Dynamic changes of left ventricular performance and left atrial volume induced by the mueller maneuver in healthy young adults and implications for obstructive sleep apnea, atrial fibrillation, and heart failure

[Valsalva and Müller maneuvers: who is who and what is what?]

The original Valsalva manoeuvre (VM) was described in detail by the Italian anatomist, physician and surgeon Antonio Maria Valsalva (1666-1723). The VM consists of a voluntary forced expiratory effort against a closed upper airway. It was used tradionally in otolaryngology for testing the openess of the eustachian tubes and expelling pus/fluid from the middle to the external ear. VM is associated with increased intrathoracic and -abdominal pressure and leads to hemodynamic changes. The use of VM for cardiovascular purposes was first described by Eduard Friedrich Weber, a German physiologist. The Müller manoeuvre (MM) represents the opposite of the VM by forced inspiration against a closed upper airway. Negative intrathoracic and abdominal pressure (ITP) with direct effects on cardiac function and hemodynamics can be generated by the MM. MM has also been used to simulate the hemodynamic effects of negative ITP in obstructive sleep apnea patients. The Müller manoeuvre was first described by the German anatomist and physician Johannes Müller (1801-1858).

Wireless and Battery-Free Sensor for Interstitial Fluid Pressure Monitoring

Congestive heart failure (CHF) is a fatal disease with progressive severity and no cure; the heart's inability to adequately pump blood leads to fluid accumulation and frequent hospital readmissions after initial treatments. Therefore, it is imperative to continuously monitor CHF patients during its early stages to slow its progression and enable timely medical interventions for optimal treatment. An increase in interstitial fluid pressure (IFP) is indicative of acute CHF exacerbation, making IFP a viable biomarker for predicting upcoming CHF if continuously monitored. In this paper, we present an inductor-capacitor (LC) sensor for subcutaneous wireless and continuous IFP monitoring. The sensor is composed of inexpensive planar copper coils defined by a simple craft cutter, which serves as both the inductor and capacitor. Because of its sensing mechanism, the sensor does not require batteries and can wirelessly transmit pressure information. The sensor has a low-profile form factor for subcutaneous implantation and can communicate with a readout device through 4 layers of skin (12.7 mm thick in total). With a soft silicone rubber as the dielectric material between the copper coils, the sensor demonstrates an average sensitivity as high as -8.03 MHz/mmHg during in vitro simulations.

Association Between Sleep Apnea Treatment and Health Care Resource Use in Patients With Atrial Fibrillation

BACKGROUND

Obstructive sleep apnea (OSA) contributes to the generation, recurrence, and perpetuation of atrial fibrillation, and it is associated with worse outcomes. Little is known about the economic impact of OSA therapy in atrial fibrillation. This retrospective cohort study assessed the impact of positive airway pressure (PAP) therapy adherence on health care resource use and costs in patients with OSA and atrial fibrillation.

METHODS AND RESULTS

Insurance claims data for ≥1 year before sleep testing and 2 years after device setup were linked with objective PAP therapy use data. PAP adherence was defined from an extension of the US Medicare 90-day definition. Inverse probability of treatment weighting was used to create covariate-balanced PAP adherence groups to mitigate confounding. Of 5867 patients (32% women; mean age, 62.7 years), 41% were adherent, 38% were intermediate, and 21% were nonadherent. Mean±SD number of all-cause emergency department visits (0.61±1.21 versus 0.77±1.55 [P=0.023] versus 0.95±1.90 [P<0.001]), all-cause hospitalizations (0.19±0.69 versus 0.24±0.72 [P=0.002] versus 0.34±1.16 [P<0.001]), and cardiac-related hospitalizations (0.06±0.26 versus 0.09±0.41 [P=0.023] versus 0.10±0.44 [P=0.004]) were significantly lower in adherent versus intermediate and nonadherent patients, as were all-cause inpatient costs ($2200±$8054 versus $3274±$12 065 [P=0.002] versus $4483±$16 499 [P<0.001]). All-cause emergency department costs were significantly lower in adherent and intermediate versus nonadherent patients ($499±$1229 and $563±$1292 versus $691±$1652 [P<0.001 and P=0.002], respectively).

CONCLUSIONS

These data suggest clinical and economic benefits of PAP therapy in patients with concomitant OSA and atrial fibrillation. This supports the value of diagnosing and managing OSA and highlights the need for strategies to enhance PAP adherence in this population.

Mueller maneuver attenuates left atrial phasic volumes and myocardial strain in healthy younger adults

The left atrium (LA) is a key, but incompletely understood, modulator of left ventricular (LV) filling. Inspiratory negative intrathoracic pressure swings alter cardiac loading conditions, which may impact LA function. We studied acute effects of static inspiratory efforts on LA chamber function, LA myocardial strain, and LV diastolic filling. We included healthy adults (10 males/9 females, 24 ± 4 yr) and used Mueller maneuvers to reduce intrathoracic pressure to -30 cmH2O for 15 s. Over six repeated trials, we used echocardiography to acquire LA- and LV-focused two-dimensional (2-D) images, and mitral Doppler inflow and annular tissue velocity spectra. Images were analyzed for LA and LV chamber volumes, tissue relaxation velocities, transmitral filling velocities, and speckle tracking-derived LA longitudinal strain. Repeated measures were made at baseline, early Mueller, late Mueller, then early release, and late release. In the late Mueller compared with baseline, LV stroke volume decreased by -10 ± 4 mL (P < 0.05) and then returned to baseline upon release; this occurred with a -11 ± 9 mL (P < 0.05) end-diastolic volume reduction. Early diastolic LV filling was attenuated, reflected by decreased tissue relaxation velocity (-2 ± 2 cm/s, P < 0.05), E-wave filling velocity (-13 ± 14 cm/s, P < 0.05), and LA passive emptying volume (-5 ± 5 mL, P < 0.05), each returning to baseline with release. LA maximal volume decreased (-5 ± 5 mL, P < 0.05) during the Mueller maneuver, but increased relative to baseline following release (+4 ± 5 mL, P < 0.05), whereas LA peak positive longitudinal strain decreased (-6 ± 6%, P < 0.05) and then returned to baseline. Attenuated LA and in turn, LV filling may contribute to acute stroke volume reductions experienced during forceful inspiratory efforts.NEW & NOTEWORTHY In healthy younger adults, the Mueller maneuver transiently reduces left atrial filling and passive emptying during the reservoir and conduit phases, respectively. Corresponding reductions are seen in left atrial reservoir and conduit phase longitudinal myocardial strain and strain rate. However, left atrial pump phase active function and mechanics are largely preserved compared with baseline. Rapid changes in LA chamber volumes and myocardial strain with recurrent forceful inspiratory efforts and relaxation may reflect acute LA stress.

Breathless nights and heart flutters: Understanding the relationship between obstructive sleep apnea and atrial fibrillation

There is an extraordinary and increasing global burden of atrial fibrillation (AF) and obstructive sleep apnea (OSA), two conditions that frequently accompany one another and that share underlying risk factors. Whether a causal pathophysiologic relationship connects OSA to the development and/or progression of AF, or whether shared risk factors promote both conditions, is unproven. With increasing recognition of the importance of controlling AF-related risk factors, numerous observational studies now highlight the potential benefits of OSA treatment in AF-related outcomes. Physicians are regularly faced with caring for this important and increasing population of patients despite a paucity of clinical guidance on the topic. Here, we review the clinical epidemiology and pathophysiology of AF and OSA with a focus on key clinical studies and major outstanding questions that should be addressed in future studies.

Does Adult Spinal Deformity Affect Cardiac Function? A Prospective Perioperative Study

STUDY DESIGN

Prospective comparative study.

OBJECTIVE

The objective of this study was to investigate perioperative cardiac function using echocardiography in patients undergoing surgery for the adult spinal deformity (ASD).

SUMMARY OF BACKGROUND DATA

Corrective surgery for ASD has increased, especially in older persons. However, perioperative complication rates remain high in ASD surgery, including cardiopulmonary complications.

MATERIALS AND METHODS

This study included patients with ASD who underwent surgery between May 2016 and April 2018. A cardiologist performed all echocardiography imaging preoperatively and 2 weeks postoperatively. Left ventricular contractility was measured using left ventricular ejection fraction (LVEF), and right ventricular contractility was measured using tricuspid annular plane systolic excursion (TAPSE) and tricuspid annular peak systolic velocity (S'). Spinopelvic radiographic parameters, the apices of thoracic kyphosis and lumbar lordosis, and the inflection point where the vertebral curvature changes from kyphosis to lordosis were also measured. Differences between preoperative and postoperative measurements for continuous variables were analyzed using a paired Student t test. Differences in continuous and categorical variables between two independent groups were analyzed using an unpaired Student t test and Fisher exact test, respectively. Multivariate logistic regression analyses were performed to detect influential factors.

RESULTS

Sixty-one patients were included [12 males and 49 females; average age, 64.0 (22-84) yr]. LVEF, TAPSE, and S', respectively changed from 64.4%, 24.9 mm, and 14.3 cm/s to 65.4%, 25 mm, and 15 cm/s postoperatively with no significance. However, in LVEF<59.3% (average-1 SD), TAPSE<17 mm, and S'<11.8 cm/s cases, respectively, these increased significantly from 55.7%, 17.9 mm, and 10.5 cm/s to 60.9%, 21.4 mm, and 14.2 cm/s postoperatively ( P =0.036, 0.029, and 0.022, respectively). The LVEF<59.3% group showed a significantly lower inflection point level (1.5 vs. 2.9) preoperatively ( P =0.007). The S'<11.8 cm/s group showed significantly larger thoracic kyphosis (28.3° vs. 19.4°) preoperatively ( P =0.013).

CONCLUSIONS

Perioperative cardiac function did not deteriorate after surgery in patients with ASD. In those with lower cardiac function preoperatively, there were significant improvements noted postoperatively. The preoperative inflection point level was significantly lower in the lower LVEF group. Preoperative thoracic kyphosis was significantly larger in the lower tricuspid annular peak systolic velocity group.

Disturbed Sleep is Not Good for the Heart: A Narrative Review

Sleep-related breathing disorders, including obstructive sleep apnea (OSA) and central sleep apnea (CSA), have a major impact on cardiovascular function. It has shown an association with hypertension, coronary artery disease, cardiac arrhythmias, sudden cardiac death, and congestive heart failure (CHF). This review focuses on highlighting the relationship between sleep apnea and CHF. We discuss the underlying pathophysiology, which involves the mechanical, neurohormonal, and inflammatory mechanisms; in addition, the similarities and differentiating clinical features of OSA in patients with CHF and without CHF. We have also discussed several treatment strategies, including weight loss, continuous positive airway pressure (CPAP), supplemental oxygen therapy, theophylline, acetazolamide, mandibular advancement device, and hypoglossal nerve stimulation (HGNS). We conclude that since there are several overlapping clinical features in patients with OSA with Heart Failure (HF) and without HF, early detection and treatment are crucial to decrease the risk of HF, coronary artery disease, and stroke.

Risk factors for new-onset atrial fibrillation during critical illness: A Delphi study

Background

New-onset atrial fibrillation (NOAF) is common during critical illness and is associated with poor outcomes. Many risk factors for NOAF during critical illness have been identified, overlapping with risk factors for atrial fibrillation in patients in community settings. To develop interventions to prevent NOAF during critical illness, modifiable risk factors must be identified. These have not been studied in detail and it is not clear which variables warrant further study.

Methods

We undertook an international three-round Delphi process using an expert panel to identify important predictors of NOAF risk during critical illness.

Results

Of 22 experts invited, 12 agreed to participate. Participants were located in Europe, North America and South America and shared 110 publications on the subject of atrial fibrillation. All 12 completed the three Delphi rounds. Potentially modifiable risk factors identified include 15 intervention-related variables.

Conclusions

We present the results of the first Delphi process to identify important predictors of NOAF risk during critical illness. These results support further research into modifiable risk factors including optimal plasma electrolyte concentrations, rates of change of these electrolytes, fluid balance, choice of vasoactive medications and the use of preventative medications in high-risk patients. We also hope our findings will aid the development of predictive models for NOAF.

Vagal milieu or electrophysiologic substrate? The link between atrial fibrillation and obstructive sleep apnea

Atrial fibrillation is the most common cardiac arrhythmia with its prevalence expected to increase to 12.1 million people in the United States by 2030. Chronic underlying conditions that affect the heart and lungs predispose patients to develop atrial fibrillation. Obstructive sleep apnea is strongly associated with atrial fibrillation. Several pathophysiological mechanisms have been proposed to elucidate this relationship which includes electrophysiological substrate modification and the contribution of the autonomic nervous system. In this comprehensive review, we highlight important relationships and plausible causality between obstructive sleep apnea and atrial fibrillation which will improve our understanding in the evaluation, management, and prevention of atrial fibrillation. This is the most updated comprehensive review of the relationship between obstructive sleep apnea and atrial fibrillation.

Association between obstructive sleep apnea and cardiovascular diseases

Obstructive sleep apnea (OSA) is a common respiratory disorder characterized by partial obstruction of upper respiratory tract and repetitive cessation of breathing during sleep. The etiology behind OSA is associated with the occurrence of intermittent hypoxemia, recurrent arousals and intrathoracic pressure swings. These contributing factors may turn on various signaling mechanisms including elevated sympathetic tone, oxidative stress, inflammation, endothelial dysfunction, cardiovascular variability, abnormal coagulation and metabolic defect ( e.g., insulin resistance, leptin resistance and altered hepatic metabolism). Given its close tie with major cardiovascular risk factors, OSA is commonly linked to the pathogenesis of a wide array of cardiovascular diseases (CVDs) including hypertension, heart failure, arrhythmias, coronary artery disease, stroke, cerebrovascular disease and pulmonary hypertension (PH). The current standard treatment for OSA using adequate nasal continuous positive airway pressure (CPAP) confers a significant reduction in cardiovascular morbidity. Nonetheless, despite the availability of effective therapy, patients with CVDs are still deemed highly vulnerable to OSA and related adverse clinical outcomes. A better understanding of the etiology of OSA along with early diagnosis should be essential for this undertreated disorder in the clinical setting.

QTc prolongation is associated with severe desaturations in stroke patients with sleep apnea

Background

Obstructive sleep apnea (OSA) is associated with vascular diseases from which stroke and sudden cardiac death are the most significant ones. It is known that disturbances of the autonomic nervous system and electrocardiographic changes are seen in patients with a previous cerebrovascular event. However, the pathophysiological cascade between breathing cessations, autonomic regulation, and cardiovascular events is not fully understood.

Methods

We aimed to investigate the acute effect of desaturation on repolarisation in OSA patients with a previous stroke. We retrospectively analysed heart-rate corrected QT (QTc) intervals before, within, and after 975 desaturations in OSA patients with a stroke history and at least moderate sleep apnea (apnea–hypopnea index ≥ 15 events/h, n = 18). For the control population (n = 18), QTc intervals related to 1070 desaturation were analysed. Desaturations were assigned to groups according to their length and duration. Groupwise comparisons and regression analyses were further executed to investigate the influence of desaturation features on repolarization.

Results

In the stroke population the QTc prolonged at least 11 ms during 27.1% of desaturations, and over 20 ms during 12.2% of desaturations. QTc was significantly prolonged during longer (> 30 s, p < 0.04) and deeper (> 7%, p < 0.03) desaturations. Less severe desaturations didn't influence QTc. In median, QTc prolonged 7.5 ms during > 45 s desaturations and 7.4 ms during > 9% deep desaturations. In the control population, QTc prolongation was observed but to a significantly lesser extent than in stroke patients. In addition, desaturation duration was found to be an independent predictor of QTc prolongation (β = 0.08, p < 0.001) among all study patients.

Conclusions

We demonstrated that longer (> 30 s) and deeper (> 7%) desaturations prolong QTc in patients with stroke history. A significant proportion of desaturations produced clinically relevant QTc prolongation. As it is known that a long QTc interval is associated with lethal arrhythmias, this finding might in part explain the pathophysiological sequelae of cardiovascular mortality in OSA patients with a history of stroke.

Impact of sleep apnea and treatments on cardiovascular disease

Cardiovascular diseases (CVDs) are the leading causes of mortality worldwide, accounting for nearly 18 million deaths per year. Among other considerations, treating CVDs requires better understanding their risk factors. Sleep-disordered breathing, especially obstructive sleep apnea (OSA), is a likely contributor to several CVDs. We review key epidemiological data that addresses the link between OSA and cardiovascular outcomes such as hypertension, atrial fibrillation (AF), stroke, atherosclerosis, and heart failure (HF), and proposed pathophysiological mechanisms underlying this association. There are several biological pathways linking OSA and an increased propensity to cardiovascular diseases, and we discuss the evidence on the benefits of treatments of OSA on the prevalence of cardiovascular complications.

Speckle tracking echocardiography in heart failure development and progression in patients with apneas

Obstructive (OA) and central apneas (CA) are highly prevalent breathing disorders that have a negative impact on cardiac structure and function; while OA promote the development of progressive cardiac alterations that can eventually lead to heart failure (HF), CA are more prevalent once HF ensues. Therefore, the early identification of the deleterious effects of apneas on cardiac function, and the possibility to detect an initial cardiac dysfunction in patients with apneas become relevant. Speckle tracking echocardiography (STE) imaging has become increasingly recognized as a method for the early detection of diastolic and systolic dysfunction, by the evaluation of left atrial and left and right ventricular global longitudinal strain, respectively. A growing body of evidence is available on the alterations of STE in OA, while very little is known with regard to CA. In this review, we discuss the current knowledge and gap of evidence concerning apnea-related STE alterations in the development and progression of HF.

Pharmacological inhibition of acetylcholine-regulated potassium current (IK,ACh) prevents atrial arrhythmogenic changes in a rat model of repetitive obstructive respiratory events

Background

In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase atrial fibrillation (AF) susceptibility by cholinergic activation.

Objective

To investigate short-term atrial electrophysiological consequences of obstructive respiratory events, simulated by intermittent negative upper airway pressure (INAP), and the role of atrial acetylcholine-regulated potassium current (I_K,ACh) activated by the M₂ receptor.

Methods

In sedated (2% isoflurane), spontaneously breathing rats, INAP was applied noninvasively by a negative pressure device for 1 minute, followed by a resting period of 4 minutes. INAP was applied repeatedly throughout 70 minutes, followed by a 2-hour recovery period. Atrial effective refractory period (AERP) and AF inducibility were determined throughout the protocol. To study INAP-induced I_K,ACh activation, protein levels of protein kinase C (PKC_Ɛ) were determined in membrane and cytosolic fractions of left atrial (LA) tissue by Western blotting. Moreover, an I_K,ACh inhibitor (XAF-1407: 1 mg/kg) and a muscarinic receptor inhibitor (atropine: 1 μg/kg) were investigated.

Results

In vehicle-treated rats, repetitive INAP shortened AERP (37 ± 3 ms vs baseline 44 ± 3 ms; P = .001) and increased LA membrane PKC_Ɛ content relative to cytosolic levels. Upon INAP recovery, ratio of PKC_Ɛ membrane to cytosol content normalized and INAP-induced AERP shortening reversed. Both XAF-1407 and atropine increased baseline AERP (control vs XAF-1407: 61 ± 4 ms; P > .001 and control vs atropine: 58 ± 3 ms; P = .011) and abolished INAP-associated AERP shortening.

Conclusion

Short-term simulated OSA is associated with a progressive, but transient, AERP shortening and a PKC_Ɛ translocation to LA membrane. Pharmacological I_K,ACh and muscarinic receptor inhibition prevented transient INAP-induced AERP shortening, suggesting an involvement of I_K,ACh in the transient arrhythmogenic AF substrate in OSA.

Obstructive sleep apnea and cardiovascular comorbidity: common pathophysiological mechanisms to cardiovascular disease

Obstructive sleep apnea (OSA) is associated with many cardiovascular and metabolic diseases. Sleep apnea causes intermittent hypoxemia, chest pressure fluctuations and a reaction from the cerebral cortex in the form of a short awakening during sleep (EEG-activation). The consequences of pathological pathways are studied in experimental models involving cell cultures, animals, and healthy volunteers. At present, the negative impact of intermittent hypoxemia on a variety of pathophysiological disorders of the heart and blood vessels (vascular tone fluctuations, thickening of the intimamedia complex in the vascular wall, direct damaging effect on the myocardium) has a great evidence base. Two other pathological components of OSA (pressure fluctuations and EEG-activation) can also affect cardiovascular system, mainly affecting the increase in blood pressure and changing cardiac hemodynamics. Although these reactions are considered separately in the review, with the development of sleep apnea they occur sequentially and are closely interrelated. As a result, these pathological pathways trigger further pathophysiological mechanisms acting on the heart and blood vessels. It is known that these include excessive sympathetic activation, inflammation, oxidative stress and metabolic dysregulation. In many respects being links of one process, these mechanisms can trigger damage to the vascular wall, contributing to the formation of atherosclerotic lesions. The accumulated data with varying degrees of reliability confirm the participation of OSA through these processes in the formation of cardiovascular disorders. There are factors limiting direct evidence of this interaction (sleep deprivation, causing similar changes, as well as the inability to share the contribution of other risk factors for cardiovascular diseases, in particular arterial hypertension, obesity, which are often associated with OSA). It is necessary to continue the study of processes that implement the pathological effect of OSA on the cardiovascular system.

Obstructive Sleep Apnea and Cardiac Arrhythmias: A Contemporary Review

Obstructive sleep apnea (OSA) is a highly prevalent disorder with a growing incidence worldwide that closely mirrors the global obesity epidemic. OSA is associated with enormous healthcare costs in addition to significant morbidity and mortality. Much of the morbidity and mortality related to OSA can be attributed to an increased burden of cardiovascular disease, including cardiac rhythm disorders. Awareness of the relationship between OSA and rhythm disorders is variable among physicians, a fact that can influence patient care, since the presence of OSA can influence the incidence, prevalence, and successful treatment of multiple rhythm disorders. Herein, we provide a review of this topic that is intentionally broad in scope, covering the relationship between OSA and rhythm disorders from epidemiology and pathophysiology to diagnosis and management, with a particular focus on the recognition of undiagnosed OSA in the general clinical population and the intimate relationship between OSA and atrial fibrillation.

Pathophysiological Mechanisms to Review Association of Atrial Fibrillation in Heart Failure With Obstructive Sleep Apnea

Sleep-disordered breathing (SDB) comprising obstructive sleep apnea (OSA) is found in more than half of patients with heart failure (HF) and may have negative impacts on cardiovascular function. Increased atherosclerotic cardiovascular disease and the development of coronary events and congestive heart failure are associated with OSA. It is associated with a substandard quality of life, increased hospitalizations, and a poor prognosis. Despite its association with severe cardiovascular morbidity and mortality, the condition is frequently underdiagnosed. The substantial clinical evidence has established OSA as an independent risk factor for bradyarrhythmias and tachyarrhythmias in the last decade. The mechanisms which lead to such arrhythmias are uncertain. In short, OSA patients have a significantly elevated risk of HF and atrial fibrillation (AF). The direct correlation between HF, SDB, and cardiac arrhythmias has been poorly understood. The purpose of this study is to get a better understanding of the relation between AF, OSA, and HF by focusing on the pathophysiological mechanisms underlying these conditions. Therefore, we searched for articles to support our association in PubMed and Google Scholar databases.

Ganglionated Plexi Ablation Suppresses Chronic Obstructive Sleep Apnea-Related Atrial Fibrillation by Inhibiting Cardiac Autonomic Hyperactivation

Background: Previous studies have reported that right pulmonary artery ganglionated plexi (GP) ablation could suppress the onset of atrial fibrillation (AF) associated with obstructive sleep apnea (OSA) within 1 h. Objective: This study aimed to investigate the effect of superior left GP (SLGP) ablation on AF in a chronic OSA canine model. Methods and Results: Fifteen beagles were randomly divided into three groups: control group (CTRL), OSA group (OSA), and OSA + GP ablation group (OSA + GP). All animals were intubated under general anesthesia, and ventilation-apnea events were subsequently repeated 4 h/day and 6 days/week for 12 weeks to establish a chronic OSA model. SLGP were ablated at the end of 8 weeks. SLGP ablation could attenuate the atrial effective refractory period (ERP) reduction and decrease ERP dispersion, the window of vulnerability, and AF inducibility. In addition, chronic OSA leads to left atrial (LA) enlargement, decreased left ventricular (LV) ejection fraction, glycogen deposition, increased necrosis, and myocardial fibrosis. SLGP ablation reduced the LA size and ameliorated LV dysfunction, while myocardial fibrosis could not be reversed. Additionally, SLGP ablation mainly reduced sympathovagal hyperactivity and post-apnea blood pressure and heart rate increases and decreased the expression of neural growth factor (NGF), tyrosine hydroxylase (TH), and choline acetyltransferase (CHAT) in the LA and SLGP. After SLGP ablation, the nucleotide-binding oligomerization domain (NOD)-like receptor signaling pathway, cholesterol metabolism pathway, and ferroptosis pathway were notably downregulated compared with OSA. Conclusions: SLGP ablation suppressed AF in a chronic OSA model by sympathovagal hyperactivity inhibition. However, there were no significant changes in myocardial fibrosis.

Arrhythmogenic mechanisms of acute obstructive respiratory events in a porcine model of drug-induced long QT

BACKGROUND

Obstructive sleep apnea is associated with increased risk of sudden cardiac death.

OBJECTIVE

The purpose of this study was to elucidate changes in ventricular repolarization and electromechanical interaction during obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) in pigs. We also investigated the effect of a reduced repolarization reserve in drug-induced long QT (LQT) following INAP-induced changes in ventricular repolarization.

METHODS

In sedated spontaneously breathing pigs, 75 seconds of INAP was applied by a negative pressure device connected to the endotracheal tube. Ventricular electromechanical coupling was determined by the electromechanical window (EMW) before (pre-INAP), during (INAP), and after INAP (post-INAP). Incidence rates of premature ventricular contractions (PVCs) were measured respectively. A drug-induced LQT was modeled by treating the pigs with the hERG1 blocker dofetilide (DOF).

RESULTS

Whereas QT interval increased during and decreased after INAP (pre-INAP: 273 ± 5 ms; INAP 281 ± 6 ms; post-INAP 254 ± 9 ms), EMW shortened progressively throughout INAP and post-INAP periods (pre-INAP 81 ± 4 ms; post-INAP 44 ± 7 ms). DOF shortened EMW at baseline. Throughout INAP, EMW decreased in a comparable fashion as before DOF (pre-INAP/+DOF 61 ± 7 ms; post-INAP/+DOF 14 ± 9 ms) but resulted in shorter absolute EMW levels. Short EMW levels were associated with increased occurrence of PVCs (pre-INAP 7 ± 2 ms vs post-INAP 26 ± 6 ms; P = .02), which were potentiated in DOF pigs (pre-INAP/+DOF 5 ± 2 ms vs post-INAP/+DOF 40 ± 8 ms; P = .006). Administration of atenolol prevented post-INAP EMW shortening and decreased occurrence of PVCs.

CONCLUSION

Transient dissociation of ventricular electromechanical coupling during simulated obstructive respiratory events creates a dynamic ventricular arrhythmogenic substrate, which is sympathetically mediated and aggravated by drug-induced LQT.

Left atrial volume indexed for height2 is a new sensitive marker for subclinical cardiac organ damage in female hypertensive patients

Left atrial enlargement (LAe) is a subclinical marker of hypertensive-mediated organ damage, which is important to identify in cardiovascular risk stratification. Recently, LA indexing for height was suggested as a more accurate marker of defining LAe. Our aim was to test the difference in LAe prevalence using body surface area (BSA) and height² definitions in an essential hypertensive population. A total of 441 essential hypertensive patients underwent complete clinical and echocardiographic evaluation. Left atrial volume (LAV), left ventricular morphology, and systolic-diastolic function were evaluated. LAe was twice as prevalent when defined using height² (LAe_h2) indexation rather than BSA (LAe_BSA) (51% vs. 23%, p < 0.001). LAe_h2, but not LAe_BSA, was more prevalent in females (p < 0.001). Males and females also differed in left ventricular hypertrophy (p = 0.046) and left ventricular diastolic dysfunction (LVDD) indexes (septal Em/Etdi: p = 0.009; lateral Em/Etdi: p = 0.003; mean Em/Etdi: p < 0.002). All patients presenting LAe_BSA also met the criteria for LAe_h2. According to the presence/absence of LAe, we created three groups (Norm = BSA-/h²-; DilH = BSA-/h²+; DilHB = BSA+/h²+). The female sex prevalence in the DilH group was higher than that in the other two groups (Norm: p < 0.001; DilHB: p = 0.036). LVH and mean and septal Em/Etdi increased from the Norm to the DilH group and from the DilH to the DilHB group (p < 0.05 for all comparisons). These results show that LAe_h2 identified twice as many patients as comparing LAe to LAe_BSA, but that both LAe_h2 and LAe_BSA definitions were associated with LVH and LVDD. In female patients, the LAe_h2 definition and its sex-specific threshold seem to be more sensitive than LAe_BSA in identifying chamber enlargement.

Low-Level Vagus Nerve Stimulation Reverses Obstructive Sleep Apnea-Related Atrial Fibrillation by Ameliorating Sympathetic Hyperactivity and Atrial Myocyte Injury

Background: Previous studies have proved that low-level vagus nerve stimulation (LLVS) could suppress acute obstructive sleep apnea (OSA), which is associated with atrial fibrillation (AF).

Objective: This study investigates the underlying electrophysiological, neural, and cardiomyocyte injury mechanisms on acute OSA-induced AF, examining whether LLVS can attenuate or reverse this remodeling.

Methods and Results: Eighteen mongrel dogs received endotracheal intubation under general anesthesia and were randomly divided into three groups: the OSA group (simulated OSA with clamping of the trachea cannula at the end of expiration for 2min followed ventilation 8min, lasting 6h, n=6), the OSA+LLVS group (simulated OSA plus LLVS, n=6), and a control group (sham clamping the trachea cannula without stimulation, n=6). In the OSA+LLVS group, the atrial effective refractory period was significantly lengthened while the sinus node recovery time and AF duration decreased after the 4th hour, and the expression level of Cx40 and Cx43 was significantly increased compared to the OSA group. Norepinephrine, TH, and ChAT were significantly decreased in the OSA+LLVS group compared with the OSA group. Mitochondrial swelling, cardiomyocyte apoptosis, and glycogen deposition, along with a higher concentration of TNF-α, IL-6 were observed in the OSA group, and the LLVS inhibited the structural remodeling and expression of inflammatory cytokines.

Conclusion: LLVS decreased the inducibility of AF partly by ameliorating sympathetic hyperactivity and atrial myocyte injury after acute OSA-induced AF.

Histopathological substrate of the atrial myocardium in the progression of obstructive sleep apnoea-related atrial fibrillation

BACKGROUND

Obstructive sleep apnoea (OSA) is closely related to atrial fibrillation (AF), and OSA-induced atrial structural remodelling is the basis of AF maintenance. However, the process of atrial structural remodelling during the progression of acute OSA to chronic OSA is still unclear.

OBJECTIVE

To investigate changes in the atrial myocardium in acute sleep apnoea (6 h) and chronic sleep apnoea (12 weeks) by echocardiography, atrial myocardium morphology analysis, PAS staining, TUNEL staining, Masson's trichrome staining and analyses of ultrastructural changes.

METHODS

Eighteen adult beagle dogs under general anaesthesia were used to establish an OSA model. The animals were divided into the control group, acute OSA group and chronic OSA group, and there were six animals in each group. Cardiac ultrasounds of dogs from the three groups were examined. Left and right atrial muscle tissues were taken for HE staining, PAS staining, TUNEL staining, Masson's trichrome staining and transmission electron microscopy.

RESULTS

In the acute OSA model, the left atrial diameter of the dogs began to increase 3 h after ventilation, and this difference was more obvious at 6 h. The morphology of the myocardial cells did not change significantly, but mitochondrial swelling was observed in some atrial myocytes at 3 h. In the chronic OSA model, the left atrial diameter gradually increased, the volume of the right and left atria increased, the glycogen and collagen volume fractions and apoptosis ratio were significantly increased in atrial myocytes, mitochondria swelling and lengthening occurred in some atrial myocytes, the matrix became lighter, the mitochondrial ridge density decreased and the myofilament arrangement was disordered. The disc was distorted and not continuous, and there was some cardiomyocyte necrosis.

CONCLUSION

With the prolongation of apnoea, the atrium gradually enlarges, myocardial cells become disordered, glycogen aggregates, the number of necrotic cells increases, fibrosis worsens, mitochondrial abnormalities occur and the arrangement of the discs are disordered, providing a basis for the maintenance of AF.

Normal and obstructive breathing physiology during sleep

PURPOSE

To estimate the severity of flow limitation in patients with OSA, the number of breaths with flattened inspiratory flow curves should be identified. Attempts to do a quantitative analysis of the flattening degree for all breaths in a nighttime recording have failed up to now.

METHODS

SOMNOmedics (Randersacker, Germany) developed an automated flattening analysis parameter called the obstructive coefficient (OC). Polysomnographic measurement including esophageal manometry was done in 25 subjects (10 healthy, 9 patients with mild OSA, and 6 with severe OSA). For each breath, the data couple of OC and esophageal pressure (EP) was used for analysis.

RESULTS

Data couples of OC and EP were recorded for 104,608 breaths. Airway patency histogram profiles for each study group showed no remarkable differences between each other. Increase in EP with increasing RDI was identified as the only marker of OSA severity. A strong shift was observed in N3 breaths from maximum OC/lowest EP values in healthy subjects to low OC values in association with maximum EP values in OSA.

CONCLUSION

The OC enables quantification of all breaths of a nighttime recording according to their degree of flattening. The relation of strong limited to less strong limited breaths is the same across the three study groups. The analysis of the corresponding EP to a given OC value for each study group identified the EP that is necessary to cause a given flow as the only parameter that discriminates degrees of severity of OSA. The trial registration number is DRKS00018095 from 2019 to 10-09.

Interaktionen schlafbezogener Atmungsstörungen mit Vorhofflimmern

Hintergrund

Vorhofflimmern (VHF) ist die häufigste Herzrhythmusstörung. Sowohl die zentrale als auch die obstruktive Schlafapnoe interagieren mit dieser Erkrankung. Intermittierende Hypoxie, oxidativer Stress, wiederkehrende Aufwachreaktionen, intrathorakale Druckveränderungen und atriales Remodeling können im Rahmen einer schlafbezogenen Atmungsstörung (SBAS) zu VHF führen.

Ziel

Dieser Artikel stellt die komplexen Zusammenhänge und Erkenntnisse jüngster Forschungen bezüglich SBAS und VHF sowie die Therapiemöglichkeiten dar.

Material und Methoden

Es erfolgten eine Literaturrecherche von Original- und Übersichtsartikeln sowie Metaanalysen, die zwischen 1963 und 2020 in der PubMed-Datenbank veröffentlicht wurden.

Ergebnisse

Die Erkenntnisse der Studien weisen auf einen bidirektionalen kausalen Zusammenhang zwischen SBAS und VHF hin. Die pathophysiologischen Auswirkungen der obstruktiven und zentralen Schlafapnoe auf VHF sind unterschiedlich. Die Studien, die die Effekte einer Therapie der SBAS auf das Rezidivrisiko von VHF nach Intervention (Kardioversion oder Pulmonalvenenisolation) untersuchen, ergeben bisher kein eindeutiges Bild.

Diskussion

Bisherige Studien bestätigen multiple Interaktionen zwischen SBAS und VHF. Aufgrund widersprüchlicher Ergebnisse hinsichtlich der Effekte einer positiven Atemwegsdrucktherapie auf das Rezidivrisiko von VHF nach Interventionen sind weitere Studien nötig.

Repeated exposure to transient obstructive sleep apnea-related conditions causes an atrial fibrillation substrate in a chronic rat model

BACKGROUND

High night-to-night variability in obstructive sleep apnea (OSA) is associated with atrial fibrillation (AF). Obstructive apneas are characterized by intermittent deoxygenation-reoxygenation and intrathoracic pressure swings during ineffective inspiration against occluded upper airways.

OBJECTIVE

We elucidated the effect of repeated exposure to transient OSA conditions simulated by intermittent negative upper airway pressure (INAP) on the development of an AF substrate.

METHODS

INAP (48 events/4 h; apnea-hypopnea index 12 events/h) was applied in sedated spontaneously breathing rats (2% isoflurane) to simulate mild-to-moderate OSA. Rats without INAP served as a control group (CTR). In an acute test series (ATS), rats were either killed immediately (n = 9 per group) or after 24 hours of recovery (ATS-REC: n = 5 per group). To simulate high night-to-night variability in OSA, INAP applications (n = 10; 24 events/4 h; apnea-hypopnea index 6/h) were repeated every second day for 3 weeks in a chronic test series (CTS).

RESULTS

INAP increased atrial oxidative stress acutely, represented in decreases of reduced to oxidized glutathione ratio (ATS: INAP: 0.33 ± 0.05 vs CTR: 1 ± 0.26; P = .016), which was reversible after 24 hours (ATS-REC: INAP vs CTR; P = .274). Although atrial oxidative stress did not accumulate in the CTS, atrial histological analysis revealed increased cardiomyocyte diameters, reduced connexin 43 expression, and increased interstitial fibrosis formation (CTS: INAP 7.0% ± 0.5% vs CTR 5.1% ± 0.3%; P = .013), which were associated with longer inducible AF episodes (CTS: INAP: 11.65 ± 4.43 seconds vs CTR: 0.7 ± 0.33 seconds; P = .033).

CONCLUSION

Acute simulation of OSA was associated with reversible atrial oxidative stress. Cumulative exposure to these transient OSA-related conditions resulted in AF substrates and was associated with increased AF susceptibility. Mild-to-moderate OSA with high night-to-night variability may deserve intensive management to prevent atrial substrate development.

Central sleep apnea and atrial fibrillation: A review on pathophysiological mechanisms and therapeutic implications

Precipitating factors and chronic diseases associated with atrial fibrillation (AF) are detailed in the literature. Emerging evidence over the last several decades suggests a potential causal relationship between central sleep apnea (CSA) and AF. Mechanisms including apnea-induced hypoxia with intermittent arousal, fluctuating levels of carbon dioxide, enhanced sympathetic/neurohormonal activation and oxidative stress causing inflammation have been implicated as etiologic causes of AF within this subpopulation. CSA affects the efficacy of pharmacologic and catheter-based antiarrhythmic treatments, which is why treating CSA prior to these interventions may lead to lower rates of AF. Subsequently, a reduction in the AF burden with transvenous phrenic nerve stimulation (TPNS) has become a topic of interest. The present review describes the relationship between these conditions, pathophysiologic mechanisms implicating the role of CSA in development of AF, and emerging therapeutic interventions.

Understanding the pathophysiological mechanisms of cardiometabolic complications in obstructive sleep apnoea: towards personalised treatment approaches

In January 2019, a European Respiratory Society research seminar entitled "Targeting the detrimental effects of sleep disturbances and disorders" was held in Dublin, Ireland. It provided the opportunity to critically review the current evidence of pathophysiological responses of sleep disturbances, such as sleep deprivation, sleep fragmentation or circadian misalignment and of abnormalities in physiological gases such as oxygen and carbon dioxide, which occur frequently in respiratory conditions during sleep. A specific emphasis of the seminar was placed on the evaluation of the current state of knowledge of the pathophysiology of cardiovascular and metabolic diseases in obstructive sleep apnoea (OSA). Identification of the detailed mechanisms of these processes is of major importance to the field and this seminar offered an ideal platform to exchange knowledge, and to discuss pitfalls of current models and the design of future collaborative studies. In addition, we debated the limitations of current treatment strategies for cardiometabolic complications in OSA and discussed potentially valuable alternative approaches.

Ballistocardiography and seismocardiography detection of hemodynamic changes during simulated obstructive apnea

OBJECTIVE

To investigate if modern seismocardiography (SCG) and ballistocardiography (BCG) are useful in the detection of hemodynamic changes occurring during simulated obstructive apneic events.

METHODS

Forty-seven healthy volunteers performed a voluntary maximum Mueller maneuver (MM) for 10 s, and SCG and BCG signals were simultaneously taken. The kinetic energy of a set of cardiac cycles before and during the apneic episode was automatically computed from the rotational and linear channels of the SCG and BCG waveforms and its temporal integral (i K) was derived (unit of measure: microjoules per second (µJ·s)). The estimated transmural pressure (eP _TM ) was assessed as the difference between systemic blood pressure and maximal inspiratory pressure (MIP). The Wilcoxon sign-rank test was used to evaluate differences in energy measurements between normal respiration and the loaded inspiration maneuver. Cardiac kinetic energies and the MIP produced during the MM were compared by linear regression analysis following log transformation in order to assess the correlation between variables.

MAIN RESULTS

The [Formula: see text] during normal breathing increased from 1.1(0.8; 1.4) to 1.9(1.4; 4.3) µJ·s during MM (p < 0.001). Meanwhile, [Formula: see text] increased from 54 (31; 92) to 84 (44; 153) µJ·s, (p < 0.001). The [Formula: see text] and [Formula: see text] of a set of cardiac cycles during the MM were negatively associated with the MIP (r: -0.59, p < 0.001 and r: -0.53, p = 0.001 for [Formula: see text] and [Formula: see text], respectively). When eP _TM was considered, this association became positive (r: +0.58, p < 0.001 and r:+0.60, p < 0.001, for [Formula: see text] and [Formula: see text], respectively). When the i K _LIN was considered as the comparative factor, correlations with the MIP and eP _TM were weak and insignificant. Men had higher values of i K than women.

SIGNIFICANCE

Simulated obstructive apnea elicits large rotational i K swings, which are related to the intensity of the inspiratory effort and, as such, to the intensity of the left ventricular afterload. Computation of cardiac kinetic energy through BCG and SCG may shed further light on the impact of obstructive respiratory events on the cardiovascular system.

Controlled Study of Central Hemodynamic Changes in Inspiratory Exercise with Different Loads in Heart Failure

Background Inspiratory muscle weakness contributes to exercise intolerance and decreased quality of life in patients with heart failure. Studies with inspiratory muscle training show improvement in inspiratory muscle strength, functional capacity and quality of life. However, little is known about the central hemodynamic response (CHR) during inspiratory exercise (IE). Objective To evaluate CHR in a single IE session with different loads (placebo, 30% and 60%) in heart failure. Methods Randomized placebo-controlled clinical trial in patients with heart failure with reduced ejection fraction, functional class II and III. Twenty patients aged 65 ± 11 years completed a single session of inspiratory exercise, in 3 cycles of 15 minutes, with a 1-hour washout, involving loads of 30% (C30), 60% (C60) and placebo, using a linear load resistor (PowerBreathe Light). The noninvasive hemodynamic study was performed by cardiothoracic bioimpedance (Niccomo™ CardioScreen®). Statistical analysis was performed with Student's t-test and Pearson's correlation, and P≤0.05 was considered significant. Results An increase in heart rate (HR) was observed with C30 (64 ± 15 vs 69 ± 15 bpm; p = 0.005) and C60 (67 ± 14 vs 73 ± 14 bpm, p = 0.002). A decrease was observed in systolic volume (SV) with C30 (73 ± 26 vs 64 ± 20 ml; p = 0.004). Cardiac output (CO), on its turn, increased only with C60 (4.6 ± 1.5 vs 5.3 ± 1.7 l/min; p = -0.001). Conclusion When using the 60% load, in a single IE session, changes in CHR were observed. HR and CD increased, as did the Borg scales and subjective sensation of dyspnea. The 30% load reduced the SV. (Arq Bras Cardiol. 2020; 114(4):656-663).

Sleep Disordered Breathing in Hypertrophic Cardiomyopathy-Current State and Future Directions

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy and sleep disordered breathing (SDB) is a treatable risk factor that has been seen to occur concurrently, and is known to propagate mortality and morbidity in a number of cardiovascular disease states including heart failure, and indeed hypertrophic cardiomyopathy. In this review, we summarize past studies that explored the simultaneous occurrence of HCM and SDB, and the pathophysiology of SDB in relation to heart failure, arrhythmias, cardiac ischemia and pulmonary hypertension in HCM. The current therapeutic modalities, with the effect of obstructive sleep apnea (OSA) treatment on HCM, are then discussed along with potential future directions.

Sex differences and higher upper normal limits for left atrial end-systolic volume in individuals in their mid-60s: data from the ACE 1950 Study

Aims

The current study aimed to describe normal values of left atrial (LA) volumes and LA emptying fraction (LAEF) in a large sample in their mid-60s from the general population and to explore sex differences.

Methods and results

In the Akershus Cardiac Examination (ACE) 1950 Study, body surface area-indexed LA maximum (LAVimax) and minimum (LAVimin) volumes and LAEF were measured in 3489 individuals aged 63.9 ± 0.6 years from the general population. A healthy group of 832 individuals was defined. Data are presented as mean ± standard deviation (SD) and a normal range of mean ± 2 SD. T-tests were used for comparisons. In the healthy group, mean LAVimax was 25.5 ± 6.2 mL/m2 and the normal range was 13.1–37.9 mL/m2. Men had significantly larger body surface area-indexed volumes than women, but there was no difference in LAEF. The mean LAVimax for healthy men was 26.4 ± 6.5 mL/m2, for healthy women 24.9 ± 5.8 mL/m2 (P &lt; 0.001) and the upper normal limits were 39.4 and 36.5 mL/m2, respectively. In the healthy group, 13.0% of all men and 5.4% of all women had LAVimax above the current upper normal limit of 34 mL/m2.

Conclusion

A large proportion of healthy individuals, in particular men, had LAVimax &gt;34 mL/m2. Our findings suggest that the recommended cut-off may be too low at the age of 65 years and above and that sex-specific cut-offs should be considered.

Atrial Fibrillation – An Orchestra of Classic and Modern Risk Factors

Over the past years, prevention and control of risk factors has begun to play an important role in the management of patients prone to develop atrial fibrillation (AF). A considerable number of risk factors that contribute to the creation of a predisposing substrate for AF has been identified over the years. Although certain AF risk factors such as age, gender, genetic predisposition, or race are unmodifiable, controlling modifiable risk factors may represent an invaluable tool in the management of AF patients. In the recent decades, numerous studies have evaluated the mechanisms linking different risk factors to AF, but the exact degree of atrial remodeling induced by each factor remains unknown. Elucidating these mechanisms is essential for initiating personalized therapies in patients prone to develop AF. The present review aims to provide an overview of the most relevant modifiable risk factors involved in AF occurrence, with a focus on the mechanisms by which these factors lead to AF initiation and perpetuation.

Relation of Left Atrial Volumes in Patients With Myocardial Infarction to Left Ventricular Filling Pressures and Outcomes

The inter-relationships between minimal and maximal left atrial volume index (LAVI), left ventricular filling pressures and survival have not been well studied. This study aimed to compare LAVImin with LAVImax with respect to (1) relative prognostic value, and (2) correlation with left ventricular end-diastolic pressures (LVEDP), in patients with myocardial infarction (MI). A retrospective study involving consecutive patients with a first-ever MI (n = 419) was undertaken. LAVIs were determined using Simpson's biplane method from 2D echocardiography performed the day after admission. LAVmin ≥ 18 mls/m² and LAVImax ≥ 34 mls/m² were considered enlarged. The primary end point was composite major adverse cardiovascular events (MACE) (death/MI/heart failure). Correlation between LVEDP and LAVI was assessed in 120 patients who underwent echocardiography and cardiac catheterization either simultaneously (n = 30) or same-day (n = 90). At a median follow-up of 24 months, there were 61 MACE events. On Cox proportional hazards multivariate analysis incorporating significant clinical predictors and LVEF, whereas both LAVImin ≥ 18 mls/m² (hazard ratio 3.15 [95% confidence interval 1.70 to 5.54], p <0.001) and LAVImax ≥ 34 mls/m² (hazard ratio 1.79 [95% confidence interval 1.02 to 3.14], p = 0.041) were independent predictors of MACE, LAVImin showed a stronger association. Intermodel comparisons of the model chi-square and Harrell's C-statistic confirmed better prognostication with LAVImin. In the invasive cohort, because LAVImin and LAVImax had a similar correlation with LVEDP ≥ 15 mm Hg (r = 0.41 [p <0.001] vs r = 0.42 [p <0.001]), LAVmin ≥ 18 mls/m² had a greater sensitivity for LVEDP ≥ 15 mm Hg than LAVImax ≥ 34 mls/m² (sensitivity 59.4% vs 34.4%). In conclusion, utilizing thresholds of ≥18 and ≥34 mls/m², respectively, LAVImin was a better predictor of survival than LAVImax, the pathophysiologic basis of which relates to a better sensitivity for elevated left ventricular filling pressures with LAVImin at these thresholds. There may be incremental clinical value in measuring LAVImin alongside LAVImax.

Importance of the Left Atrium: More Than a Bystander?

Left atrial size and function parameters are associated with adverse outcomes in multiple disease states, including heart failure with reduced and preserved ejection fraction. Recent data suggest that phasic left atrial function and left atrial stain measurements also hold prognostic information. Three-dimensional echocardiography provides more accurate and reproducible quantification of left atrial volumes than 2-dimensional echocardiography when compared with cardiac magnetic resonance reference standards. Greater accessibility to these advanced imaging techniques allows for the integration of these parameters into routine clinical practice.

Ventricular Arrhythmias in Patients with Obstructive Sleep Apnea

Obstructive Sleep Apnea (OSA) is a prevalent condition thought to increase in the future. Being mostly undiagnosed, the most serious complications are cardiovascular diseases, among which are arrhythmias. Controversy remains as to whether OSA is a primary etiologic factor for ventricular arrhythmias, because of the high incidence of cardiovascular comorbidities in OSA patients. Howev-er, there is mostly a strong evidence of a relation between OSA and ventricular arrhythmias. A few mechanisms have been proposed to be responsible for this association and some electrocardiographic changes have also been demonstrated to be more frequent in OSA patients. Treatment of OSA with Continuous Positive Airway Pressure (CPAP) has the potential to reduce arrhythmias and confer a mortality benefit.

Cardiac rhythm disorders in obstructive sleep apnea

Obstructive sleep apnea (OSA) is common among patients with cardiac rhythm disorders. OSA may contribute to arrhythmias due to acute mechanisms, such as generation of negative intrathoracic pressure during futile efforts to breath, intermittent hypoxia, and surges in sympathetic activity. In addition, OSA may lead to heart remodeling and increases arrhythmia susceptibility. Atrial distension and remodeling, that has been shown to be associated with OSA, is a well-known anatomical substrate for atrial fibrillation (AF). AF is the arrhythmia most commonly described in patients with OSA. Several observational studies have shown that the treatment of OSA with continuous positive airway pressure (CPAP) reduces recurrence of AF after electrical cardioversion and catheter ablation. There is also evidence that nocturnal hypoxemia, a hallmark of OSA, predicts sudden cardiac death (SCD) independently of well-established cardiovascular risk factors. Among patients with an implantable cardiac defibrillator, those with OSA have a higher risk of receiving treatment for life-threatening arrhythmias. Nocturnal hypoxemia may also increase vagal tone, which increases susceptibility to bradycardic and conduction rhythm disorders that have also been described in patients with OSA. In conclusion, there are several biological pathways linking OSA and increased cardiac arrhythmogenesis propensity. However, the independent association is derived from observational studies and the direction of the association still needs clarification due to the lack of large clinical trials. This review focuses on the current scientific evidence linking OSA to cardiac rhythm disorders and point out future directions.

Mechanisms of cardiovascular disease in obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is recognized as a major public health burden conveying a significant risk of cardiovascular diseases (CVD) and mortality. Continuous positive airway pressure (CPAP) is the treatment of choice for the majority of patients with OSA but the benefit of CPAP on CVD is uncertain. Thus, a greater understanding of the mechanisms by which OSA leads to CVD might identify novel therapeutic approaches. Intermittent hypoxia (IH), a hallmark feature of OSA, plays a key role in the pathogenesis and experimental studies using animal and cell culture studies suggest that IH mediates CVD through activation of multiple mechanistic pathways such as sympathetic excitation, inflammation, oxidative stress or metabolic dysregulation. Recurrent arousals, intrathoracic pressure swings and concomitant obesity likely play important additive roles in this process. In this review, the available evidence of the pathophysiological mechanisms of CVD in OSA is explored with a specific emphasis on IH, recurrent arousals and intrathoracic pressure swings as the main pathophysiological triggers.

Cardiac effects of CPAP treatment in patients with obstructive sleep apnea and atrial fibrillation

PURPOSE

Obstructive sleep apnea (OSA) has been recognized as an independent risk factor for the development and progression of atrial fibrillation (AF). We aimed to investigate the changes in heart rate and atrial and ventricular ectopy after continuous positive airway pressure (CPAP) treatment in patients with OSA and AF.

METHODS

Consecutive patients with AF underwent ambulatory sleep monitoring, and OSA was defined as an Apnea-Hypopnea-Index (AHI) ≥ 5/h. Treated patients completed in-laboratory CPAP titration study. A 24-h ECG Holter was performed at baseline and at 3 and 6 months after CPAP treatment.

RESULTS

One hundred patients (70% males) with AF were included in the final analysis. OSA was diagnosed in 85% of patients. There were no significant changes in mean 24-h heart rate in patients with paroxysmal or permanent AF at 3 and 6 months of treatment compared to baseline. In patients with paroxysmal AF (n = 29), atrial and ventricular ectopy counts/24 h significantly decreased at 3 months compared to baseline (median (IQR) 351 (2049) to 57 (182), P = 0.002; 68 (105) to 16 (133), P = 0.01 respectively). At 6 months follow-up, the atrial ectopy count/24 h significantly decreased in patients with paroxysmal AF compared to baseline (median (IQR) 351 (2049) to 31 (113), P = 0.016, n = 14). In patients with permanent AF (n = 15), there was a significant reduction in ventricular ectopy count/24 h at 3 months compared to baseline (median (IQR) 100 (1116) to 33 (418), P = 0.02).

CONCLUSIONS

There is a significant decrease in atrial and ventricular ectopy count/24 h in patients with AF and OSA at 3 and 6 months of CPAP treatment compared to baseline.

Left ventricular strain rate is reduced during voluntary apnea in healthy humans

During an apneic event, sympathetic nerve activity increases resulting in subsequent increases in left ventricular (LV) afterload and myocardial work. It is unknown how cardiac mechanics are acutely impacted by the increased myocardial work during an apneic event. Ten healthy individuals (23 ± 3 yr) performed multiple voluntary end-expiratory apnea (VEEA) maneuvers exposed to room air, while a subset ( n = 7) completed multiple VEEA exposed to hyperoxic air (100% [Formula: see text]). Beat-by-beat blood pressure, heart rate, and stroke volume were measured continuously. Effective arterial elastance (EA) was calculated as an index of cardiac afterload, and myocardial work was calculated as the rate pressure product (RPP). Tissue Doppler echocardiography was used to measure LV tissue velocities, deformation via strain, and strain rate (SR). Systolic blood pressure (Δ18 ± 13 mmHg, P < 0.01), EA (Δ0.13 ± 0.10 mmHg/ml, P < 0.01), and RPP (Δ9 ± 10 beats/min × mmHg 10^-2, P < 0.01) significantly increased with room air VEEA. This occurred in parallel with decreases in peak longitudinal systolic (Δ-0.62 ± 0.41 cm/s, P < 0.01) and early LV filling (Δ-2.81 ± 1.99 cm/s, P < 0.01) myocardial velocities. Longitudinal SR (Δ-0.30 ± 0.32 1/s, P = 0.01) was significantly decreased during room air VEEA. VEEA with hyperoxia did not alter ( P > 0.18) EA or RPP and attenuated the systolic blood pressure response compared with room air. Myocardial velocities and LV strain rate response to VEEA were unchanged ( P = 0.30) with hyperoxia. Consistent with our hypotheses, VEEA-induced increases in EA and myocardial work impact LV mechanics, which may depend, in part, on stimulation of peripheral chemoreceptors. NEW & NOTEWORTHY Transient increases in arterial blood pressure and systemic vascular resistance occur during sleep apnea events and may contribute to the associated daytime hypertension and risk of overt cardiovascular disease. To date, the link between this apnea pressor response and acute changes in left ventricular function remains poorly understood. We demonstrate that in parallel to increases in cardiac afterload a depressed left ventricular systolic function occurs at end apnea.

Gray Matter Hypertrophy and Thickening with Obstructive Sleep Apnea in Middle-aged and Older Adults

RATIONALE

Obstructive sleep apnea causes intermittent hypoxemia, hemodynamic fluctuations, and sleep fragmentation, all of which could damage cerebral gray matter that can be indirectly assessed by neuroimaging.

OBJECTIVES

To investigate whether markers of obstructive sleep apnea severity are associated with gray matter changes among middle-aged and older individuals.

METHODS

Seventy-one subjects (ages, 55-76 yr; apnea-hypopnea index, 0.2-96.6 events/h) were evaluated by magnetic resonance imaging. Two techniques were used: (1) voxel-based morphometry, which measures gray matter volume and concentration; and (2) FreeSurfer (an open source software suite) automated segmentation, which estimates the volume of predefined cortical/subcortical regions and cortical thickness. Regression analyses were performed between gray matter characteristics and markers of obstructive sleep apnea severity (hypoxemia, respiratory disturbances, and sleep fragmentation).

MEASUREMENTS AND MAIN RESULTS

Subjects had few symptoms, that is, sleepiness, depression, anxiety, and cognitive deficits. Although no association was found with voxel-based morphometry, FreeSurfer revealed increased gray matter with obstructive sleep apnea. Higher levels of hypoxemia correlated with increased volume and thickness of the left lateral prefrontal cortex as well as increased thickness of the right frontal pole, the right lateral parietal lobules, and the left posterior cingulate cortex. Respiratory disturbances positively correlated with right amygdala volume, and more severe sleep fragmentation was associated with increased thickness of the right inferior frontal gyrus.

CONCLUSIONS

Gray matter hypertrophy and thickening were associated with hypoxemia, respiratory disturbances, and sleep fragmentation. These structural changes in a group of middle-aged and older individuals may represent adaptive/reactive brain mechanisms attributed to a presymptomatic stage of obstructive sleep apnea.

Increased inspiratory resistance affects the dynamic relationship between blood pressure changes and subarachnoid space width oscillations

BACKGROUND AND OBJECTIVE

Respiration is known to affect cerebrospinal fluid (CSF) movement. We hypothesised that increased inspiratory resistance would affect the dynamic relationship between blood pressure (BP) changes and subarachnoid space width (SAS) oscillations.

METHODS

Experiments were performed in a group of 20 healthy volunteers undergoing controlled intermittent Mueller Manoeuvres (the key characteristic of the procedure is that a studied person is subjected to a controlled, increased inspiratory resistance which results in marked potentiation of the intrathoracic negative pressure). BP and heart rate (HR) were measured using continuous finger-pulse photoplethysmography; oxyhaemoglobin saturation with an ear-clip sensor; end-tidal CO2 with a gas analyser; cerebral blood flow velocity (CBFV), pulsatility and resistive indices with Doppler ultrasound. Changes in SAS were recorded with a new method i.e. near-infrared transillumination/backscattering sounding. Wavelet transform analysis was used to assess the BP and SAS oscillations coupling.

RESULTS

Initiating Mueller manoeuvres evoked cardiac SAS component decline (-17.8%, P<0.001), systolic BP, diastolic BP and HR increase (+6.3%, P<0.001; 6.7%, P<0.001 and +2.3%, P<0.05, respectively). By the end of Mueller manoeuvres, cardiac SAS component and HR did not change (+2.3% and 0.0%, respectively; both not statistically significant), but systolic and diastolic BP was elevated (+12.6% and +8.9%, respectively; both P<0.001). With reference to baseline values there was an evident decrease in wavelet coherence between BP and SAS oscillations at cardiac frequency in the first half of the Mueller manoeuvres (-32.3%, P<0.05 for left hemisphere and -46.0%, P<0.01 for right hemisphere) which was followed by subsequent normalization at end of the procedure (+3.1% for left hemisphere and +23.1% for right hemisphere; both not statistically significant).

CONCLUSIONS

Increased inspiratory resistance is associated with swings in the cardiac contribution to the dynamic relationship between BP and SAS oscillations. Impaired cardiac performance reported in Mueller manoeuvres may influence the pattern of cerebrospinal fluid pulsatility.

Atrial Fibrillation: Epidemiology, Pathophysiology, and Clinical Outcomes

The past 3 decades have been characterized by an exponential growth in knowledge and advances in the clinical treatment of atrial fibrillation (AF). It is now known that AF genesis requires a vulnerable atrial substrate and that the formation and composition of this substrate may vary depending on comorbid conditions, genetics, sex, and other factors. Population-based studies have identified numerous factors that modify the atrial substrate and increase AF susceptibility. To date, genetic studies have reported 17 independent signals for AF at 14 genomic regions. Studies have established that advanced age, male sex, and European ancestry are prominent AF risk factors. Other modifiable risk factors include sedentary lifestyle, smoking, obesity, diabetes mellitus, obstructive sleep apnea, and elevated blood pressure predispose to AF, and each factor has been shown to induce structural and electric remodeling of the atria. Both heart failure and myocardial infarction increase risk of AF and vice versa creating a feed-forward loop that increases mortality. Other cardiovascular outcomes attributed to AF, including stroke and thromboembolism, are well established, and epidemiology studies have championed therapeutics that mitigate these adverse outcomes. However, the role of anticoagulation for preventing dementia attributed to AF is less established. Our review is a comprehensive examination of the epidemiological data associating unmodifiable and modifiable risk factors for AF and of the pathophysiological evidence supporting the mechanistic link between each risk factor and AF genesis. Our review also critically examines the epidemiological data on clinical outcomes attributed to AF and summarizes current evidence linking each outcome with AF.