Magnetic resonance imaging during untreated ventricular fibrillation reveals prompt right ventricular overdistention without left ventricular volume loss

Rapid prototyping and facile customization of conductive hydrogel bioelectronics based on all laser process

Proper customization in size and shape is essential in implantable bioelectronics for stable bio-signal recording. Over the past decades, many researchers have heavily relied on conventional photolithography processes to fabricate implantable bioelectronics. Therefore, they could not avoid the critical limitation of high cost and complex processing steps to optimize bioelectronic devices for target organs with various sizes and shapes. Here, we propose rapid prototyping using all laser processes to fabricate customized bioelectronics. PEDOT:PSS is selectively irradiated by an ultraviolet (UV) pulse laser to form wet-stable conductive hydrogels that can softly interact with biological tissues (50 μm line width). The encapsulation layer is selectively patterned using the same laser source by UV-curing polymer networks (110 μm line width). For high stretchability (over 100%), mesh structures are made by the selective laser cutting process. Our rapid prototyping strategy minimizes the use of high-cost equipment, using only a single UV laser source to process the electrodes, encapsulation, and substrates that constitute bioelectronics without a photomask, enabling the prototyping stretchable microelectrode array with an area of 1 cm2 less than 10 min. We fabricated an optimized stretchable microelectrode array with low impedances (∼1.1 kΩ at 1 kHz) that can effectively record rat's cardiac signals with various health states.

Hemoglobin concentration and blood shift during dry static apnea in elite breath hold divers

Introduction

Elite breath-hold divers (BHD) enduring apneas of more than 5 min are characterized by tolerance to arterial blood oxygen levels of 4.3 kPa and low oxygen-consumption in their hearts and skeletal muscles, similar to adult seals. Adult seals possess an adaptive higher hemoglobin-concentration and Bohr effect than pups, and when sedated, adult seals demonstrate a blood shift from the spleen towards the brain, lungs, and heart during apnea. We hypothesized these observations to be similar in human BHD. Therefore, we measured hemoglobin- and 2,3-biphosphoglycerate-concentrations in BHD (n = 11) and matched controls (n = 11) at rest, while myocardial mass, spleen and lower extremity volumes were assessed at rest and during apnea in BHD.

Methods and results

After 4 min of apnea, left ventricular myocardial mass (LVMM) determined by 15O-H2O-PET/CT (n = 6) and cardiac MRI (n = 6), was unaltered compared to rest. During maximum apnea (∼6 min), lower extremity volume assessed by DXA-scan revealed a ∼268 mL decrease, and spleen volume, assessed by ultrasonography, decreased ∼102 mL. Compared to age, BMI and VO2max matched controls (n = 11), BHD had similar spleen sizes and 2,3- biphosphoglycerate-concentrations, but higher total hemoglobin-concentrations.

Conclusion

Our results indicate: 1) Apnea training in BHD may increase hemoglobin concentration as an oxygen conserving adaptation similar to adult diving mammals. 2) The blood shift during dry apnea in BHD is 162% more from the lower extremities than from the spleen. 3) In contrast to the previous theory of the blood shift demonstrated in sedated adult seals, blood shift is not towards the heart during dry apnea in humans.

Right Ventricular Dilation in Cardiac Arrest May Have Complicated Implications: A Case Report

Right ventricular (RV) dilation has been observed in patients in cardiac arrest. Historically, this phenomenon is almost always attributed to massive pulmonary embolism. However, recent advancements have revealed that there are many other causes of RV dilation in cardiac arrest. In this case report, we present the case of an elderly woman who was found in cardiac arrest with an initial normal left ventricle to RV ratio with subsequent development of RV dilation in the midst of resuscitation without changes to other hemodynamic parameters. This case further bolsters the complex nature of cardiac physiology in cardiac arrest and the need for further investigation.

The use of critical care echocardiography in peri-arrest and cardiac arrest scenarios: Pros, cons and what the future holds

Echocardiography is being increasingly deployed as a diagnostic and monitoring tool in the critically ill. This rise in popularity has led to its recommendation as a core competence in intensive care, with several training routes available. In the peri-arrest and cardiac arrest population, point of care focused echocardiography has the potential to transform patient care and improve outcomes. Be it via diagnosis of shock aetiology and reversibility or assessing response to treatment and prognostication. This narrative review discusses current and future applications of echocardiography in this patient group and provides a structure with which one can approach such patients.

[Adult advanced life support]

These European Resuscitation Council Advanced Life Support guidelines are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. This section provides guidelines on the prevention of and ALS treatments for both in-hospital cardiac arrest and out-of-hospital cardiac arrest.

European Resuscitation Council Guidelines 2021: Adult advanced life support

These European Resuscitation Council Advanced Life Support guidelines, are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. This section provides guidelines on the prevention of and ALS treatments for both in-hospital cardiac arrest and out-of-hospital cardiac arrest.

Cardiac hypoxic resistance and decreasing lactate during maximum apnea in elite breath hold divers

Breath-hold divers (BHD) enduring apnea for more than 4 min are characterized by resistance to release of reactive oxygen species, reduced sensitivity to hypoxia, and low mitochondrial oxygen consumption in their skeletal muscles similar to northern elephant seals. The muscles and myocardium of harbor seals also exhibit metabolic adaptations including increased cardiac lactate-dehydrogenase-activity, exceeding their hypoxic limit. We hypothesized that the myocardium of BHD possesses similar adaptive mechanisms. During maximum apnea ¹⁵O-H₂O-PET/CT (n = 6) revealed no myocardial perfusion deficits but increased myocardial blood flow (MBF). Cardiac MRI determined blood oxygen level dependence oxygenation (n = 8) after 4 min of apnea was unaltered compared to rest, whereas cine-MRI demonstrated increased left ventricular wall thickness (LVWT). Arterial blood gases were collected after warm-up and maximum apnea in a pool. At the end of the maximum pool apnea (5 min), arterial saturation decreased to 52%, and lactate decreased 20%. Our findings contrast with previous MR studies of BHD, that reported elevated cardiac troponins and decreased myocardial perfusion after 4 min of apnea. In conclusion, we demonstrated for the first time with ¹⁵O-H₂O-PET/CT and MRI in elite BHD during maximum apnea, that MBF and LVWT increases while lactate decreases, indicating anaerobic/fat-based cardiac-metabolism similar to diving mammals.

Pseudo-ginsengenin DQ ameliorated aconitine-induced arrhythmias by influencing Ca2+ and K+ currents in ventricular myocytes

Pseudo-ginsengenin DQ (PDQ) is the product of the oxidative cyclization of protopanaxadiol. PDQ exhibits various bioactivities, including reversal of multidrug resistance in cancer, renal protective effects against acute nephrotoxicity and attenuating myocardial ischemia injury induced by isoproterenol or ligation of coronary arterials, but its effect on arrhythmias has not been clear until now. Because of the complicated effects of ginseng on the cardiovascular system, it is necessary to investigate whether PDQ affects arrhythmias, which are always concomitant with other cardiac diseases. Aconitine was used to induce arrhythmia in vivo. To understand its electrophysiological fundamental, whole-cell patch-clamp was used to record the L-type calcium current (I_Ca,L) and potassium currents (I_K and I_K1) in the ventricular myocytes in rats. Oral administration of PDQ exerted obvious antiarrhythmic effects, as indicated by the decreased incidence rate, lower number of occurrences, and shorter duration time of ventricular tachycardia and ventricular tachycardia, decreased mortality rate and increased survival time. I_Ca,L and I_K were inhibited by PDQ treatment while I_K1 was not affected. To conclude, PDQ may have an anti-arrhythmia effect through inhibiting I_Ca,L and I_K.

Pseudo-ginsengenin DQ (PDQ) is the product of the oxidative cyclization of protopanaxadiol. PDQ could ameliorate aconitine-induced arrhythmias by influencing Ca²⁺ and K⁺ currents in ventricular myocytes.

Impact of right ventricular dysfunction on mortality in adults with cardiac arrest undergoing coronary angiogram

OBJECTIVE

We sought to identify the impact of echocardiographic right ventricular (RV) systolic dysfunction on mortality in adults with cardiac arrest (CA).

METHODS

The study population included 147 adults hospitalized with CA who underwent both echocardiogram and coronary angiogram at an academic tertiary medical center. The primary outcome of interest was all-cause in-hospital mortality.

RESULTS

Of the 147 patients studied, 20 (13.6%) had evidence of RV systolic dysfunction while 127 (86.4%) did not. Patients with RV dysfunction had higher rates of prior surgical and percutaneous coronary revascularization. They also had higher rates of mechanical ventilation, therapeutic hypothermia, vasopressor and inotrope use, and a trend towards higher rates of mechanical support. Coronary angiogram revealed higher rates of multivessel disease, right coronary artery intervention, and glycoprotein IIb-IIIa inhibitor use in those with RV dysfunction, alongside with lower echocardiographic left ventricular ejection fraction. In-hospital mortality rates were higher in adults with RV dysfunction compared to those without (55% vs 11%, p < 0.001). In multivariate analysis, RV dysfunction was the strongest independent predictor of higher mortality [odds ratio 4.71, 95% confidence interval 1.27-17.50].

CONCLUSIONS

In this observational contemporary study, RV dysfunction was independently associated with higher mortality in adults with CA undergoing coronary angiogram. RV dysfunction may be useful for risk stratification and management in this high-mortality population.

Relationship between hemodynamic parameters and severity of ischemia-induced left ventricular wall thickening during cardiopulmonary resuscitation of consistent quality

Ischemia-induced left ventricular (LV) wall thickening compromises the hemodynamic effectiveness of cardiopulmonary resuscitation (CPR). However, accurate assessment of the severity of ischemia-induced LV wall thickening during CPR is challenging. We investigated, in a swine model, whether hemodynamic parameters, including end-tidal carbon dioxide (ETCO₂) level, are linearly associated with the severity of ischemia-induced LV wall thickening during CPR of consistent quality. We retrospectively analyzed 96 datasets for ETCO₂ level, arterial pressure, LV wall thickness, and the percent of measured end-diastolic volume (%EDV) relative to EDV at the onset of ventricular fibrillation from eight pigs. Animals underwent advanced cardiovascular life support based on resuscitation guidelines. During CPR, LV wall thickness progressively increased while %EDV progressively decreased. Systolic and diastolic arterial pressure and ETCO₂ level were significantly correlated with LV wall thickness and %EDV. Linear mixed effect models revealed that, after adjustment for significant covariates, systolic and diastolic arterial pressure were not associated with LV wall thickness or %EDV. ETCO₂ level had a significant linear relationship with %EDV (P = 0.004). However, it could explain only 28.2% of the total variance of %EDV in our model. In conclusion, none of the hemodynamic parameters examined in this study appeared to provide sufficient information on the severity of ischemia-induced LV wall thickening.

Échographie et prise en charge de l’arrêt cardiaque

L’arrêt cardiorespiratoire (ACR) est une situation fréquente pour les structures d’urgences et de réanimation, et l’utilisation de l’échographie y est recommandée par les sociétés savantes. Elle doit impérativement se faire sans augmentation des temps d’interruption du massage cardiaque externe. Après formation, elle permet de détecter rapidement et facilement la présence d’une contractilité myocardique qui est un élément pronostique important pouvant aider dans la décision d’arrêter la RCP. Le recours à des protocoles bien établis avec des équipes entraînées permet d’éviter une interruption prolongée de la RCP. Cependant, aucune étude humaine de grande ampleur n’a permis de décrire de manière fiable pendant l’ACR la sémiologie échographique des causes curables que constituent l’hypovolémie, l’embolie pulmonaire, la tamponnade et le pneumothorax compressif.

The Right Ventricle Is Dilated During Resuscitation From Cardiac Arrest Caused by Hypovolemia: A Porcine Ultrasound Study

OBJECTIVES

Dilation of the right ventricle during cardiac arrest and resuscitation may be inherent to cardiac arrest rather than being associated with certain causes of arrest such as pulmonary embolism. This study aimed to compare right ventricle diameter during resuscitation from cardiac arrest caused by hypovolemia, hyperkalemia, or primary arrhythmia (i.e., ventricular fibrillation).

DESIGN

Thirty pigs were anesthetized and then randomized to cardiac arrest induced by three diffrent methods. Seven minutes of untreated arrest was followed by resuscitation. Cardiac ultrasonographic images were obtained during induction of cardiac arrest, untreated cardiac arrest, and resuscitation. The right ventricle diameter was measured. Primary endpoint was the right ventricular diameter at the third rhythm analysis.

SETTING

University hospital animal laboratory.

SUBJECTS

Female crossbred Landrace/Yorkshire/Duroc pigs (27-32 kg).

INTERVENTIONS

Pigs were randomly assigned to cardiac arrest caused by either hypovolemia, hyperkalemia, or primary arrhythmia.

MEASUREMENTS AND MAIN RESULTS

At the third rhythm analysis during resuscitation, the right ventricle diameter was 32 mm (95% CI, 29-35) in the hypovolemia group, 29 mm (95% CI, 26-32) in the hyperkalemia group, and 25 mm (95% CI, 22-28) in the primary arrhythmia group. This was larger than baseline for all groups (p = 0.03). When comparing groups at the third rhythm analysis, the right ventricle was larger for hypovolemia than for primary arrhythmia (p < 0.001).

CONCLUSIONS

The right ventricle was dilated during resuscitation from cardiac arrest caused by hypovolemia, hyperkalemia, and primary arrhythmia. These findings indicate that right ventricle dilation may be inherent to cardiac arrest, rather than being associated with certain causes of arrest. This contradicts a widespread clinical assumption that in hypovolemic cardiac arrest, the ventricles are collapsed rather than dilated.

Reduced right ventricular diameter during cardiac arrest caused by tension pneumothorax - a porcine ultrasound study

INTRODUCTION

Advanced life support (ALS) guidelines recommend ultrasound to identify reversible causes of cardiac arrest. Right ventricular (RV) dilatation during cardiac arrest is commonly interpreted as a sign of pulmonary embolism. The RV is thus a focus of clinical ultrasound examination. Importantly, in animal studies ventricular fibrillation and hypoxia results in RV dilatation. Tension pneumothorax (tPTX) is another reversible cause of cardiac arrest, however, the impact on RV diameter remains unknown.

AIM

To investigate RV diameter evaluated by ultrasound in cardiac arrest caused by tPTX or hypoxia.

METHODS

Pigs were randomized to cardiac arrest by either tPTX (n = 9) or hypoxia (n = 9) and subsequently resuscitated. Tension pneumothorax was induced by injection of air into the pleural cavity. Hypoxia was induced by reducing tidal volume. Ultrasound images of the RV were obtained throughout the study. Tension pneumothorax was decompressed after the seventh rhythm analysis. The primary endpoint was RV diameter after the third rhythm analysis.

RESULTS

At cardiac arrest the RV diameter was 17 mm (95% CI: 13; 21) in the tPTX group and 36 mm (95% CI: 33; 40) in the hypoxia group (P < 0.01, n = 9 for both). At third rhythm analysis RV diameter was smaller in the tPTX group: 12 mm (95% CI: 7; 16) vs. hypoxia group: 28 mm (25; 32) (P < 0.01). After decompression no difference existed between groups: tPTX 29 mm (95% CI: 23; 34) vs. hypoxia 29 mm (95% CI: 20; 38).

CONCLUSION

The RV diameter is smaller during cardiopulmonary resuscitation in cardiac arrest caused by tPTX when compared with hypoxia. The difference disappears after tPTX decompression.

Cardiocerebral and cardiopulmonary resuscitation - 2017 update

Sudden cardiac arrest is a major public health problem in the industrialized nations of the world. Yet, in spite of recurrent updates of the guidelines for cardiopulmonary resuscitation and emergency cardiac care, many areas have suboptimal survival rates. Cardiocerebral resuscitation, a non‐guidelines approach to therapy of primary cardiac arrest based on our animal research, was instituted in Tucson (AZ, USA) in 2002 and subsequently adopted in other areas of the USA. Survival rates of patients with primary cardiac arrest and a shockable rhythm significantly improved wherever it was adopted. Cardiocerebral resuscitation has three components: the community, the pre‐hospital, and the hospital. The community component emphasizes bystander recognition and chest compression only resuscitation. Its pre‐hospital or emergency medical services component emphasizes: (i) urgent initiation of 200 uninterrupted chest compressions before and after each indicated single defibrillation shock, (ii) delayed endotracheal intubation in favor of passive delivery of oxygen by a non‐rebreather mask, (iii) early adrenaline administration. The hospital component was added later. The national and international guidelines for cardiopulmonary resuscitation and emergency medical services are still not optimal, for several reasons, including the fact that they continue to recommend the same approach for two entirely different etiologies of cardiac arrest: primary cardiac arrest, often caused by ventricular fibrillation, where the arterial blood oxygenation is little changed at the time of the arrest, and secondary cardiac arrest from severe respiratory insufficiency, where the arterial blood is severely desaturated at the time of cardiac arrest. These different etiologies need different approaches to therapy.

The Expression of B-Type Natriuretic Peptide After CaCl2-Induced Arrhythmias in Rats

To investigate the patterns of B-type natriuretic peptide (BNP) expression after arrhythmia, BNP was assessed at different time points (0 minute, 10 minutes, 30 minutes, 1 hour, 3 hours, and 6 hours) in CaCl2-induced arrhythmia in rats through various methods such as immunohistochemistry, Western blotting, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay. Immunohistochemistry results showed that the expression of BNP in the endocardium was higher than that in the epicardium in rats undergoing sustained arrhythmias. The BNP-to-GAPDH (glyceraldehyde-3-phosphate dehydrogenase) ratios determined by Western blotting analysis revealed no change at 0 minute but increased at 10 minutes and reached the first peak (0.48 [0.03]) at 30 minutes. After a brief decline, the second peak was observed at 6 hours (0.54 [0.03]). Similar patterns of BNP messenger RNA expression were also observed by quantitative real-time polymerase chain reaction. The plasma BNP concentrations did not change after initial bouts of cardiac arrhythmias but significantly increased 30 minutes after CaCl2 injections. The results demonstrate that arrhythmia causes an elevation of BNP in the myocardium and blood, and BNP messenger RNA increases in initial arrhythmia while its protein in myocardium and plasma does not; however, both of them were elevated after sustained arrhythmia. Such an elevated BNP expression, which is directly related to the severity and duration of the arrhythmias, may suggest the existence of fatal arrhythmia in sudden cardiac death.

Systematic review of the mechanisms driving effective blood flow during adult CPR

BACKGROUND

High quality chest compressions is the most significant factor related to improved short-term and long-term outcome in cardiac arrest. However, considerable controversy exists over the mechanisms involved in driving blood flow.

OBJECTIVES

The aim of this systematic review is to elucidate major mechanisms involved in effective compression-mediated blood flow during adult cardiopulmonary resuscitation (CPR).

DESIGN AND SETTING

Systematic review of studies identified from the bibliographic databases of PubMed/Medline, Cochrane, and Scopus.

SELECTION CRITERIA

All human and animal studies including information on the responsible mechanisms of compression-related blood flow.

DATA COLLECTION AND ANALYSIS

Two reviewers (MG, TX) independently screened all potentially relevant titles and abstracts for eligibility, by using a standardized data-worksheet.

MAIN RESULTS

Forty seven studies met the inclusion criteria. Because of the heterogeneity in outcome measures, quantitative synthesis of evidence was not feasible. Evidence was critically synthesized in order to answer the review questions, taking into account study heterogeneity and validity. The number of included studies per category is as follows: blood flow during chest compression, nine studies; blood flow during chest decompression, six studies; effect of chest compression on cerebral blood flow, eight studies; active compression-decompression CPR, 14 studies; and effect of ventilation on compression-related blood flow, 13 studies.

CONCLUSION

The evidence so far is inconclusive regarding the major responsible mechanism in compression-related blood flow. Although both 'cardiac pump' and 'thoracic pump' have a key role, the effect of each mechanism is highly depended on other resuscitation parameters, such as positive pressure ventilation and compression depth.

The potential mechanism of the detrimental effect of defibrillation prior to cardiopulmonary resuscitation in prolonged cardiac arrest model

Defibrillation is no longer universally recommended as initial intervention for the reversal of ventricular fibrillation (VF) after a prolonged and untreated cardiac arrest. We sought to examine this issue in an animal model where a prolonged untreated VF was induced. The aim of this study was to investigate the potential mechanism of the detrimental effect of defibrillation prior to cardiopulmonary resuscitation (CPR) in prolonged cardiac arrest model. VF was electrically induced in 32 domestic male swine weighing 40±3 kg and remained untreated for 15 minutes. The animals were then randomly allocated to either the initial defibrillation group or the chest compression group. Mean aortic pressure, right atrial pressure and coronary perfusion pressure (CPP) were continuously measured during the performance. The dimensions of the left ventricle (LV) were assessed by echocardiographic methods. The CPP induced by CPR after defibrillation was significantly lower in the initial defibrillation group than in the chest compression group; 1 minute after defibrillation (9±3 mmHg vs. 14.8±7 mmHg (P<0.05)), and after 5 minutes 16±5 mmHg vs. 21.7±1 mmHg (P<0.05). The LV volumes were reduced from 18±2 mmHg to 14±1 mmHg after defibrillation (P<0.05). In brief, this study showed that the conducting defibrillation prior to chest compression may cause a contracture of the LV, resulting in lowering CPP, thus dropping the efficiency of chest compression in a prolonged cardiac arrest model.

At the heart of the arterial baroreflex: a physiological basis for a new classification of carotid sinus hypersensitivity

The aim of this review is to provide an update of the current knowledge of the physiological mechanisms underlying reflex syncope. Carotid sinus syncope will be used as the classical example of an autonomic reflex with relatively well-established afferent, central and efferent pathways. These pathways, as well as the pathophysiology of carotid sinus hypersensitivity (CSH) and the haemodynamic effects of cardiac standstill and vasodilatation will be discussed. We will demonstrate that continuous recordings of arterial pressure provide a better understanding of the cardiovascular mechanisms mediating arterial hypotension and cerebral hypoperfusion in patients with reflex syncope. Finally we will demonstrate that the current criteria to diagnose CSH are too lenient and that the conventional classification of carotid sinus syncope as cardioinhibitory, mixed and vasodepressor subtypes should be revised because isolated cardioinhibitory CSH (asystole without a fall in arterial pressure) does not occur. Instead, we suggest that all patients with CSH should be thought of as being 'mixed', between cardioinhibition and vasodepression. The proposed stricter set of criteria for CSH should be evaluated in future studies.

Mild hypothermia delays the development of stone heart from untreated sustained ventricular fibrillation--a cardiovascular magnetic resonance study

BACKGROUND

'Stone heart' resulting from ischemic contracture of the myocardium, precludes successful resuscitation from ventricular fibrillation (VF). We hypothesized that mild hypothermia might slow the progression to stone heart.

METHODS

Fourteen swine (27 ± 1 kg) were randomized to normothermia (group I; n=6) or hypothermia groups (group II; n=8). Mild hypothermia (34 ± 2 °C) was induced with ice packs prior to VF induction. The LV and right ventricular (RV) cross-sectional areas were followed by cardiovascular magnetic resonance until the development of stone heart. A commercial 1.5T GE Signa NV-CV/i scanner was used. Complete anatomic coverage of the heart was acquired using a steady-state free precession (SSFP) pulse sequence gated at baseline prior to VF onset. Un-gated SSFP images were obtained serially after VF induction. The ventricular endocardium was manually traced and LV and RV volumes were calculated at each time point.

RESULTS

In group I, the LV was dilated compared to baseline at 5 minutes after VF and this remained for 20 minutes. Stone heart, arbitrarily defined as LV volume <1/3 of baseline at the onset of VF, occurred at 29 ± 3 minutes. In group II, there was less early dilation of the LV (p<0.05) and the development of stone heart was delayed to 52 ± 4 minutes after onset of VF (P<0.001).

CONCLUSIONS

In this closed-chest swine model of prolonged untreated VF, hypothermia reduced the early LV dilatation and importantly, delayed the onset of stone heart thereby extending a known, morphologic limit of resuscitability.

The primacy of basics in advanced life support

PURPOSE OF REVIEW

The standards required for optimal effect of chest compressions and the degree to which most practice falls short of ideal have not been widely appreciated. This review highlights some of the important data now available and offers a haemodynamic explanation that broadens current concepts.

RECENT FINDINGS

New techniques have permitted a detailed examination of how compressions are performed in practice. The implications of recent experimental work adds a new imperative to the need for improvement.

SUMMARY

In addition to highlighting the need for improved training and audit, the greater understanding of mechanisms in resuscitation suggest that guidelines for management of adult cardiac arrest of presumed cardiac origin need further revision and simplification.

Effects of wall stress on the dynamics of ventricular fibrillation: a simulation study using a dynamic mechanoelectric model of ventricular tissue

INTRODUCTION

To investigate the mechanisms underlying the increased prevalence of ventricular fibrillation (VF) in the mechanically compromised heart, we developed a fully coupled electromechanical model of the human ventricular myocardium.

METHODS AND RESULTS

The model formulated the biophysics of specific ionic currents, excitation-contraction coupling, anisotropic nonlinear deformation of the myocardium, and mechanoelectric feedback (MEF) through stretch-activated channels. Our model suggests that sustained stretches shorten the action potential duration (APD) and flatten the electrical restitution curve, whereas stretches applied at the wavefront prolong the APD. Using this model, we examined the effects of mechanical stresses on the dynamics of spiral reentry. The strain distribution during spiral reentry was complex, and a high strain-gradient region was located in the core of the spiral wave. The wavefront around the core was highly stretched, even at lower pressures, resulting in prolongation of the APD and extension of the refractory area in the wavetail. As the left ventricular pressure increased, the stretched area became wider and the refractory area was further extended. The extended refractory area in the wavetail facilitated the wave breakup and meandering of tips through interactions between the wavefront and wavetail.

CONCLUSIONS

This simulation study indicates that mechanical loading promotes meandering and wave breaks of spiral reentry through MEF. Mechanical loading under pathological conditions may contribute to the maintenance of VF through these mechanisms.

Why do chest compressions aid delayed defibrillation?

The new resuscitation guidelines permit compressions before delayed, defibrillation, a change that has generally been welcomed. The benefits are generally assumed to relate to the immediate provision of limited coronary perfusion with protection or replenishment of myocardial metabolic reserves. In this paper we argue that the concept is inadequate to explain many experimental and clinical observations made during resuscitation attempts. We argue that changes in the size and shape of the ventricles are the most important reason for the narrow window of opportunity for defibrillation alone and for the value of compressions in extending this period. We also draw attention to the implication for clinical resuscitation and to one aspect of the current guidelines of the European Resuscitation Council that we believe to be inconsistent with the evidence that we review.

Cardiac magnetic resonance imaging investigation of sustained ventricular fibrillation in a swine model--with a focus on the electrical phase

OBJECTIVES

We sought to develop a method to evaluate the rapidly changing cardiac dimensions during sustained ventricular fibrillation (VF). We also present details of our CPR research imaging program to facilitate this avenue of clinically important research.

BACKGROUND

The changes in cardiac dimensions occurring during the initial critical electrical phase of sustained VF are not entirely known. Conventional cardiac magnetic resonance imaging (CMR) functional imaging lacks the temporal resolution necessary to capture the dynamic changes within this early time period of sustained VF. We hypothesized that changes in the middle short axis slice of the ventricles will reflect changes in ventricular volumes accurately.

METHODS

Ventricular dimensions were determined from CMR for 30 min of untreated VF in a closed chest, closed pericardium model in seven swine. Ungated steady-state free precession images (SSFP) from the cardiac base to the apex were acquired, taking care to align the anatomical short axis (SAX) imaging planes maximally. The middle slice of the ventricles was determined as the mathematical center of the stack of SAX slices. We then compared the relative changes of right ventricle (RV) and left ventricle (LV) volumes to relative changes in mid-ventricular single slice area.

RESULTS

During 30 min of sustained VF, there was an excellent correlation between the changes in exact mid-slice area and the quantitative changes in ventricular volumes (r(2)>0.95).

CONCLUSIONS

Mid-slice area data can be used as a surrogate marker of prompt ventricular volume changes during VF. By imaging the heart 10 times faster, the rapid anatomical changes occurring during the initial few minutes of sustained VF can be understood better.

Haemodynamics of cardiac arrest and resuscitation

PURPOSE OF REVIEW

This review will summarize the available data regarding the haemodynamic changes occurring following cardiac arrest in humans and animal models.

RECENT FINDINGS

Following cardiac arrest due to ventricular fibrillation without cardiopulmonary resuscitation, blood flow exponentially falls but continues for approximately 5 min until the pressure gradient between the aorta and the right heart is completely dissipated. During cardiopulmonary resuscitation forward flow occurs into the aorta during the compression phase. Coronary blood flow is retrograde during the compression phase and antegrade during the decompression phase. Carotid blood flow takes over a minute to reach plateau levels following the initiation of chest compressions, and even brief interruptions of compressions result in a dramatic reduction in carotid blood flow which takes a minute or so to recover to plateau levels when compressions are reinstituted. Coronary perfusion pressure during the release phase of cardiopulmonary resuscitation has been shown to be a powerful predictor of the likelihood of recovery of spontaneous circulation following restoration of electrical activity.

SUMMARY

Recent studies have provided important insights into the haemodynamics of cardiac arrest and of cardiopulmonary resuscitation which may inform more effective strategies for the management of cardiac arrest in the future.