Assessment of ventricular electrical heterogeneity in left bundle branch pacing and left ventricular septal pacing by using various electrophysiological methods.

INTRODUCTION: Left bundle branch area pacing (LBBAP) comprises pacing at the left ventricular septum (LVSP) or left bundle branch (LBBP). The aim of the present study was to investigate the differences in ventricular electrical heterogeneity between LVSP, LBBP, right ventricular pacing (RVP) and intrinsic conduction with different dyssynchrony measures using the ECG, vectorcardiograpy, ECG belt, and Ultrahigh frequency (UHF-)ECG. METHODS: Thirty-seven patients with a pacemaker indication for bradycardia or cardiac resynchronization therapy underwent LBBAP implantation. ECG, vectorcardiogram, ECG belt and UHF-ECG signals were recorded during RVP, LVSP and LBBP, and intrinsic activation. QRS duration (QRSd) was measured from the ECG, QRS area was calculated from the vectorcardiogram, LV activation time (LVAT) and standard deviation of activation time (SDAT) from ECG belt and electrical dyssynchrony (e-DYS16) from UHF-ECG. RESULTS: Both LVSP and LBBP significantly reduced ventricular electrical heterogeneity as compared to underlying LBBB and RV pacing in terms of QRS area (p < .001), SDAT (p < .001), LVAT (p < .001) and e-DYS16 (p < .001). QRSd was only reduced as compared to RV pacing(p < .001). QRS area was similar during LBBP and normal intrinsic conduction, e-DYS16 was similar during LVSP and normal intrinsic conduction, whereas SDAT was similar for LVSP, LBBP and normal intrinsic conduction. For all these variables there was no significant difference between LVSP and LBBP. CONCLUSION: Both LVSP and LBBP resulted in a more synchronous LV activation than LBBB and RVP. Especially LBBP resulted in levels of LV synchrony comparable to normal intrinsic conduction.

Autonomic dysfunction as a possible cause of sudden cardiac death in swimming sports.

Introduction: Human diving reflex is a well-studied phenomenon. However, very little is known about the possible relationship between augmented diving reflex and autonomic dysfunction. Methods: We retrospectively studied a group of four swimmers who underwent a diving reflex test as part of the examination due to symptoms related to autonomic dysfunction during swimming. The control group comprised 11 healthy swimmers with no history of these symptoms. A standardized diving reflex test was performed for each athlete in both groups. Hemodynamic profiles, including heart rate, stroke volume, and cardiac output, were recorded. Results: There were no statistically significant differences between the groups in any of the three parameters measured before the test. However, at the end of the test, each parameter (heart rate, stroke volume, and cardiac output) was significantly lower in the swimmers who presented with clinical symptoms related to autonomic dysfunction than in the control group. Conclusion: This observation could shed light on autonomic dysfunction as a possible cause of sudden cardiac death in swimming athletes. It also demonstrated that autonomic dysfunction is presented not only by decreased heart rate but also by stroke volume, causing a drop in cardiac output to the level of hemodynamic collapse.

How cold is too cold during maternal sepsis? Navigating between maternal hypothermia and fetal bradycardia.

Hypothermia is a relatively rare condition in pregnancy and has been associated with fetal bradycardia. The management of maternal hypothermia resulting in fetal bradycardia presents a challenging dilemma for healthcare professionals. Currently, no evidence exists to advise on the duration of this condition before obstetric interventions are necessary for a safe outcome for both mother and infant. We discuss a case of a 26-year old primigravida with a gestational age of 32 weeks, who presented with clinical urosepsis, resulting in severe hypothermia up to 32 degrees Celsius. Active warming measures were taken and intravenous antibiotic treatment was started. Fetal evaluation on the cardiotocogram showed prolonged bradycardia (90 BPM) prompting consideration of a cesarean section. However, after multidisciplinary consultation, conservative treatment was proposed since there were no other signs of fetal hypoxia; no decelerations, good variability and accelerations. The patient started to show clinical improvement and had a body core temperature of 36 degrees Celsius after approximately 60 h of active rewarming measures. Fetal heartrate baseline normalized as the maternal temperature raised. Subsequently the patient was discharged in good clinical condition and had an uncomplicated vaginal delivery of a healthy newborn at term. In conclusion, when fetal bradycardia occurs due to maternal hypothermia, in the absence of signs for fetal hypoxia on the cardiotocogram, treatment of the underlying maternal condition instead of immediate obstetrics intervention is the best clinical option. This strategy aims to address the underlying cause of maternal hypothermia and consequently fetal bradycardia while ensuring the well-being of both mother and fetus and preventing unnecessary premature delivery.

Cardioneuroablation for the management of neurally mediated syncope, sinus bradycardia, and atrioventricular block.

Through several decades of medical advances, we have improved our understanding of the role of the autonomic nervous system in the production of a myriad of clinical cardiac conditions such as vasovagal syncope, situational syncope, carotid sinus hypersensitivity, vagally mediated sinus bradycardia, and atrioventricular block. While typically not associated with mortality, these common clinical entities may result in significant patient symptoms and morbidity and are often characterized by a frustrating treatment course with a paucity of effective strategies. In recent years, there has been increased interest in the management of these conditions via direct modulation of the parasympathetic component of the autonomic nervous system. This is achieved by targeting the ganglionated plexus central to the pathogenesis of these conditions via cardioneuroablation. The primary role of this strategy is evolving and serves to augment traditional treatment strategies such as lifestyle modification and pharmacotherapy. In this review, we examine the principles governing the role of cardioneuroablation in select populations with vasovagal syncope, sinus dysfunction, and atrioventricular block including the evolving evidence in this exciting field while keeping in mind the need for robust clinical studies examining the long-term effectiveness and safety.

An Unusual Presentation of an Amniotic Fluid Embolism: Fetal Bradycardia As the First Sign.

Amniotic fluid embolism (AFE) is a potentially fatal maternal condition demanding awareness from obstetricians and anesthesiologists regarding its different manifestations. The typical presentation involves maternal respiratory distress, cardiovascular collapse, neurological changes, and coagulopathy followed by fetal distress. This unusual case study emphasizes that fetal compromise may precede maternal decompensation as the initial sign of AFE. Fetal distress is a known symptom of AFE and is typically seen due to cardiorespiratory issues that lead to reduced uteroplacental perfusion, resulting in fetal hypoxia. In the case presented, fetal bradycardia occurred before any visible maternal symptoms, suggesting that fetal distress could be induced by factors independent of the mother's cardiopulmonary status. A 34-year-old healthy G4P2012 at 41 weeks and 2 days gestation who was initially laboring on the floor was emergently taken to the operating room for a cesarean delivery due to fetal bradycardia. Around the time the fetus was delivered, the patient displayed seizure activity, followed by a complete loss of consciousness and cardiac arrest. The patient was intubated and underwent cardiopulmonary resuscitation and defibrillation, subsequently converting to a wide complex tachycardia. In the operating room, there was evidence of heavy vaginal bleeding, uterine atony, and a fulminant form of disseminated intravascular coagulopathy (DIC), which required aggressive management over the next four hours. After achieving hemodynamic stability, the patient was transferred to the surgical intensive care unit (SICU), extubated on day 3, and discharged home on day 8.

Low foetal heart rate, a potentially ominous finding: case report.

Background: Congenital long QT syndrome (LQTS) type 1 is characterized by abnormally prolonged ventricular repolarization caused by inherited defects in cardiac potassium channels. Patients are predisposed to ventricular arrhythmias and even sudden cardiac death. In some cases, foetal sinus bradycardia is the only sign, making prenatal diagnosis challenging. Physicians should be aware of this subtle presentation of LQTS. Early diagnosis and proactive treatment are crucial for preventing unexpected cardiac events. Case summary: A healthy and asymptomatic 25-year-old pregnant woman was referred to our institute for cardiac evaluation after persistent foetal sinus bradycardia was detected during repeated ultrasounds, despite the absence of any foetal morphological or functional cardiac anomalies. After a thorough assessment, the mother was diagnosed with LQTS type 1, as confirmed by molecular genetic testing. Appropriate management, including maternal medication and increased surveillance, was initiated. The infant was delivered safely, and his electrocardiogram revealed a significantly prolonged QTc interval. Genetic testing confirmed the maternally inherited variant in KCNQ1 gene, and beta-blocker therapy was started. No arrhythmic events were noted. Discussion: Detection and careful stratification of foetal heart rate (FHR) is crucial in every pregnancy. Foetal bradycardia can be caused by both maternal and foetal factors. Persistent low FHR should raise a high suspicion for LQTS. The condition may also present with atrioventricular blocks, torsades de pointes, or sudden intrauterine foetal demise. Accurate and early diagnosis of LQTS is essential for implementing appropriate management strategies, which include vigilant monitoring, effective medical treatment, careful planning of delivery, and post-natal care.

Seeing Bradycardia: How Ultrasound Improves Medical Decision-Making.

There is a broad differential for new-onset cardiac dysrhythmia, and the rapid identification of the underlying cause of these cardiac emergencies can be lifesaving. Identifying wall motion abnormalities on point-of-care ultrasound (POCUS) is not a core echocardiography application for Emergency Medicine (EM) physicians. However, ruling in a regional wall motion abnormality can expedite patient-centered care and assist the busy EM physician in high-risk cases.

Reply to the comments on "Effect of Bedside Ultrasound­Guided Versus Fluoroscopy­Guided Transvenous Cardiac Temporary Pacing in Children with Bradyarrhythmia".

The article "Effect of Bedside Ultrasound­Guided Versus Fluoroscopy­Guided Transvenous Cardiac Temporary Pacing in Children with Bradyarrhythmia" offers valuable insights into comparative short-term pacing strategies for pediatric bradyarrhythmias. There are some comments that the study overlooks the impact of genetic factors on bradyarrhythmias and treatment outcomes, lacks detailed information on the influence of medications, and does not address the cost-effectiveness of the pacing techniques. The analysis and explanation are made here, and it is hoped that through further research in the future, the conclusions will be more reliable.

Oral theophylline corrects sinus node dysfunction in acute on chronic lithium toxicity: case report and systematic review of lithium-induced Sinus node dysfunction.

Introduction: Lithium is a well-known agent to cause systemic toxicity with its narrow therapeutic window. Toxic cardiac effects are known but seldomly reported and can manifest as sinus node dysfunction (SND) ranging from delayed conduction to sinus arrest with the potential to induce asystole. Theophylline a positive chronotropic agent has been previously used for correction of sinus node dysfunction but never been utilized for the correction of lithium-induced SND. We report the first successful use of Theophylline for rate/rhythm correction of SND in a patient presenting with acute lithium toxicity along with a review summarizing the clinical features of all published literature regarding lithium-induced SND. Methods: Case report and systematic review of the literature are presented. Three independent scientific databases were queried for reports of lithium-induced SND. A clinical compendium was then generated detailing associated clinical data and descriptive statistics were performed. Results: 1,117 reports were initially retrieved with full-text review yielding a cohort of 49 unique, independent studies. (61.4%) of patients presented with a supratherapeutic lithium level, 12 (21.1%) were normotherapeutic, and 11 (19.3%) were subtherapeutic. EKG findings varied but most commonly described sinus node dysfunction with a variable degree of sinoatrial block with sinus bradycardia (54.39%) and sinus arrest (29.82%) predominating. Twelve patients (21.1%) required inotrope or vasopressor support. 10 (17.5%) of patient required temporary pacing while 7 (12.3%) required permanent pacemaker implantation. In the majority of cases no significant permanent sequelae were reported as 50 (87.7%) patients recovered, 2 (3.5%) patients had persistent sinus node dysfunction, and 2 (3.5%) patients expired as a result of acute lithium toxicity. Discussion & conclusion: In this review we report the most up-to-date and comprehensive clinical compendium of lithium-associated sinus node dysfunction along with describing a novel treatment methodology to rapidly correct lithium-induced cardiac toxicity in a patient with long-standing bipolar disorder on chronic lithium treatment. We have reviewed the available literature and provide a comprehensive summary detailing symptomatology of presentation, treatments utilized, electrocardiographic findings and patient prognoses. We have concluded that under the presumptive conditions that transient sinus node dysfunction will resolve with elimination of toxic concentrations of lithium, temporary chronotropic support provided by theophylline administration would be preferable to more invasive measures such as hemodialysis, temporary pacing, or implantation of a permanent pacemaker.

BRASH (Bradycardia, Renal Failure, Atrioventricular Nodal Blockade, Shock, and Hyperkalemia) Syndrome: A Frequently Underrecognized Condition Often Confused With Simple Hyperkalemia.

BRASH syndrome, defined by bradycardia, renal failure, atrioventricular nodal blockade, shock, and hyperkalemia, is a relatively new and often underrecognized condition. In this article, we present a case of an elderly female who developed an episode of syncope. She was found to have refractory shock and bradycardia in the emergency department. Laboratory results and other findings led to the diagnosis of a BRASH syndrome, which was refractory to medical therapy alone, requiring transvenous pacing, hemodialysis, and vasopressor support.

A stroke patient with an unusual electrocardiogram.

We present a case of a 70 year old man with a history of paroxysmal atrial flutter who was admitted to the hospital with symptoms and imaging consistent with an acute stroke. Physical exam was notable for a pulse rate of 50 beats per minute and right sided facial droop with mild dysarthria. Admission ECG shows a junctional bradycardia with evidence of dual AV node physiology, rarely manifested in a retrograde fashion on a standard ECG. The patient likely experienced parasympathetic sinus node slowing in the setting of acute stroke. During post-stroke monitoring, the patient demonstrated return of sinus rhythm with chronotropic competence and he had no additional arrhythmia during admission.

Anti-N-Methyl-D-Aspartate Receptor Encephalitis and Life-Threatening Sinus Node Dysfunction: A Case Report, Literature Review, and Analysis of 23 Cases.

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is the most common form of autoimmune encephalitis, presenting with various psychiatric manifestations, including behavioral and cognitive impairments, movement disorders, decreased consciousness, dysphasia, seizures, and autonomic dysfunction. Autonomic dysfunction may involve hyperthermia, apnea, hypotension, tachycardia, and life-threatening manifestations of sinus node dysfunction (SND), such as bradycardia, sinus pause or arrest, and asystole. The severity and significance of SND are critical, as it is not uncommon for these patients to progress into asystolic cardiac arrest, potentially contributing to morbidity and mortality. Accordingly, we present the case of an 18-year-old female with anti-NMDAR encephalitis who experienced multiple episodes of sinus pause/arrest and asystolic cardiac arrest, achieving a return of spontaneous circulation after successful CPR in all instances, ultimately requiring permanent pacemaker implantation. Additionally, we performed a literature review and analyzed 23 similar anti-NMDAR encephalitis cases with SND manifestations, including sinus pause/arrest or asystolic cardiac arrest, to identify common risk factors and describe management strategies and outcomes. Moreover, we investigated the potential association between teratoma and permanent pacemaker use in SND.

Long-Term Incidence of Bradycardia and Pacemaker Implantations Among Cross-Country Skiers: A Cohort Study.

BACKGROUND: Bradycardia is more common among well-trained athletes than in the general population, but the association with pacemaker implantations is less known. We investigated associations of endurance training with incidence of bradycardia and pacemaker implantations, including sex differences and long-term outcome, in a cohort of endurance trained individuals. METHODS: All Swedish skiers who completed >1 race in the cross-country skiing event Vasaloppet between 1989 and 2011 (n=209 108) and a sample of 532 290 nonskiers were followed until first event of bradycardia, pacemaker implantation, or death, depending on end point. The Swedish National Patient Register was used to obtain diagnoses. Cox regression was used to investigate associations of number of completed races and finishing time in Vasaloppet with incidence of bradycardia and pacemaker implantations. In addition, Cox regression was used to investigate associations of pacemaker implantations with death in skiers and nonskiers. RESULTS: Male skiers had a higher incidence of bradycardia (adjusted hazard ratio [aHR], 1.19 [95% CI, 1.05-1.34]) and pacemaker implantations (aHR, 1.17 [95% CI, 1.04-1.31]) compared with male nonskiers. Those who completed the most races and had the best performances exhibited the highest incidence. For female skiers in Vasaloppet, the incidence of bradycardia (aHR, 0.98 [95% CI, 0.75-1.30]) and pacemaker implantations (aHR, 0.98 [95% CI, 0.75-1.29]) was not different from that of female nonskiers. The indication for pacemaker differed between skiers and nonskiers, with sick sinus syndrome more common in the former and third-degree atrioventricular block in the latter. Skiers had lower overall mortality rates than nonskiers (aHR, 0.16 [95% CI, 0.15-0.17]). There were no differences in mortality rates by pacemaker status among skiers. CONCLUSIONS: In this study, male endurance skiers had a higher incidence of bradycardia and pacemaker implantations compared with nonskiers, a pattern not seen in women. Among male skiers, those who completed the most races and had the fastest finishing times had the highest incidence of bradycardia and pacemaker implantations. Within each group, mortality rates did not differ in relation to pacemaker status. These findings suggest that bradycardia associated with training leads to a higher risk for pacemaker implantation without a detrimental effect on mortality risk.

Fetal bradycardia and acidosis during maternal parenteral iron: Case reports and literature review.

Iron deficiency anemia is an important problem among pregnant women, and intravenous (IV) iron infusions have been increasingly used. Whether fetal monitoring is required during infusion has been debated, with a recent guideline by Hematologists recommending against such. We report two cases of fetal bradycardia after iron isomaltoside (IIM), in women with otherwise good maternal and fetal health. Both developed dyspnea with desaturation minutes from infusion, followed by persistent fetal bradycardia. Both underwent category 1 CS, with cord arterial pH of 7.08 and 6.94 respectively. Upon literature review, only three case reports on fetal bradycardia in IV iron were identified. For older IV iron formulations, a case was reported after IV dextran test dose, while two cases after ferric gluconate were reported. For the new formulation IIM, only one case was reported so far, but in a woman with Crohn's disease and intrauterine growth restriction. IV iron in pregnancy carries risk of anaphylactic or hypersensitivity reactions, even with the newest formulations and in women with good maternal and fetal health. While rarely reported so far, fetal bradycardia is a possible consequence, commonly preceded by respiratory symptoms. Fetal monitoring should therefore be considered during infusion.

Effect of Bedside Ultrasound-Guided Versus Fluoroscopy-Guided Transvenous Cardiac Temporary Pacing in Children with Bradyarrhythmia.

To compare the efficacy and safety of bedside ultrasound-guided and fluoroscopy-guided transvenous cardiac temporary pacing in the treatment of bradyarrhythmia in children. Children treated by temporary intravenous cardiac pacing from January 2016 to June 2023 in Hunan Provincial Children's Hospital were enrolled, and the characteristics and data of the cases were summarized. Patients were divided into bedside ultrasound-guided group (ultrasound group) and fluoroscopy-guided group (fluoroscopy group) according to the implantation guidance methods. The efficacy, safety, and incidence of complications in children were compared, and follow-up analysis was carried out. A total of 30 children were enrolled, including 18 males and 12 females, with a median age of 5.5 (2.9, 10.0) years and a median weight of 18.7 (12.7, 32.7) kg. The most common primary diseases were fulminant myocarditis (13/30 cases) and congenital high-grade AVB (10/30 cases). Among them, the proportion of congenital high AVB in the fluoroscopy group was significantly higher than that in the ultrasound group, and the difference was statistically significant (p = 0.007). The implantation process was successful in all 30 children. From the time of pacing decision to implantation, the median time of ultrasound group was 56 (30, 60) min and that of fluoroscopy group was 154 (78,180) min, with a statistically significant difference (P < 0.001). A total of 5 cases developed complications. There was no statistically significant difference between the two groups (P > 0.05). Compared with traditional fluoroscopic temporary pacing, bedside ultrasound-guided temporary pacing technology can effectively shorten the operation time and reduce the occurrence of complications and has become a better choice for children's emergency and critical care treatment. The right internal jugular vein is preferred for intravenous implantation.

Cardioneuroablation can be an effective strategy to treat glossopharyngeal neuralgia-related sinus bradycardia and pauses.

INTRODUCTION: Cardioneuroablation (CNA) has proven effectiveness in addressing hypervagotonia symptoms, such as neurocardiogenic syncope. METHODS AND RESULTS: In this case, we present the first-time application of CNA in a case of vago-glossopharyngeal neuralgia (VGPN). A 59-year-old female with near-syncope, sinus bradycardia, and sinus pauses triggered by recurrent right-sided neck pain was diagnosed with VGPN. The patient underwent successful treatment with carbamazepine and CNA. Subsequent follow-up revealed the sustained absence of sinus bradycardia or pauses, even upon neck pain resurgence after discontinuing carbamazepine. CONCLUSION: In this patient, CNA successfully prevented pauses associated with VGPN, avoiding permanent pacemaker implantation.

Exploring the impact of electrocardiographic parameters on the risk of common arrhythmias: a two-sample Mendelian randomization study.

Background: Observational studies have shown that heart rate (HR), heart rate variability (HRV), P-wave terminal force, P-wave duration, T-wave amplitude and PR interval are associated with risk factors for atrial fibrillation (AF) or bradycardia. Arrhythmias are associated with many causes of hospitalization. However, observational studies are susceptible to confounding factors that have not yet been identified. The objective of this study was to clarify the causal relationships by Mendelian randomization analysis. Methods: We conducted a two-sample and multivariate Mendelian randomization (MVMR) analysis using genome-wide association study (GWAS) data from a European population to assess the total and direct causal effects of HR, three HRV traits, P-wave terminal force, P-wave duration, T-wave top amplitude in five-lead modes, and the PR interval on the risk of AF (N=191,205), bradycardia (N=463,010), and supraventricular tachycardia (SVT) (N=463,010). Results: The results of the univariate MR analysis revealed the following significant causal effects: the higher the genetically predicted PR interval, the lower the risk of AF; the higher the HR and T-wave top amplitude (aVR leads and V3 + V4 + aVL leads), the lower the risk of bradycardia; and the higher HR and the lower PR interval, the higher the risk of SVT. The multivariate MR results indicated that the HRV_standard deviation of the normal-to-normal (SDNN) interval had an independent causal effect on the risk of AF [odds ratio (OR): 0.515; 95% confidence interval (CI): 0.278-0.954; P=0.03], and the T-wave top amplitude in the aVR leads (OR: 0.998; 95% CI: 0.996-0.999; P<0.001) and the HRV_SDNN (OR: 0.988; 95% CI: 0.976-1.000; P=0.045) had independent causal effects on the risk of bradycardia. Conclusions: The HRV_SDNN had an independent causal effect on AF, while the HRV_SDNN and T-wave top amplitude in the aVR leads had independent causal effects on bradycardia, which suggests that some of the electrocardiographic parameters have preventive effects on the incidence of AF and bradycardia.

Case Report: Bradycardia in neonatal lupus: differential diagnosis between atrioventricular block and premature atrial contractions with block.

Neonatal lupus may be associated with severe cardiac conduction problems, including high-degree or complete atrioventricular (AV) block, necessitating immediate pacemaker implantation during the neonatal period. However, cardiac manifestations of neonatal lupus may extend beyond AV block. Our case was a full-term female neonate, who presented with fetal arrhythmia and bradycardia with a heart rate of approximately 70-75 beats per minute after birth. Neonatal lupus was diagnosed later due to positive maternal and neonatal anti-SSA/Ro antibody. High-degree AV block was considered initially but bigeminy premature atrial contractions (PACs) with block was confirmed through a detailed evaluation of an electrocardiogram, which demonstrated unfixed PP intervals and fixed RR intervals. Atrial tachycardia (AT) developed when the neonate was 23 days old. The key point that differentiates high-degree AV block from PACs with block is the PP interval. The PP interval is fixed in high-degree AV block and unfixed in PACs with block. Careful differential diagnosis is required in neonates with bradycardia because it may lead to very different management. Our case presents a good illustration of why these arrhythmias need to be differentiated. Furthermore, our case may be the first of neonatal lupus with AT.

The role of cognition as a factor regulating the diving responses of animals, including humans.

The dive response involves three main components - breath holding, reduced heart rate and increased peripheral vasoconstriction - and is ubiquitous during forced dives in air-breathing vertebrates; however, numerous studies in free-diving animals have shown that the heart rate response to diving varies considerably in a manner that suggests cognitive control. Furthermore, studies on free-diving animals and controlled experiments in trained animals both indicate that the dive response can be conditioned, such that the reduction in heart rate begins before submergence and the extent of the reduction is set early in the dive. In addition, numerous species also experience an increase in heart rate and blood flow during ascent at the end of a dive, a phenomenon commonly called 'ascent tachycardia'. Collectively, these data suggest that although the dive response is under autonomic control, many species can vary its magnitude depending on the length and type of the planned dive - an indication of a role for cognition in the overall physiological responses associated with diving. Here, we provide examples of the conditioned cardiac responses - including anticipatory changes in heart rate - in several diving species and propose potential underlying mechanisms. We also discuss how the anticipatory cardiovascular responses not only improve diving capacity, but also prevent diving-related problems, such as decompression sickness or barotrauma, through a mechanism described by the selective gas exchange hypothesis.