T-wave Amplitude Research Articles

Autonomic control during acute hypoglycemia in type 1 diabetes mellitus.

We hypothesized that adults with type 1 diabetes mellitus (T1DM) would exhibit impaired heart rate variability (HRV), QT interval, T-wave amplitude, and baroreflex sensitivity (BRS) when compared with healthy controls. In addition, we hypothesized that acute hypoglycemia would result in further adverse changes in measures of autonomic and cardiovascular function. A single 180-min hyperinsulinemic (2mU/kg TBW/min), hypoglycemic (~3.3 umol/mL) clamp was completed in 10 healthy adults and 13 adults with T1DM. Counterregulatory hormones were assessed and measures of heart rate (electrocardiogram) and blood pressure (intra-arterial catheter or finger photoplethysmography) were analyzed at baseline and during the hypoglycemic clamp for measures of HRV, QT interval, T-wave amplitude, and spontaneous cardiac BRS (sCBRS). Baseline measures of HRV, sCBRS, and T-wave amplitude were blunted in adults with T1DM when compared with healthy controls. Hypoglycemia resulted in significant reductions in HRV, sCBRS, and T-wave amplitude and prolonged QT intervals; these changes were not different between adults with T1DM and healthy controls. Results from the current study show that adults with T1DM exhibit impaired autonomic and cardiovascular function. Additionally, novel findings highlight an effect of acute hypoglycemia to further reduce measures of autonomic and cardiovascular function similarly between adults with T1DM and healthy controls. These results suggest that acute hypoglycemia may worsen impairments in autonomic and cardiovascular control in patients with T1DM, thus increasing the risk of ventricular arrhythmias and cardiovascular mortality.

Effects of L-type calcium channel and human ether-a-go-go related gene blockers on the electrical activity of the human heart: a simulation study.

AimsClass III and IV drugs affect cardiac human ether-a-go-go related gene (IKr) and L-type calcium (ICaL) channels, resulting in complex alterations in repolarization with both anti- and pro-arrhythmic consequences. Interpretation of their effects on cellular and electrocardiogram (ECG)-based biomarkers for risk stratification is challenging. As pharmaceutical compounds often exhibit multiple ion channel effects, our goal is to investigate the simultaneous effect of ICaL and IKr block on human ventricular electrophysiology from ionic to ECG level.Methods and resultsSimulations are conducted using a human body torso bidomain model, which includes realistic representation of human membrane kinetics, anatomy, and fibre orientation. A simple block pore model is incorporated to simulate drug-induced ICaL and IKr blocks, for drug dose = 0, IC50, 2× IC50, 10× IC50, and 30× IC50. Drug effects on human ventricular activity are quantified for different degrees and combinations of ICaL and IKr blocks from the ionic to the body surface ECG level. Electrocardiogram simulations show that ICaL block results in shortening of the QT interval, ST elevation, and reduced T-wave amplitude, caused by reduction in action potential duration and action potential amplitude during the plateau phase, and in repolarization times. In contrast, IKr block results in QT prolongation and reduced T-wave amplitude. When ICaL and IKr blocks are combined, the degree of ICaL block strongly determines QT interval whereas the effect of IKr block is more pronounced on the T-wave amplitude.ConclusionOur simulation study provides new insights into the combined effect of ICaL and IKr blocks on human ventricular activity using a multiscale computational human torso model.

The effect of hemodialysis on electrocardiographic parameters.

Cardiovascular complications are the leading causes of premature deaths in hemodialysis patients. Due to rapid changes in volume and electrolyte concentration following dialysis, the some electrocardiographic (ECG) changes or arrhythmias might be seen. To investigate the acute effects of hemodialysis on the ECG parameters in patients with chronic end-stage renal disease (ESRD). We included the consecutive ESRD patients who underwent a hemodialysis. Before and after hemodialysis, some 12 lead ECG parameters were analyzed by two different cardiologists by using electronic digital caliper device. A total of 62 patients (mean 52 ± 15 years; 65% male) with ESRD undergoing hemodialysis were recruited to the study. P-wave amplitude, QRS amplitude, QRS duration, QTc dispersion, the sum of amplitudes in V1S + V5R derivations, total QRS amplitude, and duration were significantly greater in posthemodialysis patients compared to the prehemodialysis ones. However, T-wave amplitude and QTc duration were significantly lower in posthemodialysis patients. The ECG changes including prolangated QRS and increased QTc interval after hemodialysis should be kept in mind and assessed carefully in ESRD patients. Prolongation of these parameters may prove to be a further noninvasive marker of susceptibility to ventricular arrhythmias.

TCT-6 Positive T-wave Amplitude In Lead AVR As A Predictor For A Higher Rate Of In-hospital Coronary Artery Bypass Graft In Patients With Non-ST Elevation Myocardial Infarction

TCT-6 Positive T-wave Amplitude In Lead AVR As A Predictor For A Higher Rate Of In-hospital Coronary Artery Bypass Graft In Patients With Non-ST Elevation Myocardial Infarction

Agreement between manual and automated measurements of simple QRS/T angle

Abstract The spatial QRS/T angle (QRS/T) has been identified as a strong and independent predictor of adverse cardiac events. QRS/T can be determined from the electrocardiogram (ECG) by matrix transformation methods or formula which uses a combination of net QRS and T-wave amplitudes (QRS/Tsimple). Amplitudes can be measured automatically by using dedicated software (QRS/Tauto) or can be manually measured on a computer screen (QRS/Tmanual). This latter method allows analysis of QRS/T, when digital ECGs are not available. The aim of the study was to determine the agreement in the measurements between automatically derived QRS and T amplitudes and manually measured on the computer screen amplitudes. The relative error of the QRS/T between the two methods was estimated in 73 patients. In the case of QRS/Tmanual the inter-observer as well as intra-observer variability was estimated. The relative error between QRS/Tauto vs. QRS/Tmanual was 3.51%. Inter-observer and intra-observer variability of the QRS/Tmanual was 1.19% and 1.18% respectively. Manual measurement of the QRS/T is reliable, however, the predictive value of this parameter should be tested in clinical trials, before QRS/Tmanual can be considered a useful tool in clinical practice or retrospective studies.

Ambulatory measurement of the ECG T-wave amplitude.

Ambulatory recording of the preejection period (PEP) can be used to measure changes in cardiac sympathetic nervous system (SNS) activity under naturalistic conditions. Here, we test the ECG T-wave amplitude (TWA) as an alternative measure, using 24-h ambulatory monitoring of PEP and TWA in a sample of 564 healthy adults. The TWA showed a decrease in response to mental stress and a monotonic decrease from nighttime sleep to daytime sitting and more physically active behaviors. Within-participant changes in TWA were correlated with changes in the PEP across the standardized stressors (r = .42) and the unstandardized naturalistic conditions (mean r = .35). Partialling out changes in heart rate and vagal effects attenuated these correlations, but they remained significant. Ambulatory TWA cannot replace PEP, but simultaneous recording of TWA and PEP provides a more comprehensive picture of changes in cardiac SNS activity in real-life settings.

Detection of T-wave beat-by-beat variations prior to ventricular arrhythmias onset in ICD-stored intracardiac electrograms: the Endocardial T-Wave Alternans Study (ETWAS).

The aim of the Endocardial T-Wave Alternans Study was to prospectively assess the presence of T-wave alternans (TWA) or beat-to-beat repolarization changes on implantable cardioverter-defibrillator (ICD)-stored electrograms (EGMs) immediately preceding the onset of spontaneous ventricular tachycardia (VT) or fibrillation (VF). Thirty-seven VT/VF episodes were compared to 116 baseline reference EGMs from the same 57 patients. A Bayesian model was used to estimate the T-wave waveform in each cardiac beat and a set of 10 parameters was selected to segment each detected T wave. Beat-by-beat differences in each T-wave parameter were computed using the absolute value of the difference between each beat and the following one. Fisher criterion was used for determining the most discriminant T-wave parameters, then top-M ranked parameters yielding a normalized cumulative Fisher score > 95% were selected, and analysis was applied on these selected parameters. Simulated TWA EGMs were used to validate the algorithm. In the simulation study, TWA was detectable even in the case of the smallest simulated alternans of 25 μV. In 13 of the 37 episodes (35%) occurring in nine of 16 patients, significant larger beat-to-beat variations before arrhythmia onset were detected compared to their respective references (median one positive episode per patient). Parameters including the T-wave apex amplitude seem the more discriminant parameters. Detection of beat-by-beat repolarization variations in ICD-stored EGMs is feasible in a significant subset of cases and may be used for predicting the onset of ventricular arrhythmias.

Antiarrhythmic efficacy of CPUY102122, a multiple ion channel blocker, on rabbits with ischemia/reperfusion injury

BackgroundThe antiarrhythmic potential of a novel multichannel blocker CPUY102122 (CY22) was investigated in the present study. MethodsThe effect of CY22 on rapid delayed rectifier potassium channel current (IKr) was studied using whole-cell patch clamp techniques in Chinese Hamster Ovary cells stably expressing human Ether-à-go-go-Related Gene. We further evaluated the antioxidant effects of CY22 and demonstrated the reversal of connexin down-regulation in the development of cardiac ventricular arrhythmias, which was produced using coronary ligation/reperfusion in rabbits. CY22 and Amiodarone were administered 30min prior to the procedure. Next, electrocardiograms were recorded, protein expression of left ventricular Connexin43 (Cx43), non-phosphorylation-Cx43 (np-Cx43), Rac-1 and gp-91[phox] were assayed using Western blot analysis, microstructural changes in the myocardium were observed and redox system activity was assayed. ResultsCY22 inhibited IKr in a concentration-dependent manner with IC50 value of 2.8±0.8μmol/L. CY22 treatment significantly decreased T-wave amplitude and QTc arrhythmic scores and ameliorated the shape of the infarcted myocardium compared to the model group. CY22 decreased the serum levels of creatine kinase, lactate dehydrogenase, and myocardial levels of malondialdehyde, as well as increased superoxide dismutase activity. Cx43 expression in the left ventricle was significantly increased by CY22 treatment, which significantly decreased np-43 expression, Rac-1 activity and gp-91[phox] protein expression. ConclusionsThese results indicated that CY22 has both antiarrhythmic and cardiovascular protective effects partly by blocking IKr, the production of antioxidants and protection of Cx43.

Cardiac Repolarization and Autonomic Regulation during Short-Term Cold Exposure in Hypertensive Men: An Experimental Study

ObjectivesThe aim of our study was to assess the effect of short-term cold exposure, typical in subarctic climate, on cardiac electrical function among untreated middle-aged hypertensive men.MethodsWe conducted a population-based recruitment of 51 hypertensive men and a control group of 32 men without hypertension (age 55–65 years) who underwent whole-body cold exposure (15 min exposure to temperature −10°C, wind 3 m/s, winter clothes). Conduction times and amplitudes, vectorcardiography, arrhythmias, and heart rate variability (autonomic nervous function) were assessed.ResultsShort-term cold exposure increased T-peak to T-end interval from 67 to 72 ms (p<0.001) and 71 to 75 ms (p<0.001) and T-wave amplitude from 0.12 to 0.14 mV (p<0.001) and from 0.17 to 0.21 mV (p<0.001), while QTc interval was shortened from 408 to 398 ms (p<0.001) and from 410 to 401 ms (p<0.001) among hypertensive men and controls, respectively. Cold exposure increased both low (from 390 to 630 ms2 (p<0.001) and 380 to 700 ms2 (p<0.001), respectively) and high frequency heart rate variability (from 90 to 190 ms2 (p<0.001) and 150 to 300 ms2 (p<0.001), respectively), while low-to-high frequency-ratio was reduced. In addition, the frequency of ventricular ectopic beats increased slightly during cold exposure. The cold induced changes were similar between untreated hypertensive men and controls.ConclusionsShort-term cold exposure with moderate facial and mild whole body cooling resulted in prolongation of T-peak to T-end interval and higher T-wave amplitude while QTc interval was shortened. These changes of ventricular repolarization may have resulted from altered cardiac autonomic regulation and were unaffected by untreated hypertension.Trial RegistrationClinicalTrials.gov NCT02007031

Differences in ST-elevation and T-wave amplitudes do not reliably differentiate takotsubo cardiomyopathy from acute anterior myocardial infarction

BackgroundPrevious efforts to distinguish acute anterior ST-elevation myocardial infarction (anterior-STEMI) from various forms of takotsubo cardiomyopathy (TTC) by electrocardiography (ECG) have produced differing results. MethodsWe performed a retrospective comparison of acute ECGs between 48 apical and 9 mid-ventricular TTC patients, with 96 anterior-STEMI patients. ECG was recorded in acute phase (<24h from onset of pain), and analyzed for ST-changes, negative T-waves, abnormal Q-waves and QT-interval duration. Time from onset of pain to ECG was gathered from patient records. ResultsAnterior-STEMI patients had ST-elevation in lead V1 more frequently than apical (70% vs 15%, p<0.0001) or mid-ventricular TTC patients (70% vs 0%, p<0.0001), and higher ST-elevation amplitudes in leads V2–V5 (p<0.02). Lack of ST-elevation in lead V1 and ST-elevation amplitude <2mm in lead V2 distinguished TTC from anterior-STEMI patients with 63% sensitivity and 93% specificity, with 79% predictive value. ConclusionsIn patients with anterior ST-elevation and acute chest pain, lack of ST-elevation in lead V1 and ST-elevation amplitude <2mm in lead V2 suggests a TTC diagnosis. However, this criterion is not reliable enough in clinical practice to distinguish between TTC and anterior-STEMI patients.

5 Surface Electrocardiogram Signals Variation with Posture in Normal Adults and in Adults with Congenital Heart Disease and its Clinical Implication

IntroductionAmbulatory cardiac monitoring devices and the novel subcutaneous ICD (SICD) sensing algorithms are based on the surface electrocardiograms (ECGs) parameters for detection and discrimination of arrhythmias. However the impact of...

Characterization of electrocardiogram changes throughout a marathon.

There are few data examining cardiovascular physiology throughout a marathon. This study was devised to characterize electrocardiographic activity continuously throughout a marathon. Cardiac activity was recorded from 19 subjects wearing a Holter monitor during a marathon. The 19 subjects (14 men and 5 women) were aged 39 ± 16 years (mean ± SD) and completed a marathon in 4:32:16 ± 1:23:35. Heart rate (HR), heart rate variability (HRV), T-wave amplitude, T-wave amplitude variability, and T-wave alternans (TWA) were evaluated continuously throughout the marathon. Averaged across all subjects, HRV, T-wave amplitude variability, and TWA increased throughout the marathon. Increased variability in T-wave amplitude occurred in 86 % of subjects, characterized by complex oscillatory patterns and TWA. Three min after the marathon, HR was elevated and HRV was suppressed relative to the pre-marathon state. HRV and T-wave amplitude variability, especially in the form of TWA, increase throughout a marathon. Increasing TWA as a marathon progresses likely represents a physiologic process as no arrhythmias or cardiac events were observed.

Maternal sensitivity and infant autonomic and endocrine stress responses

BackgroundEarly environmental exposures may help shape the development of the autonomic nervous system (ANS) and hypothalamic–pituitary–adrenal (HPA) axis, influencing vulnerability for health problems across the lifespan. Little is known about the role of maternal sensitivity in influencing the development of the ANS in early life. AimsTo examine associations among maternal sensitivity and infant behavioral distress and ANS and HPA axis reactivity to the Repeated Still-Face Paradigm (SFP-R), a dyadic stress task. Study designObservational repeated measures study. SubjectsThirty-five urban, sociodemographically diverse mothers and their 6-month-old infants. Outcome measuresChanges in infant affective distress, heart rate, respiratory sinus arrhythmia (RSA), and T-wave amplitude (TWA) across episodes of the SFP-R were assessed. A measure of cortisol output (area under the curve) in the hour following cessation of the SFP-R was also obtained. ResultsGreater maternal insensitivity was associated with greater infant sympathetic activation (TWA) during periods of stress and tended to be associated with greater cortisol output following the SFP-R. There was also evidence for greater affective distress and less parasympathetic activation (RSA) during the SFP-R among infants of predominantly insensitive mothers. ConclusionsCaregiving quality in early life may influence the responsiveness of the sympathetic and parasympathetic branches of the ANS as well as the HPA axis. Consideration of the ANS and HPA axis systems together provides a fuller representation of adaptive versus maladaptive stress responses. The findings highlight the importance of supporting high quality caregiving in the early years of life, which is likely to promote later health.

Miniaturized Radio Frequency Telemetric Pacemaker With Anti-Arrhythmic Pacing Protocol1

Fatal arrhythmias and ventricular fibrillation (VF) which lead to sudden cardiac death are believed to be preceded by alternans, observed as a beat-to-beat variation of the T-wave amplitude on the ECG [1,2]. Previous studies to predict the onset of alternans involved the restitution curve, the functional relationship between the action potential duration (APD) and preceding diastolic interval (DI). It was hypothesized that alternans appears when the magnitude of the slope of the restitution curve exceeds one [3]. However, this hypothesis failed in various experimental studies [4]. One of the main reasons for failure of the restitution hypothesis was the fact that it was derived under assumption of constant or periodic pacing, where there is an inherent dependence of the DI on the immediate preceding APD. During periodic pacing, small changes in DI are translated into subsequent changes in the APD and thus, enhance instability of cardiac rhythms in the heart. However, under normal physiological conditions, intrinsic heart rate variability (HRV) ensures deviation of the heart from periodic pacing [4]. HRV is a variation in time interval between two consecutive heartbeats. Figure 1 shows a representative example of HRV as a change in RR interval for a normal sinus rhythm of a healthy adult male at rest. We can see that the RR interval, the time duration between two consecutive peaks of the ECG, varies over time.

Statistical evaluation of reproducibility of automated ECG measurements: An example from arrhythmogenic right ventricular dysplasia/cardiomyopathy clinic

BackgroundArrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is characterized by delay in depolarization of the right ventricle, detected by prolonged terminal activation duration (TAD) in V1–V3. However, manual ECG measurements have shown moderate-to-low intra- and inter-reader agreement. The goal of this study was to assess reproducibility of automated ECG measurements in the right precordial leads. MethodsPairs of ECGs recorded in the same day from Johns Hopkins ARVD/C Registry participants [n=247, mean age 35.2±15.6 years, 58% men, 92% whites, 11(4.5%) with definite ARVD/C] were retrospectively analyzed. QRS duration, intrinsicoid deflection, TAD, and T-wave amplitude in the right precordial leads, as well as averaged across all leads QRS duration, QRS axis, T axis, QTc interval, and heart rate was measured automatically, using 12SL TM algorithm (GE Healthcare, Wauwatosa, WI, USA). Intrinsicoid deflection was measured as the time from QRS complex onset to the alignment point of the QRS complex. TAD was calculated as the difference between QRS duration and intrinsicoid in V1–V3. Reproducibility was quantified by Bland–Altman analysis (bias with 95% limits of agreement), Lin's concordance coefficient, and Bradley–Blackwood procedure. ResultsBland–Altman analysis revealed satisfactory reproducibility of tested parameters. V1 QRS duration bias was −0.10ms [95% limits of agreement −12.77 to 12.56ms], V2 QRS duration bias −0.09ms [−11.13 to 10.96ms]; V1 TAD bias 0.14ms [−13.23 to 13.51ms], V2 TAD bias 0.008ms [−12.42 to 12.44ms]. ConclusionComprehensive statistical evaluation of reproducibility of automated ECG measurements is important for appropriate interpretation of ECG. Automated ECG measurements are reproducible to within 25%.

Spatial repolarization heterogeneity and survival in Chagas disease.

We investigated if cardiac spatial repolarization heterogeneity might be associated with an increased risk of death in patients with chronic Chagas disease. Repolarization heterogeneity was assessed using the V-index, a recently introduced metric founded on a biophysical model of the ECG. This metric provides an estimate of the standard deviation of the repolarization times across the heart. We analyzed 113 patients (aged 21- 67 years) enrolled between 1998 and 1999 who had a known serological status showing positive reactions to Trypanosoma cruzi. Fourteen subjects died during a 10-year follow-up period. The V-index was significantly lower in survivor (S) than in non-survivor (NS) subjects (S: 31.2 ± 13.3 ms vs NS: 41.2 ± 18.6 ms, single-tail t-test: p = 0.009, single-tail Wilcoxon rank sum test: p = 0.029). A V-index larger than 36.3 ms was related to a significantly higher risk of death in a univariate Cox proportional-hazards analysis (hazard ratio, HR = 5.34, p = 0.0046). In addition, V-index > 36.3 ms retained its prognostic value in a multivariate Cox proportional-hazards analysis after adjustment for other three clinical variables (left ventricular ejection factor < 0.50, QRS duration > 133 ms, ventricular tachycardia during stress testing or 24 hours Holter) and for T-wave amplitude variability > 30 μV, even using shrinkage, a statistical procedure that protects against over-fitting due to small sample size. The study showed that an increased dispersion of repolarization times in patients with Chagas disease, as measured by the V-index, is significantly correlated with the risk of death in a univariate survival analysis. The V-index captures prognostic information not immediately available from the analysis of other established risk factors.

Nocturnal Home Hemodialysis Associates with Improvement of Electrocardiographic Features Linked to Sudden Cardiac Death

Sudden cardiac death (SCD) remains the leading cause of death in hemodialysis patients. We performed a retrospective electrocardiograph (ECG) and chart review to determine whether hemodialysis modality, frequency, or duration could predict change in ECG parameters associated with SCD. Frequent nocturnal hemodialysis was associated with an improvement in Tpeak to Tend within 365 days (83.8-71.8 ms, p = 0.005) and past 365 days of dialysis initiation (85.9-77.1 ms, p = 0.005) and improvement in QRS amplitude variation within 365 days (0.0583-0.0297, p = 0.025) and past 365 days of dialysis initiation (0.0546-0.0332, p = 0.029). Compared with intermittent conventional hemodialysis, more frequent nocturnal (15/25 vs. 3/14, p = 0.04) and intermittent nocturnal hemodialysis (INHD) (6/8 vs. 3/14, p = 0.03) patients decreased Tpeak to Tend. More short-hours daily than INHD patients increased T-wave amplitude variation (16/25 vs. 1/8, p = 0.02). These improvements occurred before changes in Cornell or Sokolow-Lyon electrocardiographic left ventricular mass. Thus, it appears that hemodialysis modalities of longer duration are associated with improvements in electrocardiographic parameters associated with SCD. Prospective trials are required to determine whether dialysis prescription reduces SCD, cardiovascular morbidity, and mortality in hemodialysis patients.

Severe hyperkalemia can be detected immediately by quantitative electrocardiography and clinical history in patients with symptomatic or extreme bradycardia: A retrospective cross-sectional study

PurposeDetecting severe hyperkalemia is challenging. We explored its prevalence in symptomatic or extreme bradycardia and devised a diagnostic rule. Materials and MethodsThis retrospective cross-sectional study included patients with symptomatic (heart rate [HR] ≤50/min with dyspnea, chest pain, altered mentality, dizziness/syncope/presyncope, general weakness, oliguria, or shock) or extreme (HR ≤40/min) bradycardia at an emergency department for 46 months. Risk factors for severe hyperkalemia were chosen by multiple logistic regression analysis from history (sex, age, comorbidities, and medications), vital signs, and electrocardiography (ECG; maximum precordial T-wave amplitude, PR, and QRS intervals). The derived diagnostic index was validated using bootstrapping method. ResultsAmong the 169 participants enrolled, 87 (51.5%) were female. The mean (SD) age was 71.2 (12.5) years. Thirty-six (21.3%) had severe hyperkalemia. The diagnostic summed “maximum precordial T ≥8.5 mV (2),” “atrial fibrillation/junctional bradycardia (1),” “HR ≤42/min (1),” “diltiazem medication (2),” and “diabetes mellitus (1).” The C-statistics were 0.86 (0.80-0.93) and were validated. For scores of 4 or higher, sensitivity was 0.50, specificity was 0.92, and positive likelihood ratio was 6.02. The “ECG-only index,” which sums the 3 ECG findings, had a sensitivity of 0.50, specificity of 0.90, and likelihood ratio (+) of 5.10 for scores of 3 or higher. ConclusionsSevere hyperkalemia is prevalent in symptomatic or extreme bradycardia and detectable by quantitative electrocardiographic parameters and history.

A case–control study of non-monitored ECG metrics preceding in-hospital bradyasystolic cardiac arrest: Implication for predictive monitor alarms

ObjectivesWe investigated whether additional electrocardiographic (ECG) metrics not available on current patient monitors could predict bradyasystolic cardiac arrest in hospitalized adult patients. MethodsA retrospective case–control design was used to study eight ECG metrics from 22 adult bradyasystolic patients and their 45 control patients. The eight ECG metrics included heart rate, QRS width, interval from P-wave peak to QRS onset (PRp), heart rate-corrected interval from QRS onset to T-wave peak (QTpc), amplitude of QRS peak (rAmp), amplitude of P-wave (pAmp), amplitude of T-wave (tAmp), and absolute difference in the ECG amplitudes at QRS onset and offset divided by rAmp, that is, relative J-point amplitude (relJAmp). We derived the maximal true-positive rate (TPR) of detecting cardiac arrest at a globally minimal false-positive rate (FPR) for each metric and for the absolute slope values resulted from a linear fitting of the time series of these metrics. We also recorded the first time crossing the detection threshold to the time of arrest as lead time. ResultsConditions of relJAmp >20% and PRp >196.6ms, respectively, achieved a TPR of 22.7% and 27.3% with zero FPRs. The lead prediction time of these two conditions was 5.7±6.8hours and 8.0±7.2hours, respectively. Performance of triggers based on the absolute slope values depended on the window length used for linear fitting. rAmp slope of a 2-hour window, PRp slope of a 30-minute window, and relJAmp slope of a 2-hour window achieved the best TPR of 27.3% (FPR=2.3%, lead time=6.5±5.7hours), 14.3% (FPR=0.0%, lead time=10.9±10.9), and 18.2% (FPR=2.3%, lead time=8.8±9.8), respectively. McNemar test showed that only relJAmp >20.0% is significantly different from the baseline trigger of HR >149.3bpm (p=0.046). In addition, metrics-based and slope-based triggers were complementary as an “OR” combination of two single-metric triggers raised the TPR up to 45.4% with zero FPR. ConclusionsIt is feasible to compute additional metrics from continuous ECG from bedside monitors. These additional parameters can provide highly specific triggers for predicting bradyasystolic cardiac arrest. Complementary triggers based on the slope of trending of these ECG metrics can further increase the sensitivity without incurring false positives.

Beat-to-beat QT interval variability and T-wave amplitude in patients with myocardial infarction

The purpose of this study was to investigate the effects of T-wave amplitude and ECG lead on beat-to-beat QT interval variability (QTV) in patients with myocardial infarction (MI) compared to healthy subjects. Standard resting 12-lead ECGs of 79 MI patients and 69 healthy subjects were investigated. Beat-to-beat QT intervals were measured separately for each lead using a template matching algorithm. In addition, we extracted the beat-to-beat T-wave amplitude in each lead. We computed the standard deviation of beat-to-beat QT intervals as a marker of QTV for both healthy subjects and MI patients. Significant QTV differences were observed between the 12 ECG leads as well as between the groups of healthy subjects and MI patients. Beat-to-beat QTV was significantly higher in MI patients than in healthy subjects for half of the leads. Furthermore, significant T-wave amplitude differences across leads and between groups were observed. A significant inverse relation between beat-to-beat QTV and T-wave amplitude was demonstrated. The group differences in QTV remained significant after co-varying for the T-wave amplitude. In conclusion, the increase in beat-to-beat QTV that has been repeatedly reported in patients with MI is partly due to the lower T-wave amplitudes. However, QTV remains significantly increased in MI patients after covarying for this effect.