QRS Measurements Research Articles

Comparison of AliveCor KardiaMobile Six-Lead ECG with Standard ECG in Pediatric Patients.

The AliveCor KardiaMobile (ACKM) is a remote electrocardiogram (ECG) monitoring device. Little research has been conducted on its accuracy with pediatric patients. This prospective study aims to compare the ACKM six-lead device with a standard fifteen-lead ECG in measuring the QTc, QRS, and axis in pediatric patients. Pediatric patients ages 5 to 21years were enrolled prospectively to have their ECG recorded using an ACKM six-lead device following a recording with the standard 15-lead ECG. A pediatric electrophysiologist measured the QTc, QRS interval, and QRS axis for both ECGs. Bland-Altman analysis was performed to assess agreement among measurements. The study included 141 patients. The mean age was 12.3 ± 4.4years. Average heart rate was 79 ± 16bpm. The mean difference in the QTc measurements for a paired standard ECG and ACKM was -0.6ms [95% confidence interval -48 to 47ms]. Of the ACKM QTc measurements, 117 (83%) were within 30ms of the standard ECG. The mean difference in paired QRS measurements was -1.3ms [95% confidence interval -23 to 21ms]. Of the ACKM QRS measurements, 134 (95%) were within 20ms of the standard ECG. The measured axis was the same for 84% of ACKM and standard ECGs. Over 80% of the ACKM six-lead ECGs produced QTc, QRS, and axis deviation measurements within a clinically useful range of the standard ECG. However, it is not accurate enough to be used consistently in place of a standard ECG for QTc and QRS measurement for pediatric patients.

Assessment of Apple Watch Series 6 pulse oximetry and electrocardiograms in a pediatric population.

Recent technologic advances have resulted in increased development and utilization of direct-to-consumer cardiac wearable devices with various functionality. This study aimed to assess Apple Watch Series 6 (AW6) pulse oximetry and electrocardiography (ECG) in a cohort of pediatric patients. This single-center, prospective study enrolled pediatric patients ≥ 3kg and having an ECG and/or pulse oximetry (SpO2) as part of their planned evaluation. Exclusion criteria: 1) non-English speaking patients and 2) patients in state custody. Simultaneous tracings were obtained for SpO2 and ECG with concurrent standard pulse oximeter and 12-lead ECG. AW6 automated rhythm interpretations were compared to physician over-read and categorized as accurate, accurate with missed findings, inconclusive (automated interpretation: "inconclusive"), or inaccurate. A total of 84 patients were enrolled over a 5-week period. 68 patients (81%) were placed into the SpO2 and ECG arm, with 16 patients (19%) placed into the SpO2 only arm. Pulse oximetry data was successfully collected in 71/84 (85%) patients and ECG data in 61/68 (90%). ΔSpO2 between modalities was 2.0±2.6% (r = 0.76). ΔRR was 43±44msec (r = 0.96), ΔPR 19±23msec (r = 0.79), ΔQRS 12±13msec (r = 0.78), and ΔQT 20±19msec (r = 0.9). The AW6 automated rhythm analysis yielded a 75% specificity and found: 1) 40/61 (65.6%) "accurate", 2) 6/61 (9.8%) "accurate with missed findings", 3) 14/61 (23%) "inconclusive", and 4) 1/61 (1.6%) incorrect. The AW6 can accurately measure oxygen saturation when compared to hospital pulse oximeters in pediatric patients and provide good quality single lead ECGs that allow for accurate measurement of RR, PR, QRS, and QT intervals with manual interpretation. The AW6-automated rhythm interpretation algorithm has limitations for smaller pediatric patients and patients with abnormal ECGs.

False Negative ECG Device Results May Increase the Risk of Adverse Events in Clinical Oncology Trials

BackgroundSites participating in clinical trials may not have the expertise and infrastructure to accurately measure cardiac intervals on 12-lead ECGs and rely heavily on the automated ECG device generated results for clinical decision-making.MethodsUsing a dataset of over 260,000 ECGs collected in clinical oncology studies, we investigated the mean difference and the rate of false negative results between the digital ECG machine QTc and QRS measurements compared to those obtained by a centralized ECG core lab.ResultsThe mean differences between the core lab and the automated algorithm QTcF and QRS measurements were + 1.8 ± 16.0 ms and − 1.0 ± 8.8 ms, respectively. Among the ECGs with a centralized QTcF value > 450 or > 470 ms, 39.5% and 47.8% respectively had a device reported QTcF value ≤ 450 ms or ≤ 470 ms. Among the ECGs with a centrally measured QTcF > 500 ms, 55.8% had a device reported value ≤ 500 ms. Automated QTcF measurements failed to detect a QTcF increase > 60 ms for 53.9% of the ECGs identified by the core lab. Automated measurements also failed to detect QRS prolongation, though to a lesser extent than failures to detect QTc prolongation. Among the ECGs with a centrally measured QRS > 110 or 120 ms, 7.9% and 7.3% respectively had a device reported QRS value ≤ 110 ms or ≤ 120 ms.ConclusionRelying on automated measurements from ECG devices for patient inclusion and treatment (dis)continuation decisions poses a potential risk to patients participating in oncology studies.

Comparison of PR, QRS, and QT interval measurements by seven ECG interpretation programs

BackgroundElectrocardiograph-generated measurements of PR, QRS, and QT intervals are generally thought to be more precise than manual measurements on paper records. However, the performance of different programs has not been well compared. MethodsRoutinely obtained digital electrocardiograms (ECGs), including over 500 pediatric ECGs, were used to create over 2000 10 s analog ECGs that were replayed through seven commercially available electrocardiographs. The measurements for PR interval, QRS duration, and QT interval made by each program were extracted and compared against each other (using the median of the programs after correction for program bias) and the population mean values. ResultsSmall but significant systematic biases were seen between programs. The smallest and largest variation from the population mean differed by 4.7 ms for PR intervals, 5.8 ms for QRS duration, and 12.4 ms for QT intervals. In pairwise comparison programs showed similar accuracy for most ECGs, with the average absolute errors at the 75th percentile for PR intervals being 4–6 ms from the median, QRS duration 4–8 ms, and QT interval 6–10 ms. However, substantial differences were present in the numbers and extent of large, clinically significant errors (e.g at the 98th percentile), for which programs differed by a factor of two for absolute errors, as well as differences in the mix of overestimations and underestimations. ConclusionsWhen reading digital ECGs, users should be aware that small systematic differences exist between programs and that there may be large clinically important errors in difficult cases.

Timing of pulmonary valve replacement in patients with corrected Fallot to prevent QRS prolongation.

OBJECTIVESTiming of pulmonary valve replacement (PVR) remains one of the most heavily debated topics in congenital cardiac surgery. We aimed to analyse the temporal evolution of QRS duration before and after PVR.METHODSWe included 158 consecutive patients who underwent PVR after previous correction with transannular patch. All 3549 available serial standard 12-lead surface QRS measurements of 158 (100%) patients were analysed with linear mixed-effect modelling.RESULTSPVR was performed at a mean age of 28.0 ± 10.7 years, 23.4 ± 8.4 years after correction. Hospital survival was 98.1%. A longer time interval between ToF correction and PVR (P < 0.001), and an older age at correction (P = 0.015) were predictive of progressive QRS prolongation after PVR. Women on average had a shorter QRS duration (P = 0.005) after PVR. The model predicted that in patients corrected early (model age 0.5 years), PVR within 17 years after correction leads to narrowing or stabilization of QRS width. PVR beyond 17 years was associated with prolongation of QRS duration. In a patient corrected late (model age 5 years), PVR has to be performed within 15 years after correction to prevent prolongation. Finally, a longer time period between correction and PVR was associated with an increased hazard of cardiac death (hazard ratio 1.097, 95% confidence interval 1.002–1.200).CONCLUSIONSProlongation of QRS duration after PVR was associated with a longer time between correction and PVR, older age at correction and male sex. Prevention of progressive QRS prolongation by earlier PVR can potentially reduce the hazard of adverse events after PVR.

P5718Effects of the fluoroquinolones moxifloxacin and levofloxacin on the QT subintervals: sex differences in ventricular repolarization

Abstract Background The effects of medicines affecting cardiac repolarization can be further evaluated by assessing the balance of inward and outward currents. These can be detected in the ECG by analysing the QT subintervals. Pure hERG potassium channel block was shown to prolong both early repolarization (J-Tpeak) and late repolarization (Tpeak-Tend), whereas multichannel blockers may shorten or have no effect on J-Tpeak. The gender dependency of ventricular repolarization is also well known. Recently, Matsukura indicated that moxifloxacin significantly increased J-Tpeak and Tpeak-Tend and females in their study were more sensitive than males to the drug-induced J-Tpeak prolongation and QTcF. Purpose The purpose of the present study is to use data from two Thorough QT (TQT) studies to characterize the differences in depolarization (QRS), early repolarization (J-Tpeak), and late repolarization (Tpeak-Tend) between moxifloxacin and levofloxacin and further define the sex differences in QTc and subintervals. Methods Data from two TQT studies were used to further investigate the impact of moxifloxacin (400 mg) and levofloxacin (1000 and 1500 mg) on QT subintervals using validated algorithms for measurement of QRS, J-Tpeak and Tpeak–Tend intervals. Concentration-effect analyses were performed to establish a potential relationship between the ECG effects and the concentrations of the two fluoroquinolones as typically males and females also show differences in plasma concentrations due to differences in body weight. Results The relationships between moxifloxacin and levofloxacin plasma concentrations and their respective predicted ΔΔQTcF, ΔΔQRS, ΔΔJ-Tpeakc and ΔΔTpeak-Tend values are shown in Fig 1. The plasma concentrations were higher for females than males in both drugs. Moxifloxacin was shown to be a more potent prolonger of QTcF and had a pronounced effect on J-Tpeakc, consistent with its effects on both IKr and IKs channels while levofloxacin had little effect on J-Tpeakc. For moxifloxacin, the concentration-effect modelling showed a greater effect for females on QTcF and J-Tpeakc while for levofloxacin the inverse was true. Based on the assumption that repolarization reserve of females relies to a greater extent on IKs channels it would be reasonable to assume that they are more affected by a medicine that blocks IKs in addition to IKr. Figure 1 Conclusions This study showed that levofloxacin elicited a smaller ΔΔQTcF and ΔΔJ-Tpeakc prolongation when compared to moxifloxacin. The results of this study also showed a different pattern of sex difference in repolarization after administration of both drugs. which may suggest a difference in expression of IKs and possibly IKr channels.

QRS Detection and Measurement Method of ECG Paper Based on Convolutional Neural Networks.

In this paper, we propose an end-to-end approach to addressing QRS complex detection and measurement of Electrocardiograph (ECG) paper using convolutional neural networks (CNNs). Unlike conventional detection solutions that convert images to digital data, our method can directly detect QRS complex in images using Faster-RCNN, then the R-peak can be located and measured through a CNN. Validated by clinical ECG data in the St.-Petersburg Institute of Cardiological Technics 12-lead Arrhythmia Database and real ECG paper from Peking University People's Hospital, the proposed method can achieve the recall of 98.32%, the precision of 99.01% in detecting and 0.012 mv of mean absolute error in measuring. Experimental results demonstrate the superior performance of our method over conventional solutions, which would pave the way to detect and measure ECG paper using CNNs.

Relationship between QRS measurements and left ventricular morphology and function in asymptomatic individuals.

QRS amplitude and duration are associated with increased left ventricular (LV) volume, mass and dysfunction. However, the diagnostic concordance between QRS measurements and LV morphology and function, as shown by Doppler echocardiography, is not well established. We investigated the relationships of QRS duration and amplitude with echocardiographic measurements of LV morphology and systolic and diastolic function in normal individuals. Individuals without signs or symptoms of coronary artery disease or heart failure, who underwent clinical examination as a part of a cross-sectional survey for the prevalence of coronary risk factors, randomly selected from the population list in Caltanissetta, Italy, were included in the study. QRS duration and amplitude were automatically measured using inbuilt software. LV ejection and filling patterns were studied using Doppler echocardiography. We studied 184 individuals (96 men and 88 women), mean age 55.9 (11.3). QRS duration increased by 5.4ms for every 100g increase in LV mass, and by 4.6ms for each 10mm increase in LV end-diastolic diameter. The amplitude increased by 0.8mm for every 100g increase in LV mass. There was no relationship with LV dimensions. A nonlinear correlation was found between QRS amplitude and indexes of global dyssynchrony. The time-voltage QRS area correlated with LV mass, dimensions and indexes of dyssynchrony. There was no relationship between QRS measurements and ejection fraction. QRS prolongation and increase in amplitude are strongly influenced by LV increased mass and volume, as well as by dyssynchrony, independently of ejection fraction.

Association between QRS duration on prehospital ECG and mortality in patients with suspected STEMI

BackgroundQRS duration has previously shown association with mortality in patients with acute myocardial infarction treated with thrombolytics, less is known in patients with suspected ST segment elevation myocardial infarction (STEMI) when assessing QRS duration on prehospital ECG. Thus, the objective was to investigate the prognostic effect of QRS duration on prehospital ECG and presence of classic left and right bundle branch block (LBBB/RBBB) for all-cause mortality in patients with suspected STEMI. MethodIn total 2105 consecutive patients (mean age 64±13years, 72% men) with suspected STEMI were prospectively included. QRS duration was registered from automated QRS measurement on prehospital ECG and patients were divided according to quartiles of QRS duration (<89ms, 89–98ms, 99–111ms and >111ms). Primary endpoint was all-cause 30-day mortality. Predictors of all-cause mortality were assessed using Cox proportional hazards analysis. ResultsAmong all patients median QRS duration was 98ms (IQR 88–112ms). RBBB-morphology was seen in 126 patients (6.0%) and LBBB in 88 patients (4.2%), 80% were treated with percutaneous coronary intervention and the final diagnosis was STEMI in 1777 patients (84%). Thirty-day mortality was 7.6% in patients with suspected STEMI. In multivariable analysis, QRS duration>111ms (hazard ratio (HR) 3.08; 95% confidence interval (CI): 1.71–5.57, p=0.0002), LBBB – morphology (HR 3.0; 95% CI: 1.38–6.53, p=0.006) and RBBB (HR 3.68; 95% CI: 1.95–6.95, p<0.0001) were associated with 30 day all-cause mortality. ConclusionIn patients with suspected STEMI, QRS prolongation, LBBB, and RBBB on prehospital ECG are associated with increased risk of death.

Assessments of the QT/QRS restitution in perfused guinea-pig heart can discriminate safe and arrhythmogenic drugs

IntroductionDrug-induced arrhythmia remains a matter of serious clinical concern, partly due to low prognostic value of currently available arrhythmic biomarkers. MethodsThis study examined whether arrhythmogenic risks can be predicted through assessments of the rate adaptation of QT interval, ventricular effective refractory period (ERP), or the QT/QRS ratio, in perfused guinea-pig hearts. ResultsWhen the maximum restitution slope was taken as a metric of proarrhythmia, neither QT interval nor ERP measurements at progressively increased pacing rates were found to fully discriminate arrhythmogenic drugs (dofetilide, quinidine, flecainide, and procainamide) from those recognized as safe antiarrhythmics (lidocaine and mexiletine). For example, the slope of QT restitution was increased by dofetilide and quinidine, but remained unchanged by flecainide, procainamide, lidocaine, and mexiletine. With ERP rate adaptation, even though the restitution slope was increased by dofetilide, all class I agents reduced the slope value independently of their safety profile. The QRS measurements revealed variable drug effects, ranging from significant use-dependent conduction slowing (flecainide, quinidine, and procainamide) to only modest increase in QRS (lidocaine and mexiletine), or no change at all (dofetilide). However, with the QT/QRS rate adaptation, the restitution slope was significantly increased by all agents which have been reported to produce proarrhythmic effects (dofetilide, quinidine, flecainide, and procainamide), but not changed by lidocaine and mexiletine. DiscussionThese findings suggest that the slope of the QT/QRS rate adaptation can be considered as a novel electrophysiological biomarker in predicting potential arrhythmic risks associated with pharmacotherapy in cardiac patients.

Capturing the His‐Purkinje System is Not Possible from Conventional Right Ventricular Apical and Nonapical Pacing Sites

Direct His bundle capture may negate ventricular electrical dyssynchrony induced by right ventricular (RV) apical pacing. We sought to evaluate if direct His bundle pacing is possible with conventional pacemaker lead implantation at various sites in the RV. Consecutive patients underwent RV pacing using standard implantable active fixation pacing leads in a random order in the RV outflow tract, middle RV, and RV apex at stimulation threshold and at increasing voltages of 2.5, 5, 7.5, and 10 volts (V). At each location, QRS width and morphology on 12-lead electrocardiograph (ECG) were compared in sinus and paced rhythm at the different voltages. Twelve patients underwent a total of 2,160 paced QRS measurements. Progressive increases in stimulation voltage did not change QRS morphology or duration regardless of site of pacing (RV outflow tract, middle RV, and RV apex) in any of the 12 ECG leads. In addition, apart from the stimulation threshold between the RV outflow tract and RV apex, there was no statistically significant difference in QRS duration between the three pacing sites. In patients with a baseline normal QRS duration, none of the three conventional RV pacing sites were able to produce QRS narrowing and capture the His-Purkinje system. Furthermore, based on paced QRS duration as an indirect surrogate of electrical LV dyssynchrony, there was no clear advantage of one pacing site over another.

Optimization of cardiac resynchronization therapy according to the surface ECG

Background: Atrioventricular and interventricular delay (VVD) optimization is an important part of CRT correction. The lack of this procedure or incorrect performance may reduce the positive effect of cardiac resynchronization and enhance Heart Failure (HF). Widely used selection of VVD methods with different ways of echocardiography requires special skills and time-consuming. Aim: To assess the impact of VVD optimization in CRT devices based on changes in the width of the QRS complex using ECG on intracardiac hemodynamic parameters in the long-term period. Materials and methods: 96 patients after CRT implantation were divided into 2 groups (I - with selection of VVD, n=48, II - without selection of VVD, n=48) with sinus rhythm, complete left bundle branch block, ejection fraction (EF) ≤35%.QRS complex was measured before CRT implantation (QRSown), then every 6 months: QRS measurement in the temporary device suppression mode (QRSno-st), measuring the width of the stimulated QRS complex (QRSst) during the VVD optimization process. VVD selection was implemented by gradual change the delay time of stimulation of the right/left ventricle (from 0 to 40 ms) and simultaneous measurement of the stimulated QRS width on ECG. The final VVD result was assumed to the narrowest QRS. Echocardiography was performed in all patients before CRT implantation and then every 6 months. Observation period was 2 years. Results: For 24 month follow-up there was significant reducion in the QRSst width in Group I, p = 0.042. Final values of the QRSst and QRSno-st width were lower in Group I, p = 0.015 and p = 0.001 respectively. There are no significant differences in baseline QRS and QRSst between the groups. End-systolic and end-diastolic LV volume significantly decreased in both groups; reduction in the end-systolic volume was greater in Group I compared to Group II, p = 0.039. EF increased in both groups; percentage increase in EF was significantly higher in Group I, p = 0.048. Functional class (FC) of HF decreased in both groups; the final FC value was significantly lower in Group I, 2.12 versus 2.64 in Group II, p = 0.001. Conclusions: VVD optimization in CRT devices using ECG influences on hemodynamic parameters in the long-term period. The narrowest QRS can be the sign of optimal cardiac synchronization. This safe and reproducible method improves the electrical systole of the myocardium and can adjust the conduction system of ventricles that leads subsequently to a decrease in FC of HF.

Standardization of QRS duration measurement and LBBB criteria in CRT trials and clinical practice.

Based on the clinical trials so far, there is a major controversy regarding the benefit of CRT in patients with QRS≤150 milliseconds. Some studies have shown that a fair number of patients with QRS ≤150 milliseconds benefit from CRT and it is needless to say that careful attention should be paid to CRT non-responders considering the risk of complications and cost-benefit ratio. Lack of uniformity in QRS measurement in all these trials could have a major influence on variable study outcomes. This is of concern because when the QRS is close to 120 milliseconds in patients with NYHA class III/IV symptoms or QRS close to 150 milliseconds in NYHA class I/II patients, the decision to recommend CRT implantation or undertake further risk stratification investigations is critically dependent on the EKG interpretation. In this paper we intent to raise the important question for need of standardized electrocardiographic criteria (QRS measurement and LBBB) in patients enrolled in CRT trials considering the variability in study results, high rates of CRT non response in the eligible population and the associated health care cost burden.

Selection of Patient for Cardiac Resynchronization Therapy: Role of QT Corrected Dispersion

About 30 to 50% of patients undergoing cardiac resynchronization therapy (CRT) may not show clinical or echocardiographic improvement, despite fulfilling guidelines recommendations for CRT. For this reason, we need a more accurate method to assess CRT eligibility. The aims of this study were to verify, on a 12-month follow-up, the usefulness of QT corrected dispersion (QTcD) in a patient's selection for CRT. We stratified 53 patients who underwent CRT, into two groups based on the estimation of QTcD, that is, QTcD > 60 ms and QTcD ≤ 60 ms. In all patients were performed New York Heart Association (NYHA) class determination, six-minute walking test, QtcD, and QRS measurements, and complete echocardiographic assessment at 1, 3, 6, and 12 months after implantation. At baseline, there were no significant differences in clinical, echocardiographic, and electrocardiographic parameters duration between two groups. At 12-month follow-up between the two groups, there were significant differences in NYHA (1.2 ± 0.4 vs 2 ± 0.6; P < 0.01), six-minute walking distance (422 ± 68 vs 364 ± 68; P < 0.01), left ventricular (LV) ejection fraction (34 ± 7% vs 28 ± 6%; P < 0.01), LV end-diastolic diameter (57 ± 7 vs 63 ± 8; P < 0.01), and LV intraventricular dyssynchrony (24 ± 14 vs 39 ± 23; P < 0.01). This study suggests that QTc dispersion in addition to QRS duration could improve the sensitivity of electrocardiogram in a patient's selection for CRT.

Is Nurse Interpretation of the ECG QRS Width Reliable?

Electrocardiogram (ECG) data are critical in formulating management strategies following sodium channel antagonist overdose. Poison centers frequently rely on verbal reports of the ECG obtained from bedside nurses. No previous study has addressed the quality of ECG data obtained in this manner. Therefore, we sought to test the ability of nurses to recognize and measure a widened QRS complex, the hallmark of myocardial sodium channel toxicity. Thirty-six emergency department and critical care nurses employed at a tertiary care hospital participated in this prospective study. The study subjects were divided into three groups and asked to interpret 12 ECGs (five normal and seven wide QRS). For each ECG, participants (1) determined if the QRS was narrow or wide and (2) measured the QRS duration. The groups differed in delivery of instruction regarding QRS measurement. Group 1 received visual instructions; group 2 received scripted verbal instructions, and group 3 served as controls, receiving no specific QRS measurement instructions. The nurse data was compared with physician interpretation (consensus of three physicians). Between-group analysis tested for impact of potential real-time educational intervention. Overall, the nurses identified a wide QRS complex most of the time (77%), but had difficulty in accurately measuring the QRS duration (44%). Real-time visual or verbal instruction did not improve accuracy (p = NS between groups). The results suggest that verbal ECG data from nurse callers is not sufficient to make an accurate clinical assessment in the setting of sodium channel poisoning.

The use of alternate QRS measurement methods to improve detection of propafenone-induced QRS prolongation

The use of alternate QRS measurement methods to improve detection of propafenone-induced QRS prolongation

Reliability and Reproducibility of QRS Duration in the Selection of Candidates for Cardiac Resynchronization Therapy

A QRS >120 ms remains the recommended criterion for the selection of cardiac resynchronization therapy (CRT) candidates. However, the reproducibility of this measurement has not been studied thoroughly. QRS duration was measured by 3 experienced cardiologists and by automatic measurement on 228 electrocardiograms (ECGs) randomly collected from 188 subjects, including neonates, healthy adults, patients with complete and incomplete bundle branch block, and CRT candidates. All ECGs were recorded at a 25 mm/s sweep speed. Forty recordings were duplicated and 50 ECGs were recorded at both 25 and 50 mm/s. Significant interobserver differences (P < 0.001) were found between each combination of paired observers, with an up to 50-ms absolute variability between cardiologists and low concordance with computerized measurements. Intraobserver absolute variability was also significant (P < 0.01) for the 3 observers. These significant differences persisted (P < 0.01) when focusing our interest on the ECGs in the 100-140 ms range (defined as at least one out of the 4 measures in this range). Considering the 120 ms limit, 22 (27.5%) ECGs were differently classified by at least one of the cardiologists. We observed similar interobserver differences between each combination of paired observers with a 50 mm/s sweep speed. Manual QRS duration measurements were associated with significant inter- and intraobserver variability and low concordance with computerized measurements. The measurement of QRS is, therefore, operator-dependent and a reevaluation of the measurement methods may be essential to develop clinical and investigative standards.

Exercise Electrocardiogram Testing

Exercise testing remains the most widely accessible and relatively inexpensive method for initial evaluation of suspected coronary disease and for evaluation of its severity.1–3 Clinical usefulness has been limited, however, by poor sensitivity of standard ST-segment depression criteria for assessment of anatomic and functional coronary disease severity and for prediction of risk.1,2,4–6 Recent data make it clear that symptomatic obstructive plaques that typically result in exercise-mediated ischemia may be less relevant to infarction and sudden death than less obstructive unstable plaques.7 These limitations mandate a rethinking of the exercise ECG along 2 distinct lines: First, is it possible to improve the diagnostic value of the exercise ECG? Second, separate from its ability to diagnose obstructive coronary artery lesions, can the exercise test be used as a prognostic tool that can encourage effective prevention of premature deaths or coronary events? Both goals take us beyond the ST segment. Reversible ST-segment depression is the characteristic finding associated with exercise-induced, demand-driven ischemia in patients with significant coronary obstruction but no flow limitation at rest. This process differs from the flow-limited acute coronary syndromes because exercise-related ischemia is generally limited to the subendocardium and is proportional to increases in myocardial oxygen demand. Ventricular waveforms of the ECG can be related to the net uncanceled transmural gradients between endocardial and epicardial myocardium, as extrapolated from the work of Holland and Brooks, among others.8–10 Accordingly, isoelectric TQ and ST segments in normal and in nonischemic patients can be related to comparable resting membrane and action potential plateau voltages in endocardial and epicardial action potentials. During exercise, progressive ischemia results in changing endocardial action potentials during both diastole and systole. Less negative endocardial cell resting membrane potential leads to current flow across the ischemic boundary during diastole, leading to elevation of the TQ …

Does minimization of the QRS duration result in increased stroke volume during inter-ventricular timing optimization in cardiac resynchronization therapy?

Cardiac resynchronization therapy improves cardiac function by synchronizing ventricular contraction. Hemodynamic benefit is achieved by optimization of the atrioventricular (AV) delay via pulse-doppler echocardiographic (echo) assessment. Additional hemodynamic benefit may be achieved by optimization of the inter-ventricular (VV) pacing interval. Presently, optimization of the VV interval requires doppler echo evaluationof stroke volume (SV) atmultipleVVsettings using the velocity time integral (VTI) across the aortic valve. We investigated the hypothesized inverse relationship of QRS interval to SV to determine if QRS measurement could replace echo derived SV for V-V optimization. Method: Nineteen patients (pts) were evaluated at a visit 370days / 140 post-implantation of the bi-ventricular (BiV) pacemaker InSync III 8042 (Medtronic, Minneapolis). Following an echo guided AV optimization (transmitral flow), pts underwent simultaneous echo guided SV and QRS interval VV assessments. Both methods obtained measurements with the left ventricle (LV) paced 80, 40, 20, and 4ms prior to the right ventricle (RV) and the RV paced 20, 40 and 80ms before the LV. The SV was calculated by taking an average (Avg) of three VTI measurements from each device setting. The QRS durations were measured from a three lead electrocardiogram (ECG) signal through a 9790 Medtronic programmer, where four consecutive QRS intervals were measured on ECG Leads I, II, and III. The Avg SV at each VV setting was compared to the QRS durations of the Lead I Avg, Lead II Avg, Lead III Avg, Total Avg, Narrowest, and Widest QRS at the respective VV setting. Results: Accounting for multiple measures per patient, the relationship between SV and QRS width was examined. The Lead I Avg, Lead II Avg, Lead III Avg, Total Avg, Narrowest, and Widest were examined as explanatory variables for change in SV. No statistically significant relationship existed between any QRS width measurement and SV (all P 0.37). Conclusion: In these 19 pts there was no relationship between reduction in QRS duration and change in SV. Therefore, for the purposes of VV optimization, minimization of the QRS width does not result in increased SV. Passive Restraint Following Myocardial Infarction Modifies Left Ventricular and Myocyte Remodeling and Improves Isolated Myocyte Contractile Response Rupak Mukherjee, Emily S. Reese, Marlina M. Multani, William M. Yarbrough, KathrynB.Dowdy, JosephT.Mingoia, JenniferW.Hendrick,Robert E.Stroud,Amy E. Hardin, Julie E. McLean, Jennifer S. Leiser, Aaron S. Blom, James J. Pilla, John Affuso, Michael A. Acker, Francis G. Spinale1—Division of Cardiothoracic Surgery Research, Medical University of South Carolina, Charleston, SC; Departments of Surgery and Radiology, University of Pennsylvania, Philadelphia, PA

Acute effects of escalating doses of amiodarone in isolated guinea pig hearts.

Cardiac effects of escalating concentrations of amiodarone were determined on isolated perfused guinea pig hearts (Langendorff preparations). Spontaneously beating hearts were instrumented for the measurement of RR, PQ, QRS, QT and QTc durations (from a bipolar electrogram), and dP/dtmax and dP/dtmin from an isovolumetric left ventricular pressure curve. Ten hearts were exposed to escalating concentrations of amiodarone (10-7, 10-6, 10-5 and 10-4 M) in dimethyl sulfoxide (DMSO)/Krebs-Henseleit or to DMSO/Krebs-Henseleit (vehicle). Measurements were collected during the last minute of a 15-min concentration. Means of all parameters were compared by ANOVA with repeated measures design. When compared with vehicle, amiodarone prolonged QT and QTc durations at concentrations >10-6 M. The apparent lengthening of RR, PQ and QRS at concentrations >10-6 M did not achieve statistical significance. Similarly, the apparent decreases in dP/dtmax and dP/dtmin at concentrations >10-6 M did not achieve statistical significance. The putative therapeutic concentration of amiodarone is between 2 and 4 x 10-6 M. In this study, at a concentration of 10-6 M, only RR and dP/dtmin tended to change, but they were not different from vehicle. Thus, amiodarone in this preparation has little potential for cardiac toxicity at therapeutic concentrations.