Maximal acceleration of calcium release refractoriness by β-adrenergic stimulation requires dual activation of protein kinase A and CaMKII in mouse ventricular myocytes

Time-dependent refractoriness of calcium (Ca2+) release in cardiac myocytes is an important factor in determining whether pro-arrhythmic release patterns develop. At the subcellular level of the Ca2+ spark, recent studies have suggested that recovery of spark amplitude is controlled by local sarcoplasmic reticulum (SR) refilling whereas refractoriness of spark triggering depends on both refilling and the sensitivity of the ryanodine receptor (RyR) release channels that produce sparks. Here we studied regulation of Ca2+ spark refractoriness in mouse ventricular myocytes by examining how β-adrenergic stimulation influenced sequences of Ca2+ sparks originating from individual RyR clusters. Our protocol allowed us to separately measure recovery of spark amplitude and delays between successive sparks, and data were interpreted quantitatively through simulations with a stochastic mathematical model. We found that, compared with spark sequences measured under control conditions: (1) β-adrenergic stimulation with isoproterenol accelerated spark amplitude recovery and decreased spark-to-spark delays; (2) activating protein kinase A (PKA) with forskolin accelerated amplitude recovery but did not affect spark-to-spark delays; (3) inhibiting PKA with H89 retarded amplitude recovery and increased spark- to-spark delays; (4) preventing phosphorylation of the RyR at serine 2808 with a knock-in mouse prevented the decrease in spark-to-spark delays seen with β-adrenergic stimulation; (5) inhibiting either PKA or Ca2+/calmodulin-dependent protein kinase II (CaMKII) during β-adrenergic stimulation prevented the decrease in spark-to-spark delays seen) without inhibition. The results suggest that activation of either PKA or CaMKII is sufficient to speed SR refilling, but activation of both kinases appears necessary to observe increased RyR sensitivity. The data provide novel insight into β-adrenergic regulation of Ca2+ release refractoriness in mouse myocytes.

Role of electrophysiological studies in predicting risk of ventricular arrhythmia in early repolarization syndrome.

BACKGROUND The early repolarization (ER) pattern is associated with an increased risk of arrhythmogenic sudden death. However, strategies for risk stratification of patients with the ER pattern are not fully defined. OBJECTIVES This study sought to determine the role of electrophysiology studies (EPS) in risk stratification of patients with ER syndrome. METHODS In a multicenter study, 81 patients with ER syndrome (age 36 ± 13 years, 60 males) and aborted sudden death due to ventricular fibrillation (VF) were included. EPS were performed following the index VF episode using a standard protocol. Inducibility was defined by the provocation of sustained VF. Patients were followed up by serial implantable cardioverter-defibrillator interrogations. RESULTS Despite a recent history of aborted sudden death, VF was inducible in only 18 of 81 (22%) patients. During follow-up of 7.0 ± 4.9 years, 6 of 18 (33%) patients with inducible VF during EPS experienced VF recurrences, whereas 21 of 63 (33%) patients who were noninducible experienced recurrent VF (p = 0.93). VF storm occurred in 3 patients from the inducible VF group and in 4 patients in the noninducible group. VF inducibility was not associated with maximum J-wave amplitude (VF inducible vs. VF noninducible; 0.23 ± 0.11 mV vs. 0.21 ± 0.11 mV; p = 0.42) or J-wave distribution (inferior, odds ratio [OR]: 0.96 [95% confidence interval (CI): 0.33 to 2.81]; p = 0.95; lateral, OR: 1.57 [95% CI: 0.35 to 7.04]; p = 0.56; inferior and lateral, OR: 0.83 [95% CI: 0.27 to 2.55]; p = 0.74), which have previously been demonstrated to predict outcome in patients with an ER pattern. CONCLUSIONS Our findings indicate that current programmed stimulation protocols do not enhance risk stratification in ER syndrome.

Infection rate of emergency bolt-kit vs. non-emergency conventional implanted silver bearing external ventricular drainage catheters.

BACKGROUND Bolt-kit systems are increasingly used as an alternative to conventional external cerebrospinal fluid (CSF) drainage systems. Since 2009 we regularly utilize bolt-kit external ventricular drainage (EVD) systems with silver-bearing catheters inserted manually with a hand drill and skull screws for emergency ventriculostomy. For non-emergency situations, we use conventional ventriculostomy with subcutaneous tunneled silver-bearing catheters, performed in the operating room with a pneumatic drill. This retrospective analysis compared the two techniques in terms of infection rates. METHODS 152 patients (aged 17-85 years, mean=55.4 years) were included in the final analysis; 95 received bolt-kit silver-bearing catheters and 57 received conventionally implanted silver-bearing catheters. The primary endpoint combined infection parameters: occurrence of positive CSF culture, colonization of catheter tips, or elevated CSF white blood cell counts (>4/μl). Secondary outcome parameters were presence of microorganisms in CSF or on catheter tips. Incidence of increased CSF cell counts and number of patients with catheter malposition were also compared. RESULTS The primary outcome, defined as analysis of combined infection parameters (occurrence of either positive CSF culture, colonization of the catheter tips or raised CSF white blood cell counts >4/μl)was not significantly different between the groups (58.9% bolt-kit group vs. 63.2% conventionally implanted group, p=0.61, chi-square-test). The bolt-kit group was non-inferior and not superior to the conventional group (relative risk reduction of 6.7%; 90% confidence interval: -19.9% to 25.6%). Secondary outcomes showed no statistically significant difference in the incidence of microorganisms in CSF (2.1% bolt-kit vs. 5.3% conventionally implanted; p=0.30; chi-square-test). CONCLUSIONS This analysis indicates that silver-bearing EVD catheters implanted with a bolt-kit system outside the operating room do not significantly elevate the risk of CSF infection as compared to conventional implant methods.

Transcranial Doppler-guided deairing of a pediatric ventricular assist device: experience with twins

We report the intraoperative courses of 2 consecutive Berlin Heart Excor® Pediatric Ventricular Assist Device implantations, in which transcranial Doppler ultrasonography helped to detect macroscopically undetected residual air bubbles captured in the pump after air removal had been correctly performed according to manufacturer's specifications. Our experience with these cases suggests that a beat-to beat deairing maneuver guided by transcranial Doppler is a useful strategy for reducing cerebral exposure to perioperative gaseous microembolism.

Clinical role of atrial arrhythmias in patients with arrhythmogenic right ventricular dysplasia

BACKGROUND: The clinical role of atrial fibrillation/atrial flutter (AF-AFl) and variables predicting these arrhythmias are not well defined in patients with arrhythmogenic right ventricular dysplasia (ARVD). We hypothesized that transthoracic echocardiography (TTE) and 12-lead electrocardiography (ECG) would be helpful in predicting AF-AFl in these patients. METHODS AND RESULTS: ECGs and TTEs of 90 patients diagnosed with definite or borderline ARVD (2010 Task Force Criteria) were analyzed. Data were compared in (1) patients with AF-AFl and (2) all other patients. A total of 18 (20%) patients experienced AF-AFl during a median follow-up of 5.8 years (interquartile range 2.0-10.4). Kaplan-Meier analysis revealed reduced times to AF-AFl among patients with echocardiographic RV fractional area change <27% (P<0.001), left atrial diameter ≥24.4 mm/m(2)(parasternal long-axis, P=0.001), and right atrial short-axis diameter ≥22.1 mm/m(2)(apical 4-chamber view, P=0.05). From all ECG variables, P mitrale conferred the highest hazard ratio (3.37, 95% confidence interval 0.92-12.36, P=0.067). Five patients with AF-AFl experienced inappropriate implantable cardioverter-defibrillator (ICD) shocks compared with 4 without AF-AFl (36% vs. 9%, P=0.03). AF-AFl was more prevalent in heart-transplant patients and those who died of cardiac causes (56% vs. 16%, P=0.014). CONCLUSIONS: AF-AFl is associated with inappropriate ICD shocks, heart transplantation, and cardiac death in patients with ARVD. Evidence of reduced RV function and atrial dilation helps to identify the ARVD patients at increased risk for AF-AFl.

Details of left ventricular radial wall motion supporting the ventricular theory of the third heart sound obtained by cardiac MR.

OBJECTIVE Obtaining new details of radial motion of left ventricular (LV) segments using velocity-encoding cardiac MRI. METHODS Cardiac MR examinations were performed on 14 healthy volunteers aged between 19 and 26 years. Cine images for navigator-gated phase contrast velocity mapping were acquired using a black blood segmented κ-space spoiled gradient echo sequence with a temporal resolution of 13.8 ms. Peak systolic and diastolic radial velocities as well as radial velocity curves were obtained for 16 ventricular segments. RESULTS Significant differences among peak radial velocities of basal and mid-ventricular segments have been recorded. Particular patterns of segmental radial velocity curves were also noted. An additional wave of outward radial movement during the phase of rapid ventricular filling, corresponding to the expected timing of the third heart sound, appeared of particular interest. CONCLUSION The technique has allowed visualization of new details of LV radial wall motion. In particular, higher peak systolic radial velocities of anterior and inferior segments are suggestive of a relatively higher dynamics of anteroposterior vs lateral radial motion in systole. Specific patterns of radial motion of other LV segments may provide additional insights into LV mechanics. ADVANCES IN KNOWLEDGE The outward radial movement of LV segments impacted by the blood flow during rapid ventricular filling provides a potential substrate for the third heart sound. A biphasic radial expansion of the basal anteroseptal segment in early diastole is likely to be related to the simultaneous longitudinal LV displacement by the stretched great vessels following repolarization and their close apposition to this segment.

[Ventricular assist device – Possibilities of long-term mechanical circulatory support]

In Switzerland 200’000 people suffer from congestive heart failure. Approximately 10’000 patients find themselves in an advanced state of the disease. When conservative treatment options are no longer available heart transplantation is the therapy of choice. Should this not be an option due to long waiting lists or medical issues assist device therapy becomes an option. Assist device therapy is separated in short-term and long-term support. Long-term support is nowadays performed with ventricular assist devices (VADs). The native heart is still in place and supported in parallel to the remaining function of the heart. The majority of patients are treated with a left ventricular assist device (LVAD). The right ventrical alone (RVAD) as well as bi-ventricular support (BiVAD) is rarely needed. The modern VADs are implantable and create a non-pulsative bloodflow. A percutaneous driveline enables energy supply and pump-control. Indication strategies for VAD implantations include bridge to transplant (short term support), bridge to candidacy and bridge to transplant. VADs become more and more a definite therapeutic option (destination therapy). VAD therapy might be a realistic alternative to organ transplantation in the near future.

Slow conduction in mixed cultured strands of primary ventricular cells and stem cell-derived cardiomyocytes

Modern concepts for the treatment of myocardial diseases focus on novel cell therapeutic strategies involving stem cell-derived cardiomyocytes (SCMs). However, functional integration of SCMs requires similar electrophysiological properties as primary cardiomyocytes (PCMs) and the ability to establish intercellular connections with host myocytes in order to contribute to the electrical and mechanical activity of the heart. The aim of this project was to investigate the properties of cardiac conduction in a co-culture approach using SCMs and PCMs in cultured cell strands. Murine embryonic SCMs were pooled with fetal ventricular cells and seeded in predefined proportions on microelectrode arrays to form patterned strands of mixed cells. Conduction velocity (CV) was measured during steady state pacing. SCM excitability was estimated from action potentials measured in single cells using the patch clamp technique. Experiments were complemented with computer simulations of conduction using a detailed model of cellular architecture in mixed cell strands. CV was significantly lower in strands composed purely of SCMs (5.5 ± 1.5 cm/s, n = 11) as compared to PCMs (34.9 ± 2.9 cm/s, n = 21) at similar refractoriness (100% SCMs: 122 ± 25 ms, n = 9; 100% PCMs: 139 ± 67 ms, n = 14). In mixed strands combining both cell types, CV was higher than in pure SCMs strands, but always lower than in 100% PCM strands. Computer simulations demonstrated that both intercellular coupling and electrical excitability limit CV. These data provide evidence that in cultures of murine ventricular cardiomyocytes, SCMs cannot restore CV to control levels resulting in slow conduction, which may lead to reentry circuits and arrhythmias.

Changes in Left Ventricular Torsion Early Postoperatively After Aortic Valve Replacement and at Long-Term Follow-up.

OBJECTIVE In patients with aortic stenosis, left ventricular systolic torsion (pT) is increased to overcome excessive afterload. This study assessed left ventricular torsion before and immediately after surgical valve replacement and tested the instant effect of fluid loading. DESIGN Prospective, clinical single-center study. SETTING Intensive care unit of a university hospital. PARTICIPANTS 12 patients undergoing elective aortic valve replacement for aortic stenosis. INTERVENTIONS Echocardiography was performed on the day before surgery, within 18 hours after surgery including a fluid challenge, and after 2.5 years. MEASUREMENTS AND MAIN RESULTS pT decreased early postoperatively by 21.2% (23.4° ± 5.6° to 18.4° ± 6.9°; p = 0.012) and reached preoperative values at 2.5 years follow-up (24 ± 7). Peak diastolic untwisting velocity occurred later early postoperatively (13% ± 8% to 21% ± 9.4%; p = 0.019) and returned toward preoperative values at follow-up (10.2 ± 4.7°). The fluid challenge increased central venous pressure (8 ± 4 mmHg to 11 ± 4 mmHg; p = 0.003) and reduced peak systolic torsion velocity (138.7 ± 37.6/s to 121.3 ± 32/s; p = 0.032). pT decreased in 3 and increased in 8 patients after fluid loading. Patients whose pT increased had higher early mitral inflow velocity postoperatively (p = 0.04) than those with decreasing pT. Patients with reduced pT after fluid loading received more fluids (p = 0.04) and had a higher positive fluid balance during the intensive care unit stay (p = 0.03). Torsion after fluid loading correlated with total fluid input (p = 0.001) and cumulative fluid balance (p = 0.002). CONCLUSIONS pT decreased early after aortic valve replacement but remained elevated despite elimination of aortic stenosis. After 2.5 years, torsion had returned to preoperative levels.

Investigation of hemodynamics in an in vitro system simulating left ventricular support through the right subclavian artery using 4-dimensional flow magnetic resonance imaging.

OBJECTIVES Left ventricular assist devices are an important treatment option for patients with heart failure alter the hemodynamics in the heart and great vessels. Because in vivo magnetic resonance studies of patients with ventricular assist devices are not possible, in vitro models represent an important tool to investigate flow alterations caused by these systems. By using an in vitro magnetic resonance-compatible model that mimics physiologic conditions as close as possible, this work investigated the flow characteristics using 4-dimensional flow-sensitive magnetic resonance imaging of a left ventricular assist device with outflow via the right subclavian artery as commonly used in cardiothoracic surgery in the recent past. METHODS An in vitro model was developed consisting of an aorta with its supra-aortic branches connected to a left ventricular assist device simulating the pulsatile flow of the native failing heart. A second left ventricular assist device supplied the aorta with continuous flow via the right subclavian artery. Four-dimensional flow-sensitive magnetic resonance imaging was performed for different flow rates of the left ventricular assist device simulating the native heart and the left ventricular assist device providing the continuous flow. Flow characteristics were qualitatively and quantitatively evaluated in the entire vessel system. RESULTS Flow characteristics inside the aorta and its upper branching vessels revealed that the right subclavian artery and the right carotid artery were solely supported by the continuous-flow left ventricular assist device for all flow rates. The flow rates in the brain-supplying arteries are only marginally affected by different operating conditions. The qualitative analysis revealed only minor effects on the flow characteristics, such as weakly pronounced vortex flow caused by the retrograde flow via the brachiocephalic artery. CONCLUSIONS The results indicate that, despite the massive alterations in natural hemodynamics due to the retrograde flow via the right subclavian and brachiocephalic arteries, there are no drastic consequences on the flow in the brain-feeding arteries and the flow characteristics in the ascending and descending aortas. It may be beneficial to adjust the operating condition of the left ventricular assist device to the residual function of the failing heart.