Body Mass Index as a Predictor of Sudden Cardiac Death and Usefulness of the Electrocardiogram for Risk Stratification

Obesity and sudden cardiac death: Prevalence, pathogenesis, prevention and intervention

Obesity and sudden cardiac death (SCD) share common risk factors. Obesity, in and of itself, can result in the development of SCD. Numerous epidemiologic and clinical studies have demonstrated the close relationships between obesity and SCD, however, the underlying mechanisms remain incompletely understood. Various evidences support the significance of excess adiposity in determining the risk of SCD, including anatomical remodeling, electrical remodeling, metabolic dysfunction, autonomic imbalance. Weight reduction has improved obesity related comorbidities, and reversed abnormal cardiac remodeling. Indeed, it is still unknown whether weight loss contributes to decreased risk of SCD. Further high-quality, prospective trials are needed to strengthen our understanding on weight management and SCD.

Obesity in young sudden cardiac death: Rates, clinical features, and insights into people with body mass index >50kg/m2

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55.0% of young sudden cardiac death (SCD) patients in Victoria, Australia are obese.

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This obesity prevalence exceeds that in the age-matched general Australian population, with all classes of obesity over-represented in our SCD cohort.

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Patients with BMI>50 kg/m² represented 8.5% of young SCD. Almost two thirds of patients with BMI>50 kg/m² died from left ventricular hypertrophy, with fewer than 10% dying from coronary disease.

Objective

To contextualize obesity rates in young sudden cardiac death (SCD) against the age-matched national population, and identify clinical and pathologic features in WHO class II and III obesity.

Methods

A prospective state-wide out-of-hospital cardiac arrest registry included all SCDs in Victoria, Australia from 2019–2021. Body mass indices (BMIs) of patients 18-50 years were compared to age-referenced general population. Characteristics of SCD patients with WHO Class II obesity (BMI ≥30kg/m²) and non-obesity (BMI<30kg/m²) were compared. Clinical characteristics of people with BMI>50kg/m² were assessed.

Results

504 patients were included. Obesity was strongly over-represented in young SCD compared to the age-matched general population (55.0% vs 28.7%, p<0.0001). Obese SCD patients more frequently had hypertension, diabetes and obstructive sleep apnoea (p<0.0001, p=0.009 and p=0.001 respectively), ventricular fibrillation as their arrest rhythm (p=0.008) and left ventricular hypertrophy (LVH) (p<0.0001). Obese patients were less likely to have toxicology positive for illicit substances (22.0% vs 32.6%, p=0.008) or history of alcohol abuse (18.8% vs 26.9%, p=0.030). Patients with BMI>50 kg/m² represented 8.5% of young SCD. LVH (n=26, 60.5%) was their predominant cause of death and only 10 (9.3%) patients died from coronary disease.

Conclusion

Over half of young Australian SCD patients are obese, with all obesity classes over-represented compared to the general population. Obese patients had more cardiac risk factors. Almost two thirds of patients with BMI>50 kg/m² died from LVH, with fewer than 10% dying from coronary disease.

The Impact of Obesity on Sudden Cardiac Death Risk

PURPOSE OF REVIEW

We aimed to describe the epidemiology of sudden cardiac death (SCD) in the obese, elaborating on the potential pathophysiological mechanisms linking obesity, SCD, and the outcomes in SCD survivors, as well as looking into the intriguing "obesity paradox" in these patients.

RECENT FINDINGS

Several studies show increased mortality in patients with BMI > 30 kg/m² admitted to the hospital following SCD. At the same time, other studies have implied that the "obesity paradox," described in various cardiovascular conditions, applies to patients admitted after SCD, showing lower mortality in the obese compared to normal weight and underweight patients. We found a significant body of evidence to support that while obesity increases the risk for SCD, the outcomes of obese patients post SCD are better. These findings should not be interpreted as supporting weight gain, as it is always better to prevent the "disaster" from happening than to improve your chances of surviving it. Obesity is shown to be significantly associated with increased risk for SCD; however, there is a growing body of evidence, supporting the "obesity paradox" in the survival of SCD victims. Prospectively, well-designed studies are needed to confirm these findings.

Cutoff value for hypertrophic heart weight in the Japanese population

BACKGROUND

Cardiac hypertrophy is a clinical risk factor for cardiovascular death (CVD) frequently recorded in autopsy reports, but the diagnostic criteria for the condition have not been clearly-established for autopsy. This study aimed to estimate the cutoff value for hypertrophic heart weight that can efficiently assist the postmortem diagnosis of CVD.

METHODS

We analyzed accumulated autopsy data from 3534 individuals aged 0-101 years.

RESULTS

We found that heart weight increased linearly with a person's age until 20 years, after which it remained stable. The mean heart weight in CVD cases was 473 g in men and 379 g in women. The mean heart weight in non-CVD cases was 385 g in men and 320 g in women. Receiver operating characteristic curve analysis for CVD assessment revealed that the cutoff value of heart weight was 407 g (odds ratio of 4.2) in men and 327 g (2.6) in women, and that of heart weight/body height was 2.38 g/cm (4.0) in men and 2.15 g/cm (2.6) in women, respectively. Overall, heart weight was a more useful predictor of CVD in men than in women. In logistic regression analysis, the predictive power of heart weight for CVD was higher than that of body mass index in both sexes.

CONCLUSION

Thus, the criteria for hypertrophic heart weight are practical and useful for autopsy recordings, and it can be helpful for postmortem diagnosis of CVD. Our report is the first to reveal the cutoff value for hypertrophic heart weight in the Japanese population.

Effect of Cardiorespiratory Fitness on Risk of Sudden Cardiac Death in Overweight/Obese Men Aged 42 to 60 Years

The purpose of this study was to examine the subject and combined associations of cardiorespiratory fitness (fitness) and body mass index (BMI) with the risk of sudden cardiac death (SCD) in middle-aged men. This prospective study was based on a population sample of 2,357 men aged 42 to 60 years, who were followed up in the Kuopio Ischemic Heart Disease cohort study. Fitness was directly measured by peak oxygen uptake (VO_2peak) during progressive exercise testing to volitional fatigue. Participants were divided into 4 groups (fit-normal weight, unfit-normal weight, fit-overweight/obese, and unfit-overweight/obese) based on the median values of fitness and BMI. A total of 253 (10.7%) SCDs occurred during an average follow-up of 22 years. After adjusting for potential confounders, the hazard ratio (HR) and 95% confidence interval (CI) for SCD was 1.80 (95% CI 1.21 to 2.68) for BMI ≥30.0 kg/m² versus normal weight cohort, that is, BMI corresponding to 18.5 to 24.9 kg/m². However, these associations were no longer statistically significant after adjusting for VO_2peak (1.49, 95% CI 0.98 to 2.24). Compared with the lower levels of fitness, upper levels of fitness had a 39% lower risk of SCD (HR 0.61, 95% CI 0.40 to 0.92) after adjusting for potential confounders, including BMI. In the combined associations of fitness and BMI with the risk of SCD, unfit-overweight/obese men had 1.80 times (95% CI 1.06 to 3.06) increased risk of SCD, but fit-overweight/obese men were not at increased risk of SCD (HR 1.22, 95% CI 0.66 to 2.25) as compared with their fit-normal weight counterparts. In conclusion, both overweight/obesity and fitness were independently associated with the risk of SCD; however, fitness appears to attenuate the risk of SCD in overweight/obese men, suggesting that improving fitness may reduce the risk of SCD in this population.

Body mass index, abdominal fatness, and the risk of sudden cardiac death: a systematic review and dose-response meta-analysis of prospective studies

Although overweight and obesity are established risk factors for some types of heart disease including ischemic heart disease, heart failure and atrial fibrillation, less is known about the association between adiposity and sudden cardiac death. We conducted a systematic review and meta-analysis of prospective studies to clarify the association between adiposity and risk of sudden cardiac death. PubMed and Embase databases were searched up to July 20th 2017. Summary relative risks (RRs) and 95% confidence intervals (CIs) were calculated using random effects models. The summary RR was 1.16 (95% CI 1.05-1.28, I2 = 68%, n = 14) per 5 unit increment in BMI, and 1.82 (95% CI 1.61-2.07, I2 = 0%, n = 3) per 0.1 unit increase in waist-to-hip ratio, and 1.03 (95% CI 0.93-1.15, I2 = 0%, n = 2) per 10 cm increase in waist circumference. The heterogeneity in the analysis of BMI and sudden cardiac death persisted across most subgroup analyses. The association was stronger among studies with longer follow-up compared to short follow-up and was observed in the European and American studies, but not in the Asian studies. There was a J-shaped association between BMI and sudden cardiac death and the lowest risk was observed in the normal weight range, however, the increased risk with a low BMI was attenuated among studies with a longer duration of follow-up. This meta-analysis suggest an increased risk of sudden cardiac death with increasing BMI and waist-to-hip ratio, however, further studies with stratification for smoking status are needed of waist circumference, weight changes and adiposity at younger ages.

Body Mass Index and Sudden Cardiac Death in Japanese Patients After Acute Myocardial Infarction: Data From the JCAD Study and HIJAMI-II Registry

Background

Although an “obesity paradox” exists in patients after myocardial infarction, the association between obesity and the risk of sudden cardiac death (SCD) is limited. The aim of this study was to determine whether obesity is associated with an increased risk of SCD in Japanese survivors of acute myocardial infarction.

Methods and Results

Pooled data from 2 cohort studies in Japan, JCAD (Japanese Coronary Artery Disease) study and the Heart Institute of Japan Acute Myocardial Infarction‐II (HIJAMI‐II) registry, comprising of 6216 patients (mean age 65±11 years, 75.2% male) with acute myocardial infarction who were discharged alive, were studied. The patients were categorized into the following body mass index (BMI) groups at baseline according to the World Health Organization classification for Asian populations: BMI <18.5 kg/m² (n=335), 18.5 to 23 kg/m² (n=2371), 23 to 27.5 kg/m² (n=2823), and ≥27.5 kg/m² (n=687). The main outcomes were all‐cause mortality and SCD. During an average follow‐up period of 3.6±1.4 years, all‐cause mortality was 10.1%, and SCD was 1.2%. Patients with BMI <18.5 kg/m² had the highest rate of all‐cause mortality (adjusted hazard ratio, 1.61; 95% confidence interval, 1.20–2.16), but high BMI (≥27.5 kg/m²) was not associated with mortality compared with patients in the group with BMI ≥18.5 and <23 kg/m². However, the long‐term risk of SCD was increased in the group with BMI ≥27.5 kg/m² (adjusted hazard ratio, 2.97; 95% confidence interval, 1.24–7.15). Multivariate analysis revealed that BMI ≥27.5 kg/m² was associated with an increased risk of SCD (hazard ratio, 2.78; 95% confidence interval, 1.35–5.74).

Conclusions

Obesity (BMI ≥27.5 kg/m²) was associated with the risk of SCD in Japanese patients after myocardial infarction, although an obesity paradox was found for all‐cause mortality.

Does Sudden Unexplained Nocturnal Death Syndrome Remain the Autopsy-Negative Disorder: A Gross, Microscopic, and Molecular Autopsy Investigation in Southern China

OBJECTIVE

To look for previously unrecognized cardiac structural abnormalities and address the genetic cause for sudden unexplained nocturnal death syndrome (SUNDS).

METHODS

Data for 148 SUNDS victims and 444 controls (matched 1:3 on sex, race, and age of death within 1 year) were collected from Sun Yat-sen University from January 1, 1998, to December 31, 2014, to search morphological changes. An additional 17 patients with Brugada syndrome (BrS) collected from January 1, 2006, to December 31, 2014, served as a comparative disease cohort. Target-captured next-generation sequencing for 80 genes associated with arrhythmia/cardiomyopathy was performed in 44 SUNDS victims and 17 patients with BrS to characterize the molecular spectrum.

RESULTS

The SUNDS victims had slight but statistically significant increased heart weight and valve circumference compared with controls. Twelve of 44 SUNDS victims (SCN5A, SCN1B, CACNB2, CACNA1C, AKAP9, KCNQ1, KCNH2, KCNJ5, GATA4, NUP155, ABCC9) and 6 of 17 patients with BrS (SCN5A, CACNA1C; P>.05) carried rare variants in primary arrhythmia-susceptibility genes. Only 2 of 44 SUNDS cases compared with 5 of 17 patients with BrS hosted a rare variant in the most common BrS-causing gene, SCN5A (P=.01). Using the strict American College of Medical Genetics guideline-based definition, it was found that only 2 of 44 (KCNQ1) SUNDS and 3 of 17 (SCN5A) patients with BrS hosted a "(likely) pathogenic" variant. Fourteen of 44 SUNDS cases with cardiomyopathy-related variants had a subtle but significantly decreased circumference of cardiac valves, and tended to die on average 5 to 6 years younger compared with the remaining 30 cases (P=.02).

CONCLUSION

We present the first comprehensive autopsy evidence that SUNDS victims may have concealed cardiac morphological changes. SUNDS and BrS may result from different molecular pathological underpinnings. The distinct association between cardiomyopathy-related rare variants and SUNDS warrants further investigation.

Role of risk stratification and genetics in sudden cardiac death

Sudden cardiac death (SCD) is a major public health issue due to its increasing incidence in the general population and the difficulty in identifying high-risk individuals. Nearly 300 000 - 350 000 patients in the United States and 4-5 million patients in the world die annually from SCD. Coronary artery disease and advanced heart failure are the main etiology for SCD. Ischemia of any cause precipitates lethal arrhythmias, and ventricular tachycardia and ventricular fibrillation are the most common lethal arrhythmias precipitating SCD. Pulseless electrical activity, bradyarrhythmia, and electromechanical dissociation also result in SCD. Most SCDs occur outside of the hospital setting, so it is difficult to estimate the public burden, which results in overestimating the incidence of SCD. The insufficiency and limited predictive value of various indicators and criteria for SCD result in the increasing incidence. As a result, there is a need to develop better risk stratification criteria and find modifiable variables to decrease the incidence. Primary and secondary prevention and treatment of SCD need further research. This critical review is focused on the etiology, risk factors, prognostic factors, and importance of risk stratification of SCD.