASUREMENTS AND RESULTS

Lung transplant patients had decreased baseline time and frequency domain measures of heart rate variability compared to healthy subjects (root mean square of successive differences in R-R intervals, 11.2 +/- 1.1 vs 30.3 +/- 4.5 ms, respectively [p < 0.005]; LnHP, 2.4 +/- 0.2 vs 4.8 +/- 0.4 ms(2), respectively [p < 0.005]). In addition, lung transplant patients demonstrated an attenuated reduction in LnHP/LnTP following head-up tilt in comparison to healthy subjects (p < 0.05). The baseline recumbent plasma norepinephrine level was increased in lung transplant patients compared to healthy subjects (3.25 +/- 0.43 vs 2.00 +/- 0.27 nmol/L, respectively; p < 0.05), and levels increased in both groups with upright head-up tilt. There were no differences between the two groups in heart rate or mean systolic BP responses to both the Valsalva maneuver and cold pressor testing.

CONCLUSIONS

Lung transplant patients have both reduced PNSA and increased SNSA at rest. Furthermore, these patients appear to have a preserved capacity to respond to autonomic perturbation by increasing SNSA. The mechanisms underlying these observations and their prognostic implications remain to be determined.

Sudden cardiac death in the United States, 1989 to 1998

BACKGROUND

Sudden cardiac death (SCD) is a major clinical and public health problem.

METHODS AND RESULTS

United States (US) vital statistics mortality data from 1989 to 1998 were analyzed. SCD is defined as deaths occurring out of the hospital or in the emergency room or as "dead on arrival" with an underlying cause of death reported as a cardiac disease (ICD-9 code 390 to 398, 402, or 404 to 429). Death rates were calculated for residents of the US aged >/=35 years and standardized to the 2000 US population. Of 719 456 cardiac deaths among adults aged >/=35 years in 1998, 456 076 (63%) were defined as SCD. Among decedents aged 35 to 44 years, 74% of cardiac deaths were SCD. Of all SCDs in 1998, coronary heart disease (ICD-9 codes 410 to 414) was the underlying cause on 62% of death certificates. Death rates for SCD increased with age and were higher in men than women, although there was no difference at age >/=85 years. The black population had higher death rates for SCD than white, American Indian/Alaska Native, or Asian/Pacific Islander populations. The Hispanic population had lower death rates for SCD than the non-Hispanic population. From 1989 to 1998, SCD, as the proportion of all cardiac deaths, increased 12.4% (56.3% to 63.9%), and age-adjusted SCD rates declined 11.7% in men and 5.8% in women. During the same time, age-specific death rates for SCD increased 21% among women aged 35 to 44 years.

CONCLUSIONS

SCD remains an important public health problem in the US. The increase in death rates for SCD among younger women warrants additional investigation.

The role of evoked potentials in anoxic-ischemic coma and severe brain trauma

The early recognition of comatose patients with a hopeless prognosis-regardless of how aggressively they are managed-is of utmost importance. Median somatosensory evoked potentials supplement and enhance neurologic examination findings in anoxic-ischemic coma and severe brain trauma, and are useful as an early guide to outcome. The key finding is that bilateral absence of cortical evoked potentials, generated by thalamocortical tracts, reliably predicts unfavorable outcome in comatose patients after cardiac arrest, and correlates strongly with death or persistent vegetative state in severe brain trauma. The author studied 50 comatose patients with preserved brainstem function after cardiac arrest. All 23 patients with bilateral absence of cortical evoked potentials died without awakening. Neuropathologic study in seven patients disclosed widespread ischemic changes or frank cortical laminar necrosis. The remaining 27 patients with normal or delayed central conduction times had an uncertain prognosis because some died without awakening or entered a persistent vegetative state. The majority of patients with normal central conduction times had a good outcome, whereas a delay in central conduction times increased the likelihood of neurologic deficit or death. This report includes a systematic review of the literature concerning adults in anoxic-ischemic coma and severe brain trauma, in which somatosensory evoked potentials were used as an early guide to predict clinical outcome. Greater use of somatosensory evoked potentials in anoxic-ischemic coma and severe brain trauma would identify those patients unlikely to recover and would avoid costly medical care that is to no avail.

Drug therapy of sustained ventricular tachyarrhythmias. Is there still a role?

This article provides a review of the risks faced by patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) in the absence of a reversible or transient cause so that the goals of therapy can be clearly defined. The therapeutic approaches that have been proposed to achieve these goals are outlined and evidence comparing these various approaches to therapy is then summarized in order to propose an algorithm for the optimal use of antiarrhythmic drug therapies as primary therapy for selected VT/VF patients. Options for the ancillary uses of antiarrhythmic drug therapies in ICD patients are considered.

Disease-related syncope. Analysis of a community-based hospital registry

Syncope is characterized by sudden and transient loss of consciousness that follows a reduction or interruption of cerebral blood flow. The present study was designed to assess the prevalence of disease-related syncope in a wide sample of in-patients admitted for different diseases. A total of 16 809 patients (age range 18-99 years) were recruited from three hospitals in Florence in 1998. The community-based registry was reviewed to identify all patients suffering from complaints associated with syncope. Each disease-related syncope was matched with the number of patients suffering from that disease. Furthermore, each disease was expressed as a percentage of total cases included in the study. The odds ratio was calculated to determine the index of significant correlation between syncope and occasional diseases. Total syncopes were 775 (prevalence 4.46%), vasovagal syncopes were 336 (1.9% of total sample and 44% of total syncopes), and the disease-related syncopes were 439 (56% of total syncopes). We found a significant association between syncope and orthostatic hypotension, complete heart block, chronic cerebral disease, migraine, acute gastrointestinal haemorrhages and aortic stenosis. Furthermore, we found a significant association with acute gastrointestinal haemorrhage, which has not been described previously. Significant relationships emerged from our data which yield a new insight into the association between syncope and a wide range of systemic diseases.

Psychological functioning in children and adolescents undergoing radiofrequency catheter ablation

This study examined 38 patients (age 6-18 years) with recurrent cardiac arrhythmias who underwent radiofrequency catheter ablation of ectopic myocardial foci. Psychological functioning was assessed by the Pediatric Symptom Checklist, Short Mood and Feeling Questionnaire, Revised Children's Manifest Anxiety Scale, and Arrhythmia Anxiety Queries prior to ablation and at 3-month follow-up. The patients resembled a normal population without elevations in anxiety or depression. After ablation, the patients showed reductions in the "fear of their heart problem" and increases in "the things that they enjoy." The patients who underwent a curative ablation had better functioning than those who did not show improvement. Children appear to have the opportunity for an improved quality of life after ablation.

Variation of spectral power immediately prior to spontaneous onset of ventricular tachycardia/ventricular fibrillation in implantable cardioverter defibrillator patients

INTRODUCTION

Short-term heart rate variability (HRV) may change immediately before onset of a ventricular arrhythmia (ONSET).

METHODS AND RESULTS

Power spectrum analysis was performed on instantaneous heart rate (IHR; including all beats) and normal heart rate (NHR; excluding ectopics) curves obtained at equally spaced 0.5-second intervals using a cubic spline. The database consisted of 135 sets of 1,024 RR intervals leading to ventricular arrhythmia (VA) and controls from 78 patients. Total periodogram and time course of spectral power were obtained. Ten spectral bands of 0.1-Hz bandwidth (0 to 1 Hz) were analyzed. A simple threshold technique was retrospectively used to predict the onset of a VA. RR intervals that led to VA ONSET had significantly higher total spectral power than controls (P < 0.001 for both NHR and IHR for every band). Spectral power remained constant until 100 seconds before ONSET and then increased significantly in the time window immediately preceding ONSET (P < 0.02 compared with others). Using a simple threshold method, a predictive accuracy of 68%+/-1.4% was obtained with different window sizes. Using specific spectral bands, the predictive accuracy of VA ONSET could be improved to 76% for IHR and 71% for NHR (0.8- to 0.9-Hz band).

CONCLUSION

Our results suggest that a sustained higher power increase in NHR and IHR occurs during the course of 12.11+/-.57 minutes, followed by a sudden elevation in spectral power within 100 seconds of ONSET, and may be a precursor to ventricular tachycardia/ventricular fibrillation episodes.

Nuclear morphometry of the myocardial cells as a diagnostic tool in cases of sudden death due to coronary thrombosis

Sudden cardiac death due to underlying coronary artery thrombosis is one of the leading causes of death. However, in a significant percentage of individuals who died suddenly, no indication of myocardial infarction is found during post-mortem examination, especially when the time interval between appearance of symptoms and death is short. In the present study, we have evaluated certain nuclear morphometric parameters, such as, minimum, maximum, mean and standard deviation of perimeter and area in 20 individuals who died of coronary artery thrombosis, within 1 h from symptoms onset. Furthermore, the above parameters were compared with those of a control population of 20 individuals whose sudden death was caused by traffic accidents. Statistical elaboration of the results by means of t-test, Mann-Whitney (U-test) and analysis of covariance (adjusting for age), showed a statistically significant difference for all variables except for the minimum area. With stepwise discriminant analysis method, the mean perimeter was selected as the best predictor of cardiac death. Mean perimeter achieved a correct reclassification percentage (based on Fisher's linear discriminant function) of 92.5% (85% and 100% for cases and controls, respectively). Moreover, by applying the cut-off of 172 microns, we could identify the individuals who died suddenly because of coronary artery thrombosis with a specificity of 100% (sensitivity 85%, P < 0.001). Our results show that nuclear morphometry of the myocardial cells is a reliable diagnostic tool for the diagnosis of coronary thrombosis based lesion in cases of sudden death, even when methods trying to verify the presence of infarction fail to do so.

Cocaine increases the endothelial release of immunoreactive endothelin and its concentrations in human plasma and urine: reversal by coincubation with sigma-receptor antagonists

BACKGROUND

Cocaine-associated vascular events are not completely explained by adrenergic stimulation. The purposes of this study were to investigate whether vasoconstrictive endothelin-1 is released by cocaine and to elucidate the mechanisms involved.

METHODS AND RESULTS

Endothelin-1 was measured by radioimmunoassay and high-performance liquid chromatography (1) in the supernatant of porcine aortic endothelial cells after treatment with cocaine (10(-7) to 10(-4) mol/L) and a sigma-receptor antagonist, haloperidol (10(-6) mol/L) or ditolylguanidine (10(-5) mol/L) and (2) in plasma and urine of 12 cocaine-intoxicated patients and 13 healthy control subjects. Radioligand binding assays were performed on endothelial membrane preparations. In cell culture, cocaine significantly increased endothelin accumulation above baseline at 3 to 24 hours; endothelin release rates per hour increased dose-dependently, reaching a plateau of 175+/-23% of control at hour 4 to 5. Coincubation of cocaine with haloperidol or ditolylguanidine abolished or reduced cocaine-induced endothelin release. Endothelial membrane preparations specifically and displaceably bound the highly selective sigma-ligand [3H]ditolylguanidine (25x10(-9) mol/L), with 1400 binding sites estimated per cell. Endothelin-1 levels in plasma (22.7+/-5.6 versus 7.3+/-0.8 pmol/L) and urine (41.5+/-10.1 versus 12.7+/-3.8 pmol/L) of cocaine-intoxicated patients were significantly increased compared with control values.

CONCLUSIONS

The data suggest that cocaine increases the endothelin-1 release in vitro and in vivo. The cocaine-induced vasoconstriction/vasospasm may therefore be facilitated by the release of endothelin-1. Cocaine appears to be an exogenous stimulator at endothelial sigma-receptors. The endogenous ligands of this antiopioid system may prove to play a role in vasospastic angina, acute myocardial infarction, and sudden cardiac death.

Variation in the mineral content of commercially available bottled waters: implications for health and disease

PURPOSE

Although the annual consumption of bottled water in North America is 12.7 gallons per capita, little is known about the potential health effects of these waters. We reviewed the amounts of major minerals found in commercially available bottled waters, the recommended daily allowances for these minerals, and their beneficial and harmful effects.

METHODS

We obtained the mineral content of various commercially available bottled waters in North America and Europe from The Pocket Guide to Bottled Water. We then conducted a Medline search to identify articles examining the beneficial and harmful effects of magnesium, sodium, and calcium.

RESULTS

Great variation exists in the mineral content of commercially available bottled waters. Among the bottled waters that we reviewed, the magnesium content ranges from 0 to 126 mg per liter, the sodium content ranges from 0 to 1,200 mg per liter, and the calcium content ranges from 0 to 546 mg per liter. Epidemiologic and clinical studies suggest that magnesium may reduce the frequency of sudden death, that sodium contributes to the occurrence of hypertension, and that calcium may help prevent osteoporosis.

CONCLUSION

The ideal bottled water should be rich in magnesium and calcium and have a low sodium content. Because there is great variation in the mineral content of commercially available bottled waters, the actual mineral content of bottled water should be considered when selecting one for consumption.

Autonomic modulation of QT intervals in post-myocardial infarction patients with and without ventricular fibrillation

The autonomic nervous system plays an important role in the genesis of sudden cardiac death. The aim of this study was to evaluate spatial autonomic QT interval modulation at the myocardial level. Circadian patterns of QT intervals and heart rate variability (HRV) components and their hourly linear correlations were determined by Holter recordings in 15 healthy subjects (controls), in 15 post-myocardial infarction (MI) patients resuscitated from ventricular fibrillation (VF) (VF group), and in 15 matched infarction patients without a history of arrhythmia events (MI group). QT intervals were measured in modified leads V1 and V5 individually at same stable heart rates during each hour and related to hourly measures of HRV. Controls had highly significant correlations between QT intervals and the high-frequency component of HRV (parasympathetic modulation), and between QT intervals and low- to high-frequency ratio (sympathetic modulation) uniformly in both leads (r from 0.62 to 0.81, p <0.001). The MI group had impaired sympathetic modulation in V5 (r = 0.34, p = NS), but had uniform and exaggerated sensitivity to parasympathetic modulation. In the VF group the QT difference between V1 and V5 leads correlated with parasympathetic modulation (r = 0.401, p <0.05) and sympathetic modulation (r = 0.446, p <0.05). Thus, normal subjects exhibit spatially uniform autonomic QT modulation. Myocardial damage can result in abolished, exaggerated, or regionally discordant QT modulation, and this may generate arrhythmic vulnerability.