Reginald Liew

The impact of CT image integration into an electroanatomic mapping system on clinical outcomes of catheter ablation of atrial fibrillation.

Background: A detailed appreciation of left atrial/pulmonary vein (LA/PV) anatomy may be important in improving the safety and success of catheter ablation (CA) for atrial fibrillation (AF).

Generation of patient-specific induced pluripotent stem cell-derived cardiomyocytes as a cellular model of arrhythmogenic right ventricular cardiomyopathy

AIMS Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a primary heart muscle disorder associated with sudden cardiac death. Its pathophysiology is still poorly understood. We aimed to produce an in vitro cellular model of ARVC using patient-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes and determine whether the model could recapitulate key features of the disease phenotype. METHODS AND RESULTS Dermal fibroblasts were obtained from a 30-year-old man with a clinical diagnosis of ARVC, harbouring a plakophilin 2 (PKP2) gene mutation. Four stable iPSC lines were generated using retroviral reprogramming, and functional cardiomyocytes were derived. Gene expression levels of desmosomal proteins (PKP2 and plakoglobin) in cardiomyocytes from ARVC-iPSCs were significantly lower compared with cardiomyocytes from control iPSCs (P< 0.01); there were no significant differences in the expression of desmoplakin, N-cadherin, and connexin 43 between the two groups. Cardiomyocytes derived from ARVC-iPSCs exhibited markedly reduced immunofluorescence signals when stained for PKP2 and plakoglobin, but similar levels of staining for desmoplakin, N-cadherin, and connexin 43 compared with control cardiomyocytes. Transmission electron microscopy showed that ARVC-iPSC cardiomyocytes were larger and contained darker lipid droplets compared with control cardiomyocytes. After 2 weeks of cell exposure to adiopgenic differentiation medium, ARVC-iPSC cardiomyocytes were found to contain a significantly greater amount of lipid, calculated using Oil Red O staining, compared with controls (734 ± 35.6 vs. 8.1 ± 0.49 a.u., respectively; n = 7, P = 0.001). CONCLUSION Patient-specific iPSC-derived cardiomyocytes display key features of ARVC, including reduced cell surface localization of desmosomal proteins and a more adipogenic phenotype.

Modeling type 3 long QT syndrome with cardiomyocytes derived from patient-specific induced pluripotent stem cells

BACKGROUND Type 3 long QT syndrome (LQT3) is the third most common form of LQT syndrome and is characterized by QT-interval prolongation resulting from a gain-of-function mutation in SCN5A. We aimed to establish a patient-specific human induced pluripotent stem cell (hiPSC) model of LQT3, which could be used for future drug testing and development of novel treatments for this inherited disorder. METHODS AND RESULTS Dermal fibroblasts obtained from a patient with LQT3 harboring a SCN5A mutation (c.5287G>A; p.V1763M) were reprogrammed to hiPSCs via repeated transfection of mRNA encoding OCT-4, SOX-2, KLF-4, C-MYC and LIN-28. hiPSC-derived cardiomyocytes (hiPSC-CMs) were obtained via cardiac differentiation. hiPSC-CMs derived from the patients healthy sister were used as a control. Compared to the control, patient hiPSC-CMs exhibited dominant mutant SCN5A allele gene expression, significantly prolonged action potential duration or APD (paced CMs of control vs. patient: 226.50 ± 17.89 ms vs. 536.59 ± 37.1 ms; mean ± SEM, p < 0.005), an increased tetrodotoxin (TTX)-sensitive late or persistent Na(+) current (control vs. patient: 0.65 ± 0.11 vs. 3.16 ± 0.27 pA/pF; n = 9, p < 0.01), a positive shift of steady state inactivation and a faster recovery from inactivation. Mexiletine, a NaV1.5 blocker, reversed the elevated late Na(+) current and prolonged APD in LQT3 hiPSC-CMs. CONCLUSIONS We demonstrate that hiPSC-CMs derived from a LQT3 patient recapitulate the biophysical abnormalities that define LQT3. The clinical significance of such an in vitro model is in the development of novel therapeutic strategies and a more personalized approach in testing drugs on patients with LQT3.

Re-trafficking of herg reverses long QT syndrome 2 phenotype in human iPS-derived cardiomyocytes

AIMS Long QT syndrome 2 (LQTS2) caused by missense mutations in hERG channel is clinically associated with abnormally prolonged ventricular repolarization and sudden cardiac deaths. Modelling monogenic arrhythmogenic diseases using human-induced pluripotent stem cells (hiPSCs) offers unprecedented mechanistic insights into disease pathogenesis. We utilized LQTS2-hiPSC-derived cardiomyocytes (CMs) to elucidate pathological changes and to demonstrate reversal of LQTS2 phenotype in a therapeutic intervention using a pharmacological agent, (N-[N-(N-acetyl-l-leucyl)-l-leucyl]-l-norleucine) (ALLN). METHODS AND RESULTS We generated LQTS2-specific CMs (A561V missense mutation in KCNH2) from iPSCs using the virus-free reprogramming method. These CMs recapitulate dysfunction of hERG potassium channel with diminished IKr currents, prolonged repolarization durations, and elevated arrhythmogenesis due to reduced membrane localization of glycosylated/mature hERG. Dysregulated expression of folding chaperones and processing proteasomes coupled with sequestered hERG in the endoplasmic reticulum confirmed trafficking-induced disease manifestation. Treatment with ALLN, not only increased membrane localization of mature hERG but also reduced repolarization, increased IKr currents and reduced arrhythmogenic events. Diverged from biophysical interference of hERG channel, our results show that modulation of chaperone proteins could be therapeutic in LQTS2 treatment. CONCLUSION Our in vitro study shows an alternative approach to rescue diseased LQTS2 phenotype via corrective re-trafficking therapy using a small chemical molecule, such as ALLN. This potentially novel approach may have ramifications in other clinically relevant trafficking disorders.

Clinical applications of patient-specific induced pluripotent stem cells in cardiovascular medicine

The emergence of induced pluripotent stem cell (iPSC) technology has had a great impact on the field of medicine ever since the ground-breaking discovery in 2006 that overexpression of four specific transcription factors was able to turn back the developmental clock of somatic cells into an embryonic-like state. The resulting iPSCs carry the developmental potential of human embryonic stem cells (hESC) without the embryo and have been heralded as a powerful tool to study development and disease. This technology has made it possible for the first time for researchers to transform end-differentiated cells from a particular individual into another cell type that remains specific to that individual, paving the way for novel methods of in vitro disease modelling and therapeutic applications. This paper reviews some of the key areas in cardiovascular medicine in which iPSC technology has been applied and discusses the future directions and ongoing challenges ahead in this exciting field.

Prediction of sudden arrhythmic death following acute myocardial infarction

Many patients who survive an acute myocardial infarction (AMI) remain at risk of sudden cardiac death despite optimal medical treatment. AMI survivors are currently risk assessed and selected for implantable cardioverter defibrillator (ICD) insertion mainly on the basis of their left ventricular ejection fraction. Several other cardiovascular tests are available that can detect the myocardial substrate abnormalities and help refine risk. These investigations include ECG-based tests (signal averaged ECG and T-wave alternans), Holter-based recordings (heart rate variability and heart rate turbulence) and imaging techniques (cardiac magnetic resonance). Recent evidence also points towards a potential role for other indices on the 12-lead ECG and genetic profiling in risk prediction. This study reviews the current evidence for the use of these tests in AMI survivors and addresses their pros and cons in guiding the selection of ICD recipients.

Electrophysiology of human cardiac atrial and ventricular telocytes

Telocytes (TCs) with exceptionally long cellular processes of telopodes have been described in human epicardium to act as structural supporting cells in the heart. We examined myocardial chamber‐specific TCs identified in atrial and ventricular fibroblast culture using immunocytochemistry and studied their electrophysiological property by whole‐cell patch clamp. Atrial and ventricular TCs with extended telopodes and alternating podoms and podomers that expressed CD34, c‐Kit and PDGFR‐β were identified. These cells expressed large conductance Ca2+‐activated K+ current (BKCa) and inwardly rectifying K+ current (IKir), but not transient outward K+ current (Ito) and ATP‐sensitive potassium current (KATP). The active channels were functionally competent with demonstrated modulatory response to H2S and transforming growth factor (TGF)‐β1 whereby H2S significantly inhibited the stimulatory effect of TGF‐β1 on current density of both BKCa and IKir. Furthermore, H2S attenuated TGF‐β1‐stimulated KCa1.1/Kv1.1 (encode BKCa) and Kir2.1 (encode IKir) expression in TCs. Our results show that functionally competent K+ channels are present in human atrial and ventricular TCs and their modulation may have significant implications in myocardial physiopathology.

Pharmacoelectrophysiology of Viral-Free Induced Pluripotent Stem Cell–Derived Human Cardiomyocytes

Development of pharmaceutical agents for cardiac indication demands elaborate safety screening in which assessing repolarization of cardiac cells remains a critical path in risk evaluations. An efficient platform for evaluating cardiac repolarization in vitro significantly facilitates drug developmental programs. In a proof of principle study, we examined the effect of antiarrhythmogenic drugs (Vaughan Williams class I-IV) and noncardiac active drugs (terfenadine and cisapride) on the repolarization profile of viral-free human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Extracellular field potential (FP) recording using microelectrode arrays demonstrated significant delayed repolarization as prolonged corrected FP durations (cFPDs) by class I (quinidine and flecainide), class III (sotalol and amiodarone), and class IV (verapamil), whereas class II drugs (propranolol and nadolol) had no effects. Consistent with their sodium channel-blocking ability, class I drugs also significantly reduced FPmin and conduction velocity. Although lidocaine (class IB) had no effects on cFPDs, verapamil shortened cFPD and FPmin by 25 and 50%, respectively. Furthermore, verapamil reduced beating frequencies drastically. Importantly, the examined drugs exhibited dose-response curve on prolongation of cFPDs at an effective range that correlated significantly with therapeutic plasma concentrations achieved clinically. Consistent with clinical outcomes, drug-induced arrhythmia of tachycardia and bigeminy-like waveforms by quinidine, flecainide, and sotalol was demonstrated at supraphysiological concentrations. Furthermore, off-target effects of terfenadine and cisapride on cFPD and Na( + ) channel blockage were similarly revealed. These results suggest that hiPSC-CMs may be useful for safety evaluation of cardioactive and noncardiac acting drugs for personalized medicine.

Declining case fatality rates for acute myocardial infarction in South Asian and white patients in the past 15 years

Objectives: To determine whether case fatality rates in South Asian (Bangladeshi, Indian and Pakistani) patients with acute myocardial infarction have shown similar declines to those reported for white patients during the past 15 years. Design: Cross-sectional, observational study. Setting: Coronary care unit in east London. Patients: 2640 patients—29% South Asian—admitted with acute myocardial infarction between January 1988 and December 2002. Main outcome measures: Differences over time in rates of in-hospital death, ventricular fibrillation and left ventricular failure. Results: The proportion of South Asians increased from 22% in 1988–92 to 37% in 1998–2002. Indices of infarct severity were similar in South Asian and white patients, with declining frequencies of ST elevation infarction (88.2% to 77.5%, p < 0.0001), Q wave development (78.1% to 56.9%, p < 0.0001) and mean (interquartile range) peak serum creatine kinase concentrations (1250 (567–2078) to 1007 (538–1758) IU/l, p < 0.0001) between 1988–92 and 1998–2002. Rates of in-hospital death (13.0% to 9.4%, p < 0.01), ventricular fibrillation (9.2% to 6.0%, p < 0.001) and left ventricular failure (33.2% to 26.5%, p < 0.0001) all declined; these changes did not interact significantly with ethnicity. Odds ratios for the effect of time on risk of death increased from 0.81 (95% CI 0.70 to 0.93) to 1.02 (95% CI 0.87 to 1.21) after adjustment for ethnicity and indices of infarct severity (ST elevation, peak creatine kinase, Q wave development and treatment with a thrombolytic). Conclusions: In the past 15 years, death from acute myocardial infarction among South Asians has declined at a rate similar to that seen in white patients. This is largely caused by reductions in indices of infarct severity.

Prospective Randomized Study to Assess the Efficacy of Site and Rate of Atrial Pacing on Long-Term Progression of Atrial Fibrillation in Sick Sinus Syndrome

Background— Atrial-based pacing is associated with lower risk of atrial fibrillation (AF) in sick sinus syndrome compared with ventricular pacing; nevertheless, the impact of site and rate of atrial pacing on progression of AF remains unclear. We evaluated whether long-term atrial pacing at the right atrial (RA) appendage versus the low RA septum with (ON) or without (OFF) a continuous atrial overdrive pacing algorithm can prevent the development of persistent AF. Methods and Results— We randomized 385 patients with paroxysmal AF and sick sinus syndrome in whom a pacemaker was indicated to pacing at RA appendage ON (n=98), RA appendage OFF (n=99), RA septum ON (n=92), or RA septum OFF (n=96). The primary outcome was the occurrence of persistent AF (AF documented at least 7 days apart or need for cardioversion). Demographic data were homogeneous across both pacing site (RA appendage/RA septum) and atrial overdrive pacing (ON/OFF). After a mean follow-up of 3.1 years, persistent AF occurred in 99 patients (25.8%; annual rate of persistent AF, 8.3%). Alternative site pacing at the RA septum versus conventional RA appendage (hazard ratio=1.18; 95% confidence interval, 0.79–1.75; P=0.65) or continuous atrial overdrive pacing ON versus OFF (hazard ratio=1.17; 95% confidence interval, 0.79–1.74; P=0.69) did not prevent the development of persistent AF. Conclusions— In patients with paroxysmal AF and sick sinus syndrome requiring pacemaker implantation, an alternative atrial pacing site at the RA septum or continuous atrial overdrive pacing did not prevent the development of persistent AF. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00419640.