Biogeographic response of marine plankton to Cenozoic environmental changes.

In palaeontological studies, groups with consistent ecological and morphological traits across a clade's history (functional groups)1 afford different perspectives on biodiversity dynamics than do species and genera2,3, which are evolutionarily ephemeral. Here we analyse Triton, a global dataset of Cenozoic macroperforate planktonic foraminiferal occurrences4, to contextualize changes in latitudinal equitability gradients1, functional diversity, palaeolatitudinal specialization and community equitability. We identify: global morphological communities becoming less specialized preceding the richness increase after the Cretaceous-Palaeogene extinction; ecological specialization during the Early Eocene Climatic Optimum, suggesting inhibitive equatorial temperatures during the peak of the Cenozoic hothouse; increased specialization due to circulation changes across the Eocene-Oligocene transition, preceding the loss of morphological diversity; changes in morphological specialization and richness about 19 million years ago, coeval with pelagic shark extinctions5; delayed onset of changing functional group richness and specialization between hemispheres during the mid-Miocene plankton diversification. The detailed nature of the Triton dataset permits a unique spatiotemporal view of Cenozoic pelagic macroevolution, in which global biogeographic responses of functional communities and richness are decoupled during Cenozoic climate events. The global response of functional groups to similar abiotic selection pressures may depend on the background climatic state (greenhouse or icehouse) to which a group is adapted.

Late Cenozoic cooling restructured global marine plankton communities.

The geographic ranges of marine organisms, including planktonic foraminifera1, diatoms, dinoflagellates2, copepods3 and fish4, are shifting polewards owing to anthropogenic climate change5. However, the extent to which species will move and whether these poleward range shifts represent precursor signals that lead to extinction is unclear6. Understanding the development of marine biodiversity patterns over geological time and the factors that influence them are key to contextualizing these current trends. The fossil record of the macroperforate planktonic foraminifera provides a rich and phylogenetically resolved dataset that provides unique opportunities for understanding marine biogeography dynamics and how species distributions have responded to ancient climate changes. Here we apply a bipartite network approach to quantify group diversity, latitudinal specialization and latitudinal equitability for planktonic foraminifera over the past eight million years using Triton, a recently developed high-resolution global dataset of planktonic foraminiferal occurrences7. The results depict a global, clade-wide shift towards the Equator in ecological and morphological community equitability over the past eight million years in response to temperature changes during the late Cenozoic bipolar ice sheet formation. Collectively, the Triton data indicate the presence of a latitudinal equitability gradient among planktonic foraminiferal functional groups which is coupled to the latitudinal biodiversity gradient only through the geologically recent past (the past two million years). Before this time, latitudinal equitability gradients indicate that higher latitudes promoted community equitability across ecological and morphological groups. Observed range shifts among marine planktonic microorganisms1,2,8 in the recent and geological past suggest substantial poleward expansion of marine communities even under the most conservative future global warming scenarios.

Life before impact in the Chicxulub area: unique marine ichnological signatures preserved in crater suevite.

To fully assess the resilience and recovery of life in response to the Cretaceous-Paleogene (K-Pg) boundary mass extinction ~ 66 million years ago, it is paramount to understand biodiversity prior to the Chicxulub impact event. The peak ring of the Chicxulub impact structure offshore the Yucatán Peninsula (México) was recently drilled and extracted a ~ 100 m thick impact-generated, melt-bearing, polymict breccia (crater suevite), which preserved carbonate clasts with common biogenic structures. We pieced this information to reproduce for the first time the macrobenthic tracemaker community and marine paleoenvironment prior to a large impact event at the crater area by combining paleoichnology with micropaleontology. A variable macrobenthic tracemaker community was present prior to the impact (Cenomanian-Maastrichtian), which included soft bodied organisms such as annelids, crustaceans and bivalves, mainly colonizing softgrounds in marine oxygenated, nutrient rich, conditions. Trace fossil assemblage from these upper Cretaceous core lithologies, with dominant Planolites and frequent Chondrites, corresponds well with that in the overlying post-impact Paleogene sediments. This reveals that the K-Pg impact event had no significant effects (i.e., extinction) on the composition of the macroinvertebrate tracemaker community in the Chicxulub region.

Globally distributed iridium layer preserved within the Chicxulub impact structure.

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.

Probing the hydrothermal system of the Chicxulub impact crater.

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth's crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth's crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.

Morphospace expansion paces taxonomic diversification after end Cretaceous mass extinction.

Highly resolved palaeontological records can address a key question about our current climate crisis: how long will it be before the biosphere rebounds from our actions? There are many ways to conceptualize the recovery of the biosphere; here, we focus on the global recovery of species diversity. Mass extinction may be expected to be followed by rapid speciation, but the fossil record contains many instances where speciation is delayed-a phenomenon about which we have a poor understanding. A probable explanation for this delay is that extinctions eliminate morphospace as they curtail diversity, and the delay in diversification is a result of the time needed for new innovations to rebuild morphospace, which can then be filled out by new species. Here, we test this morphospace reconstruction hypothesis using the morphological complexity of planktic foraminifer tests after the Cretaceous-Palaeogene mass extinction. We show that increases in complexity precede changes in diversity, indicating that plankton are colonizing new morphospace, then slowly filling it in. Preliminary diversification is associated with a rapid increase in the complexity of groups refilling relict Cretaceous ecospace. Subsequent jumps in complexity are driven by evolutionary innovations (development of spines and photosymbionts), which open new niche space. The recovery of diversity is paced by the construction of new morphospace, implying a fundamental speed limit on diversification after an extinction event.

Rapid recovery of life at ground zero of the end-Cretaceous mass extinction.

The Cretaceous/Palaeogene mass extinction eradicated 76% of species on Earth1,2. It was caused by the impact of an asteroid3,4 on the Yucatán carbonate platform in the southern Gulf of Mexico 66 million years ago 5 , forming the Chicxulub impact crater6,7. After the mass extinction, the recovery of the global marine ecosystem-measured as primary productivity-was geographically heterogeneous 8 ; export production in the Gulf of Mexico and North Atlantic-western Tethys was slower than in most other regions8-11, taking 300 thousand years (kyr) to return to levels similar to those of the Late Cretaceous period. Delayed recovery of marine productivity closer to the crater implies an impact-related environmental control, such as toxic metal poisoning 12 , on recovery times. If no such geographic pattern exists, the best explanation for the observed heterogeneity is a combination of ecological factors-trophic interactions 13 , species incumbency and competitive exclusion by opportunists 14 -and 'chance'8,15,16. The question of whether the post-impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems. If there is a relationship between the distance from the impact and the recovery of marine productivity, we would expect recovery rates to be slowest in the crater itself. Here we present a record of foraminifera, calcareous nannoplankton, trace fossils and elemental abundance data from within the Chicxulub crater, dated to approximately the first 200 kyr of the Palaeocene. We show that life reappeared in the basin just years after the impact and a high-productivity ecosystem was established within 30 kyr, which indicates that proximity to the impact did not delay recovery and that there was therefore no impact-related environmental control on recovery. Ecological processes probably controlled the recovery of productivity after the Cretaceous/Palaeogene mass extinction and are therefore likely to be important for the response of the ocean ecosystem to other rapid extinction events.

The formation of peak rings in large impact craters.

Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust.

Endocardial electrogram characteristics of epicardial ventricular arrhythmias.

INTRODUCTION: While most ventricular arrhythmias (VA) can be ablated successfully using an endocardial (endo) approach, epicardial (epi) mapping and ablation is sometimes required. There may be suggestive clues on the surface electrocardiogram; however, identification of an epi origin of VA with certainty remains problematic. METHODS AND RESULTS: All patients referred for ablation of ventricular tachycardia or frequent ventricular ectopy from June 2007 to July 2011 were evaluated. Patients with completed endo and epi electroanatomical activation maps of an epi VA were included (n = 10). Bipolar electrograms (EGMs) in the area of earliest endo activation were analyzed and compared to the area of early epi activation. An EGM component was characterized as far field if it was monophasic and there was inability to capture. We identified 3 characteristics from endo mapping that consistently indicated need for epi ablation: (1) Diffusely early activation (>2 cm(2) region of sites with equally earliest activation within 10 milliseconds). (2) Sequence of a far-field EGM followed by a near-field EGM in the region of earliest endo activation. (3) Inability to capture the far-field component of the earliest EGM (stim-QRS < egm-QRS time) or reproduce morphological features of the VA complex with stimulation at the earliest endo site of activation. CONCLUSIONS: The presence of a diffusely early area of activation and inability to capture a far-field endo EGM indicates that epi ablation may be needed to eliminate a VA.

Percutaneous transhepatic access for catheter ablation of cardiac arrhythmias.

AIMS: Femoral venous access may be limited in certain patients undergoing electrophysiology (EP) study and ablation. The purpose of this study is to review a series of patients undergoing percutaneous transhepatic access to allow for ablation of cardiac arrhythmias. METHODS AND RESULTS: Six patients with a variety of cardiac arrhythmias and venous abnormalities underwent percutaneous transhepatic access. Under fluoroscopic and ultrasound guidance, a percutaneous needle was advanced into a hepatic vein and exchanged for a vascular sheath over a wire. Electrophysiology study and radiofrequency ablation was then performed. All tachycardias, including atrial tachycardia, atrial flutter, atrioventricular nodal tachycardia, and atrial fibrillation, were ablated. Procedural times ranged from 227 to 418 min. Fluoroscopy times ranged from 32 to 95 min. There were no complications. All six patients have been arrhythmia-free in follow-up (5-49 months, mean 23.1 months). CONCLUSION: Percutaneous transhepatic access is safe and feasible in patients with limited venous access who are undergoing EP study and ablation for a range of cardiac arrhythmias.

Use of stored implanted cardiac defibrillator electrograms in catheter ablation of ventricular fibrillation.

BACKGROUND: Ventricular fibrillation (VF) can be abolished by targeting triggering ventricular ectopy, most often originating in the Purkinje network or right ventricular outflow tract (RVOT). This strategy relies upon the induction of premature ventricular complex (PVC) and/or VF. We sought to evaluate a VF ablation strategy that utilizes analysis of stored implantable cardioverter defibrillator (ICD) electrograms. METHODS: Eleven consecutive patients experiencing frequent VF episodes (≥three episodes in prior month) underwent electrophysiology study and ablation of VF triggers. PVC and VF induction was intentionally avoided or not possible in all of these patients. Pacemapping at likely sites for PVC triggers of VF using an analysis of the morphology and relative timing of the stored far- and near-field ICD electrograms of VF triggers was used to identify potential culprit locations. Radiofrequency energy was applied to these sites for ablation of the identified VF trigger. RESULTS: Areas targeted for ablation included the left posterior fascicle (six), left anterior fascicle (three), RVOT (three) and left ventricular outflow tract (one); two patients had two separate triggers. Ablation was completed successfully without any complications. With a mean follow-up of 288 days (range 45-649), 10 patients are free of VF. CONCLUSION: Ablation of VF triggers can be performed successfully with good short-term outcomes in patients with and without underlying heart disease. Use of stored ICD electrograms with a focus on likely target areas permit ablation without the need for PVC or VF induction. This can be useful when ectopy is not present for mapping and to avoid potentially dangerous initiation of multiple episodes of VF.

P-wave rejection in a transplanted heart.

BACKGROUND: Heart block can occur at multiple levels in patients with prior cardiac transplant. This diagnosis is usually ascertained using the surface electrocardiogram. RESULTS: A 24-year-old man with prior cardiac transplant presented with apparent complete atrioventricular nodal block and junctional escape on the surface ECG. During pacemaker implantation, we demonstrated sinus rhythm in the recipient atrium, block across the atrioatrial anastomosis, and sinus arrest with intact AV nodal conduction in the donor atrium. CONCLUSION: This case illustrates an unusual presentation of sinus arrest occurring 2 years after heart transplantation that appeared to be complete heart block.

Typical atrial flutter in an atypical patient.

Arrhythmias in adult congenital heart disease (ACHD) pose unique procedural challenges, especially with intravascular access. We report a unique case of ablation via a left-sided hepatic vein approach in a patient with situs inversus totalis. A 28-year-old woman with situs inversus totalis, ventriculoseptal defect, and dextro-transposition of the great arteries underwent ablation for documented narrow-complex tachycardia. Because of bilateral iliac venous occlusions, the coronary sinus (CS) was accessed through the left internal jugular vein. Rapid atrial pacing resulted in a tachycardia with an atrial cycle length of 225 msec and 2:1 atrioventricular association. Entrainment from the proximal and distal CS was consistent with typical atrial flutter around the left-sided tricuspid valve. Because of the iliac vein occlusions, access for ablation was obtained via a left-sided hepatic vein (Figure 1). Resetting from the cavotricuspid isthmus and three-dimensional electroanatomic mapping (Figure 2) confirmed typical atrial flutter, which, given the dextrocardia, occurred in a clockwise fashion around the tricuspid valve. Ablation was performed at the cavotricuspid isthmus resulting in arrhythmia termination and isthmus block. This case highlights the many unusual challenges that patients with ACHD can pose to the proceduralist, including atypical cardiac anatomy and difficult intravascular access. Unusual and creative approaches are often necessary to treat these patients successfully.

Diagnostic utility of signal-averaged electrocardiography for detection of cardiac sarcoidosis.

INTRODUCTION: Cardiac sarcoidosis (CS) occurs in up to 25% of patients with pulmonary involvement. Early diagnosis is critical because sudden death from ventricular arrhythmias can be the initial presentation. We sought to evaluate the diagnostic utility of signal-averaged ECG (SAECG) for detection of cardiac involvement of sarcoidosis. METHODS: Subjects with biopsy proven sarcoidosis and symptoms suggestive of possible cardiac involvement were included in the cohort. Standard criteria for SAECG were used. Subjects were considered to have CS if they met criteria established by the Japanese Ministry of Health and Welfare modified to include cardiac MRI. RESULTS: Of the 88 patients in the cohort 27 had evidence of CS independent of the SAECG results. The SAECG was abnormal in 14 of these 27 patients and 11 of the 61 of the subjects without cardiac involvement (P < 0.01). The sensitivity of SAECG detection of CS was 52% with a specificity of 82%. For the entire cohort, SAECG had a positive predictive value (PPV) of 0.56 and a negative predictive value (NPV) of 0.79. Within a subgroup of 67 patients with an unfiltered QRS duration of <100 ms, the specificity for diagnosing cardiac sarcoidosis improves to 100% with a reduced sensitivity of 36.8. Of the SAECG parameters, LAS40 was significantly associated with the diagnosis of cardiac sarcoidosis for the entire cohort (P < 0.01) and among the subgroup of patients with an unfiltered QRS duration of <100 ms (P < 0.01). CONCLUSIONS: SAECG is a useful screening tool in the evaluation of sarcoidosis for detection of cardiac involvement.

Fluctuation in ventricular sensing leading to underdetection of ventricular fibrillation in a patient with cardiac sarcoidosis.

In this case report, we describe markedly fluctuating ventricular sensing through an implantable cardioverter defibrillator (ICD) over a period of 29 months in a patient with cardiac sarcoidosis. We conclude that the fluctuations in the measured R wave are the result of waxing and waning inflammation associated with sarcoid activity. The patient had a stable medical course throughout the time period studied, including stable immunosuppression and stable electrolytes. We believe this is an example of an important complication of ICD implants in patients with cardiac sarcoidosis and that frequent sensing evaluations are prudent in these patients.

Ventricular tachycardia storm successfully treated with immunosuppression and catheter ablation in a patient with cardiac sarcoidosis.

We describe the case of a 43-year-old male with cardiac sarcoidosis and ventricular tachycardia storm successfully treated with catheter ablation and immunosuppression. Antiarrhythmics alone, and in combination with immusuppressive agents, failed to successfully manage the ventricular tachycardia episodes. Catheter ablation in conjunction with immunosuppression proved to be the most successful treatment strategy. The reported efficacy of catheter ablation for ventricular tachycardia in cardiac sarcoidosis is variable.

Utility of postoperative testing of implantable cardioverter-defibrillators.

BACKGROUND: Implantable cardioverter-defibrillators (ICDs) can provide life-saving therapies for ventricular arrhythmias. Arrhythmia induction and defibrillation threshold testing is often performed at implantation and postoperatively during long-term follow-up to ensure proper device function. METHODS: We sought to evaluate the prevalence and predictors of occult device malfunction at follow-up defibrillation testing in asymptomatic individuals. A cohort of 853 patients underwent 1,578 defibrillation tests during the 13-year study period. Defibrillation efficacy was evaluated primarily by the two-shock (2S) method, with an adequate safety margin ≥ 10 joules (J) less than the maximum energy delivered by the ICD. RESULTS: A total of 38 testing failures requiring intervention were discovered during testing (2.4% of all tests). There were 11 ICD system failures resulting in failure to defibrillate, six with underdetection of ventricular fibrillation, and 21 clinically significant increases in defibrillation threshold. There was a higher incidence of failure in older ICD systems (1996-2002) compared to newer ICD systems (2003-2009), reaching statistical significance (3.6% vs 1.0%; P < 0.01). There were 178 subjects (20.8%) with a >20-J safety margin on previous testing, detected R waves >7.0 mV, and all system components implanted after 2003 at the time of testing who did not have any testing failures (0% vs 5.6%; P < 0.01). CONCLUSION: Postoperative defibrillation testing identifies a small number of ICD malfunctions in asymptomatic individuals. ICD testing failure is seen more frequently in older systems and in those with borderline results from prior interrogation or testing. These findings suggest that serial postoperative defibrillation testing is not indicated in asymptomatic patients without suspicion for specific problems.

Effect of left ventricular assist device placement on preexisting implantable cardioverter-defibrillator leads.

BACKGROUND: The left ventricular assist device (LVAD) is a therapy for patients with end-stage heart failure, many of whom have a preexisting implantable cardioverter-defibrillator (ICD). We investigated whether the implantation of a LVAD affects ICD function. METHODS AND RESULTS: Patients implanted with a LVAD between September 2000 and February 2009 were studied. Right ventricular (RV), right atrial, and left ventricular lead impedance, sensing, and capture thresholds were recorded before and after LVAD placement and subsequent lead-related interventions were noted. Of the 61 patients receiving a LVAD, data were collected from 30 patients who had preexisting ICDs. Significant pre-post differences were noted for all RV lead parameters: sensing amplitude decreased from 9.2+/-3.1 to 5.7+/-3.6 millivolts (P < .001); impedance decreased from 479+/-118 to 418+/-94 ohms (P=.008); and threshold increased from 4.3+/-6.7 to 11.0+/-16.8 microjoules (P=.021). As a result of alterations in lead parameters, 4 patients (13%) required lead revisions and 6 patients (20%) required ICD testing. CONCLUSIONS: Differences in ICD lead function were observed after LVAD placement resulting in clinically significant interventions. These data suggest that ICD interrogation be performed post-LVAD placement and that patients be counseled for the potential need for lead revisions and ICD testing when consented for a LVAD.

Implantable cardioverter-defibrillator shocks in patients with a left ventricular assist device.

BACKGROUND: Left ventricular assist device (LVAD) use is becoming increasingly common for patients with end-stage heart failure. However, the rate of implantable cardioverter-defibrillator (ICD) shocks and the effect of these shocks on outcomes in patients with LVADs remain unknown. METHODS: Medical records were reviewed from patients with both an ICD and a LVAD from September 2000 to February 2009. The association between ICD shocks and survival while receiving device support was assessed using Cox proportional hazards modeling. RESULTS: Thirty-three of 61 patients with a LVAD also had an ICD and form the basis of this report. The mean duration of LVAD support was 238 days. One or more ICD shocks were delivered to 14 patients (42%) with 8 (24%) receiving appropriate shocks for ventricular arrhythmias and 6 (18%) receiving inappropriate shocks. No patients received both appropriate and inappropriate shocks. When compared with receiving no ICD shock, receiving any ICD shock or an appropriate ICD shock were both associated with an increase in the risk of death (hazard ratio [HR] 4.5, 95% confidence interval [CI] 1.2 to 17.3, p = 0.027, and HR 5.3, 95% CI 1.3 to 22.6, p = 0.023, respectively); receipt of an inappropriate shock showed a non-significant trend for an increased risk of death (HR 3.2, 95% CI 0.7 to 16.1, p = 0.151). CONCLUSIONS: ICD shocks are common after implantation of LVADs, with nearly equal numbers of appropriate and inappropriate shocks. ICD shocks are associated with higher mortality. Larger studies are needed for assessing the independent relationship of ICDs to a variety of clinical outcomes in patients with LVADs.