Does the induction of ventricular flutter or fibrillation at electrophysiologic testing after myocardial infarction have any prognostic significance?

Arrhythmic risk stratification in ischemic, non-ischemic and hypertrophic cardiomyopathy: A two-step multifactorial, electrophysiology study inclusive approach

Annual arrhythmic sudden cardiac death ranges from 0.6% to 4% in ischemic cardiomyopathy (ICM), 1% to 2% in non-ischemic cardiomyopathy (NICM), and 1% in hypertrophic cardiomyopathy (HCM). Towards a more effective arrhythmic risk stratification (ARS) we hereby present a two-step ARS with the usage of seven non-invasive risk factors: Late potentials presence (≥ 2/3 positive criteria), premature ventricular contractions (≥ 30/h), non-sustained ventricular tachycardia (≥ 1episode/24 h), abnormal heart rate turbulence (onset ≥ 0% and slope ≤ 2.5 ms) and reduced deceleration capacity (≤ 4.5 ms), abnormal T wave alternans (≥ 65μV), decreased heart rate variability (SDNN < 70ms), and prolonged QT_c interval (> 440 ms in males and > 450 ms in females) which reflect the arrhythmogenic mechanisms for the selection of the intermediate arrhythmic risk patients in the first step. In the second step, these intermediate-risk patients undergo a programmed ventricular stimulation (PVS) for the detection of inducible, truly high-risk ICM and NICM patients, who will benefit from an implantable cardioverter defibrillator. For HCM patients, we also suggest the incorporation of the PVS either for the low HCM Risk-score patients or for the patients with one traditional risk factor in order to improve the inadequate sensitivity of the former and the low specificity of the latter.

The role of implantable cardioverter-defibrillators and sudden cardiac death prevention: indications, device selection, and outcome

Multiple randomized multicentre clinical trials have established the role of the implantable cardioverter-defibrillator (ICD) as the mainstay in the treatment of ventricular tachyarrhythmias and sudden cardiac death (SCD) prevention. These trials have focused mainly on heart failure patients with advanced left ventricular dysfunction and were mostly conducted two decades ago, whereas a more recent trial has provided conflicting results. Therefore, much remains to be determined on how best to balance the identification of patients at high risk of SCD together with who would benefit most from ICD implantation in a contemporary setting. Implantable cardioverter-defibrillators have also evolved from the simple, defibrillation-only devices implanted surgically to more advanced technologies of multi-chamber devices, with physiologic bradycardic pacing, including cardiac resynchronization therapy, atrial and ventricular therapeutic pacing algorithms, and subcutaneous ICDs. These multiple options necessitate individualized approach to device selection and programming. This review will focus on the current knowledge on selection of patients for ICD treatment, device selection and programming, and future directions of implantable device therapy for SCD prevention.

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Risk Stratification for Sudden Cardiac Death After Myocardial Infarction

Sudden cardiac death (SCD) accounts for ∼50% of mortality after myocardial infarction (MI). Most SCDs result from ventricular tachyarrhythmias, and the tachycardias that precipitate cardiac arrest result from multiple mechanisms. As a result, it is highly unlikely that any single test will identify all patients at risk for SCD. Current guidelines for use of implantable cardioverter-defibrillators (ICDs) to prevent SCD are based primarily on measurement of left ventricular ejection fraction (LVEF). Although reduced LVEF is associated with increased total cardiac mortality after MI, the focus of current guidelines on LVEF omits ∼50% of patients who die suddenly. In addition, there is no evidence of a mechanistic link between reduced LVEF and arrhythmias. Thus, LVEF is neither sensitive nor specific as a tool for post-MI risk stratification. Newer tests to screen for predisposition to ventricular arrhythmias and SCD examine abnormalities of ventricular repolarization, autonomic nervous system function, and electrical heterogeneity. These tests, as well as older methods such as programmed stimulation, the signal-averaged electrocardiogram, and spontaneous ventricular ectopy, do not perform well in patients with LVEF ≤30%. Recent observational studies suggest, however, that these tests may have greater utility in patients with LVEF >30%. Because SCD results from multiple mechanisms, it is likely that combinations of risk factors will prove more precise for risk stratification. Prospective trials that evaluate the performance of risk stratification schema to determine ICD use are necessary for cost-effective reduction of the incidence of SCD after MI.

Quantitative spectral assessment of intracardiac electrogram characteristics associated with post infarct fibrosis and ventricular tachycardia

Background

Post-myocardial infarction (MI) remodeling contributes to increased electrophysiological and structural heterogeneity and arrhythmogenesis. Utilising the post-infarct ovine model our aim was to determine unipolar electrogram frequency characteristics consequent to this remodeling and the development of Ventricular Tachycardia (VT).

Methods and results

Mapping studies were performed on 14 sheep at >1 month post-MI induction. Sheep were divided into VT inducible (n = 7) and non-inducible (n = 7) groups. Multielectrode needles (n = 20) were deployed within and surrounding ventricular scar for electrophysiological assessment of electrogram amplitude and width. Spectral analysis of electrograms was undertaken using wavelet and fast fourier transformations (WFFT) to calculate root mean square (RMS) power intervals spanning 0-300Hz in 20Hz intervals. Quantitative assessment between electrophysiological and histological parameters including collagen density, and structural organization of the myocardium was performed.

Increasing myocardial scar density resulted in attenuation of electrogram amplitude and RMS values. (all p<0.01). Between groups there were no differences in electrogram amplitude (p = 0.37), however WFFT analysis revealed significantly higher RMS values in the VT group (p<0.05) in association with high frequency fractional components of the electrogram. As scar density increased, greater between-group differences in RMS were observed spanning this high frequency (200-280Hz) spectrum and which were proportionally dependent on the degree of structural disorganisation of the myocardium (p<0.001) and number of extrastimuli required to induce VT (p<0.05).

Conclusion

High frequency unipolar electrogram spectral characteristics were quantitatively co-influenced by the presence of fibrosis and degree of myocardial structural dissorganisation and were associated with the propensity for development of VT.

Electrophysiology testing for risk stratification of patients with ischaemic cardiomyopathy: a call for action

Current guidelines recommendations, based on the results of primary sudden cardiac death prevention trials, use the left ventricular ejection fraction (LVEF) as a sole criterion for the indication of implantable cardioverter defibrillator therapy for primary prevention purposes. In this article, we review the sensitivity and specificity of LVEF for predicting arrhythmic vs. non-arrhythmic cardiac death and examine existing evidence on the use of electrophysiology testing for risk stratification of ischaemic patients with reduced left ventricular function.

Risk Stratification of Sudden Cardiac Death After Acute Myocardial Infarction

Despite advances in the diagnosis and treatment of acute coronary syndromes and an overall improvement in outcomes, mortality after myocardial infarction (MI) remains high. Sudden death, which is most frequently due to ventricular tachycardia or ventricular fibrillation, is the cause of death in 25% to 50% of patients with prior MI, and therefore represents an important public health problem. Use of the implantable cardioverter-defibrillator (ICD), which is the primary method of reducing the chance of arrhythmic sudden death after MI, is costly to the medical system and is associated with procedural and long-term risks. Additionally, assessment of left ventricular ejection fraction (LVEF), which is the primary method of assessing a patient's post-MI sudden death risk and appropriateness for ICD implantation, lacks both sensitivity and specificity for sudden death, and may not be the optimal way to select the subgroup of post-MI patients who are most likely to benefit from ICD implantation. To optimally utilize ICDs, it is therefore critical to develop and prospectively validate sudden death risk stratification methods beyond measuring LVEF. A variety of tests that assess left ventricular systolic function/morphology, potential triggers for ventricular arrhythmias, ventricular conduction/repolarization, and autonomic tone have been proposed as sudden death risk stratification tools. Multivariable models have also been developed to assess the competing risks of arrhythmic and non-arrhythmic death so that ICDs can be utilized more effectively. This manuscript will review the epidemiology of sudden death after MI, and will discuss the current state of sudden death risk stratification in this population.

Sudden death: Neurogenic causes, prediction and prevention

Sudden death is a major health problem all over the world. The most common causes of sudden death are cardiac but there are also other causes such as neurological conditions (stroke, epileptic attacks and brain trauma), drugs, catecholamine toxicity, etc. A common feature of all these diverse pathologies underlying sudden death is the imbalance of the autonomic nervous system control of the cardiovascular system. This paper reviews different pathologies underlying sudden death with emphasis on the autonomic nervous system contribution, possibilities of early diagnosis and prognosis of sudden death using various clinical markers including autonomic markers (heart rate variability and baroreflex sensitivity), present possibilities of management and promising prevention by electrical neuromodulation.

Contractile function assessment by intraventricular balloon alters the ability of regional ischaemia to evoke ventricular fibrillation

BACKGROUND AND PURPOSE

In drug research using the rat Langendorff heart preparation, it is possible to study left ventricular (LV) contractility using an intraventricular balloon (IVB), and arrhythmogenesis during coronary ligation-induced regional ischaemia. Assessing both concurrently would halve animal requirements. We aimed to test the validity of this approach.

EXPERIMENTAL APPROACH

The electrocardiogram (ECG) and LV function (IVB) were recorded during regional ischaemia of different extents in a randomized and blinded study.

KEY RESULTS

IVB-induced proarrhythmia was anticipated, but in hearts with an ischaemic zone (IZ) made deliberately small, an inflated IVB reduced ischaemia-induced ventricular fibrillation (VF) incidence as a trend. Repeating studies in hearts with large IZs revealed the effect to be significant. There were no changes in QT interval or other variables that might explain the effect. Insertion of an IVB that was minimally inflated had no effect on any variable compared with 'no IVB' controls. The antiarrhythmic effect of verapamil (a positive control drug) was unaffected by IVB inflation. Removal of an inflated (but not a non-inflated) IVB caused a release of lactate commensurate with reperfusion of an endocardial/subendocardial layer of IVB-induced ischaemia. This was confirmed by intracellular (31) phosphorus ((31) P) nuclear magnetic resonance (NMR) spectroscopy.

CONCLUSIONS AND IMPLICATIONS

IVB inflation does not inhibit VF suppression by a standard drug, but it has profound antiarrhythmic effects of its own, likely to be due to inflation-induced localized ischaemia. This means rhythm and contractility cannot be assessed concurrently by this approach, with implications for drug discovery and safety assessment.

Sudden Cardiac Death Risk Stratification - An Update

Sudden cardiac death (SCD) remains a major public health problem worldwide, yet current methods to identify those at greatest risk are inadequate. High-risk individuals may benefit from potentially life-saving treatment, such as insertion of an implantable-cardioverter defibrillator (ICD). However, such treatments are expensive and have their own associated risks. Furthermore, most cases of SCD occur in the general adult population who may be relatively asymptomatic but yet have an underlying predisposition to SCD. Hence, there is great interest and clinical need in improving methods for risk stratification of SCD to identify those at greatest risk and implement the most appropriate treatment. This review provides an update on current risk-stratification methods for SCD in high-risk groups, in particular patients with reduced left ventricular function following acute myocardial infarction and those with non-ischaemic dilated cardiomyopathy, and highlights some novel methods that may have a role to play in future risk-stratification schemes. Approaches and challenges for SCD risk stratification among the general public are also discussed.

[Risk stratification for sudden cardiac death in ischemic heart disease. Programmed ventricular stimulation]

Programmed ventricular stimulation was used extensively in the 1970s and has markedly improved our knowledge about the electrophysiological mechanisms of reentrant ventricular arrhythmias. In numerous observational but also randomized studies, it was shown that the induction of a monomorphic ventricular tachycardia by programmed ventricular stimulation was associated with an increased risk of spontaneous ventricular tachycardia or even sudden cardiac death in the future. Despite these results and the guidelines of ACC and ESC recommending the use of programmed ventricular stimulation in patients with recent and remote myocardial infarction, reduced ejection fraction, and complex ventricular arrhythmias or syncope, programmed ventricular stimulation is only seldom used and does not play a relevant role in clinical practice today. The purpose of this overview is to reevaluate the importance of programmed ventricular stimulation for the risk evaluation of patients with ischemic heart disease in consideration of the current literature.

Reperfusion-induced sustained ventricular tachycardia, leading to ventricular fibrillation, in chronically instrumented, intact, conscious mice

Reperfusion‐induced lethal ventricular arrhythmias are observed during relief of coronary artery spasm, with unstable angina, exercise‐induced ischemia, and silent ischemia. Accordingly, significant efforts are underway to understand the mechanisms responsible for reperfusion‐induced lethal arrhythmias and mice have become increasingly important in these efforts. However, although reperfusion‐induced sustained ventricular tachycardia leading to ventricular fibrillation (VF) has been recorded in many models, reports in mice are sparse and of limited success. Importantly, none of these studies were conducted in intact, conscious mice. Accordingly, a chronically instrumented, intact, conscious murine model of reperfusion‐induced lethal arrhythmias has the potential to be of major importance for advancing the concepts and methods that drive cardiovascular therapies. Therefore, we describe, for the first time, the use of an intact, conscious, murine model of reperfusion‐induced lethal arrhythmias. Male mice (n = 9) were instrumented to record cardiac output and the electrocardiogram. In addition, a snare was placed around the left main coronary artery. Following recovery, the susceptibility to sustained ventricular tachycardia produced by 3 min of occlusion and reperfusion of the left main coronary artery was determined in conscious mice by pulling on the snare. Reperfusion culminated in sustained ventricular tachycardia, leading to VF, in all nine conscious mice. The procedures conducted in conscious C57BL/6J mice, a strain commonly used in transgenic studies, can be utilized in genetically modified models to enhance our understanding of single gene defects on reperfusion‐induced lethal ventricular arrhythmias in intact, conscious, and complex animals.

We describe, for the first time, the use of an intact, conscious, murine model of reperfusion‐induced lethal arrhythmias. This model has the potential to be of major importance for advancing the concepts and methods that drive antiarrhythmic therapies.

Long-term arrhythmia-free survival in patients with severe left ventricular dysfunction and no inducible ventricular tachycardia after myocardial infarction

BACKGROUND

A negative electrophysiology study (EPS) may delineate a subgroup of patients with severely impaired left ventricular ejection fraction (LVEF) whose care can be safely managed long-term without an implantable cardioverter-defibrillator.

METHODS AND RESULTS

Consecutive patients treated with primary percutaneous coronary intervention for ST-segment-elevation myocardial infarction underwent early (median 4 days) LVEF assessment. Patients with LVEF ≤40% underwent EPS. A prophylactic implantable cardioverter-defibrillator was implanted for a positive (inducible monomorphic ventricular tachycardia) but not a negative (no inducible ventricular tachycardia or inducible ventricular fibrillation/flutter) EPS result. Patients who would have become eligible for a late primary prevention implantable cardioverter-defibrillator with LVEF ≤30% or ≤35% with New York Heart Association class II/III heart failure were included and analyzed according to EPS result. Patients with LVEF >40%, ineligible for EPS, were followed up as control subjects (n=1286). The primary end point was survival free of death or arrhythmia (resuscitated cardiac arrest or sustained ventricular tachycardia/ventricular fibrillation). EPS performed in 128 patients with LVEF ≤30% or with LVEF ≤35% and heart failure was negative in 63% (n=80) and positive in 37% (n=48). Implantable-cardioverter defibrillators were implanted in <0.1%, 4%, and 90% of control, EPS-negative, and EPS-positive patients, respectively. The distribution of time to death or arrhythmia was comparable in control patients and EPS-negative patients with LVEF ≤30% or with LVEF ≤35% and heart failure (P=0.738), who both differed significantly from EPS-positive patients (P<0.001). At 3 years, 91.8 ± 3.2%, 93.4 ± 1.0%, and 62.7 ± 7.5% of control, EPS-negative, and EPS-positive patients were free of death or arrhythmia, respectively.

CONCLUSIONS

Revascularized patients with ST-segment-elevation myocardial infarction with severely impaired left ventricular function but no inducible ventricular tachycardia have a favorable long-term prognosis without the protection of an implantable cardioverter-defibrillator.

Usefulness of inducible ventricular tachycardia to predict long-term adverse outcomes in arrhythmogenic right ventricular cardiomyopathy

The role of the electrophysiologic (EP) study for risk stratification in patients with arrhythmogenic right ventricular cardiomyopathy is controversial. We investigated the role of inducible sustained monomorphic ventricular tachycardia (SMVT) for the prediction of an adverse outcome (AO), defined as the occurrence of cardiac death, heart transplantation, sudden cardiac death, ventricular fibrillation, ventricular tachycardia with hemodynamic compromise or syncope. Of 62 patients who fulfilled the 2010 Arrhythmogenic Right Ventricular Cardiomyopathy Task Force criteria and underwent an EP study, 30 (48%) experienced an adverse outcome during a median follow-up of 9.8 years. SMVT was inducible in 34 patients (55%), 22 (65%) of whom had an adverse outcome. In contrast, in 28 patients without inducible SMVT, 8 (29%) had an adverse outcome. Kaplan-Meier analysis showed an event-free survival benefit for patients without inducible SMVT (log-rank p = 0.008) with a cumulative survival free of an adverse outcome of 72% (95% confidence interval [CI] 56% to 92%) in the group without inducible SMVT compared to 26% (95% CI 14% to 50%) in the other group after 10 years. The inducibility of SMVT during the EP study (hazard ratio [HR] 2.99, 95% CI 1.23 to 7.27), nonadherence (HR 2.74, 95% CI 1.3 to 5.77), and heart failure New York Heart Association functional class II and III (HR 2.25, 95% CI 1.04 to 4.87) were associated with an adverse outcome on univariate Cox regression analysis. The inducibility of SMVT (HR 2.52, 95% CI 1.03 to 6.16, p = 0.043) and nonadherence (HR 2.34, 95% CI 1.1 to 4.99, p = 0.028) remained as significant predictors on multivariate analysis. This long-term observational data suggest that SMVT inducibility during EP study might predict an adverse outcome in patients with arrhythmogenic right ventricular cardiomyopathy, advocating a role for EP study in risk stratification.

Risk Stratification for Sudden Cardiac Death after Acute Myocardial Infarction

Many patients who survive an acute myocardial infarction (AMI) remain at risk of recurrent cardiac events and sudden cardiac death after discharge, despite optimal medical treatment. Assessment of the degree of left ventricular dysfunction and residual myocardial ischaemia is useful to identify the patients at greatest risk. In addition, there is increasing evidence that a number of other cardiovascular tests can be used to detect autonomic dysfunction and myocardial substrate abnormalities postAMI that increase the risk of life-threatening ventricular arrhythmias. These investigations include ECG-based tests (signal averaged ECG and T-wave alternans), Holter-based recordings (heart rate variability and heart rate turbulence) and imaging techniques echocardiography and cardiac magnetic resonance), as well as invasive electrophysiological testing. This article reviews the current evidence for the use of these additional cardiac investigations among survivors of AMI to aid in their risk stratification for malignant ventricular arrhythmias and sudden cardiac death. Key words: Electrophysiological study, Holter recording, Non-invasive tests, Ventricular tachycardia

Sustained Polymorphic Arrhythmias Induced by Programmed Ventricular Stimulation have Prognostic Value in Patients Receiving Defibrillators

BACKGROUND

Patients with ischemic cardiomyopathy (ICM) who have monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation (PVS) are at increased risk of sudden cardiac death (SCD). Among a primary prevention population, the prognostic significance of induced polymorphic ventricular arrhythmias is unknown.

METHODS

A total of 105 consecutive patients who received an implantable cardioverter-defibrillator (ICD) for primary prevention of SCD in the setting of ICM and non-sustained VT were retrospectively evaluated. Seventy-five patients (group I) had induction of monomorphic VT and 30 patients (group II) had a sustained ventricular arrhythmia other than monomorphic VT (ventricular flutter, ventricular fibrillation, and polymorphic VT) induced during PVS.

RESULTS

Baseline characteristics were similar between group I and group II except for ejection fraction (25% vs. 31%, P = 0.0001) and QRS duration (123 milliseconds vs. 109 milliseconds, P = 0.04). Sixteen of 75 (21.3%) patients in group I and 6 of 30 (20%) patients in group II received appropriate ICD therapy (P = 0.88). Survival free from ICD therapy was similar between groups (P = 0.54). There was a trend toward increased all-cause mortality among patients in group I by Kaplan-Meier analysis (P = 0.08). However, when adjusted for age, EF, and QRS duration mortality was similar (P = 0.45).

CONCLUSIONS

There is no difference in rates of appropriate ICD discharge or mortality between patients dichotomized by type of rhythm induced during PVS. These results suggest that patients in this population who have inducible VF or sustained polymorphic VT have similar rates of subsequent clinical ventricular tachyarrhythmias as those with inducible monomorphic VT.

High risk of ventricular arrhythmias in patients with nonischemic dilated cardiomyopathy presenting with syncope

It is not entirely clear whether the presentation of syncope in patients with nonischemic dilated cardiomyopathy (NIDC) is an ominous prognostic indicator, because randomized controlled implantable cardioverter-defibrillator (ICD) trials generally exclude such patients. This study compared 108 consecutive patients with NIDC presenting with syncope with 71 consecutive patients with NIDC who presented with sustained ventricular arrhythmias, with regard to freedom from any ventricular arrhythmias or life-threatening arrhythmias and all-cause mortality. There was no significant difference between the groups in the 3 outcomes during the follow-up of 43.5 +/- 32.1 months. Male gender and ICD therapy predicted increased risk for any ventricular arrhythmias. A reduced left ventricular ejection fraction and increased age were predictive of increased mortality. In conclusion, patients with NIDC presenting with syncope are a high-risk group, with event rates similar to patients with NIDC presenting with sustained arrhythmias, and should be considered for ICD therapy.

Phase 2 ventricular arrhythmias in acute myocardial infarction: a neglected target for therapeutic antiarrhythmic drug development and for safety pharmacology evaluation

Ventricular fibrillation (VF), a cause of sudden cardiac death (SCD) in the setting of acute myocardial infarction (MI), remains a major therapeutic challenge. In humans, VF may occur within minutes or hours after the onset of chest pain, so its precise timing in relation to the onset of ischaemia is variable. Moreover, because VF usually occurs unobserved, out of hospital, and is usually lethal in the absence of intervention, its precise timing of onset is actually unknown in most patients. In animal models, the timing of susceptibility to VF is much better characterised. It occurs in two distinct phases. Early VF (defined as phase 1 VF, with possible subphases 1a and 1b in some animal species) occurs during the first 30 min of ischaemia when most myocardial injury is still reversible. Late VF, defined as phase 2 VF, occurs when myocardial necrosis is becoming established (after more than 90 min of ischaemia). Although much is known about the mechanisms and pharmacology of phase 1 VF, little is known about phase 2 VF. By reviewing a range of different types of data we have outlined the likely mechanisms and clinical relevance of phase 2 VF, and have evaluated possible future directions to help evolve a strategy for its suppression by drugs. The possibility that a proarrhythmic effect on phase 2 VF contributes to the adverse cardiac effects of certain cardiac and noncardiac drugs is also discussed in relation to the emerging field of safety pharmacology. It is concluded that suppression of phase 2 as well as phase 1 VF will almost certainly be necessary if drugs of the future are to achieve what drugs of the past and present have failed to achieve: full protection against SCD. Likewise, safety will require avoidance of exacerbation of phase 2 as well as phase 1 VF.

Significance of Inducible Ventricular Flutter-Fibrillation After Myocardial Infarction

AIM

The purpose of this study was to determine the factors associated with the induction of ventricular flutter/fibrillation (VFl/VF)and its prognostic significance in post-myocardial infarction.

METHODS

Programmed ventricular stimulation was performed after myocardial infarction (MI) for syncope (n = 232) or systematically (n = 755); 230 patients had an induced VFl/VF and were followed during 4 +/- 2 years.

RESULTS

VFl/VF was induced in 49/232 patients (21%) with syncope versus 181/755 asymptomatic patients (24%) (NS) and 94/410 patients (23%) with left ventricular ejection fraction (LVEF) <40% versus 136/577 patients (22.5%) with LVEF >40% (NS). Cardiac mortality was 9%; LVEF was 33 +/- 15% in patients who died, 43 +/- 13% in alive patients (P < 0.004). In patients with LVEF <40%, induced VFl/VF, mortality rate was 31% in those with syncope, 10% in asymptomatic patients (P < 0.001), because of an increase of deaths by heart failure; patients with LVEF >40% with or without syncope had a low mortality (5% and 3%). After linear logistic regression, VFl/VF and LVEF were predictors of total cardiac mortality, but only LVEF <40% predicted sudden death.

CONCLUSION

Syncope and the level of LVEF did not increase the incidence of VFl/VF induction after MI, but modified the cardiac mortality: induced VF increased total cardiac mortality in patients with syncope and LVEF <40%, but did not increase sudden death. In patients with LVEF >40%, induced VFl/VF has no significance neither in asymptomatic patients nor in those with syncope.

Numerical Simulation of Paced Electrogram Fractionation: Relating Clinical Observations to Changes in Fibrosis and Action Potential Duration

Simulating paced electrogram fractionation.

INTRODUCTION

Paced electrogram fractionation analysis (PEFA) may identify a re-entrant substrate in patients at risk of ventricular fibrillation (VF) by detecting prolonged, fractionated ventricular electrograms ("fractionation") in response to premature extrastimuli. Numerical simulations of action potential (AP) propagation through human myocardium following such premature stimulation were performed to study the relationship between electrogram fractionation, fibrosis, and changes in AP currents.

METHODS AND RESULTS

Activation in a resistive monodomain 2 cm2 sheet of myocardium containing nonconducting fibrous tissue was modeled using standard numerical methods for solutions of partial differential equations using the Priebe-Beukelmann (PB) AP equations. Myocardial fibrosis significantly influenced electrogram morphology. High densities of closely spaced fibrous septa caused functional block and altered propagation paths at short coupling intervals, and produced large increases in electrogram duration similar to those associated with increased risk of VF in clinical studies. Prolongation of the cardiac AP using the heart failure variant of the PB model further increased the amount of fractionation and thereby replicated clinical recordings more closely than did fibrosis alone. Increasing AP dispersion by a variable reduction in the potassium current I(Kr) simulated results seen in patients with the long QT syndrome with an abrupt increase in electrogram duration, while a uniform reduction in I(Kr) alone did not result in fractionated electrograms. In contrast, increases in cytosolic Ca2+ and Ca2+ buffering by troponin to simulate HCM had little effect on fractionation.

CONCLUSIONS

These results relate the effects of fibrosis, AP abnormalities, and dispersion of AP duration to the characteristic electrograms recorded in patients at risk of sudden death.

Differences in mechanisms and outcomes of syncope in patients with coronary disease or idiopathic left ventricular dysfunction as assessed by electrophysiologic testing

OBJECTIVES

This study evaluated the causes of syncope and the significance and differences in left ventricular (LV) dysfunction, coronary disease, and idiopathic dilated cardiomyopathy (DCM).

BACKGROUND

Risk stratification of and indications for an automated defibrillator could differ according to the cause of LV dysfunction.

METHODS

Electrophysiologic study, including atrial and ventricular programmed stimulation, was performed in 119 patients with coronary disease (group I) and 61 patients with DCM (group II) with an left ventricular ejection fraction (LVEF) <40% and syncope. Patients were followed from one to six years (mean 4 +/- 2 years).

RESULTS

Sustained monomorphic ventricular tachycardia (VT) was induced in 44 group I patients (37%) and 13 group II patients (21%); ventricular flutter (>270 beats/min) or ventricular fibrillation (VF) was induced in 24 group I patients (19%) and 9 group II patients (15%); and various other arrhythmias were identified. Syncope remained unexplained in 34 group I patients (30%) and 16 group II patients (27%). Prognosis depended on the heart disease: VT or VF induction was a predictive factor of mortality in coronary disease and identified a group with high cardiac mortality (46%), compared with patients with a negative study, who had a lower mortality (6%; p < 0.001) than in other studies. Cardiac mortality was only correlated with LVEF in DCM.

CONCLUSIONS

Various causes could explain syncope in 70% of patients with coronary disease and DCM, but differences were noted: VT was frequent in coronary disease with a bad prognosis, and ischemia could explain syncope; in DCM, different causes such as atrial tachycardia could be responsible for syncope, but the prognosis only depended on LVEF.

Long-term prognosis of inducible ventricular flutter: not an innocent finding

BACKGROUND

The prognostic significance of ventricular flutter (VFL) induced during programmed electrical stimulation (PES) is currently unknown.

METHODS

This study examined patients who had PES-induced VFL and assessed their long-term prognosis compared with patients who had inducible sustained monomorphic ventricular tachycardia (SMVT).

RESULTS

Of 3414 patients undergoing PES, 74 (2%) had sustained VFL. They were compared with a group of 71 patients undergoing PES in the same time frame who had inducible SMVT. Patients with inducible VFL had a higher ejection fraction than patients with SMVT (0.39 vs 0.33; P =.05). More aggressive pacing was required for arrhythmia induction in patients with VFL, with more stimuli (2.7 +/- 0.5 vs 2.2 +/- 0.6; P <.01) and tighter S(2), S(3), and S(4) intervals. After a mean follow-up of 30 +/- 31 months, the mortality rate was 34% in patients with VFL and 30% in patients with SMVT (P =.41). No difference in the 2 groups in overall survival or a combined end point of sudden death or appropriate implantable cardioverter defibrillator shock was revealed with Kaplan-Meier analysis.

CONCLUSION

The long-term prognosis of patients with inducible VFL is similar to that of patients with inducible SMVT, even when VFL is induced with a relatively aggressive protocol.

Significance of inducible ventricular flutter/fibrillation in risk stratification in patients with coronary artery disease

BACKGROUND

Although inducible ventricular fibrillation (VF) has been used as an indication for prophylactic implantation of cardioverter-defibrillators (ICDs) in patients with coronary artery disease (CAD), the significance of inducible VF remains controversial.

METHODS

Among 364 CAD patients who underwent electrophysiologic (EP) study for risk stratification, 23 patients, 12 without any history of VF or cardiac arrest (group A) and 11 with previously documented VF or cardiac arrest (group B), exhibited inducible ventricular flutter (VFL) or VF and subsequently underwent ICD implantation. Additionally, 11 CAD patients without previous VF or cardiac arrest, who had no inducible ventricular tachyarrhythmias but received an ICD, were included for comparison (group C).

RESULTS

During 2 years of follow-up, 1 (8%), 5 (45%), and 1 (9%) patients had appropriate ICD shocks in groups A, B, and C, respectively. The survival free from appropriate ICD shocks was significantly lower in group B compared to groups A and C (p<0.05). There were no significant differences in age, sex, ejection fraction (EF), or induction protocol between groups A and B or between groups A and C.

CONCLUSIONS

In CAD patients with inducible VFL/VF, patients without any history of VF or cardiac arrest had significantly lower incidence of appropriate ICD shocks when compared to those with such clinical events. Conversely, in CAD patients without any history of VF or cardiac arrest, incidence of appropriate ICD shocks was similar regardless of inducible VFL/VF. Inducible VFL/VF is therefore not useful as an indication for prophylactic ICD implantation in this patient population.

Ventricular flutter induced during electrophysiologic studies in patients with old myocardial infarction: clinical and electrophysiologic predictors, and prognostic significance

INTRODUCTION

Induction of ventricular flutter during electrophysiologic (EP) studies (similar to that of ventricular fibrillation [VF]) often is viewed as a nonspecific response with limited prognostic significance. However, data supporting this dogma originate from patients without previously documented ventricular tachyarrhythmias. We examined the significance of ventricular flutter in patients with and without spontaneous ventricular arrhythmias.

METHODS AND RESULTS

We conducted a cohort study of all patients with myocardial infarction (MI) undergoing EP studies at our institution. Of 344 consecutive patients, 181 had previously documented spontaneous sustained ventricular arrhythmias, 61 had suspected ventricular arrhythmias, and 102 had neither. Ventricular flutter was induced in 65 (19%) of the patients. Left ventricular ejection fraction was highest among patients with inducible VF (35 +/- 13), lowest for patients with inducible sustained monomorphic ventricular tachycardia (SMVT; 27 +/- 9), and intermediate for patients with inducible ventricular flutter (30 +/- 10). Similarly, the coupling intervals needed to induce the arrhythmia were shortest for VF (200 +/- 28 msec), intermediate for ventricular flutter (209 +/- 27 msec), and longest for SMVT (230 +/- 35 msec). During 5 +/- 8 years of follow-up, the risk for ventricular tachycardia/VF was high for patients with SMVT and ventricular flutter and low for patients with inducible VF and noninducible patients (46%, 34%, 17%, and 14%, P < 0.005).

CONCLUSION

Patients with inducible ventricular flutter appear to be "intermediate" between patients with inducible VF and patients with SMVT in terms of clinical and electrophysiologic correlates. However, the prognostic value of inducible ventricular flutter is comparable to that of SMVT.

Comparative follow up of patients with implanted cardioverter-defibrillators after induction of sustained monomorphic ventricular tachycardias or ventricular fibrillation by programmed stimulation

OBJECTIVE

To investigate the prognostic value of induced monomorphic ventricular tachycardia (VT) and ventricular flutter or fibrillation (VF) during programmed electrical stimulation in patients with a high risk for sudden arrhythmogenic cardiac death.

DESIGN

Prospective cohort study.

PATIENTS

102 patients at high risk for arrhythmogenic sudden cardiac death who received an automated implantable cardioverter-defibrillator (AICD) were evaluated. 56 patients received the AICD for primary prevention and 46 for secondary prevention. 58 patients had induction of a monomorphic VT (VT group) and 44 had induction of a polymorphic VT, ventricular flutter, or ventricular fibrillation (VF group) during programmed electrical stimulation. Average follow up was 20 months in both groups.

MAIN OUTCOME MEASURES

Appropriate AICD protocol.

RESULTS

In patients who received the AICD for primary prevention, 16 of 32 patients in the VT group, compared with only four of 24 patients in the VF group, received an appropriate AICD protocol (p = 0.02). In the entire study population, 479 appropriate AICD protocols were recorded in 28 (48%) patients in the VT group and 28 appropriate protocols in 11 (25%) patients in the VF group. Cumulative Kaplan-Meier event-free survival curves were significantly different (p = 0.02).

CONCLUSION

Induction of VF during programmed electrical stimulation is of no prognostic value even in high risk patients without previously documented ventricular fibrillation.

Significance of inducible ventricular fibrillation in patients with coronary artery disease and unexplained syncope

OBJECTIVES

This study was designed to determine the incidence and prognostic significance of inducible ventricular fibrillation (VF) in patients with coronary artery disease (CAD) and unexplained syncope.

BACKGROUND

Current American College of Cardiology/American Heart Association practice guidelines recommend implantation of internal cardioverter-defibrillators (ICDs) in patients with unexplained syncope in whom either ventricular tachycardia (VT) or VF is inducible during electrophysiologic (EP) testing. Although the prognostic significance of inducible monomorphic VT is known, the significance of inducible VF remains undefined.

METHODS

We evaluated 118 consecutive patients with CAD and unexplained syncope who underwent EP testing. Sustained monomorphic VT was inducible in 53 (45%) patients; in 20 (17%) patients, VF was the only inducible arrhythmia; and no sustained ventricular arrhythmia was inducible in the remaining 45 (38%) patients. The latter two groups of 65 (55%) patients make up the study population.

RESULTS

There were 16 deaths among the study population during a follow-up period of 25.3 +/- 19.6 months. The overall one- and two-year survival in these patients was 89% and 81%, respectively. No significant difference in survival was observed between patients with and without inducible VF (80% power to detect a fourfold survival difference).

CONCLUSIONS

In 17% of patients with CAD and unexplained syncope, VF is the only inducible ventricular arrhythmia. Within the limits of this pilot study, long-term follow-up of patients with and without inducible VF demonstrates no difference in survival between the two groups. Therefore, the practice of ICD implantation in patients with CAD, unexplained syncope and inducible VF, especially with triple ventricular extrastimuli, may merit reconsideration.

Role of Antiarrhythmic Therapy in Patients at Risk for Sudden Cardiac Death: An Evidence-Based Review

Sudden cardiac death (SCD) accounts for more than half of all cardiac deaths occurring each year in the United States. Although it has several causes, patients at greatest risk are those with coronary artery disease and impaired left ventricular function, heart failure secondary to ischemia or idiopathic dilated cardiomyopathy, hypertrophic cardiomyopathy, documented sustained ventricular tachycardia or ventricular fibrillation, and survivors of cardiac arrest. The presence of asymptomatic ventricular arrhythmias, positive signal-averaged electrocardiogram (ECG), low heart rate variability index, or inducible ventricular tachycardia or ventricular fibrillation increases the risk. In primary prevention trials in patients with ischemic heart disease, beta-blockers reduced both total mortality and SCD, whereas class I antiarrhythmic drugs, especially class IC, increased mortality. Among class III agents, d,l-sotalol and dofetilide have a neutral effect on mortality, whereas d-sotalol increases mortality. Amiodarone has a neutral effect on total and cardiac mortality but does reduce the risk of arrhythmic death and cardiac arrest. Three primary prevention trials in patients with ischemic heart disease were conducted with implantable cardioverter-defibrillators (ICDs). Patients with low ejection fractions (EFs), asymptomatic ventricular arrhythmias, and inducible ventricular tachycardia or ventricular fibrillation had significant reductions in total, cardiac, and arrhythmic death with ICDs compared with either no drug therapy or conventional antiarrhythmic agents. The ICDs did not reduce mortality in patients with low EFs and a positive signal-averaged ECG undergoing coronary bypass graft. In those with heart failure, beta-blockers reduced total and SCD mortality, but dofetilide and amiodarone had a neutral effect on mortality. In the secondary prevention of SCD, antiarrhythmic drugs alone generally are not thought to improve survival. In three trials in patients with documented sustained ventricular tachycardia or ventricular fibrillation, or survivors of SCD, ICDs reduced cardiac and arrhythmic mortality. Total mortality, however, was significantly reduced in only one of these trials. The role of antiarrhythmic drugs in secondary prevention of SCD is limited to patients in whom ICD is inappropriate or in combination with ICD. Antiarrhythmics can be given selectively with ICDs to decrease episodes of ventricular tachycardia or fibrillation to reduce ICD discharges, to suppress episodes of nonsustained ventricular tachycardia that trigger ICD discharges, to slow the rate of ventricular tachycardia to increase hemodynamic stability, to allow effective antitachycardia pacing, or to suppress supraventricular arrhythmias.

[Predictors of sudden death in coronary artery disease]

Although advances in the management of acute myocardial infarction have resulted in a decline in long-term risk of sudden death, it continues to be high in certain subsets of patients. Thus, it is important to identify and treat these patients. Left ventricular ejection fraction less than 0.40, frequent premature ventricular ectopy on Holter monitoring, late potentials on signal-averaged electrocardiogram, impaired heart rate variability, abnormal baroreflex sensitivity and inducible sustained monomorphic ventricular tachycardia during electrophysiological study are predictors of sudden death and arrhythmic events. Although the negative predictive value of each factor is high, the positive predictive accuracy is low. Several tests can be combined to obtain higher positive predictive values. In fact, in some studies combined noninvasive tests have been used to select patients for ventricular stimulation study. Some preventive treatment can be applied in these patients. Available data do not justify prophylactic therapy with amiodarone in high-risk survivors of acute myocardial infarction. Sudden death and total mortality have been significantly reduced in postinfarction patients by long-term beta blockade. Hence, beta blockers should be given to all patients with acute myocardial infarction who do not have contraindications to their use. The MADIT study has shown the beneficial effect of implantable cardioverter defibrillator in reducing mortality in patients with prior myocardial infarction, an ejection fraction less than 0.36, asymptomatic nonsustained ventricular tachycardia, and inducible sustained ventricular tachycardia, unsuppressable by procainamide. Besides, several studies are under way to evaluate the prophylactic use of implantable defibrillator for improving survival in high-risk patients.

Implantable defibrillator event rates in patients with unexplained syncope and inducible sustained ventricular tachyarrhythmias: a comparison with patients known to have sustained ventricular tachycardia

OBJECTIVES

To assess the clinical significance of inducible ventricular tachyarrhythmias among patients with unexplained syncope.

BACKGROUND

Induction of sustained ventricular arrhythmias at electrophysiology study in patients with unexplained syncope and structural heart disease is usually assigned diagnostic significance. However, the true frequency of subsequent spontaneous ventricular tachyarrhythmias in the absence of antiarrhythmic medications is unknown.

METHODS

In a retrospective case-control study, the incidence of implantable cardiac defibrillator (ICD) therapies for sustained ventricular arrhythmias among patients with unexplained syncope or near syncope (syncope group, n = 22) was compared with that of a control group of patients (n = 32) with clinically documented sustained ventricular tachycardia (VT). Sustained ventricular arrhythmias were inducible in both groups and neither group received antiarrhythmic medications. All ICDs had stored electrograms or RR intervals. Clinical variables were similar between groups except that congestive cardiac failure was more common in the syncope group.

RESULTS

Kaplan-Meier analysis of the time to first appropriate ICD therapy for syncope and control groups produced overlapping curves (p = 0.9), with 57 +/- 11% and 50 +/- 9%, respectively, receiving ICD therapy by one year. In both groups, the induced arrhythmia was significantly faster than spontaneous arrhythmias, but the cycle lengths of induced and spontaneous arrhythmias were positively correlated (R = 0.6, p < 0.0001). During follow-up, three cardiac transplantations and seven deaths occurred in the syncope group, and two transplantations and five deaths occurred in the control group (36-month survival without transplant 52 +/- 11% and 83 +/- 7%, respectively, p = 0.03).

CONCLUSIONS

In patients with unexplained syncope, structural heart disease and inducible sustained ventricular arrhythmias, spontaneous sustained ventricular arrhythmias occur commonly and at a similar rate to patients with documented sustained VT. Thus, electrophysiologic testing in unexplained syncope can identify those at risk of potentially life-threatening tachyarrhythmias, and aggressive treatment of these patients is warranted.

Cost-effectiveness analysis of invasive and noninvasive tests in high risk patients treated with amiodarone after acute myocardial infarction

OBJECTIVES

We sought to evaluate 1) the cost-effectiveness of amiodarone therapy in postinfarction patients; and 2) the influence of alternative diagnostic strategies (noninvasive only vs. noninvasive and electrophysiologic testing) on survival benefit and cost-effectiveness ratio of amiodarone therapy.

BACKGROUND

The cost-effectiveness of amiodarone therapy in postinfarction patients is still unknown, and no study has determined which diagnostic strategy should be used to maximize amiodarone survival benefit while improving its cost-effectiveness ratio.

METHODS

We designed a postinfarction scenario wherein heart rate variability analysis on 24-h Holter monitoring was used as a screening test for 2-year amiodarone therapy in a cohort of survivors (mean age 57 years) of a recent myocardial infarction. Three different therapeutic strategies were compared: 1) no amiodarone; 2) amiodarone in patients with depressed heart rate variability; 3) amiodarone in patients with depressed heart rate variability and a positive programmed ventricular stimulation. Total variable costs and quality-adjusted life expectancy during a 20-year period were predicted with use of a Markov simulation model. Costs and charges were calculated with reference to an Italian and American hospital.

RESULTS

Amiodarone therapy in patients with depressed heart rate variability and a positive programmed ventricular stimulation was dominated by a blend of the two alternatives. Compared with the no-treatment strategy, the incremental cost-effectiveness ratio of amiodarone therapy in patients with depressed heart rate variability was $10,633 and $39,422 per gained quality-adjusted life-year using Italian costs and American charges, respectively.

CONCLUSIONS

Compared with a noninterventional option, amiodarone prescription in all patients with depressed heart rate variability seems to be a more appropriate approach than the alternative based on the combined use of heart rate variability and electrophysiologic study.

Can antiarrhythmic drugs survive survival trials?

Sudden cardiac death due to arrhythmic events is the major cause of mortality among early post-myocardial infarction (MI) patients, accounting for > 250,000 deaths annually in the United States alone. Antiarrhythmic drugs can be used in such patients as well as in those who have not had a recent MI but are at high risk for sudden cardiac death (e.g., those with ventricular tachycardia/fibrillation, or who have survived cardiac arrest). Most antiarrhythmic drugs available, however, have limitations arising from their toxic and proarrhythmic potential. Thus, research and development of new agents and treatment modalities are desirable. This article seeks to enumerate the lessons of past clinical trials with these agents and to provide guidelines for future trials. That a variety of antiarrhythmic drugs have been associated with an increased mortality has been a disturbing observation. It is therefore imperative that candidates for antiarrhythmic therapy be selected appropriately. We recommend that future clinical trials use stringent criteria for the identification of patients at "high risk" for arrhythmia or sudden cardiac death, and limit recruitment to such patients. Traditional markers, such as the increased frequency and complexity of ventricular premature beats, and low left ventricular ejection fraction, have not been successful in identifying these high-risk patients. However, decreased heart rate variability and cardiac late potentials recorded on a signal-over-aged electrocardiogram appear to be more specific markers of post-MI arrhythmia or sudden cardiac death and may, in conjunction with the traditional markers, be used to improve selection of trial populations. Since the risk of sudden cardiac death diminishes with time after MI, it is also recommended that the temporal window of treatment with antiarrhythmic agents be limited to 1 year post-MI. It is also important to define clearly the endpoints of efficacy evaluations. A short-term reduction on markers like ventricular ectopic beats, for example, does not translate into a long-term decrease in arrhythmia-related mortality. Therefore, a reduction in overall mortality is the only meaningful endpoint to define the true risk-benefit ratio. To limit exposure to the potentially adverse effects of these agents, target populations for prophylactic antiarrhythmic drugs should be limited to recent post-MI patients at high risk for sudden cardiac death due to arrhythmia. Avoiding exposure of low-risk patients to antiarrhythmic drugs is equally imperative. "Low risk" of all-cause mortality includes the group of post-MI patients with a left ventricular ejection fraction >36%. Risk must be continuously evaluated in the setting of other pharmacologic (angiotensin-converting enzyme [ACE] inhibitors, aspirin, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors ["statins"], and others) and/or nonpharmacologic interventions (coronary artery bypass graft, angioplasty, implantable cardioverter/defibrillator). There is also a need to improve noninvasive techniques for identifying patients in the high-risk category-at present, the presence of ventricular premature beats and a left ventricular ejection fraction <36% is considered somewhat predictive of sudden cardiac death. Thus, patients with a recent MI and moderately low left ventricular ejection fraction (< or = 36% but not <20%) may be considered for antiarrhythmic therapy. A subset analysis of patients with low heart rate variability can provide valuable additional information. It is important to note that although all-cause mortality is a valid endpoint for such trials, stratification by specific cause of mortality is desirable.

Radiofrequency catheter ablation of postinfarction ventricular tachycardia: long-term success and the significance of inducible nonclinical arrhythmias

BACKGROUND

Radiofrequency (RF) catheter ablation is effective therapy for monomorphic ventricular tachycardia (VT) in patients without structural heart disease. In patients with postinfarction VT; however, this procedure has been used predominantly as adjunctive therapy, targeting only the patient's clinically documented arrhythmia. By targeting all inducible, sustained VT morphologies, we sought to determine the utility of RF catheter ablation as a primary cure in patients who present with hemodynamically tolerated VT.

METHODS AND RESULTS

RF ablation was attempted in 35 patients with a previous myocardial infarction and recurrent, hemodynamically tolerated VT. A mean of 3.9+/-2.7 VTs were induced per patient (range, 1 to 10). The clinically documented arrhythmia was successfully ablated in 30 of 35 patients (86%), and on follow-up electrophysiological testing, 11 patients had no inducible VT and were discharged without other therapy. Nineteen patients had inducible "nonclinical" arrhythmias on follow-up testing, and the majority underwent cardiac defibrillator implantation. Freedom from recurrent arrhythmias, including sudden death, was 91% in patients without inducible VT and 53% in patients with persistently inducible "nonclinical" arrhythmias (P<.05; mean follow-up, 17+/-12 and 12+/-11 months, respectively).

CONCLUSIONS

In patients with well-tolerated VT, RF catheter ablation may be useful as a primary cure if no other ventricular arrhythmias are inducible on follow-up testing. Ablation of all hemodynamically tolerated arrhythmias should be attempted in patients with multiple inducible VT morphologies because of the high rate of recurrence of unablated VTs in these patients.