βIII-tubulin suppression enhances the activity of Amuvatinib to inhibit cell proliferation in c-Met positive non-small cell lung cancer cells

Non-Small Cell Lung Carcinoma (NSCLC) remains a leading cause of cancer death. Resistance to therapy is a significant problem, highlighting the need to find new ways of sensitising tumour cells to therapeutic agents. βIII-tubulin is associated with aggressive tumours and chemotherapy resistance in a range of cancers including NSCLC. βIII-tubulin expression has been shown to impact kinase signalling in NSCLC cells. Here, we sought to exploit this interaction by identifying co-activity between βIII-tubulin suppression and small-molecule kinase inhibitors. To achieve this, a forced-genetics approach combined with a high-throughput drug screen was used. We show that activity of the multi-kinase inhibitor Amuvatinib (MP-470) is enhanced by βIII-tubulin suppression in independent NSCLC cell lines. We also show that this compound significantly inhibits cell proliferation among βIII-tubulin knockdown cells expressing the receptor tyrosine kinase c-Met. Together, our results highlight that βIII-tubulin suppression combined with targeting specific receptor tyrosine kinases may represent a novel therapeutic approach for otherwise difficult-to-treat lung carcinomas.

Quality indicators of the atrial fibrillation management from the European (EORP) and Asia-Pacific (APHRS) registries

Background

The 2020 ESC guideline for atrial fibrillation (AF) recommends universal quality indicators to identify areas for improvement in clinical practice. It also recommends using clinical registries to monitor clinical practice and identify areas for improvement. We have analysed two large comprehensive prospective clinical registries of patients with AF, the EURObservational Research Programme (EORP) and the Asia Pacific Heart Rhythm Society (APHRS), to compare the achievement of the ESC quality indicators in two major world populations.

Methods

The EORP and APHRS registries used the same electronic case report forms to collect data. T-test and Chi-squared test were used to compare registries. Logistic regression was used to identify pharmacological rate control therapy predictors in permanent AF. The model was adjusted for age, oral anticoagulation (OAC), EHRA and CHA2DS2-VASc scores, heart rate on the latest ECG and the region of recruitment (Europe or Asia) (STATA Corp, version 13).

Results

All 11096 EORP patients (59.3% males, age 69±11 years) and 5460 APHRS patients (66.3% males, age 68±12 years) had CHA2DS2-VASc and HAS-BLED scores documented at enrolment. The EORP register included a higher proportion of patients with CHA2DS2VASc ≥2 (81% vs 70%, p<0.001). These patients had similar OAC use (87%) in both registries, but NOAC use was higher in the APHRS (67% vs 34%, p<0.001), while dual antithrombotic use was more common in the EORP (14% vs 8%, p<0.001). The Table lists paraments that may impact OAC prescription.

In patients with permanent AF, heart rate (82±20 vs 78±20, p<0.001) and antiarrhythmic pharmacotherapy (9% vs 5%) was higher in the EORP registry. On logistic regression, independent predictors of rate control with antiarrhythmic pharmacotherapy were higher EHRA 3 score (adjusted odds ratio (aOR) 1.8; 95% confidence interval (CI) 1.3–2.5, p<0.001); faster heart rate (aOR 1.01; 95% CI 1.00–1.02, p<0.001); younger age (aOR 0.97; 95% CI 0.96–0.98, p<0.001) and being recruited to the APHRS (aOR 0.56; 95% CI 0.40–0.79, p=0.001).

APHRS vs EORP patients with non-permanent AF were less symptomatic (EHRA score I in 56% vs 38%) with less frequent use of antiarrhythmics (25% vs 37%), rhythm-management interventions (32% vs 46%), but higher use of catheter ablation (p<0.001 for all).

Conclusion

There are significant regional variations in achievement of the ESC quality indicator for AF. The variations may be due to differences in healthcare systems, but they may also reflect the population characteristics.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Since the start of EORP, the following companies have supported theprogramme: Abbott Vascular Int. (2011-2014), Amgen Cardiovascular(2009-2018), AstraZeneca (2014-2017), Bayer AG (2009-2018),Boehringer Ingelheim (2009-2019), Boston Scientific (2009-2012), TheBristol Myers Squibb and Pfizer Alliance (2011-2016), The Alliance DaiichiSankyo Europe GmbH and Eli Lilly and Company (2011-2017), Edwards(2016-2019), Gedeon Richter Plc. (2014-2017), Menarini Int. Op. (2009-2012), MSD-Merck & Co. (2011-2014), Novartis Pharma AG (2014-2017), ResMed (2014-2016), Sanofi (2009-2011), and SERVIER (2009-2018).The Atrial Fibrillation NETwork (AFNET), conducting the registryin Germany, received support from The Bristol Myers Squibb/PfizerAlliance (2014-2018) and the German Centre for CardiovascularResearch (DZHK).

βIII-Tubulin Gene Regulation in Health and Disease

Microtubule proteins form a dynamic component of the cytoskeleton, and play key roles in cellular processes, such as vesicular transport, cell motility and mitosis. Expression of microtubule proteins are often dysregulated in cancer. In particular, the microtubule protein βIII-tubulin, encoded by the TUBB3 gene, is aberrantly expressed in a range of epithelial tumours and is associated with drug resistance and aggressive disease. In normal cells, TUBB3 expression is tightly restricted, and is found almost exclusively in neuronal and testicular tissues. Understanding the mechanisms that control TUBB3 expression, both in cancer, mature and developing tissues will help to unravel the basic biology of the protein, its role in cancer, and may ultimately lead to the development of new therapeutic approaches to target this protein. This review is devoted to the transcriptional and posttranscriptional regulation of TUBB3 in normal and cancerous tissue.

Abstract 1442: Identifying the molecular basis by which βIII-tubulin promotes tumor cell survival and drug resistance in non-small cell lung cancer

Lung cancer is the leading cause of cancer-related mortality worldwide with the most common sub-type, non-small cell lung carcinoma (NSCLC), accounting for >80% of cases. Despite advances in treatments, 5-year survival rates for this disease remain dismal. Advanced NSCLC responds poorly to current therapy and the mechanisms underlying its resistance and aggressive nature are not well defined. Microtubules form a component of the cell cytoskeleton and alterations in the expression of microtubule proteins are increasingly correlated with more aggressive and treatment-refractory cancers. βIII-tubulin is a neuronal-specific isotype that is aberrantly expressed in a range of cancers including NSCLC, and has been found to be correlated with reduced patient survival.

Our group has recently demonstrated that βIII-tubulin contributes to activation of the PI3K/AKT cell-survival pathway in NSCLC cells[1]. One of the key negative regulators of this pathway is the tumor suppressor PTEN. PTEN can inhibit cell growth, migration and invasion, and a loss of PTEN function is often associated with cancer progression through AKT hyperactivation.

Here, using forced-genetics cell models, we show that AKT activation is reduced by βIII-tubulin knockdown, and that re-expression of βIII-tubulin restores these levels in NSCLC cells. Interestingly, we also found that βIII-tubulin knockdown resulted in increased PTEN mRNA along with altered levels of Snail-1/β-catenin, suggesting a possible role for βIII-tubulin in regulating the transcriptional pathway of the PTEN tumor suppressor. Building on these findings, we also identified, through a high-throughput cell-based drug screen, several receptor tyrosine kinase inhibitors that synergize with βIII-tubulin knockdown to reduce NSCLC cell proliferation and tumoroid growth.

Together, our data demonstrate an important role for βIII-tubulin in modulating the activation and/or expression levels of signaling proteins which form part of a major pro-survival pathway in NSCLC. In addition, our results suggest that inhibition of βIII-tubulin in combination with drugs that target multiple kinases may offer a novel therapeutic strategy for the treatment of NSCLC to improve patient outcomes.

[1] McCarroll et al., TUBB3/betaIII-tubulin acts through the PTEN/AKT signaling axis to promote tumorigenesis and anoikis resistance in non-small cell lung cancer. Cancer Research. 2015;75:415-425.

Citation Format: Simon Brayford, Wee Siang Teo, Amelia Parker, Laura McVeigh, Joshua A. McCarroll, Maria Kavallaris. Identifying the molecular basis by which βIII-tubulin promotes tumor cell survival and drug resistance in non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1442.

β-tubulin carboxy-terminal tails exhibit isotype-specific effects on microtubule dynamics in human gene-edited cells

This study used human gene-edited cell models and image analysis to reveal that the tubulin C-terminal tails specifically regulate the dynamics of individual microtubules and coordinate microtubule behavior across the cell.

Microtubules are highly dynamic structures that play an integral role in fundamental cellular functions. Different α- and β-tubulin isotypes are thought to confer unique dynamic properties to microtubules. The tubulin isotypes have highly conserved structures, differing mainly in their carboxy-terminal (C-terminal) tail sequences. However, little is known about the importance of the C-terminal tail in regulating and coordinating microtubule dynamics. We developed syngeneic human cell models using gene editing to precisely modify the β-tubulin C-terminal tail region while preserving the endogenous microtubule network. Fluorescent microscopy of live cells, coupled with advanced image analysis, revealed that the β-tubulin C-terminal tails differentially coordinate the collective and individual dynamic behavior of microtubules by affecting microtubule growth rates and explorative microtubule assembly in an isotype-specific manner. Furthermore, βI- and βIII-tubulin C-terminal tails differentially regulate the sensitivity of microtubules to tubulin-binding agents and the microtubule depolymerizing protein mitotic centromere-associated kinesin. The sequence of the β-tubulin tail encodes regulatory information that instructs and coordinates microtubule dynamics, thereby fine-tuning microtubule dynamics to support cellular functions.

An Emerging Role for Tubulin Isotypes in Modulating Cancer Biology and Chemotherapy Resistance

Tubulin proteins, as components of the microtubule cytoskeleton perform critical cellular functions throughout all phases of the cell cycle. Altered tubulin isotype composition of microtubules is emerging as a feature of aggressive and treatment refractory cancers. Emerging evidence highlighting a role for tubulin isotypes in differentially influencing microtubule behaviour and broader functional networks within cells is illuminating a complex role for tubulin isotypes regulating cancer biology and chemotherapy resistance. This review focuses on the role of different tubulin isotypes in microtubule dynamics as well as in oncogenic changes that provide a survival or proliferative advantage to cancer cells within the tumour microenvironment and during metastatic processes. Consideration of the role of tubulin isotypes beyond their structural function will be essential to improving the current clinical use of tubulin-targeted chemotherapy agents and informing the development of more effective cancer therapies.

Abstract 4037: High throughput kinase inhibitor screen reveals novel inhibitor combinations acting in synergy with TUBB3/βIII-tubulin suppression in non-small cell lung cancer

Background: Non-Small Cell Lung Cancer (NSCLC) survival rates remain dismal and this malignancy is poorly responsive to current therapy. The mechanisms contributing to this resistance phenotype and aggressive behavior of this disease are not well defined. TUBB3/βIII-tubulin is aberrantly expressed in NSCLC and its expression correlates negatively with disease free survival of patients. Our group has previously shown that βIII-tubulin plays a functional role in chemotherapy resistance and tumorigenesis in NSCLC via modulation of the PTEN/AKT signaling pathway1, 2. This study aimed to identify kinase inhibitors that synergize with βIII-tubulin inhibition in NSCLC using a high-throughput cell-based screen.

Methods: A high-throughput cell-based screen of a kinase inhibitor library was performed against our previously described1, 2 NSCLC H460 cells, expressing either βIII-tubulin shRNA or control non-targeting shRNA. The primary screen consisted of a total of 210 kinase inhibitors tested at a single, fixed concentration and cell viability determined using the Alamar blue assay. Secondary screens were performed using a five point dose response. Further validation of the kinase inhibitors was performed against two independent NSCLC, H460 and A549 expressing either βIII-tubulin shRNA or control non-targeting shRNA.

Results: A number of kinase inhibitors that act on key signalling cascades were identified to act in synergy with TUBB3/βIII-tubulin knockdown to inhibit NSCLC cell growth. Interestingly, several different inhibitors which target mTOR were identified as top candidates for acting in combination with βIII-tubulin knockdown to inhibit NSCLC cell growth. Treatment of cells with clinically approved mTOR inhibitors, Temsirolimus and Rapamycin, resulted in a significant decrease in cell viability in the βIII-tubulin knockdown cells compared to control. Notably, mTOR acts downstream of AKT signalling and further highlights a potential connection with βIII-tubulin and the AKT signal transduction cascade. Other kinase inhibitors that act on key signaling cascades including Amuvatinib-Multi Kinase Inhibitor (Flt3, Met, Kit, c-Ret & PDGFR); Mubritinib-HER-2 inhibitor; and Neratinib HER2, EGFR, also acted in combination with βIII-tubulin knockdown to inhibit NSCLC cell growth.

Conclusions: Our results suggest that clinically approved therapies designed to target mTOR combined with inhibition of TUBB3/βIII-tubulin may offer a novel therapeutic strategy for the treatment of NSCLC patients.

References: 1 McCarroll et al. Cancer Research 2010; 70: 4995-5003. 2 McCarroll et al. Cancer Research 2015; 75: 415-425.

Citation Format: Wee Siang Teo, Tanya Dwarte, Tim W. Failes, Greg M. Arndt, Joshua A. McCarroll, Maria Kavallaris. High throughput kinase inhibitor screen reveals novel inhibitor combinations acting in synergy with TUBB3/βIII-tubulin suppression in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4037. doi:10.1158/1538-7445.AM2017-4037

Recent Progress in Energy-Driven Water Splitting

Hydrogen is readily obtained from renewable and non-renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non-renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost-effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic-integrated solar-driven water electrolysis.

From matrix nano- and micro-phase tougheners to composite macro-properties

In this paper, firstly, the morphology and toughness of a range of bulk epoxy polymers, which incorporate a second phase of well-dispersed silica nanoparticles and/or rubber microparticles, have been determined. Secondly, the macro-properties of natural-fibre reinforced-plastic (NFRP) composites based upon these epoxy polymers have been ascertained, using (i) unidirectional flax fibres or (ii) regenerated-cellulose fibres in the architecture of a plain-woven fabric. Thirdly, the toughening mechanisms which are induced in these materials by the presence of the silica nanoparticles, the rubber microparticles and the natural fibres have been identified. Finally, the values of the toughness of the bulk epoxy polymers and corresponding NFRPs have been quantitatively modelled. The increased toughness recorded for the bulk epoxy polymer due to the presence of the silica nanoparticles and/or rubber microparticles was indeed typically transferred to the NFRP composites when using such epoxies as the matrices for the fibres. Thus, the important role that may be played by modifications to the epoxy matrices in order to increase the toughness of the composites was very clearly demonstrated by these results. However, notwithstanding, the toughening mechanisms induced by the fibres were essentially responsible for the very high toughnesses of the NFRP composites, compared with the bulk epoxy polymers. The modelling studies successfully predicted the values of toughness of the bulk epoxy polymers and of the NFRP composites. These studies also quantified the extent to which each toughening mechanism, induced by the second-phase nano- and microparticles and the natural fibres, contributed to the overall values of toughness of the materials. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'.

New insights into the role of ID proteins in breast cancer metastasis: a MET affair

The establishment of lethal metastases depends on the capacity of a small number of cancer cells to regenerate a tumor after entering a target organ. Stankic and colleagues have identified a role for the inhibitor of differentiation protein, ID1, as a critical regulator of breast cancer stem-like properties and metastatic colonization. Under the control of tumor growth factor-beta signaling, ID1 induces mesenchymal-epithelial transition at the metastatic site by antagonizing the activity of the basic helix-loop-helix transcription factor Twist1. This study sheds light on mechanisms that initiate metastatic outgrowth, and strengthens the concept that epithelial-mesenchymal plasticity is crucial at different stages of metastasis.

Pneumocystis carinii (jirovecii) pneumonia (PCP): the most common opportunistic infection observed in HIV/AIDS cases at the University Malaya Medical Centre, Kuala Lumpur, Malaysia

This retrospective study was conducted among 59 HIV/AIDS patients with opportunistic infections admitted to the University Malaya Medical Centre between 2000 and 2009. Fifty-five point nine percent of cases were Chinese, 25.4% were Malays, 11.9% were Indians and 6.8% were of unknown ethnic origin. The male:female ratio was 2.9:1 (44 males and 15 females). The highest prevalence (38.9%) occurred in the 30-39 year old age group. Men comprised 47.7% and women 53.3%; the majority of both were married. The majority of cases were Malaysians (89.8%) and the rest (10.2%) were immigrants. Most of the patients (18.6%) were non-laborers, followed by laborers (11.9%), the unemployed (5.1%) and housewives (3.4%). The most common risk factor was unprotected sexual activity (20.3%). The two most common HIV/AIDS related opportunistic infections were Pneumocystis carinii (jirovecii) pneumonia (PCP) (62.7%) and toxoplasmosis (28.8%). Seventy-two point nine percent of patients had a CD4 count <200 cells/microl and 5.1% had a CD4 count >500 cells/microl. Eleven point nine percent of cases died during study period. A low CD4 count had a greater association with opportunistic infections. Most of the patients presented with fever (44.1%), cough (42.4%) and shortness of breath (28.8%). Detection of the etiologic pathogens aids clinicians in choosing appropriate management strategies.

Novel electrogram device with web-based service centre for ambulatory ECG monitoring

INTRODUCTION

Arrhythmias are often intermittent, and a normal electrocardiogram (ECG) may not be diagnostic. The purpose of this study was to evaluate the usefulness of HeartWave500 (HW), a novel web-based ambulatory ECG monitoring device.

METHODS

A total of 120 patients from the National Heart Centre, Singapore were prospectively randomised in a three to one ratio to either HW or a standard transtelephonic (TT) event recorder. HW records five leads and transmits to an internet server, while TT transmits audio data to a central station. Monitoring was conducted for two weeks. The diagnostic yield was calculated in two ways: the percentage of patients successfully diagnosed as a function of time, and the absolute number of new diagnoses per patient per week.

RESULTS

33 patients (14 male, 19 female; mean age 49.6 + or - 11.1 years) were randomised to TT. 87 patients (32 male, 55 female; mean age 43.7 + or - 12.2 years) were randomised to HW. At the end of two weeks, the percentage of patients diagnosed with any arrhythmia was similar for both groups (66.7 percent for TT versus 67.8 percent for HW). There was a trend toward significance for the number of diagnoses per patient per week for Week 2 between TT and HW (0.58 + or - 0.75 versus 0.34 + or - 0.55, p is 0.06). Transmitted ECGs were read earlier for HW (18 minutes versus 1107 minutes, Mann-Whitney non-parametric test, p is less than 0.05). Transmitted recordings that were unreadable were also significantly lower for HW (8.0 percent versus 17.6 percent, chi-square test, p is less than 0.05).

CONCLUSION

HW and TT have similar diagnostic yields. There is a trend toward a shorter monitoring time for HW. The ability of HW to record and transmit via the web, the earlier review of data and low unreadable data make HW an attractive alternative to TT.

Electrocardiographical case. Young woman with frequent syncope attacks

A 29-year-old woman with frequent syncope attacks was referred for electrophysiological study and consideration for radio-frequency ablation of her ventricular arrhythmias. Her ECG showed features of right ventricular outflow tract premature contraction. Differential diagnoses for the causes of syncope in this patient include: right ventricular outflow tract tachycardia, arrythmogenic right ventricular dysplasia, and neurocardiogenic syncope. She underwent a tilt table test, which showed a malignant cardioinhibitory response. She developed abrupt syncope with 32 seconds of asystole during the test. She was given intravenous atropine and was resuscitated. A dual chamber rate-responsive pacemaker was implanted for her the next day. She was discharged well subsequently. Although the prognosis in patients with prolonged aystole in malignant vasovagal syncope is unknown, most doctors will still choose to implant a permanent pacemaker for patients with malignant neurocardiogenic syncope when the sinus arrest is prolonged.

Electrocardiographical case. Asymptomatic patient with deep T-wave inversions

A 45-year-old man was found to have an abnormal myocardial perfusion scan. He was asymptomatic, with no chest pain, breathlessness or palpitations. Clinical examination was unremarkable. The 12-lead electrocardiography (ECG) showed increased QRS voltage in leads V3-V6, and deep T-wave inversions noted in leads V3-V6, with an absence of septal Q waves. These ECG features were characteristic of apical variant hypertrophic cardiomyopathy (HCM). He underwent a coronary angiogram that revealed normal coronary arteries, and a left ventriculogram which showed apical HCM. Transthoracic echocardiography further confirmed the diagnosis. No drug therapy was instituted as he was asymptomatic. Apical HCM is discussed.

Electrocardiographical case. Acute severe chest tightness

The early diagnosis of acute myocardial infarction is crucial for the institution of appropriate reperfusion therapy. We describe a 56-year-old man who developed sudden onset of severe chest tightness. Inferior, posterior and right ventricular ST elevation myocardial infarction was diagnosed on electrocardiography (ECG). The ECG interpretation, differential diagnosis and management are discussed.

Electrocardiographical case. An elderly lady with chest pain. Diagnosis: isolated posterior myocardial infarct (MI)

A 72-year-old woman with diabetes mellitus, hypertension and dyslipidaemia presented with severe chest pain of four hours duration. Her electrocardiogram (ECG) showed tall R waves in leads V1-2, and ST segment depression in leads V1- 4, consistent with an isolated posterior myocardial infarction (MI). Emergency coronary angiogram showed an occluded left circumflex coronary artery, and primary angioplasty and stenting was performed. The ECG criteria for isolated posterior MI and pitfalls in using the conventional 12-lead ECG are discussed.

Electrocardiographical case. Elderly woman with sudden onset of post-operative dyspnoea

A 70-year-old Chinese woman developed breathlessness, tachycardia and hypotension on the fourth day after total hip replacement. 12-lead electrocardiogram (ECG) showed sinus tachycardia with ST depression in I, II, V5 and V6. The ECG changes of sinus tachycardia along with a typical history is suggestive of pulmonary embolism. Diagnosis, treatment and the use of IVC filter for pulmonary embolism are discussed.

Electrocardiographical case. Asymptomatic patient with ST-segment elevation

A 46-year-old man complained of recurrent episodes of giddiness which was not associated with chest pain or breathlessness. There was no family history of sudden death. Clinical examination was unremarkable.12-lead electrocardiogram (ECG) showed ST segment elevation in the right precordial leads, with coved ST segment elevation at its J point followed by a negative T wave with no isoelectric separation, specifically in V2. These ECG features are characteristic of the Brugada syndrome. He underwent a flecanide challenge which produced further elevation of ST segment at its J point and spontaneous ventricular ectopy. Electrophysiological studies induced ventricular fibrillation with 3 extra stimuli. An implantable cardioverter-defibrillator was implanted for prevention of sudden cardiac death. The Brugada syndrome is discussed.

A case series of sotalol-induced torsade de pointes in patients with atrial fibrillation--a tale with a twist

INTRODUCTION

Sotalol is a potent antiarrhythmic often used in patients with atrial fibrillation. However, it has been associated with a risk of provoking other potentially dangerous arrhythmias, especially if used in high doses and in patients with uncorrected electrolyte imbalance or impaired renal and cardiac function.

CLINICAL PICTURE

We present 4 patients with atrial fibrillation treated with sotalol who developed torsade de pointes due to marked prolongation of the QT interval. While 1 patient had renal failure, all had normal left ventricular function. One patient had been treated with sotalol for more than 10 months before developing torsade de pointes precipitated by hypokalaemia, while another had tolerated sotalol for a 3-month period before the drug was discontinued, and only developed torsade de pointes when the drug was restarted 2 years later. Significantly, the doses used in all patients were relatively low, in contrast to most other reported cases where higher doses were used.

CONCLUSION

As with all antiarrhythmic therapy, these cases illustrate the need for close follow-up of patients treated with sotalol, even if relatively low doses are used. In addition, patients who had previously tolerated the drug well are still susceptible to its proarrhythmic effects.

Treatment of heart failure--role of biventricular pacing for heart failure not responding well to drug therapy

OBJECTIVE

Patients with heart failure may have conduction abnormalities in up to 30%, further aggravating cardiac output. Drugs worsen these abnormalities and resynchronisation therapy with biventricular pacing improves cardiac function by effecting a more coordinated and efficient ventricular contraction. We report here the technique of biventricular pacing and its results.

METHODOLOGY

Patients with NYHA Class III to IV heart failure, widened QRS (> or = 130 ms) complex on the ECG and impaired LVEF < or = 40% were enrolled.

RESULTS

Biventricular pacing was performed in 29 patients (26 males, three females) from August 1999 to December 2001. The mean age of the patients was 59.6 +/- 12.8 years and 62% had underlying ischemic heart disease. All were in NYHA class III or more. Twenty-three had LBBB, four RBBB and two had widened paced QRS complex. The QRS duration was 161 +/- 21 ms and LVEF was 22 +/- 8%. All the left ventricular leads were implanted successfully. The procedure time was 167.0 +/- 79.6 mins and the fluoroscopy time was 43.8 +/- 41.4 mins. There were no significant complications. The NYHA class improved from a mean of 3.1 to 2.0 and exercise time from 252 +/- 95 seconds to 392 +/- 152 seconds at six months post implant (p=0.049). On follow-up (one month to 28 months), 25 (86%) patients had improvement in heart failure symptoms and 26 (90%) of the patients remained alive.

CONCLUSION

Biventricular pacing can be safely performed and results in improvement in symptoms and exercise tolerance in heart failure patients with ventricular dyssynchrony not responding to drug therapy.

Immediate and mid-term safety and efficacy of single lead VDD pacemakers for patients with atrioventricular block and normal sinus node function--a single centre experience

INTRODUCTION

Single lead atrial synchronous ventricular pacing (VDD) is increasingly being used in place of conventional dual chamber pacing (DDD) for patients with atrioventricular block and preserved sinus node function. Compared to the latter, VDD pacemakers provide similar haemodynamic benefits derived from atrial synchronous pacing, with the added benefit of an easier implant procedure.

OBJECTIVE

To review the use, safety and efficacy of VDD pacing in a single tertiary referral centre.

MATERIALS AND METHODS

A review of all patients with atrioventricular block and normal sinus node function implanted with a VDD pacemaker over a 2-year period at a local tertiary cardiac referral centre. Data on complications, atrial sensing performance and maintenance of atrioventricular synchrony during implant and at subsequent follow-up visits were obtained from a prospectively maintained registry and analysed.

RESULTS

Forty-one patients (17 males, 24 females) with a mean age of 72 +/- 9 years received VDD pacing for various forms of high-grade atrioventricular block. The average implantation time was 46.8 +/- 17.1 minutes, and a pneumothorax in 1 patient was the only complication. Electrical measurements at implantation and subsequent follow-up visits revealed an initial rapid decrease in atrial signal amplitude (mean atrial P wave at implant 3.1 +/- 1.1 mV, predischarge 1.9 +/- 1.3 mV) which began to stabilise after 3 months, reaching a mean atrial P wave value of 1.3 +/- 0.3 mV at 24 months. The atrial sensing performance (percentage of atrial synchronous ventricular complexes) was 97% over a mean follow-up period of 9.9 months. Four patients (10%) developed paroxysmal atrial tachyarrhythmias. Sinus node dysfunction was not observed in any of our patients during the follow-up period.

CONCLUSION

In patients with atrioventricular block and preserved sinus node function, single lead VDD pacing is safe and effective in maintaining a physiological atrial synchronous pacing mode.