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.

Clinical outcomes of patients with diabetes mellitus and acute myocardial infarction treated with primary angioplasty or fibrinolysis

OBJECTIVE

To compare the early and late outcomes of primary percutaneous transluminal coronary angioplasty (PTCA) with fibrinolytic treatment among diabetic patients with acute myocardial infarction (AMI).

DESIGN

Retrospective observational study with data obtained from prospective registries.

SETTING

Tertiary cardiovascular institution with 24 hour acute interventional facilities.

PATIENTS

202 consecutive diabetic patients with AMI receiving reperfusion treatment within six hours of symptom onset.

INTERVENTIONS

Fibrinolytic treatment was administered to 99 patients, and 103 patients underwent primary PTCA. Most patients undergoing PTCA received adjunctive stenting (94.2%) and glycoprotein IIb/IIIa inhibition (63.1%).

MAIN OUTCOME MEASURES

Death, non-fatal reinfarction, and target vessel revascularisation at 30 days and one year were assessed.

RESULTS

Baseline characteristics were similar in these two treatment groups except that the proportion of patients with Killip class III or IV was considerably higher in those treated with PTCA (15.5% v 6.1%, p = 0.03) and time to treatment was significantly longer (103.7 v 68.0 minutes, p < 0.001). Among those treated with PTCA, the rates for in-hospital recurrent ischaemia (5.8% v 17.2%, p = 0.011) and target vessel revascularisation at one year (19.4% v 36.4%, p = 0.007) were lower. Death or reinfarction at one year was also reduced among those treated with PTCA (17.5% v 31.3%, p = 0.02), with an adjusted relative risk of 0.29 (95% confidence interval 0.15 to 0.57) compared with fibrinolysis.

CONCLUSION

Among diabetic patients with AMI, primary PTCA was associated with reduced early and late adverse events compared with fibrinolytic treatment.

Myocardial infarction in Singapore: a nationwide 10-year study of multiethnic differences in incidence and mortality

INTRODUCTION AND METHODS

Cardiovascular diseases have progressively increased in importance as a major contributor of morbidity and mortality in Asia. However, many countries in Asia do not have nationwide systematically-collected and standardised data on myocardial infarction (MI). To accurately document the extent of atherosclerotic coronary heart disease in Singapore, a nationwide myocardial infarct registry was established in the mid-1986. Possible myocardial infarct events were identified through daily national lists of cardiac enzymes, hospital discharge codes, mortuary records and the national death registry. Data obtained from clinical history, cardiac enzymes and 12-lead electrocardiogram Minnesota codes were entered into an algorithm based on the WHO MONICA study. Cases identified as "definite" MI were included in the decade's review for this study.

RESULTS

From 1988 to 1997, 13,048 myocardial infarct events were diagnosed with 3367 deaths. There was a 39.1% decline in mortality, with an average decline of 6.5% per year [95% confidence intervals (CI), -3.9% to -9.1%]. However, the decline in incidence was only 20.8% with an average decline of 2.4% per year (95% CI, -6.6% to -1.2%). The highest incidence and mortality rates for both genders were seen in the Indians, followed by the Malays and the Chinese.

CONCLUSION

Over 10 years, from 1988 to 1997, we documented a significant fall in mortality from MI in Singapore. There was a smaller decline in the incidence of infarction. Singapore implemented a National Healthy Lifestyle Programme in 1992 as a 10-year effort. The disparity in the incidence and mortality may suggest that a more dramatic and immediate impact has taken place in mortality through therapeutic programmes; primary preventive programmes would be more difficult to evaluate and have a more gradual impact. Only with continual accurate data collection through the whole country, over a much longer period, can the relative value of preventive and therapeutic programmes in coronary heart disease be assessed.

Slow-infusion of calcium channel blockers in the emergency management of supraventricular tachycardia

OBJECTIVE

To compare the efficacy of verapamil and diltiazem as slow infusions in terminating spontaneous supraventricular tachycardia (SVT) in the emergency department (ED).

METHOD

Patients of at least 10 years of age who presented to our ED with regular narrow complex tachycardia not converted with a vagal manoeuvre with an ECG diagnosis of SVT were included. Those who were haemodynamically unstable were excluded. Patients were randomized to undergo either verapamil infusion at a rate of 1 mg/min to a maximum of 20 mg or diltiazem infusion at a rate of 2.5 mg/min to a maximum of 50 mg.

RESULTS

Eighty-one patients were randomized to receive verapamil infusion and 80 were randomized to receive the diltiazem infusion. There is no difference in success rate between verapamil (98.8%) and diltiazem (96.3%) infusion. The dose of medication required to convert 25,50 and 75% of SVTs were 4.0,5.0 and 8.0 mg for the verapamil infusion and 10.0,12.5 and 17.5 mg for the diltiazem infusion. There was one complication in each group.

CONCLUSION

Calcium channel blockers infusions were safe and efficacious in terminating spontaneous SVT. There was no difference between the success rates of verapamil and diltiazem infusions.

Two case reports on incessant left ventricular tachycardia: curative therapy with radiofrequency ablation

INTRODUCTION

Incessant ventricular tachycardia is a rare arrhythmia which can be life threatening. Treatment with anti-arrhythmic agents may occasionally fail.

CLINICAL PICTURE

We report 2 cases of incessant ventricular tachycardia. The first case was a young man with idiopathic left ventricular tachycardia who was in incessant ventricular tachycardia despite treatment with multiple anti-arrhythmic drugs and developed dilated cardiomyopathy. The second case was an asymptomatic girl with the incidental finding of an incessant ventricular tachycardia which originated from the left ventricular outflow tract.

TREATMENT AND OUTCOME

Both patients underwent electrophysiologic study and radiofrequency ablation with complete termination of the tachycardia.

CONCLUSION

Radiofrequency catheter ablation in experienced centres should be the first-line therapy for incessant ventricular tachycardia.

A case series of drug-induced long QT syndrome and Torsade de Pointes

INTRODUCTION

Torsade de Pointes (Tdp) is a form of polymorphic ventricular tachycardia in the setting of prolonged QT interval. Any drug that prolongs repolarisation, and hence QT interval, may cause Tdp. Predisposing factors of drug-induced Tdp include female sex, bradyarrhythmia and hypokalaemia.

METHODS

We retrospectively analysed the case notes of 13 patients with drug-induced LQTS from 1991 to 2000 from National Heart Centre and Changi General Hospital.

RESULTS

Causative drugs in the series were amiodarone (seven patients, 54%), sotalol (two patients), quinidine (one patient), phenothiazine (two patients) and astemizole (one patient). There were eight females and all were Chinese. The mean age was 72 +/- nine years. The patients commonly present with syncope (38%) and cardiac arrest (38%). The mean corrected QTC interval was 545 ms. The most common precipitating factor was hypokalaemia (31%). Nine patients require cardiopulmonary resuscitation and two patients (15%) died. Nine patients (69%) had underlying structural heart disease such as ischaemic heart disease, valvular heart disease and hypertensive heart disease. The left ventricular ejection fraction was normal in six patients. The onset of Tdp ranged from Day 2 to Day 5 in the seven patient with amiodarone-induced LQTS. These were inpatients who were given intravenous loading doses of amiodarone. Both patients with sotalol-induced LQTS were females on sotalol 80 mg and 240 mg per day with Tdp occurring on Day 2 and 10 months respectively.

CONCLUSION

Tdp is a potentially life-threatening arrhythmia. The list of torsadogenic drugs is ever expanding. Physicians need to know the drugs which can lead to Tdp. Careful assessment of risk-benefit ratio is important before prescribing such drugs. Amiodarone-induced Tdp is not uncommon in our local population. Initiation of a class III agent, especially amiodarone, should be done judiciously, with monitoring of the QT interval and avoidance of hypokalaemia.

Dual-site atrial pacing for atrial fibrillation in patients without bradycardia

Atrial pacing has been shown to delay the onset of atrial fibrillation (AF) when compared with ventricular pacing in patients with sick sinus syndrome. The role for pacing in the control of AF in patients without bradycardia is uncertain. We performed a randomized, crossover, single-blinded study in 22 patients (14 women, aged 63 +/- 10 years) with paroxysmal AF refractory to treatment with oral sotalol (202 +/- 68 mg/day) and no bradycardic indication for pacing. All patients received a dual-chamber pacemaker with 2 atrial pacing leads positioned at the high right atrium and coronary sinus ostium, respectively. Patients were randomized in a crossover fashion to be paced for 12 weeks, either with high right atrial (RA) pacing at 30 beats/min ("Off") or dual-site RA pacing with an overdrive algorithm that maintained atrial pacing at a rate slightly above the sinus rate ("On"). Treatment on resulted in a significantly higher percentage of atrial pacing and a reduction in atrial ectopic frequency than the treatment off period. The time to the first clinical AF recurrence was prolonged (15 +/- 17 to 50 +/- 35 days, p = 0.006), and total AF burden was reduced (45 +/- 34% vs 22 +/- 29%, p = 0.04) in the on-treatment phase. However, there was no difference in AF checklist symptom scores or overall quality-of-life measures. Dual-site RA pacing with continued sinus overdrive prolonged the time to AF recurrence and decreased AF burden in patients with paroxysmal AF. The absence of a major impact on symptom control suggests that pacing should be used as an adjunctive therapy with other treatment modalities for AF.

Comparison of effectiveness of an 8-mm versus a 4-mm tip electrode catheter for radiofrequency ablation of typical atrial flutter

An 8-mm catheter does not appear superior to 4-mm tip electrode for atrial flutter ablation. The potential advantage of allowing higher energy delivery on a larger surface is compensated by the lack of consistent contact with the endocardial surface.

Initial experience with an autocapture pacemaker system

INTRODUCTION

Autocapture management aims to extend pacemaker longevity without compromising on patient safety by automatically monitoring the pacing threshold and adjusting the pacemaker output for consistent capture. This paper describes our initial experience with the Pacesetter Regency pacemaker with autocapture management.

MATERIALS AND METHODS

Nineteen patients were implanted with single chamber pacemakers with autocapture management. Autocapture was programmed "ON" the day after implantation if Evoked Response (ER) amplitude was at least 2.8 mV. The patients were followed up at 2 weeks, 2 months and 6 months. At each visit, pacing threshold and lead impedance were measured. Autocapture was turned "ON" during follow-up if it had not been done previously.

RESULTS

In 16 out of 19 patients, autocapture could be turned "ON" the day after implantation. One patient had an ER signal that was less than 2.8 mV and 2 patients were in fast atrial fibrillation of more than 120 beats per minute which precluded ER signal testing. These patients could not have autocapture programmed "ON".

CONCLUSION

The benefits of autocapture management can only be realised if an ER signal of at least 2.8 mV is obtained. This requires intraoperative testing of the ER signal. Since there is no commercially available pacing system analyser presently that can measure this, modification of the standard implantation procedure with some prolongation of procedure time is needed.

The differential diagnosis of supraventricular tachycardia using clinical and electrocardiographic features

INTRODUCTION

Noninvasive determination of the mechanism of supraventricular tachycardia (SVT) is useful in order to decide on the appropriate mode of therapy. The aim of this study was to evaluate the usefulness of the clinical and electrocardiographic features in diagnosing the type of SVT.

METHODS

Design--A retrospective review of case records and electrocardiograms (ECG) of patients with definitive diagnosis of the mechanism of supraventricular tachycardia (SVT) made during electrophysiological study (EPS) and catheter ablation. Setting--A tertiary referral centre for electrophysiological studies and radiofrequency catheter ablation of arrhythmias. Sample--One hundred consecutive patients with SVT who had EPS and catheter ablation at our institution. Chief Outcome--Comparison of clinical and ECG pacemeters among 3 different types of SVT, namely atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT) and atrial tachycardia (AT).

RESULTS

There were 68 atrioventricular nodal reentrant tachycardia (AVNRT), 26 atrioventricular reentrant tachycardia (AVRT) and 6 atrial tachycardia (AT). AVRT had the earliest mean age of presentation at 26.8 +/- 11.9 years. Sex and age of onset of symptoms alone were, however, not valuable in diagnosing the type of SVT. P waves were more discernible in AVRT and AT than in AVNRT (69%, 67% and 44% respectively, P = 0.071). AVNRT had the shortest mean RP' interval (86.3 +/- 47.6 msec), while AT had the longest (187 +/- 80.6 msec, P < 0.0001). Conversely for mean P'R interval, AT had the shortest (125 +/- 30 msec), AVNRT had the longest (262.7 +/- 73.7 msec, P = 0.001). AVNRT had the smallest mean RP':P'R ratio (0.6 +/- 0.9), while AT had the largest (2.2 +/- 0.6, P = 0.001). The presence of pseudo r' in V1 and pseudo s' in II/III/aVF was diagnostic of AVNRT with a specificity of 90% and 100%, respectively, and positive predictive value of 97% and 100%, respectively.

CONCLUSION

Pseudo s' in II/III/aVF is highly predictive of AVNRT. Measurement of RP' and PR' interval and ratio are also useful in determining the SVT mechanism.

Electrocardiographic case: diagnosis of acute myocardial infarction in the presence of left bundle branch block

The electrocardiographic features associated with acute myocardial infarction (AMI) are often easily recognised. However, interpretation is made more difficult in the presence of confounding patterns such as a left bundle branch block (LBBB). This may result in missed cases which may otherwise have benefited from acute revascularisation therapy. Though not straightforward, the diagnosis of AMI in the presence of LBBB can be made with a reasonable amount of accuracy. We report a case of acute myocardial infarction with LBBB that was appropriately diagnosed and underwent acute revascularisation by angioplasty. A detailed knowledge of the typical electrocardiographic features associated with LBBB, especially the ST segment morphologies, is very important. This will greatly aid recognition of an evolving AMI and help us decide on the most appropriate therapy.

Pacemaker implantation in Singapore in 1997

INTRODUCTION

Previous reports on pacemaker implantation in Singapore have been from a single institution and hence may not accurately reflect the practice in Singapore. As part of the World survey on pacemaker implantation, a survey of all pacemaker implantations in Singapore in 1997 was performed.

METHOD

Information was obtained from the pacemaker manufacturers and a survey form was sent to all doctors involved in pacemaker implantation.

RESULT

In 1997, 206 pacemakers were implanted or replaced in Singapore. This gives a pacemaker rate of 69 per million. For new implants only, there were 61 implants per million. More detailed information regarding the patient and implantation was obtained in 160 (78%) patients. The mean age of the patients was 68.5 +/- 14.4 years (range 2-97 years). There were 142 (89%) new implants and 18 (11%) replacements. 62.5% of the patients were females. Seventy-nine percent of the patients were older than 60 years old and 17.5% were older than 80 years. Seventy-five percent of the pacemakers were single chamber pacemakers. Twenty-five percent were dual chamber pacemakers. Only 1.4% of the pacemakers used epi-myocardial leads and all these were in children. Heart block was the most common indication for pacing and consisted of 52.8% of the patients while 43.0% of patients were implanted for the sick sinus syndrome.

CONCLUSION

Pacemaker implantation in Singapore in 1997 was 69 per million. Heart block remains the most common indication for implant and single chamber pacing is still the most commonly used mode of pacing. The majority of the implants were in persons older than 60 years. With an increasing ageing population in Singapore, the implant rate for pacemakers will be expected to increase significantly.

Incessant ectopic atrial tachycardia and tachycardia-related cardiomyopathy: therapeutic options and potential for cure

Incessant ectopic atrial tachycardia (IEAT) is a rare cause of cardiomyopathy. Cardiomyopathy is reversible by curative ablation using surgery or radiofrequency current. We report our experience with 5 patients with IEAT. Three patients presented with palpitations and were diagnosed to have paroxysmal supraventricular tachycardia (2 patients) and atrial flutter with 1:1 conduction (1 patient), but 2 presented insidiously with congestive cardiac failure. All the initial echocardiograms showed left ventricular dysfunction. The patients underwent electrophysiological studies which confirmed the diagnosis of IEAT. The first patient had surgical cryoablation and the other patients had successful radiofrequency catheter ablation. Follow-up for 2 to 7 years has shown no recurrences. All patients had significant improvement in left ventricular function on echocardiography. In conclusion, curative ablation by surgery or radiofrequency current is safe and effective. Because of its low morbidity, radiofrequency catheter ablation should be the treatment of choice for IEAT, especially if complicated by tachycardia-related cardiomyopathy.

Treatment and prevention of sudden cardiac death--what have we learnt from randomised clinical trials?

Sudden cardiac death is most commonly caused by ventricular tachycardia or fibrillation. Three groups of patients at highest risk for sudden cardiac death are survivors of previous sudden cardiac death, those with recurrent documented episodes of sustained ventricular tachycardia and patients with recurrent syncope of unknown origin. The experience with antiarrhythmic drugs has been discouraging. Only beta-blockers have been shown to unequivocally reduce both arrhythmic and total mortality in randomised trials. Class I antiarrhythmic drugs increase mortality, especially in an ischemic substrate. Class III drugs such as sotalol and amiodarone have had variable success. Racemic sotalol has both beta-blocker as well as Class III actions and some of the benefits may be due to the former effect. D-sotalol which has only pure Class III action, increases mortality in the post myocardial infarction patient. Amiodarone is superior to Class I antiarrhythmic drugs for patients with previous cardiac arrest. In the high-risk myocardial infarction patient, it seems to reduce sudden death but not total mortality. In the cardiac failure patient, the effect of amiodarone on total mortality is controversial. Several randomised trials of implantable cardioverter-defibrillator (ICD) therapy versus drugs have however concluded that the ICD is superior to drugs in reducing total mortality. In comparison with many other high volume therapies used in medicine today, ICD is still a cost-effective therapy.

T wave alternans and acute rheumatic myocarditis: a case report

T wave alternans is an uncommonly recorded cardiac rhythm. We report here an unusual case of a 13-year-old girl with acute rheumatic carditis and acute nephritis, who developed T wave alternans associated with a prolonged QT interval. These electrocardiographic changes were evident only after the initial acute stage of the disease process and should be borne in mind for patients with acute rheumatic carditis as they may be associated with more malignant arrhythmias.

Curative therapy of cardiac tachyarrhythmias with catheter ablation--a review of the experience with the first 1000 patients

INTRODUCTION

Cardiac tachyarrhythmias present as supraventricular or ventricular tachycardia. Catheter ablation has completely revolutionised the treatment of patients with these arrhythmias.

METHOD

We reviewed the experience of radiofrequency catheter ablation in a single centre.

RESULTS

A total of 1,022 patients underwent radiofrequency catheter ablation from October 1991-December 1997. There were 480 patients who had AV nodal re-entrant tachycardia, 429 patients with accessory pathways, 7 patients with both AV nodal re-entrant tachycardia and accessory pathways, 4 patients with both AV nodal re-entrant tachycardia and atrial tachycardia. Twenty-seven patients had atrial tachycardia ablation, 28 had atrial flutter ablation and 11 patients had AV node ablation for atrial fibrillation. The mean age of the supraventricular tachycardia patients was 41 +/- 15 years (10-80 years). The mean duration of procedure was 108 +/- 60 minutes (15 to 480 minutes) and the mean fluoroscopy time was 19 +/- 17 minutes (3-122 minutes). Another 14 patients had ablation for right ventricular outflow tract ventricular tachycardia and 22 patients had ablation for idiopathic left ventricular tachycardia. The mean age of the ventricular tachycardia patients was 35 +/- 14 years (19-65 years). The mean duration of the ventricular tachycardia ablation procedure was 185 +/- 63 minutes (110-285 minutes) and the duration of fluoroscopy was 33 +/- 16 minutes (range 14-68 minutes). Of the 1,022 patients, 1,002 (98%) of the patients were successfully ablated. There were significant complications in less than 1% of the patients and no mortality associated with the procedure. The recurrence rate was 5% and could be successfully reablated when the procedure was repeated.

CONCLUSION

Radiofrequency catheter ablation is thus an extremely safe and successful procedure and has replaced drug therapy as the treatment of choice for patients with supraventricular tachycardia and non-ischaemic ventricular tachycardia. It provides curative therapy without the need for life-long drug therapy.

The Brugada syndrome in a Chinese population

Sudden cardiac death has been reported in patients with a unique electrocardiographic (ECG) abnormality showing right bundle branch block and ST segment elevation in the precordial leads. This syndrome was first described by Brugada and Brugada and has not been previously described in a Chinese population. We report here the first three cases in Singapore. The first patient was a 49-year-old man who presented with syncope, associated with generalized convulsions. The second patient was a 25-year-old man who complained of palpitations but no syncope. The third patient was a 77-year-old man who presented with recurrent episodes of syncope and collapsed with ventricular fibrillation. All patients had no past cardiac or drug history of note. The neurological examination and investigations were normal. All three patients showed a unique right bundle branch block pattern with ST segment elevation in leads V1-3. The echocardiogram and 24-h ambulatory ECG monitoring, were normal. Single vessel disease was present in the third patient. Electrophysiological studies performed in all three patients were able to induce ventricular fibrillation. The patient with resuscitated cardiac death underwent an implantable cardioverter defibrillator implantation. The importance of this syndrome is that the recognition of the unique ECG pattern enables early identification and treatment of these patients.

Interventional electrophysiology and its role in the treatment of cardiac arrhythmia

Cardiac arrhythmias can present as benign ectopics or as life-threatening arrhythmias and sudden cardiac death. Clinical cardiac electrophysiology is the study of the electrophysiology of the heart and all aspects of management of cardiac arrhythmias. The invasive electrophysiological study was initially purely diagnostic, but recent advances in technology has allowed us to intervene and hence the term interventional electrophysiology. The interventional therapies include permanent pacing for bradyarrhythmias, arrhythmia surgery for arrhythmias, percutaneous catheter ablation and implantable devices for tachyarrhythmias. The treatment of bradyarrhythmias with permanent pacemaker implantation represents the first interventional therapy for patients with cardiac arrhythmias. From 1973 to June 1996, a total of 791 pacemakers have been implanted at the Singapore General Hospital. Previously, patients with tachyarrhythmias could only be cured by open heart surgery utilising intraoperative map guided surgery and ablation of the arrhythmia. Only 17 patients with supraventricular tachycardia (SVT) and 3 patients with VT have undergone this procedure. Catheter ablation has completely revolutionised the treatment of these patients. From October 1991 until December 1996, 860 patients have undergone radiofrequency (RF) catheter ablation for SVT and non-ischaemic VT. Ninety-eight per cent of the patients with SVT have been successfully ablated and 94% of the patients with VT were successfully ablated. RF ablation has become the technique of choice to cure patients with recurrent paroxysmal SVT due to AV re-entrant tachycardia using an accessory pathway, AV nodal re-entrant tachycardia, atrial tachycardia and atrial flutter. It is also used for AV nodal ablation followed by pacemaker insertion or AV nodal modification in patients with poorly controlled atrial fibrillation. Patients with idiopathic non-ischaemic VT arising from the left ventricle or right ventricular outflow tract can similarly be cured. For all these patients, RF ablation offers curative therapy, thus eliminating recurrent symptoms, life-threatening attacks, tachycardia cardiomyopathy and need for life-long drug therapy. For patients with resuscitated sudden cardiac death or at high risk for sudden death, the implantable cardioverter defibrillator (ICD) is the only technique that has significantly improved survival from sudden cardiac death. Since August 1992, 11 patients have had the ICD implanted, with 9 surviving. The 2 deaths were due to cardiac failure and not to sudden death. Thus the ICD can prevent sudden death, but the main limitation is the cost of the device and it is not suitable in patients who have severe heart failure. In conclusion, interventional electrophysiology represents a tremendous leap forward in the management of cardiac arrhythmias. With catheter ablation, it offers a safe curative therapy for patients with recurrent SVTs and VTs and with the ICD, prevents sudden cardiac death in patients who have been resuscitated from it or who are at risk for it. The future will see us improving our success in ablating patients with monomorphic ischaemic VT and even atrial fibrillation, and the role of prophylactic ICDs in high risk patients will be better defined.

Comparison of Treatment of Supraventricular Tachycardia by Valsalva Maneuver and Carotid Sinus Massage

STUDY OBJECTIVE

To compare the efficacy of the Valsalva maneuver with that of carotid sinus massage (CSM) in terminating paroxysmal supraventricular tachycardia (SVT) in the ED.

METHODS

This prospective, randomized case study was performed in the ED of a tertiary care institution. Patients were at least 10 years of age with regular narrow complex tachycardia and had an ECG diagnosis of SVT. Patients with regular narrow complex tachycardia were randomly assigned to undergo either the Valsalva maneuver or CSM. If the tachycardia was not terminated by the method chosen by randomization, then the alternative method of vagal maneuver was used. If the tachycardia was not converted by both methods of vagal stimulation, patients would undergo either synchronized electrical cardioversion or a pharmacologic method of conversion at the discretion of the treating physician, depending on the patient's hemodynamic status.

RESULTS

One hundred forty-eight instances of SVT were studied. Sixty-two patients underwent Valsalva maneuver first with conversion in 12 (success rate of 19.4%). Eighty-six underwent CSM first with conversion in 9 (success rate 10.5%). Carotid sinus massage was used in the 50 cases of SVT in which conversion was not achieved with the Valsalva maneuver. Conversion occurred in 7 cases (success rate 14.0%). For the 77 cases of SVT in which initial CSM did not achieve conversion, conversion occurred in 13 with the Valsalva maneuver (success rate 16.9%). The Valsalva maneuver and CSM achieved conversion in a total of 41 instances of SVT (success rate 27.7%).

CONCLUSION

Vagal maneuvers are efficacious in terminating about one quarter of spontaneous SVT cases. There is no detectable difference in efficacy between the Valsalva maneuver and CSM. [Lim SH, Anantharaman V, Teo WS, Goh PP, Tan ATH: Comparison of treatment of supraventricular tachycardia by Valsalva maneuver and carotid sinus massage. Ann Emerg Med January 1998;31:30-35.].

Comparison of treatment of supraventricular tachycardia by Valsalva maneuver and carotid sinus massage

STUDY OBJECTIVE

To compare the efficacy of the Valsalva maneuver with that of carotid sinus massage (CSM) in terminating paroxysmal supraventricular tachycardia (SVT) in the ED.

METHODS

This prospective, randomized case study was performed in the ED of a tertiary care institution. Patients were at least 10 years of age with regular narrow complex tachycardia and had an ECG diagnosis of SVT. Patients with regular narrow complex tachycardia were randomly assigned to undergo either the Valsalva maneuver or CSM. If the tachycardia was not terminated by the method chosen by randomization, then the alternative method of vagal maneuver was used. If the tachycardia was not converted by both methods of vagal stimulation, patients would undergo either synchronized electrical cardioversion or a pharmacologic method of conversion at the discretion of the treating physician, depending on the patient's hemodynamic status.

RESULTS

One hundred forty-eight instances of SVT were studied Sixty-two patients underwent Valsalva maneuver first with conversion in 12 (success rate of 19.4%). Eighty-six underwent CSM first with conversion in 9 (success rate 10.5%). Carotid sinus massage was used in the 50 cases of SVT in which conversion was not achieved with the Valsalva maneuver. Conversion occurred in 7 cases (success rate 14.0%). For the 77 cases of SVT in which initial CSM did not achieve conversion, conversion occurred in 13 with the Valsalva maneuver (success rate 16.9%). The Valsalva maneuver and CSM achieved conversion in a total of 41 instances of SVT (success rate 27.7%).

CONCLUSION

Vagal maneuvers are efficacious in terminating about one quarter of spontaneous SVT cases. There is no detectable difference in efficacy between the Valsalva maneuver and CSM.