Showing papers by "Stuart M. Cobbe published in 2012"
TL;DR: The utility of microvolt T‐wave alternans testing in an unselected population of patients with HF is investigated and the clinical characteristics associated with the MTWA results are evaluated.
Abstract: Aims
Observational studies in selected populations have suggested that microvolt T-wave alternans (MTWA) testing may identify patients with heart failure (HF) at risk of sudden cardiac death. The aims of this study were to investigate the utility of MTWA testing in an unselected population of patients with HF and to evaluate the clinical characteristics associated with the MTWA results.
Methods and results
A total of 1003 patients hospitalized with decompensated HF were enrolled. MTWA testing was planned 1 month post-discharge; 648 patients returned for MTWA testing. Mean age was 70.8 ± 10.6 years and 58% were male. Of these patients who returned, 318 (49%) were ineligible for MTWA testing due to atrial fibrillation (AF), pacemaker dependency, or physical inability to undertake the test. Of the MTWA tests, 100 (30%) were positive, 78 (24%) were negative, and 152 (46%) were indeterminate; 112/152 indeterminate tests (74%) occurred because of failure to achieve target heart rate (HR) due to chronotropic incompetence or physical limitations. There were differences in patient characteristics according to MTWA result. Independent predictors of a negative result included younger age and higher left ventricular ejection fraction (LVEF). Independent predictors of a positive result included higher HR during MTWA testing and lower LVEF. Independent predictors of an indeterminate result included older age and history of previous/paroxysmal AF.
Conclusions
Only half of patients with HF are eligible for MTWA testing and the most common result is an indeterminate test. Patients with positive and indeterminate tests have different clinical characteristics. MTWA treadmill testing is not widely applicable in typical HF patients and is unlikely to refine risk stratification for sudden death on a population level.
26 citations
TL;DR: ECG amplitude decline in VF is due to a combination of decreased systolic activation at the cellular level and increased desynchronization of inter-cellular electrical activity.
Abstract: Introduction: Clinically in ventricular fibrillation (VF), ECG amplitude and frequency decrease as ischemia progresses and predict defibrillation success. In-vitro ECG amplitude declines without ischemia, independent of VF frequencies. This study examines the contribution of cellular electrical activity and global organization to ECG amplitude changes during VF. Methods and results: Rabbit hearts were Langendorff-perfused (40mL/min, Tyrode’s solution) and loaded with RH237. During VF, ECG and epicardial optical action potentials were recorded (photodiode array; 256sites, 15×15mm). After 60s of VF, perfusion was either maintained, global ischemia produced by low-flow (6mL/min), or solution [K+]o raised to 8mM. Peak-to-peak amplitude was determined for all signals. During VF, in control, ECG amplitude decreased to a steady-state (~57% baseline), whereas in low-flow steady-state was not reached with the amplitude continuing to fall to 33% of baseline by 600s. Optically, LV amplitude declined more than RV, reaching significance in control (LV vs. RV; 33+/-5% vs. 638%, p<0.01). During VF in 8mM[K+]o, amplitude changes were more complex; ECG amplitude increased with time (105±13%), whilst LV amplitude decreased (60±15%, p<0.001). Microelectrode studies showed amplitude reduction in control and 8mM[K+]o (to ~79% and ~93% baseline respectively). Evaluation of electrical coordination by cross-correlation of optical signals showed as VF progressed coordination reduced in control (baseline 0.36±0.02 to 0.28±0.003, p<0.01), maintained in low-flow (0.41±0.03 to 0.37±0.005, p=NS) and increased in 8mM[K+]o (0.36±0.02 to 0.53±0.08, p<0.05). Conclusions: ECG amplitude decline in VF is due to a combination of decreased systolic activation at the cellular level and increased desynchronization of intercellular electrical activity.
9 citations
TL;DR: The evidence regarding clinical utility of microvolt T-wave alternans testing is reviewed, suggesting that it may be used to identify patients at risk of life-threatening ventricular arrhythmias and conflicting results from recent clinical studies are reviewed.
2 citations
TL;DR: However, Dr Madias suggests that implantable cardioverter-defibrillators (ICDs) may be recommended for certain patients including those ineligible for MTWA testing.
Abstract: We appreciate the interest of Dr Madias in our study regarding microvolt T-wave alternans testing
He addresses the important issue of eligibility for MTWA testing and identifies several recent studies where a large proportion of unselected patients have been ineligible for MTWA testing
However, Dr Madias suggests that implantable cardioverter-defibrillators (ICDs) may be recommended for certain patients including those ineligible for MTWA testing and proposes that MTWA testing may have a role in specific settings There is no evidence to support any role for MTWA in the contemporary risk stratification of patients with heart failure At present the use of MTWA testing can be justified for research purposes only Patients should not be exposed to a test that has never been shown to be of any clinical value An ICD should only be considered in patients fulfilling the evidence-based criteria laid out in guidelines