Charakterisierung der arrhythmogenen Substrate für Vorhofflimmern in einem neuen Rattenmodell für obstruktive Schlafapnoe

Vorhofflimmern ist die häufigste anhaltende Arrhythmie des Menschen und ist mit einer Vielzahl kardiovaskulärer Risikofaktoren und Komorbiditäten assoziiert. Eine dieser epidemiologisch eng vergesellschafteten Erkrankungen ist die obstruktive Schlafapnoe. Pathognomonisch für diese schlafbezogene Atmungsstörung ist ein nächtlicher Kollaps der oberen Atemwege bei erhaltenem Atemantrieb. Dies führt einerseits zu einem Abfall des Sauerstoffgehaltes im Blut und andererseits zu ausgeprägten negativ thorakalen Druckschwankungen während frustraner Atembemühungen gegen verlegte obere Atemwege. Während der nächtlich obstruktiv respiratorischen Ereignisse wird der Vorhof somit sowohl erhöhten transmuralen Druckgradienten als auch intermittierender Hypoxieepisoden ausgesetzt. Die unterschiedlichen Rollen intermittierender Hypoxie und intrathorakaler Druckschwankungen sind besonders hinsichtlich einer möglichen Begünstigung für Arrhythmien bisher noch nicht ausreichend geklärt. Ziel dieser Arbeit war es ein neues Rattenmodell für obstruktive Schlafapnoe zu entwickeln, um die Entstehung eines Schlafapnoe-assoziierten atrialen arrhythmogenen Substrates zu untersuchen. Zunächst sollten transiente, akut reversible Effekte intermittierender Hypoxieepisoden alleine, im Vergleich zu Hypoxieepisoden zusammen mit negativ thorakalen Druckschwankungen untersucht werden. Da obstruktive Schlafapnoe sich zumeist durch einen dynamischen Krankheitsverlauf mit einer hohen Nacht-zu-Nacht-Variabilität auszeichnet, sollte geklärt werden, ob die Akkumulation repetitiv akuter Effekte jeden zweiten Tag über drei Wochen zur Entstehung eines strukturellen und arrhythmogenen Substrates im Vorhof beiträgt. In anästhesierten Ratten wurde hierfür für eine Minute entweder intermittierende Hypoxie (IH) alleine oder ein simuliert obstruktiv respiratorisches Ereignis induziert. Das Manöver der intermittierenden Hypoxie ist durch eine Vergrößerung des Todraumvolumens simuliert worden, das Manöver des simulierten obstruktiv respiratorischen Ereignisses hingegen durch die Anlage eines definierten negativen Druckes im Bereich der oberen Atemwege über eine Versuchsmaske (INAP, Intermittent Negative Airway Pressure). Beide Manöver resultierten in einem vergleichbaren Abfall der Sauerstoffsättigung. Das INAP-Manöver zeichnete sich darüber hinaus durch negativ intrathorakale Druckschwankungen während ineffektiven Atembemühungen aus. In einer akuten Testserie (ATS) wurden diese einminütigen Manöver alle fünf Minuten wiederholt. Nach vier Stunden wurden acht IH-Tiere und acht INAP-Tiere direkt und je fünf IH- und INAP- Tiere nach einer Erholungspause von 24 Stunden getötet (ATS-REC). In einer chronischen Testserie (CTS) wurden einminütige IH- oder INAP-Manöver alle zehn Minuten über vier Stunden jeden zweiten Tag appliziert. Nach drei Wochen wurden auch diese Tiere mit einer Latenz von 24 Stunden nach letztem Manöver getötet. In allen Versuchen wurden Ratten mit identischer Narkoseart und -dauer als Kontrollen (CTR) verwandt. In terminalen Versuchen wurden in allen Ratten invasive linksventrikuläre Druckmessungen als auch transösophageale Vorhofstimulationen zur Induktion von Vorhofflimmern durchgeführt. Vorhofgewebe und Gewebe des linken Ventrikels wurden für histologische sowie biochemische Analysen asserviert. Im Vorhof der ATS-behandelten Tiere führten vier Stunden repetitiver INAP-Manöver, nicht aber IH alleine, zu einem transienten Absinken der antioxidativen Kapazität im Vorhofgewebe. Dies war innerhalb von 24 Stunden nach einem Versuchstag in den ATS-REC Ratten sowie nach dem letzten Versuchstag in den CTS-Tieren komplett reversibel. In den CTS-Versuchstieren führte eine Applikation des INAP alle zwei Tage zu einem signifikanten Herabregulation von Connexinen und zu einer Tendenz zu erhöhter interstitieller Fibrose und vergrößerter Kardiomyozytendurchmesser im linken Vorhof. Diese Veränderungen waren mit signifikant längeren induzierbaren Vorhofflimmerzeiten in Ratten der INAP-Gruppe vergesellschaftet. Die induzierbaren Vorhofflimmerzeiten zeigten sich in den Tieren der IH-Gruppe nicht verlängert. Im Rahmen dieser Arbeit wurde ein neues Rattenmodell für Schlafapnoe zur Untersuchung der Entstehung eines atrialen arrhythmogenen Substrates entwickelt. Zusammenfassend führten in diesem Tiermodell vier Stunden simuliert obstruktiv respiratorischer Ereignisse im Sinne der INAP-Manöver, aber nicht IH alleine, zu einem transienten Abfall der antioxidativen Kapazität im Vorhof. Die kumulative Exposition gegenüber dieser transienten Abfälle der antioxidativen Kapazität war mit der Entstehung arrhythmogener Substrate im Vorhof assoziiert. Diese waren charakterisiert durch erniedrigte Connexinlevel und einer längeren induzierbaren Vorhofflimmerdauer. Die Erkenntnisse dieser Arbeit unterstützen die Hypothese, dass die Anzahl obstruktiv respiratorischer Ereignisse während der Nacht und nicht die Anzahl der Sauerstoffentsättigungen alleine zum Substrat von Vorhofflimmern beitragen, selbst dann, wenn diese Stressoren nur jede zweite Nacht auftreten. Ob die gezielte Verhinderung obstruktiv respiratorischer Ereignisse das entscheidende Therapieziel bei Patienten mit Vorhofflimmern und obstruktiven Schlafapnoe darstellt, und ob eine Therapie der obstruktiven Schlafapnoe auch bei Patienten mit sehr hoher Tag-zu-Tag Variabilität des Schweregrades der obstruktiven Schlafapnoe nötig ist, muss in weiteren Studien untersucht werden.Characterization of arrhythmogenic substrates for atrial fibrillation in a novel rat model for obstructive sleep apnea Atrial fibrillation is the most common sustained arrhythmia and associated with a magnitude of cardiovascular comorbidities, one of which is obstructive sleep apnea. Obstructive sleep apnea is characterized by two main features: intermittent desaturations and inefficient breathing attempts against occluded upper airways leading to pronounced intrathoracic pressure fluctuations. Thus, the heart and especially the atria are exposed to intermittent hypoxia and repetitive stretch due to the thoracic pressure fluctuations. However, it remains to be elaborated how much these two individual features of sleep apnea contribute to an atrial arrhythmogenic substrate. In this study we therefore established a novel rat model for sleep apnea, in which we investigated sleep apnea associated atrial arrhythmogenic substrates. Acute reversible effects of intermittent hypoxia were compared to intermittent hypoxia plus intrathoracic pressure fluctuations. In a chronic group, we investigated whether the accumulation of the acute reversible effects every other day throughout 3 weeks, in terms of a high night-to-night variability of sleep apnea, could induce a structural substrate for atrial fibrillation. In anesthetized rats, either one minute of intermittent hypoxia (IH) or a simulated obstructive respiratory event was simulated. Intermittent hypoxia was applied via an increase in respiratory dead space, whereas the obstructive respiratory event was simulated by applying intermittent negative airway pressure (INAP) with a negative pressure device via a customized rat mask. Both maneuver resulted in comparable oxygen desaturations. Apart from that, the INAP-maneuver was characterized by negative thoracic pressure swings during ineffective breathing attempts. In an acute test-series (ATS), maneuvers were applied for one minute which was repeated every five minutes. After four hours of protocol, eight IH- and INAP-rats were sacrificed immediately and five IH- and INAP-rats were sacrificed with a latency of 24 hours after the last maneuver (ATS-REC). In a chronic test series (CTS), IH and INAP was applied for one minute every ten minutes for four hours every second day. After three weeks, these animals were also sacrificed with a latency of 24 hours after the last maneuver. In all trials, rats with the same weight and anesthesia were used as respective controls. In a terminal procedure, left ventricular pressures and transesophageal atrial fibrillation inducibility and induced atrial fibrillation duration were determined. Atrial and ventricular tissue was harvested afterwards for histological and biochemical analysis. In the ATS, four hours of repetitive INAP, but not IH alone, decreased transiently atrial antioxidative capacity, which was reversible after 24 hours of rest after the last maneuver in the ATS-REC and CTS. In CTS-rats, application of INAP every other day for three weeks, downregulated atrial connexins and showed a tendency towards increased atrial interstitial fibrosis and atrial hypertrophy. These changes were associated with increased induced atrial fibrillation durations in the INAP-group. The IH-group however did not show an increase in induced atrial fibrillation durations. In summary, the cumulative exposure of acute transient decreases in atrial antioxidative capacity induced by simulated respiratory events (INAP) was associated with an atrial arrhythmogenic substrate. This was characterized by decreased levels of connexins and increased inducible atrial fibrillation durations. This study supports the notion that the count of obstructive respiratory events at night and not simply the counts of desaturations are crucial and contribute to atrial arrhythmogenic substrates, even though those stimuli only occur every other night. If the targeted prevention of obstructive respiratory events and of a high night-to-night variability of sleep apnea in patients with atrial fibrillation is the main and most essential treatment strategy remains to be elaborated

Pharmacological inhibition of sodium-proton-exchanger subtype 3-mediated sodium absorption in the gut reduces atrial fibrillation susceptibility in obese spontaneously hypertensive rats

Background: Increased sodium uptake has been shown to contribute to hypertension and cardiac endorgan damage. The sodium-proton-exchanger subtype 3 (NHE3) is an important mediator of intestinal sodium absorption. Whether a reduction in intestinal sodium absorption can prevent the development of an atrial arrhythmogenic substrate in hypertension is unknown. Methods: Eight-week-old obese spontaneously hypertensive rats (SHR-ob) were treated for six weeks with the gut-specific NHE3-inhibitor SAR (1-(beta-D-glucopyranosyl)-3-{3-[(4S)-6,8-dichloro-2-methyl-1, 2,3,4-tetrahydroiso-chinolin-4-yl]phenyl}urea, 1 mg/kg/d in chow, SHR-ob SAR, n = 7) and compared to aged-matched placebo-treated SHR-ob (SHR-ob PLAC, n = 8). Cardiac magnetic resonance imaging was performed at the end of the treatment period to assess atrial emptying function. Afterwards, local conduction disturbances and inducible atrial fibrillation (AF) duration were determined and histological analysis to quantify atrial fibrosis amount were performed. Results: Inhibition of intestinal NHE3 by SAR increased fecal sodium excretion, resulted in marked changes in feces electrolyte concentrations and water content, reduced blood pressure and preserved atrial emptying function (active total percent emptying: SHR-ob SAR: 0.47 +/- 0.05% vs. SHR-ob PLAC: 0.38 +/- 0.007, p <0.0001). Atrial fibrosis content was lower (21.4 +/- 2.5% vs. 36.7 +/- 1.2%, p <0.0001) and areas of slow conduction were smaller (2.5 +/- 0.09% vs. 5.3 +/- 0.2%, p <0.0001) in SHR-ob SAR compared to SHR-ob PLAC. Left atrial burst stimulation resulted in shorter inducible AF-durations in SHR-ob SAR compared to SHR-ob PLAC. Conclusions: Reduction of intestinal sodium absorption and subsequent changes in feces milieu by pharmacological NHE3 inhibition in the gut preserved atrial emptying function and reduced AF susceptibility. Whether pharmacological NHE3 inhibition in the gut prevents AF in humans warrants further study. (C) 2020 The Authors. Published by Elsevier B.V

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

Mechanisms and therapeutic opportunities in atrial fibrillation in relationship to alcohol use and abuse

Excessive drinking has detrimental effects on the cardiovascular system. Atrial fibrillation (AF) following alcohol binge drinking, also named "holiday heart syndrome", is well established. However, even chronic lower levels of alcohol intake may also increase AF risk. In this review article, we aim to provide a comprehensive overview of the epidemiology and pathophysiology by which alcohol may be responsible for AF and discuss whether alcohol abstinence is required for optimal rhythm control as well as to maintain sinus rhythm in patients with AF. The pathophysiological mechanisms responsible for the relationship between alcohol consumption and AF may include both direct and chronic effects increasing AF-burden. Acute effects may include arrhythmogenic changes (such as shortening in atrial refractoriness, slowing in conduction velocity and increased atrial ectopy) and an autonomic imbalance. Chronic changes contributing to the development of an arrhythmogenic substrate involve atrial structural and functional remodeling process due to atrial dilatation, elevated pressures and fibrosis formation. Additionally, alcohol consumption contributes to developing concomitant AF risk factors such as obesity, sleep-disordered breathing, and hypertension. Alcohol abstinence is associated with a reduction in AF-recurrence and overall burden and moreover improves AF-risk factor development such as obesity, hypertension, sleep apnea and AF-related consequences such as stroke. In conclusion, alcohol consumption is associated with atrial arrhythmia and a wide range of cardiovascular comorbidities. Although further evidence is needed, current knowledge indicates that there might not be a safe level of alcohol consumption which is not increasing AF-risk

Mechanisms and therapeutic opportunities in atrial fibrillation in relationship to alcohol use and abuse

Excessive drinking has detrimental effects on the cardiovascular system. Atrial fibrillation (AF) following alcohol binge drinking, also named "holiday heart syndrome", is well established. However, even chronic lower levels of alcohol intake may also increase AF risk. In this review article, we aim to provide a comprehensive overview of the epidemiology and pathophysiology by which alcohol may be responsible for AF and discuss whether alcohol abstinence is required for optimal rhythm control as well as to maintain sinus rhythm in patients with AF. The pathophysiological mechanisms responsible for the relationship between alcohol consumption and AF may include both direct and chronic effects increasing AF-burden. Acute effects may include arrhythmogenic changes (such as shortening in atrial refractoriness, slowing in conduction velocity and increased atrial ectopy) and an autonomic imbalance. Chronic changes contributing to the development of an arrhythmogenic substrate involve atrial structural and functional remodeling process due to atrial dilatation, elevated pressures and fibrosis formation. Additionally, alcohol consumption contributes to developing concomitant AF risk factors such as obesity, sleep-disordered breathing, and hypertension. Alcohol abstinence is associated with a reduction in AF-recurrence and overall burden and moreover improves AF-risk factor development such as obesity, hypertension, sleep apnea and AF-related consequences such as stroke. In conclusion, alcohol consumption is associated with atrial arrhythmia and a wide range of cardiovascular comorbidities. Although further evidence is needed, current knowledge indicates that there might not be a safe level of alcohol consumption which is not increasing AF-risk

Personalized management of sleep apnea in patients with atrial fibrillation:An interdisciplinary and translational challenge

International audienc