High-frequency ventricular ectopy can increase sympathetic neural activity in humans

Functional-Molecular Mechanisms of Sympathetic-Parasympathetic Dysfunction in PVC-Induced Cardiomyopathy Revealed by Dual Stressor PVC-Exercise Challenge

BACKGROUND

The significance of autonomic dysfunction in premature ventricular contraction-induced cardiomyopathy (PVC-CM) remain unknown.

OBJECTIVES

Utilizing a novel "dual stressor" provocative challenge combining exercise with premature ventricular contraction (PVCs), the authors characterized the functional and molecular mechanisms of cardiac autonomic (cardiac autonomic nervous system) remodeling in a PVC-CM animal model.

METHODS

In 15 canines (8 experimental, 7 sham), we implanted pacemakers and neurotelemetry devices and subjected animals to 12 weeks of bigeminal PVCs to induce PVC-CM. Sympathetic nerve activity (SNA), vagal nerve activity (VNA), and heart rate were continuously recorded before, during, and after treadmill exercise challenge with and without PVCs, at baseline and after development of PVC-CM. Western blot and enzyme-linked immunosorbent assay were used to evaluate molecular markers of neural remodeling.

RESULTS

Exercise triggered an increase in both SNA and VNA followed by late VNA withdrawal. With PVCs, the degree of exercise-induced SNA augmentation was magnified, whereas late VNA withdrawal became blunted. After PVC-CM development, SNA was increased at rest but failed to adequately augment during exercise, especially with PVCs, coupled with impaired VNA and heart rate recovery after exercise. In the remodeled cardiac autonomic nervous system, there was widespread sympathetic hyperinnervation and elevated transcardiac norepinephrine levels but unchanged parasympathetic innervation, indicating sympathetic overload. However, cardiac nerve growth factor was paradoxically downregulated, suggesting an antineurotrophic counteradaptive response to PVC-triggered sympathetic overload.

CONCLUSIONS

Sympathetic overload, sympathetic dysfunction, and parasympathetic dysfunction in PVC-CM are unmasked by combined exercise and PVC challenge. Reduced cardiac neurotrophic factor might underlie the mechanisms of this dysfunction. Neuromodulation therapies to restore autonomic function could constitute a novel therapeutic approach for PVC-CM.

Propensity-score matched comparison of renal and neurohormonal effects of catheter ablation for frequent premature ventricular contractions in patients with and without systolic dysfunction

Background

Catheter ablation (CA) for premature ventricular contractions (PVCs) restores cardiac and renal functions in patients with reduced left ventricular ejection fraction (LVEF); however, its effects on preserved EF remain unelucidated.

Methods

The study cohort comprised 246 patients with a PVC burden of >10% on Holter electrocardiography. Using propensity matching, we compared the changes in B-type natriuretic peptide (BNP) levels and estimated glomerular filtration rate (eGFR) in patients who underwent CA or did not.

Results

Postoperative BNP levels were decreased significantly in the CA group, regardless of the degree of LVEF, whereas there was no change in those of the non-CA group. Among patients who underwent CA, BNP levels decreased from 44.1 to 33.0 pg/mL in those with LVEF ≥50% (p = .002) and from 141.0 to 87.9 pg/mL in those with LVEF <50% (p < .001). Regarding eGFR, postoperative eGFR was significantly improved in the CA group of patients with LVEF ≥50% (from 71.4 to 74.7 mL/min/1.73 m2, p = .006), whereas it decreased in the non-CA group. A similar trend was observed in the group with a reduced LVEF. Adjusted for propensity score matching, there was a significant decrease in the BNP level and recovery of eGFR after CA in patients with LVEF >50%.

Conclusions

This study showed that CA for frequent PVCs decreases BNP levels and increases eGFR even in patients with preserved LVEF.

Predictors and possible mechanisms of premature ventricular contraction induced cardiomyopathy

Premature ventricular complexes (PVCs) are encountered frequently in clinical practice. While PVCs may have various causes, a small number of individuals with PVCs develop cardiomyopathy in the absence of other potential etiologies. When correctly identified, patients with PVC-incuded cardiomyopathy can have dramatic improvement of their cardiomyopathy with treatment of their PVCs. In this focused review, we discuss potential predictors of PVC-induced cardiomyopathy, including PVC frequency, PVC characteristics, and modifiable patient risk factors. We also review some proposed mechanisms of PVC-induced cardiomyopathy and conclude with future directions for research and clinical practice.

A Novel ECG-Based Deep Learning Algorithm to Predict Cardiomyopathy in Patients With Premature Ventricular Complexes

BACKGROUND

Premature ventricular complexes (PVCs) are prevalent and, although often benign, they may lead to PVC-induced cardiomyopathy. We created a deep-learning algorithm to predict left ventricular ejection fraction (LVEF) reduction in patients with PVCs from a 12-lead electrocardiogram (ECG).

OBJECTIVES

This study aims to assess a deep-learning model to predict cardiomyopathy among patients with PVCs.

METHODS

We used electronic medical records from 5 hospitals and identified ECGs from adults with documented PVCs. Internal training and testing were performed at one hospital. External validation was performed with the others. The primary outcome was first diagnosis of LVEF ≤40% within 6 months. The dataset included 383,514 ECGs, of which 14,241 remained for analysis. We analyzed area under the receiver operating curves and explainability plots for representative patients, algorithm prediction, PVC burden, and demographics in a multivariable Cox model to assess independent predictors for cardiomyopathy.

RESULTS

Among the 14,241-patient cohort (age 67.6 ± 14.8 years; female 43.8%; White 29.5%, Black 8.6%, Hispanic 6.5%, Asian 2.2%), 22.9% experienced reductions in LVEF to ≤40% within 6 months. The model predicted reductions in LVEF to ≤40% with area under the receiver operating curve of 0.79 (95% CI: 0.77-0.81). The gradient weighted class activation map explainability framework highlighted the sinus rhythm QRS complex-ST segment. In patients who underwent successful PVC ablation there was a post-ablation improvement in LVEF with resolution of cardiomyopathy in most (89%) patients.

CONCLUSIONS

Deep-learning on the 12-lead ECG alone can accurately predict new-onset cardiomyopathy in patients with PVCs independent of PVC burden. Model prediction performed well across sex and race, relying on the QRS complex/ST-segment in sinus rhythm, not PVC morphology.

Risk Factors and Heart Rate Variability Associated with Left Ventricular Enlargement in Patients with Frequent Premature Ventricular Contractions

INTRODUCTION

Premature ventricular contractions (PVCs) were now well recognized to carry the risk of inducing left ventricular (LV) enlargement and were closely related to the cardiac autonomic nervous activity quantified by heart rate variability (HRV) analysis. However, the relationship between LV enlargement and HRV in patients with frequent PVCs is still unclear. This study aimed to investigate the risk factors and HRV for LV enlargement in patients with frequent PVCs.

METHODS

Patients with frequent PVCs (n = 571), whose PVC burden counts >10,000/24 h or PVC burden >10%, were recruited. Patients were divided into LV enlargement group (n = 161), defined as female left ventricular end-diastolic diameter (LVEDD) >49.8 mm or male LVEDD >54.2 mm, and LV normal group (n = 410). Two groups were compared on their clinical, electrocardiographic, and HRV parameters. Logistic regression analysis was used to predict the risk factors of LV enlargement in patients with frequent PVCs. The parameters of echocardiography, Holter monitoring, and HRV were collected after ablation.

RESULTS

There were significant differences between the patients with left enlargement and with normal LV structure, in terms of sex, left ventricular ejection fraction (LVEF), level of N-terminal pro-brain natriuretic peptide (NT-proBNP), 24-h PVC burden, with nonsustained ventricular tachycardia, multifocal PVCs, QRS duration of PVC, and values of very low-frequency power of HRV parameter (all p < 0.05). Multivariate analysis showed that female gender (odds ratio [OR] = 2.753, p < 0.001), increased NT-proBNP (OR = 1.011, p = 0.022), increased LVEF (OR = 0.292, p < 0.001), increased 24-h PVC burden (OR = 1.594, p < 0.001), increased standard deviation of all NN intervals (SDNN) (OR = 1.100, p = 0.003), increased the proportion of consecutive NN intervals that differ by more than 50 ms (pNN50) (OR = 0.844, p = 0.026) were predictors for LV enlargement in patients with frequent PVCs. 84.4% (54/64) of patients with LV enlargement at baseline had normalized their LV structure after ablation. The values of SDNN, standard deviation of the averages of NN intervals in all 5-min segments, the square root of the mean of the sum of the squares of differences between adjacent NN intervals, pNN50, low-frequency power (LF), LF/high-frequency power ratio of patients were significantly decreased after ablation (all p < 0.05).

CONCLUSION

Female gender, increased level of NT-proBNP, lower LVEF, higher PVC burden, increased sympathetic parameters SDNN, and reduced parasympathetic parameters pNN50 were the independent risk factors of LV enlargement in patients with frequent PVCs. LV enlargement induced by PVCs can be reversible after PVC elimination by ablation. The activities of sympathetic and parasympathetic were reduced after ablation.

The Burden of Ventricular Premature Complex Is Associated With Cardiovascular Mortality

Background

Ventricular premature complex (VPC) is one of the most common ventricular arrhythmias. The presence of VPC is associated with an increased risk of heart failure (HF).

Method

We designed a single-center, retrospective, and large population-based cohort to clarify the role of VPC burden in long-term prognosis in Taiwan. We analyzed the database from the National Cheng Kung University Hospital-Electronic Medical Record (NCKUH-EMR) and NCKUH-Holter (NCKUH-Holter). A total of 19,527 patients who underwent 24-h Holter ECG monitoring due to palpitation, syncope, and clinical suspicion of arrhythmias were enrolled in this study.

Results

The clinical outcome of interests involved 5.65% noncardiovascular death and 1.53% cardiovascular-specific deaths between 2011 and 2018. Multivariate Cox regression analysis, Fine and Gray's competing risk model, and propensity score matching demonstrated that both moderate (1,000–10,000/day) and high (>10,000/day) VPC burdens contributed to cardiovascular death in comparison with a low VPC burden (<1,000/day).

Conclusion

A higher VPC burden via Holter ECG is an independent risk factor of cardiovascular mortality.

Atrial fibrillation in patients with systolic heart failure: pathophysiology mechanisms and management

Heart failure (HF) and atrial fibrillation (AF) demonstrate a constantly increasing prevalence during the 21^st century worldwide, as a result of the aging population and the successful interventions of the clinical practice in the deterioration of adverse cardiovascular outcomes. HF and AF share common risk factors and pathophysiological mechanisms, creating the base of a constant interrelation. AF impairs systolic and diastolic function, resulting in the increasing incidence of HF, whereas the structural and neurohormonal changes in HF with preserved or reduced ejection fraction increase the possibility of the AF development. The temporal relationship of the development of either condition affects the diagnostic algorithms, the prognosis and the ideal therapeutic strategy that leads to euvolaemia, management of non-cardiovascular comorbidities, control of heart rate or restoration of sinus rate, ventricular synchronization, prevention of sudden death, stroke, embolism, or major bleeding and maintenance of a sustainable quality of life. The indicated treatment for the concomitant HF and AF includes rate or/and rhythm control as well as thromboembolism prophylaxis, while the progress in the understanding of their pathophysiological interdependence and the introduction of the genetic profiling, create new paths in the diagnosis, the prognosis and the prevention of these diseases.

Clinical and translational insights on premature ventricular contractions and PVC-induced cardiomyopathy

The medical community's understanding of the consequences of premature ventricular contractions (PVCs) and PVC-induced cardiomyopathy has been derived mostly from observational and large population-based studies. Due to the difficulty of predicting the development of PVC-cardiomyopathy, the acute and chronic cardiac effects of PVCs and the mechanism of PVC-cardiomyopathy have been derived from pre-clinical studies with large animal models. Recently, these studies have described myocardial substrates that could potentially increase morbidity and mortality in patients with frequent PVCs and PVC-cardiomyopathy. In this paper, we provide an up-to-date comprehensive review of these pre-clinical and clinical studies.

Advancing Research on the Complex Interrelations Between Atrial Fibrillation and Heart Failure: A Report From a US National Heart, Lung, and Blood Institute Virtual Workshop

The interrelationships between atrial fibrillation (AF) and heart failure (HF) are complex and poorly understood, yet the number of patients with AF and HF continues to increase worldwide. Thus, there is a need for initiatives that prioritize research on the intersection between AF and HF. This article summarizes the proceedings of a virtual workshop convened by the US National Heart, Lung, and Blood Institute to identify important research opportunities in AF and HF. Key knowledge gaps were reviewed and research priorities were proposed for characterizing the pathophysiological overlap and deleterious interactions between AF and HF; preventing HF in people with AF; preventing AF in individuals with HF; and addressing symptom burden and health status outcomes in AF and HF. These research priorities will hopefully help inform, encourage, and stimulate innovative, cost-efficient, and transformative studies to enhance the outcomes of patients with AF and HF.

Arrhythmia-Induced Cardiomyopathy: JACC State-of-the-Art Review

Arrhythmias coexist in patients with heart failure (HF) and left ventricular (LV) dysfunction. Tachycardias, atrial fibrillation, and premature ventricular contractions are known to trigger a reversible dilated cardiomyopathy referred as arrhythmia-induced cardiomyopathy (AiCM). It remains unclear why some patients are more prone to develop AiCM despite similar arrhythmia burdens. The challenge is to determine whether arrhythmias are fully, partially, or at all responsible for an observed LV dysfunction. AiCM should be suspected in patients with mean heart rate >100 beats/min, atrial fibrillation, and/or premature ventricular contractions burden ≥10%. Reversal of cardiomyopathy by elimination of the arrhythmia confirms AiCM. Therapeutic choice depends on the culprit arrhythmia, patient comorbidities, and preferences. Following recovery of LV function, patients require continued follow-up if an abnormal myocardial substrate is present. Appropriate diagnosis and treatment of AiCM is likely to improve quality of life and clinical outcomes and to reduce hospital admission and health care spending.

Persistent Proarrhythmic Neural Remodeling Despite Recovery From Premature Ventricular Contraction-Induced Cardiomyopathy

BACKGROUND

The presence and significance of neural remodeling in premature ventricular contraction-induced cardiomyopathy (PVC-CM) remain unknown.

OBJECTIVES

This study aimed to characterize cardiac sympathovagal balance and proarrhythmia in a canine model of PVC-CM.

METHODS

In 12 canines, the investigators implanted epicardial pacemakers and radiotelemetry units to record cardiac rhythm and nerve activity (NA) from the left stellate ganglion (SNA), left cardiac vagus (VNA), and arterial blood pressure. Bigeminal PVCs (200 ms coupling) were applied for 12 weeks to induce PVC-CM in 7 animals then disabled for 4 weeks to allow complete recovery of left ventricular ejection fraction (LVEF), versus 5 sham controls.

RESULTS

After 12 weeks of PVCs, LVEF (p = 0.006) and dP/dT (p = 0.007) decreased. Resting SNA (p = 0.002) and VNA (p = 0.04), exercise SNA (p = 0.01), SNA response to evoked PVCs (p = 0.005), heart rate (HR) at rest (p = 0.003), and exercise (p < 0.04) increased, whereas HR variability (HRV) decreased (p = 0.009). There was increased spontaneous atrial (p = 0.02) and ventricular arrhythmias (p = 0.03) in PVC-CM. Increased SNA preceded both atrial (p = 0.0003) and ventricular (p = 0.009) arrhythmia onset. Clonidine suppressed SNA and abolished all arrhythmias. After disabling PVC for 4 weeks, LVEF (p = 0.01), dP/dT (p = 0.047), and resting VNA (p = 0.03) recovered to baseline levels. However, SNA, resting HR, HRV, and atrial (p = 0.03) and ventricular (p = 0.03) proarrhythmia persisted. There was sympathetic hyperinnervation in stellate ganglia (p = 0.02) but not ventricles (p = 0.2) of PVC-CM and recovered animals versus sham controls.

CONCLUSIONS

Neural remodeling in PVC-CM is characterized by extracardiac sympathetic hyperinnervation and sympathetic neural hyperactivity that persists despite normalization of LVEF. The altered cardiac sympathovagal balance is an important trigger and substrate for atrial and ventricular proarrhythmia.

Premature ventricular contractions activate vagal afferents and alter autonomic tone: implications for premature ventricular contraction-induced cardiomyopathy

Mechanisms behind development of premature ventricular contraction (PVC)-induced cardiomyopathy remain unclear. PVCs may adversely modulate the autonomic nervous system to promote development of heart failure. Afferent neurons in the inferior vagal (nodose) ganglia transduce cardiac activity and modulate parasympathetic output. Effects of PVCs on cardiac parasympathetic efferent and vagal afferent neurotransmission are unknown. The purpose of this study was to evaluate effects of PVCs on vagal afferent neurotransmission and compare these effects with a known powerful autonomic modulator, myocardial ischemia. In 16 pigs, effects of variably coupled PVCs on heart rate variability (HRV) and vagal afferent neurotransmission were evaluated. Direct nodose neuronal recordings were obtained in vivo, and cardiac-related afferent neurons were identified based on their response to cardiovascular interventions, including ventricular chemical and mechanical stimuli, left anterior descending (LAD) coronary artery occlusion, and variably coupled PVCs. On HRV analysis before versus after PVCs, parasympathetic tone decreased (normalized high frequency: 83.6 ± 2.8 to 72.5 ± 5.3; P < 0.05). PVCs had a powerful impact on activity of cardiac-related afferent neurons, altering activity of 51% of neurons versus 31% for LAD occlusion (P < 0.05 vs. LAD occlusion and all other cardiac interventions). Both chemosensitive and mechanosensitive neurons were activated by PVCs, and their activity remained elevated even after cessation of PVCs. Cardiac afferent neural responses to PVCs were greater than any other intervention, including ischemia of similar duration. These data suggest that even brief periods of PVCs powerfully modulate vagal afferent neurotransmission, reflexly decreasing parasympathetic efferent tone.NEW & NOTEWORTHY Premature ventricular contractions (PVCs) are common in many patients and, at an increased burden, are known to cause heart failure. This study determined that PVCs powerfully modulate cardiac vagal afferent neurotransmission (exerting even greater effects than ventricular ischemia) and reduce parasympathetic efferent outflow to the heart. PVCs activated both mechano- and chemosensory neurons in the nodose ganglia. These peripheral neurons demonstrated adaptation in response to PVCs. This study provides additional data on the potential role of the autonomic nervous system in PVC-induced cardiomyopathy.

Autonomic dysfunction: Diagnosis and management

The autonomic nervous system is designed to maintain physiologic homeostasis. Its widespread connections make it vulnerable to disruption by many disease processes including primary etiologies such as Parkinson's disease, multiple system atrophy, dementia with Lewy bodies, and pure autonomic failure and secondary etiologies such as diabetes mellitus, amyloidosis, and immune-mediated illnesses. The result is numerous symptoms involving the cardiovascular, gastrointestinal, and urogenital systems. Patients with autonomic dysfunction (AUD) often have peripheral and/or cardiac denervation leading to impairment of the baroreflex, which is known to play a major role in determining hemodynamic outcome during orthostatic stress and low cardiac output states. Heart rate and plasma norepinephrine responses to orthostatic stress are helpful in diagnosing impairment of the baroreflex in patients with orthostatic hypotension (OH) and suspected AUD. Similarly, cardiac sympathetic denervation diagnosed with MIBG scintigraphy or ¹⁸F-DA PET scanning has also been shown to be helpful in distinguishing preganglionic from postganglionic involvement and in diagnosing early stages of neurodegenerative diseases. In this chapter, we review the causes of AUD, the pathophysiology and resulting cardiovascular manifestations with emphasis on the diagnosis and treatment of OH.

Premature Ventricular Contraction Coupling Interval Variability Destabilizes Cardiac Neuronal and Electrophysiological Control: Insights From Simultaneous Cardioneural Mapping

BACKGROUND

Variability in premature ventricular contraction (PVC) coupling interval (CI) increases the risk of cardiomyopathy and sudden death. The autonomic nervous system regulates cardiac electrical and mechanical indices, and its dysregulation plays an important role in cardiac disease pathogenesis. The impact of PVCs on the intrinsic cardiac nervous system, a neural network on the heart, remains unknown. The objective was to determine the effect of PVCs and CI on intrinsic cardiac nervous system function in generating cardiac neuronal and electric instability using a novel cardioneural mapping approach.

METHODS AND RESULTS

In a porcine model (n=8), neuronal activity was recorded from a ventricular ganglion using a microelectrode array, and cardiac electrophysiological mapping was performed. Neurons were functionally classified based on their response to afferent and efferent cardiovascular stimuli, with neurons that responded to both defined as convergent (local reflex processors). Dynamic changes in neuronal activity were then evaluated in response to right ventricular outflow tract PVCs with fixed short, fixed long, and variable CI. PVC delivery elicited a greater neuronal response than all other stimuli (P<0.001). Compared with fixed short and long CI, PVCs with variable CI had a greater impact on neuronal response (P<0.05 versus short CI), particularly on convergent neurons (P<0.05), as well as neurons receiving sympathetic (P<0.05) and parasympathetic input (P<0.05). The greatest cardiac electric instability was also observed after variable (short) CI PVCs.

CONCLUSIONS

Variable CI PVCs affect critical populations of intrinsic cardiac nervous system neurons and alter cardiac repolarization. These changes may be critical for arrhythmogenesis and remodeling, leading to cardiomyopathy.

Premature Ventricular Complex Ablation in Structural Heart Disease

Frequent premature ventricular complexes (PVCs) in patients with underlying structural heart disease, particular after myocardial infarction, can predict increased mortality. Use of antiarrhythmic medications to suppress PVCs in this setting can result in a further increase in mortality. High PVC burdens in patients with structural heart disease can cause or worsen cardiomyopathy and successful elimination of PVCs with catheter ablation can improve or, in some cases normalize, cardiac function. PVCs may also trigger more malignant ventricular arrhythmias, particularly in patients with previous myocardial infarction, and when identified can be mapped and ablated.

Assessment of the effects of frequent ventricular extrasystoles on the left ventricle using speckle tracking echocardiography in apparently normal hearts

Objective:

Impairment in left ventricular (LV) function due to excessive ventricular extrasystoles (VESs) occurs during long-time follow-up. Speckle tracking echocardiography (STE) has been shown to be superior to conventional methods for evaluating cardiac functions. We aimed to use STE for early detection of LV dysfunction in patients with apparently normal hearts who have frequent VESs.

Methods:

Fifty-five patients with frequent VESs were identified according to the Lown classification (Grade 2; unifocal more than 30 times in 1 h). Subjects aged 22-60 years with frequent VESs that had been detected for at least 1 year were included in the study according to the inclusion criteria. Forty-five subjects with similar demographic characteristics, but without VESs, were included as the control group. All participants were evaluated by STE.

Results:

Fifty-five patients with frequent VESs (mean age 47 years, range 22-60 years; 42.2% male) and 45 control subjects (mean age 46 years, range 22–60 years; 37.8% male) were enrolled in the study. Global LV longitudinal strain (GLS) was decreased in patients with frequent VESs (-18.41±3.37 and -21.82±2.43; p<0.001). In addition, global LV circumferential strain was decreased in patients with frequent VESs (-16.83±6.06, -20.51±6.02; p<0.001). The frequency and exposure time of VESs were negatively correlated with GLS (r=-0.398, p<0.001; r=-0.191, p=0.001, respectively).

Conclusion:

STE revealed that LV functions were decreased in patients with VESs. This deterioration increased with the frequency and exposure time of VESs. Impairment of LV function due to excessive VESs occurs during long-time follow-up. STE may be used for early detection of LV dysfunction.

Device-based autonomic modulation in arrhythmia patients: the role of vagal nerve stimulation

OPINION STATEMENT

Vagal nerve stimulation (VNS) has shown promise as an adjunctive therapy for management of cardiac arrhythmias by targeting the cardiac parasympathetic nervous system. VNS has been evaluated in the setting of ischemia-driven ventricular arrhythmias and atrial arrhythmias, as well as a treatment option for heart failure. As better understanding of the complexities of the cardiac autonomic nervous system is obtained, vagal nerve stimulation will likely become a powerful tool in the current cardiovascular therapeutic armamentarium.

Coupling interval dispersion and body mass index are independent predictors of idiopathic premature ventricular complex-induced cardiomyopathy

INTRODUCTION

Patients with frequent premature ventricular complexes (PVCs) might be at risk for the developing or exacerbation of left ventricular (LV) dysfunction. However, some patients with a high-PVC burden do not develop cardiomyopathy, while other patients with low-PVC burden can develop cardiomyopathy. The purpose of this study was to evaluate the positive predictors of idiopathic PVCs-induced cardiomyopathy.

METHODS AND RESULTS

We investigated 214 patients undergoing successful ablation of PVCs who had no other causes of cardiomyopathy. We divided the study cohort into 2 groups: ejection fraction (EF) ≥ 50% (normal LV) and EF < 50% (LV dysfunction). We analyzed the clinical characteristics, including the electrocardiogram and findings at electrophysiology study. Among these patients, 51 (24%) had reduced LVEF and 163 (76%) had normal LV function. Patients with LV dysfunction had significantly longer coupling interval (CI) dispersion (maximum-CI-minimum-CI) and had significantly higher PVC burden compared to those with normal LV function (CI-dispersion: 115 ± 25 milliseconds vs. 94 ± 19 milliseconds; P < 0.001; PVC burden: 19% vs. 15%; P = 0.04). Furthermore, patients with LV dysfunction had significantly higher body mass index (BMI) compared to those with normal LV function (BMI > 30 kg/m(2) ; 37% vs. 13%; P = 0.001). Logistic regression analysis showed that CI-dispersion, PVC burden, and BMI (>30 kg/m(2) ) are independent predictors of PVC-induced cardiomyopathy.

CONCLUSIONS

In addition to the PVC burden, the CI-dispersion and BMI are associated with PVC-induced cardiomyopathy.

Deterioration of the circadian variation of heart rate variability in Brugada syndrome may contribute to the pathogenesis of ventricular fibrillation

AIMS

Abnormal sympathetic innervation triggers ventricular fibrillation (VF). We examined the circadian variation of autonomic nervous system and its relevance to risk stratification of VF in patients with Brugada syndrome (Brs).

METHODS

We enrolled 12 male Brs patients with documented VF (Brs-S; mean age, 42±4 years), 17 without documented VF (Brs-N; mean age 48±4 years), and 16 age- and gender-matched controls. The clinical data, 12-lead electrocardiography (ECG), signal-averaged ECG, electrophysiological study (EPS), and heart rate variability from 24h Holter ECG were compared between the groups.

RESULTS

The low frequency components (LF) in Brs-S and Brs-N and high frequency components (HF) in Brs-S patients were significantly lower than in the controls (409.8±128.6ms(2), 329.5±108ms(2) vs. 945.3±111.3ms(2); 135.1±73.8ms(2) vs. 391.8±63.9ms(2), respectively). The circadian variation of the LF and LF/HF decreased in the Brs patients, the standard deviation (SD) of LF/HF (<2.5) and SD of LF (<400ms(2)) had sufficiently high sensitivity (96.6%) and specificity (92.9%) for the diagnosis of Brs. Most of the Brs-S patients (83.3%) were located under the line formed by the SD/mean of HF=SD/mean of LF in the scatter plots.

CONCLUSION

Lack of the circadian variation of autonomic function occurs in Brs, and this may contribute to the pathogenesis of VF.

Periodic limb movements during sleep and cardiac arrhythmia in older men (MrOS sleep)

STUDY OBJECTIVES

To determine if periodic limb movements during sleep (PLMS) are associated with nocturnal cardiac arrhythmia.

METHODS

2,793 community-dwelling older men underwent polysomnography with measurement of limb movements and EKG. Logistic regression assessed association of periodic limb movement index and periodic limb movement arousal index with arrhythmia including atrial fibrillation and non-sustained ventricular tachycardia detected by polysomnography. Models were adjusted for age, race, cardiovascular risk factors, and clinic site. Secondary analyses were subset to men without calcium channel/β-adrenergic medication usage, and stratified by congestive heart failure or myocardial infarction history.

RESULTS

In the overall cohort, periodic limb movement index, and periodic limb movement arousal index were not associated with ventricular or atrial arrhythmia after considering potential confounders. In men not taking calcium channel/β-blocking medication, increased adjusted odds of non-sustained ventricular tachycardia were observed for periodic limb movement index (OR = 1.30 per SD increase; 95% CI 1.00, 1.68) and periodic limb movement arousal index (OR = 1.29 per SD increase; 95% CI 1.03, 1.62). In men with CHF or MI, there was a suggested association of atrial fibrillation with periodic limb movement index (OR = 1.29, 95% CI 0.96, 1.73 per SD increase; p = 0.09) or periodic limb movement arousal index (OR = 1.21, 95% CI 0.94, 1.57 per SD increase; p = 0.14), although results were not statistically significant.

CONCLUSIONS

There is not an association between PLMS and cardiac arrhythmia in all older men but in subsets of men, particularly those with structural heart disease and not on calcium channel or β-adrenergic medication, cardiac arrhythmia does associate with PLMS.

A nonsynonymous polymorphism in semaphorin 3A as a risk factor for human unexplained cardiac arrest with documented ventricular fibrillation

Unexplained cardiac arrest (UCA) with documented ventricular fibrillation (VF) is a major cause of sudden cardiac death. Abnormal sympathetic innervations have been shown to be a trigger of ventricular fibrillation. Further, adequate expression of SEMA3A was reported to be critical for normal patterning of cardiac sympathetic innervation. We investigated the relevance of the semaphorin 3A (SEMA3A) gene located at chromosome 5 in the etiology of UCA. Eighty-three Japanese patients diagnosed with UCA and 2,958 healthy controls from two different geographic regions in Japan were enrolled. A nonsynonymous polymorphism (I334V, rs138694505A>G) in exon 10 of the SEMA3A gene identified through resequencing was significantly associated with UCA (combined P = 0.0004, OR 3.08, 95%CI 1.67-5.7). Overall, 15.7% of UCA patients carried the risk genotype G, whereas only 5.6% did in controls. In patients with SEMA3A(I334V), VF predominantly occurred at rest during the night. They showed sinus bradycardia, and their RR intervals on the 12-lead electrocardiography tended to be longer than those in patients without SEMA3A(I334V) (1031±111 ms versus 932±182 ms, P = 0.039). Immunofluorescence staining of cardiac biopsy specimens revealed that sympathetic nerves, which are absent in the subendocardial layer in normal hearts, extended to the subendocardial layer only in patients with SEMA3A(I334V). Functional analyses revealed that the axon-repelling and axon-collapsing activities of mutant SEMA3A(I334V) genes were significantly weaker than those of wild-type SEMA3A genes. A high incidence of SEMA3A(I334V) in UCA patients and inappropriate innervation patterning in their hearts implicate involvement of the SEMA3A gene in the pathogenesis of UCA.

Recruitment pattern of sympathetic muscle neurons during premature ventricular contractions in heart failure patients and controls

Premature ventricular contractions (PVC) elicit larger bursts of multiunit muscle sympathetic nerve activity (MSNA), reflecting the ability to increase postganglionic axonal recruitment. We tested the hypothesis that chronic heart failure (CHF) limits the ability to recruit postganglionic sympathetic neurons as a response to PVC due to the excessive sympathetic activation in these patients. Sympathetic neurograms of sufficient signal-to-noise ratio were obtained from six CHF patients and from six similarly aged control individuals. Action potentials (APs) were extracted from the multiunit sympathetic neurograms during sinus rhythm bursts and during the post-PVC bursts. These APs were classified on the basis of the frequency per second, the content per burst, and the peak-to-peak amplitude, which formed the basis of binning the APs into active clusters. Compared with controls, CHF had higher APs per burst and higher number of active clusters per sinus rhythm burst (P < 0.05). Compared with sinus rhythm bursts, both groups increased AP frequency and the number of active clusters in the post-PVC burst (P < 0.05). However, compared with controls, the increase in burst integral, AP frequency, and APs per burst during the post-PVC burst was less in CHF patients. Nonetheless, the PVC-induced increase in active clusters per burst was similar between the groups. Thus, these CHF patients retained the ability to recruit larger APs but had a diminished ability to increase overall AP content.

Atrial bigeminy results in decreased left ventricular function: an insight into the mechanism of PVC-induced cardiomyopathy

BACKGROUND

Premature ventricular complexes have been recently recognized as a reversible cause of cardiomyopathy. The purpose of this study was to determine if premature complexes independent of "dyssynchrony" resulted in increased left ventricular (LV) dimensions and decreased LV function.

METHODS

Ten mongrel dogs underwent the implantation of a pacemaker and were randomized to a control group (n = 5) or a paced group (n = 5). In the paced group, the pacemaker was connected to two endocardial atrial leads, one inserted into the atrial port and the other one into the ventricular port with an atrioventricular delay adjusted to ensure the presence of coupled pacing simulating atrial bigeminy with conducted beats in the absence of aberrancy. Echocardiographic parameters of LV size (LV end-diastolic diameter [LV-EDD], LV end-systolic diameter [LV-ESD]), and LV ejection fraction (LVEF) were measured at baseline and after 4 weeks of monitoring (control group) or pacing (paced group).

RESULTS

In the control group, LV size decreased with no significant changes in LVEF: 55% at baseline versus 70% at 4 weeks (P = 0.23). In the paced group, LV-EDD decreased with no significant change in LV-ESD. Unlike the control group, LVEF decreased significantly from 69 ± 9% at baseline to 32 ± 22% after 4 weeks of pacing (P = 0.05).

CONCLUSION

We have shown that 4 weeks of coupled pacing simulating atrial bigeminy significantly reduced LV function. Our findings suggest that premature complexes independent of ventricular dyssynchrony might lead to the development of cardiomyopathy.

Role of adenosine A2A receptor signaling in the nicotine-evoked attenuation of reflex cardiac sympathetic control

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1-16μg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100μg/kg i.v.) dose-dependently reduced BRS(SNP) in contrast to no effect on BRS(PE). BRS(SNP) was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS(SNP) were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS(SNP) was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A(2A) antagonist), or VUF5574 (A(3) antagonist). In contrast, BRS(SNP) was preserved after blockade of A(1) (DPCPX) or A(2B) (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS(SNP) depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A(2A) receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms.