Highlights
- Sarcomeric HCM (Sar+) is diagnosed significantly earlier (median age 38) and carries a higher burden of HCM-related mortality and life-years lost compared to nonsarcomeric HCM (Sar-).
- Nonsarcomeric HCM is more prevalent in older patients and is strongly associated with comorbidities such as hypertension and obesity, suggesting a different, potentially modifiable pathogenic pathway.
- Atrial fibrillation (AF) acts as a critical disease-modifier in both groups, significantly increasing the risk of systolic dysfunction, ventricular arrhythmias, and death.
- The impact of AF and left ventricular systolic dysfunction is more severe in Sar+ patients, justifying more aggressive surveillance and lower thresholds for advanced therapeutic interventions.
Background
Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease, characterized by unexplained left ventricular hypertrophy (LVH). For decades, the discovery of mutations in genes encoding the cardiac sarcomere (such as MYH7 and MYBPC3) provided a clear genetic etiology for approximately 30% to 50% of cases. However, a significant portion of the HCM population—often referred to as “genetically elusive” or nonsarcomeric—displays similar phenotypic hypertrophy without identifiable pathogenic variants.
Recent clinical practice guidelines emphasize the importance of genetic testing for risk stratification and family screening. Yet, the long-term divergence in disease trajectory between sarcomeric and nonsarcomeric HCM has remained partially obscured by the heterogeneity of the disease. While prior studies suggested that sarcomere-positive patients face worse outcomes, the influence of modern management, the presence of metabolic comorbidities, and the specific causes of death require the large-scale, longitudinal granularity provided by multicenter registries like the Sarcomeric Human Cardiomyopathy registry (SHaRe).
Key Content
Demographic and Phenotypic Divergence
Evidence from the SHaRe registry, encompassing over 6,100 patients, highlights a stark contrast in the baseline characteristics of Sar+ and Sar- cohorts. Sarcomeric HCM typically presents in the fourth decade of life (median 38.1 years), whereas nonsarcomeric HCM is often diagnosed in the mid-fifties (median 54.3 years). This age gap of nearly 16 years suggests that sarcomeric mutations drive an earlier onset of myocardial remodeling.
Interestingly, the nonsarcomeric population shows a higher prevalence of metabolic syndrome components, including hypertension and obesity. This suggests that in the absence of a primary genetic driver, environmental and lifestyle factors may play a larger role in the phenotypic expression of LVH. Furthermore, Sar+ patients are less likely to present with left ventricular (LV) outflow tract obstruction compared to their Sar- counterparts, yet they exhibit a higher proportion of women, potentially reflecting differences in genetic penetrance or healthcare-seeking behavior.
Clinical Trajectories and Arrhythmic Burden
When adjusted for age, the biological aggression of sarcomeric HCM becomes more apparent. Sar+ patients experience a significantly higher burden of cardiovascular complications. The age-standardized incidence (ASI) ratios demonstrate that Sar+ patients are at a 28% higher risk for atrial fibrillation, a 31% higher risk for LV systolic dysfunction (defined as LVEF <50%), and a 37% higher risk for ventricular arrhythmias than those with nonsarcomeric disease.
These findings suggest that the presence of a sarcomere mutation predisposes the myocardium to greater electrical instability and more rapid progression toward heart failure. While the Sar- group is by no means "low risk," their complications often occur much later in life and are frequently concomitant with age-related cardiovascular decline.
Mortality Dynamics and Life-Years Lost
One of the most profound findings in recent longitudinal analyses is the distribution of mortality. While all-cause mortality rates appear similar between the two groups (10.4% vs. 9.4%), the *timing* and *cause* of death differ dramatically. Sar+ patients die at a significantly younger age—on average 7.8 years earlier than Sar- patients. Survival analysis models estimate that patients with sarcomeric HCM lose approximately 3.5 years of life between the ages of 44 and 85 specifically due to their condition.
Furthermore, sarcomeric HCM is associated with a 61% higher risk of HCM-related mortality (HR 1.61), which includes sudden cardiac death, heart failure-related death, and stroke. In contrast, mortality in the nonsarcomeric group is more often influenced by non-cardiac causes or general age-related comorbidities, highlighting that Sar+ disease is a more potent independent driver of premature death.
The Role of Atrial Fibrillation as a Disease Modifier
Atrial fibrillation (AF) emerged as the single most influential modifier of disease progression for both genotypes. The development of AF is not merely a marker of atrial stretch but a harbinger of clinical decline. In the SHaRe cohort, AF was associated with a 2.5-fold increase in the risk of LV systolic dysfunction and a 3-fold increase in ventricular arrhythmias.
Crucially, a genotype-interaction was observed: the impact of AF and LV dysfunction on adverse outcomes was nearly doubled in Sar+ patients compared to Sar- patients. This indicates that a “second hit” (like AF) to a myocardium already compromised by a sarcomeric mutation leads to a much steeper decline in clinical status, often resulting in severe heart failure or death.
Expert Commentary
The data from the SHaRe registry represent a paradigm shift in how we approach HCM risk stratification. Historically, clinical focus was placed primarily on the degree of hypertrophy and the presence of obstruction. We now understand that the genetic substrate is a fundamental determinant of the patient’s “biological clock.”
For clinicians, these findings necessitate a more vigilant surveillance strategy for Sar+ patients, even when they appear stable in their 30s and 40s. Because Sar+ patients are more sensitive to the deleterious effects of AF and systolic dysfunction, there is a strong argument for earlier intervention with rhythm control strategies and perhaps a lower threshold for ICD implantation or advanced heart failure therapies.
Conversely, for the nonsarcomeric population, the high prevalence of obesity and hypertension suggests that aggressive management of metabolic risk factors might slow the progression of hypertrophy or prevent the onset of AF. The pathogenesis of Sar- HCM may be polygenic or multi-factorial, meaning that lifestyle modifications could have a more significant impact on this group’s trajectory than in those with monogenic sarcomeric mutations.
Conclusion
Genotype is a powerful tool for refining the prognosis of Hypertrophic Cardiomyopathy. Sarcomeric HCM is characterized by an earlier clinical onset, a higher rate of HCM-specific complications, and significant life-years lost. Nonsarcomeric HCM, while manifesting later, is more deeply intertwined with modifiable metabolic factors. Future research must focus on whether genotype-specific therapies—such as mavacamten or gene-editing technologies—can specifically alter the aggressive trajectory of Sar+ disease, and whether intensive risk factor modification can mitigate the burden of disease in the genetically elusive population.
References
- Vissing CR, Axelsson Raja A, Helms AS, et al. Differences in Disease Trajectory, Comorbidities, and Mortality in Sarcomeric and Nonsarcomeric Hypertrophic Cardiomyopathy. Circulation. 2024;149(10):[Online Ahead of Print]. PMID: 41800474.
- Ho CY, et al. Genotype and Outcomes in Phenotype-Positive Hypertrophic Cardiomyopathy: A SHaRe Predictors Study. Circulation. 2018;138(14):1387-1398. PMID: 29748186.
- Ommen SR, et al. 2020 AHA/ACC Guideline for the Diagnosis and Treatment of Patients With Hypertrophic Cardiomyopathy. J Am Coll Cardiol. 2020;76(25):e159-e240. PMID: 33217350.
