Martin Hayward

Equilibrium contrast cardiovascular magnetic resonance for the measurement of diffuse myocardial fibrosis: preliminary validation in humans.

Background— Diffuse myocardial fibrosis is a final end point in most cardiac diseases. It is missed by the cardiovascular magnetic resonance (CMR) late gadolinium enhancement technique. Currently, quantifying diffuse myocardial fibrosis requires invasive biopsy, with inherent risk and sampling error. We have developed a robust and noninvasive technique, equilibrium contrast CMR (EQ–CMR) to quantify diffuse fibrosis and have validated it against the current gold standard of surgical myocardial biopsy. Methods and Results— The 3 principles of EQ–CMR are a bolus of extracellular gadolinium contrast followed by continuous infusion to achieve equilibrium; a blood sample to measure blood volume of distribution (1−hematocrit); and CMR to measure pre- and postequilibrium T1 (with heart rate correction). The myocardial volume of distribution is calculated, reflecting diffuse myocardial fibrosis. Clinical validation occurred in patients undergoing aortic valve replacement for aortic stenosis or myectomy in hypertrophic cardiomyopathy (n=18 and n=8, respectively). Surgical biopsies were analyzed for picrosirius red fibrosis quantification on histology. The mean histological fibrosis was 20.5±11% in aortic stenosis and 17.1±7.4% in hypertrophic cardiomyopathy. EQ–CMR correlated strongly with biopsy histological fibrosis: aortic stenosis, r2=0.86, Kendall Tau coefficient (T)=0.71, P<0.001; hypertrophic cardiomyopathy, r2=0.62, T=0.52, P=0.08; combined r2=0.80, T=0.67, P<0.001. Conclusions— We have developed and validated a new technique, EQ–CMR, to measure diffuse myocardial fibrosis as an add-on to a standard CMR scan, which allows for the noninvasive quantification of the diffuse fibrosis burden in myocardial diseases.

Effect of remote ischaemic preconditioning on myocardial injury in patients undergoing coronary artery bypass graft surgery: a randomised controlled trial

BACKGROUND Whether remote ischaemic preconditioning, an intervention in which brief ischaemia of one tissue or organ protects remote organs from a sustained episode of ischaemia, is beneficial for patients undergoing coronary artery bypass graft surgery is unknown. We did a single-blinded randomised controlled study to establish whether remote ischaemic preconditioning reduces myocardial injury in these patients. METHODS 57 adult patients undergoing elective coronary artery bypass graft surgery were randomly assigned to either a remote ischaemic preconditioning group (n=27) or to a control group (n=30) after induction of anaesthesia. Remote ischaemic preconditioning consisted of three 5-min cycles of right upper limb ischaemia, induced by an automated cuff-inflator placed on the upper arm and inflated to 200 mm Hg, with an intervening 5 min of reperfusion during which the cuff was deflated. Serum troponin-T concentration was measured before surgery and at 6, 12, 24, 48, and 72 h after surgery. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00397163. FINDINGS Remote ischaemic preconditioning significantly reduced overall serum troponin-T release at 6, 12, 24, and 48 h after surgery. The total area under the curve was reduced by 43%, from 36.12 microg/L (SD 26.08) in the control group to 20.58 microg/L (9.58) in the remote ischaemic preconditioning group (mean difference 15.55 [SD 5.32]; 95% CI 4.88-26.21; p=0.005). INTERPRETATION We have shown that adult patients undergoing elective coronary artery bypass graft surgery at a single tertiary centre could benefit from remote ischaemic preconditioning, using transient upper limb ischaemia.

Human gene for physical performance

A specific genetic factor that strongly influences human physical performance has not so far been reported, but here we show that a polymorphism in the gene encoding angiotensin-converting enzyme does just that. An ‘insertion’ allele of the gene is associated with elite endurance performance among high-altitude mountaineers. Also, after physical training, repetitive weight-lifting is improved eleven-fold in individuals homozygous for the ‘insertion’ allele compared with those homozygous for the ‘deletion’ allele.

Tracking the Evolution of Non–Small-Cell Lung Cancer

BACKGROUND Among patients with non‐small‐cell lung cancer (NSCLC), data on intratumor heterogeneity and cancer genome evolution have been limited to small retrospective cohorts. We wanted to prospectively investigate intratumor heterogeneity in relation to clinical outcome and to determine the clonal nature of driver events and evolutionary processes in early‐stage NSCLC. METHODS In this prospective cohort study, we performed multiregion whole‐exome sequencing on 100 early‐stage NSCLC tumors that had been resected before systemic therapy. We sequenced and analyzed 327 tumor regions to define evolutionary histories, obtain a census of clonal and subclonal events, and assess the relationship between intratumor heterogeneity and recurrence‐free survival. RESULTS We observed widespread intratumor heterogeneity for both somatic copy‐number alterations and mutations. Driver mutations in EGFR, MET, BRAF, and TP53 were almost always clonal. However, heterogeneous driver alterations that occurred later in evolution were found in more than 75% of the tumors and were common in PIK3CA and NF1 and in genes that are involved in chromatin modification and DNA damage response and repair. Genome doubling and ongoing dynamic chromosomal instability were associated with intratumor heterogeneity and resulted in parallel evolution of driver somatic copy‐number alterations, including amplifications in CDK4, FOXA1, and BCL11A. Elevated copy‐number heterogeneity was associated with an increased risk of recurrence or death (hazard ratio, 4.9; P=4.4×10‐4), which remained significant in multivariate analysis. CONCLUSIONS Intratumor heterogeneity mediated through chromosome instability was associated with an increased risk of recurrence or death, a finding that supports the potential value of chromosome instability as a prognostic predictor. (Funded by Cancer Research UK and others; TRACERx ClinicalTrials.gov number, NCT01888601.)

Evidence for Multiple Mechanisms in Human Ventricular Fibrillation

Background— The mechanisms that sustain ventricular fibrillation (VF) in the human heart remain unclear. Experimental models have demonstrated either a periodic source (mother rotor) or multiple wavelets as the mechanism underlying VF. The aim of this study was to map electrical activity from the entire ventricular epicardium of human hearts to establish the relative roles of these mechanisms in sustaining early human VF. Methods and Results— In 10 patients undergoing cardiac surgery, VF was induced by burst pacing, and 20 to 40 seconds of epicardial activity was sampled (1 kHz) with a sock containing 256 unipolar contact electrodes connected to a UnEmap system. Signals were interpolated from the electrode sites to a fine regular grid (100×100 points), and dominant frequencies (DFs) were calculated with a fast Fourier transform with a moving 4096-ms window (10-ms increments). Epicardial phase was calculated at each grid point with the Hilbert transform, and phase singularities and activation wavefronts were identified at 10-ms intervals. Early human VF was sustained by large coherent wavefronts punctuated by periods of disorganized wavelet behavior. The initial fitted DF intercept was 5.11±0.25 (mean±SE) Hz (P<0.0001), and DF increased at a rate of 0.018±0.005 Hz/s (P<0.01) during VF, whereas combinations of homogeneous, heterogeneous, static, and mobile DF domains were observed for each of the patients. Epicardial reentry was present in all fibrillating hearts, typically with low numbers of phase singularities. In some cases, persistent phase singularities interacted with multiple complex wavelets; in other cases, VF was driven at times by a single reentrant wave that swept the entire epicardium for several cycles. Conclusions— Our data support both the mother rotor and multiple wavelet mechanisms of VF, which do not appear to be mutually exclusive in the human heart.

Whole heart action potential duration restitution properties in cardiac patients: a combined clinical and modelling study

Steep action potential duration (APD) restitution has been shown to facilitate wavebreak and ventricular fibrillation. The global APD restitution properties in cardiac patients are unknown. We report a combined clinical electrophysiology and computer modelling study to: (1) determine global APD restitution properties in cardiac patients; and (2) examine the interaction of the observed APD restitution with known arrhythmia mechanisms. In 14 patients aged 52–85 years undergoing routine cardiac surgery, 256 electrode epicardial mapping was performed. Activation–recovery intervals (ARI; a surrogate for APD) were recorded over the entire ventricular surface. Mono‐exponential restitution curves were constructed for each electrode site using a standard S1–S2 pacing protocol. The median maximum restitution slope was 0.91, with 27% of all electrode sites with slopes < 0.5, 29% between 0.5 and 1.0, and 20% between 1.0 and 1.5. Eleven per cent of restitution curves maintained slope > 1 over a range of diastolic intervals of at least 30 ms; and 0.3% for at least 50 ms. Activation–recovery interval restitution was spatially heterogeneous, showing regional organization with multiple discrete areas of steep and shallow slope. We used a simplified computer model of 2‐D cardiac tissue to investigate how heterogeneous APD restitution can influence vulnerability to, and stability of re‐entry. Our model showed that heterogeneity of restitution can act as a potent arrhythmogenic substrate, as well as influencing the stability of re‐entrant arrhythmias. Global epicardial mapping in humans showed that APD restitution slopes were organized into regions of shallow and steep slopes. This heterogeneous organization of restitution may provide a substrate for arrhythmia.

Effect of remote ischaemic preconditioning on clinical outcomes in patients undergoing cardiac bypass surgery: a randomised controlled clinical trial

Objectives Remote ischaemic preconditioning (RIPC), using brief cycles of limb ischaemia/reperfusion, is a non-invasive, low-cost intervention that may reduce perioperative myocardial injury (PMI) in patients undergoing cardiac surgery. We investigated whether RIPC can also improve short-term clinical outcomes. Methods One hundred and eighty patients undergoing elective coronary artery bypass graft (CABG) surgery and/or valve surgery were randomised to receive either RIPC (2–5 min cycles of simultaneous upper arm and thigh cuff inflation/deflation; N=90) or control (uninflated cuffs placed on the upper arm and thigh; N=90). The study primary end point was PMI, measured by 72 h area under the curve (AUC) serum high-sensitive troponin-T (hsTnT); secondary end point included short-term clinical outcomes. Results RIPC reduced PMI magnitude by 26% (−9.303 difference (CI −15.618 to −2.987) 72 h hsTnT-AUC; p=0.003) compared with control. There was also evidence that RIPC reduced the incidence of postoperative atrial fibrillation by 54% (11% RIPC vs 24% control; p=0.031) and decreased the incidence of acute kidney injury by 48% (10.0% RIPC vs 21.0% control; p=0.063), and intensive care unit stay by 1 day (2.0 days RIPC (CI 1.0 to 4.0) vs 3.0 days control (CI 2.0 to 4.5); p=0.043). In a post hoc analysis, we found that control patients administered intravenous glyceryl trinitrate (GTN) intraoperatively sustained 39% less PMI compared with those not receiving GTN, and RIPC did not appear to reduce PMI in patients given GTN. Conclusions RIPC reduced the extent of PMI in patients undergoing CABG and/or valve surgery. RIPC may also have beneficial effects on short-term clinical outcomes, although this will need to be confirmed in future studies. Trial registration number ClinicalTrials.gov ID: NCT00397163.

Postconditioning protects human atrial muscle through the activation of the RISK pathway

Ischemic postconditioning (IPost) has been demonstrated to reduce myocardial injury in patients undergoing primary coronary angioplasty for an acute myocardial infarction.Pre-clinical animal studies suggest that pro-survival protein kinases of the Reperfusion Injury Salvage Kinase (RISK) pathway such as Akt and Erk1/2 mediate the cardioprotective effect of IPost.Whether IPost can protect human myocardial tissue ex vivo and whether it recruits the RISK pathway in human myocardium are both not known. To investigate this, atrial appendages were harvested from patients undergoing cardiac surgery. From these samples atrial trabeculae were isolated and mounted on a superperfusion apparatus and subjected to 90 min of hypoxia followed by 120 min of reoxygenation at the end of which function expressed as a percentage of the recovery of baseline contractile function was determined.Atrial trabeculae were randomized to control, hypoxic preconditioning (HPre), hypoxic postconditioning comprising either four 30-s (HPost-30) or 60-s (HPost-60) episodes of alternating hypoxia and reoxygenation, and HPost in the presence or absence of UO126 (a MEK1/2 inhibitor) or LY294002 (a PI3K inhibitor).HPre and HPost-60 improved the recovery of baseline contractile function (45.4±3.2% with HPre and 45.2±2.2% with HPost-60 vs 26.7±2.1 % in control: N≥ 6/group: P<0.05), whereas HPost-30 failed to cardioprotect (28.3±3.4% with HPost-30 vs 26.7±2.1 % in control: N≥ 6/group: P>0.05). The cardioprotective effect of HPost-60 was abolished in the presence of either LY (28.1±2.5% with HPost-60+LY vs 45.2±2.2% with HPost-60: N≥ 6/group: P<0.05) or UO (32.7±1.8% with HPost-60+UO vs 45.2±2.2% with HPost-60:N=7/group: P<0.05). The kinase inhibitors alone had no effect on functional recovery (28.2±3.6% with LY and 30.1±4.8% with UO vs 26.7±2.1 % in control: N≥ 5/group: P>0.05). In conclusion, we demonstrate for the first time that postconditioning protects human myocardium ex vivo and that this effect is dependent on the activation of the RISK pathway.

Organization of ventricular fibrillation in the human heart: experiments and models.

Sudden cardiac death is a major health problem in the industrialized world. The lethal event is typically ventricular fibrillation (VF), during which the co‐ordinated regular contraction of the heart is overthrown by a state of mechanical and electrical anarchy. Understanding the excitation patterns that sustain VF is important in order to identify potential therapeutic targets. In this paper, we studied the organization of human VF by combining clinical recordings of electrical excitation patterns on the epicardial surface during in vivo human VF with simulations of VF in an anatomically and electrophysiologically detailed computational model of the human ventricles. We find both in the computational studies and in the clinical recordings that epicardial surface excitation patterns during VF contain around six rotors. Based on results from the simulated three‐dimensional excitation patterns during VF, which show that the total number of electrical sources is 1.4 ± 0.12 times greater than the number of epicardial rotors, we estimate that the total number of sources present during clinically recorded VF is 9.0 ± 2.6. This number is approximately fivefold fewer compared with that observed during VF in dog and pig hearts, which are of comparable size to human hearts. We explain this difference by considering differences in action potential duration dynamics across these species. The simpler spatial organization of human VF has important implications for treatment and prevention of this dangerous arrhythmia. Moreover, our findings underline the need for integrated research, in which human‐based clinical and computational studies complement animal research.

The divergent roles of protein kinase C epsilon and delta in simulated ischaemia–reperfusion injury in human myocardium

Experimental studies suggest that cardioprotection can be achieved through either the activation of PKC-epsilon prior to the index ischaemic episode or the inhibition of PKC-delta at the onset of reperfusion. However, whether these PKC isoforms exert such divergent roles in human myocardium, subjected to simulated ischaemia-reperfusion injury, is unclear. Human atrial trabeculae were isolated from right atrial appendages harvested from patients undergoing elective cardiac surgery. These were subjected to 90 min of hypoxia followed by 120 min of reoxygenation, at the end of which the recovery of baseline contractile function was determined. Atrial trabeculae were randomised to receive various treatment protocols comprising a peptide activator of PKC-epsilon, a peptide inhibitor of PKC-delta and their respective inactive control peptides. Administering the PKC-delta peptide inhibitor at reoxygenation improved the recovery of function at all the concentrations tested (39.3+/-1.4% at 5 nM, 52.4+/-2.9% at 50 nM and 46.8+/-2.9% at 500 nM versus the control group, 27.5+/-1.4%: N > or = 6/group: P<0.02). Preconditioning with the PKC-epsilon peptide activator improved the recovery of function (40.0+/-0.8% at 50 nM and 49.7+/-3.1% at 500 nM versus the control group 27.5+/-1.4%: N > or = 6/group: P<0.02). This cardioprotective effect was comparable to that achieved by a standard hypoxic preconditioning protocol (52.3+/-3.2%). Interestingly, administering the PKC-epsilon activator (500 nM) at the onset of reperfusion also improved the recovery of contractile function (40.7+/-2.1% versus 27.5+/-1.5%: N > or = 6/group: P < 0.05). In human myocardium, cardioprotection can be achieved by either inhibiting PKC-delta or activating PKC-epsilon at the onset of reperfusion. In addition, PKC-epsilon activation offers cardioprotection when administered as a preconditioning strategy.