Changes in the slope of the first major deflection of the ECG complex during acute coronary occlusion

Comparison of electrocardiographic characteristics of adults and children for automated external defibrillator algorithms

Accurate rhythm identification is vital for appropriate shock delivery during pediatric resuscitation with an automated external defibrillator. Currently, extensive testing of pediatric algorithms is recommended. The aims of our study were to determine age-related differences in electrocardiographic (ECG) tracings in children and adults and to determine if differences warrant evaluating each algorithm against pediatric rhythms. We hypothesized that the ECG characteristics of heart rate, amplitude, and conduction velocity differ between children younger than 8 years and adults. We evaluated 442 separate ECG tracings from 199 pediatric patients and 839 samples from 170 adults to measure differences in the 3 variables. Rhythms chosen were normal sinus rhythm (NSR), supraventricular tachycardia (SVT), and ventricular tachycardia (VT). Significant differences were found between heart rates of children and adults with NSR and SVT but not VT. There were significant differences between adult and pediatric signal amplitudes in both NSR and SVT but no difference in signal amplitude of VT. When NSR between adults and children was compared, adults proved to have a faster conduction velocity. There was no difference in conduction velocity of SVT or VT between children and adults. We conclude that common rhythms in pediatric patients have differing characteristics, which may affect the accuracy of an automated external defibrillator algorithm, and that specific testing with tracings obtained from children is warranted.

"ECG variability contour" method reveals amplitude changes in both ischemic patients and normal subjects during Dipyridamole stress: a preliminary report

To detect and quantify consistent ECG amplitude changes, the "ECG variability contour" (EVC) method was proposed. Using this method we investigated amplitude changes in subjects undergoing myocardial perfusion imaging (MPI) with Dipyridamole (Dp). Fifty-three patients having reversible perfusion defects and 19 normal subjects (NS) who were free of: perfusion defects on their MPI, standard ST-T changes during Dp stress, and a negative clinical follow up. Mean ∏¹(<∏¹>) was similar for the NS and patient group (6.2 ± 6.1 vs. 6.3 ± 6.2, P = 0.95). <∏¹> was 4.6 ± 3.0 in patients not having ST-T changes during Dp stress (n = 42), whereas in patients having ST-T changes (n = 11) it was 13.1 ± 10.2 (P < 0.001). For both groups <∏(QRS)> was smaller than <∏(ST)>, which in turn was smaller than <∏(T)>. The values of <∏(QRS)>, <∏(ST)>, and <∏(T)> for the NS, patients without and with ST-T changes were: 26.8 ± 28.6, 42.6 ± 41.8, 44.9 ± 36.5; 19.6 ± 20.8, 26.4 ± 31.4, 38.7 ± 27.3; 51.0 ± 30.0, 71.0 ± 36.8, 75.1 ± 20.9, respectively (P < 0.05 for all comparisons of patients with versus without ST-T changes). This study showed that Dp stress, with or without hypoperfusion, had a clear effect on myocyte electrophysiology, expressed by consistent ECG amplitude changes, detected by the EVC method. The EVC method did not distinguish between NS and patients in this clinical setting.

Changes in the initial slope of the QRS in ischemic patients and normal subjects undergoing scintigraphy with dipyridamole

The effect of dipyridamole (Dp) on the linear portion of the first major deflection of the QRS in human electrocardiograms (which we refer to as Fslope) was investigated in the context of myocardial perfusion imaging (MPI), in normal subjects (NS, n=19) and in patients with cardiovascular ischemia (as manifested by a positive MPI scan, n=53). In the majority of participants, Fslope decreased (84% of 19 NS and 77% of 53 patients, p=0.69). The decrease in Fslope was more pronounced in patients with ST-T deviation as compared to those without (32.6±24.5 vs. 22.4±23.1, p=0.24), and in patients vs. NS (24.9±23.5 vs. 19.6±23.4, p=0.44). A change in Fslope is a sensitive (but not specific) measure for detecting the effect of Dp on the myocardium in the setting of scintigraphy.

Discrimination between demand and supply ischemia episodes in Holter recordings

ST segment changes provide a sensitive marker in the diagnosis of myocardial ischemia in Holter recordings. However not only the mechanisms of ischemia result in ST segment deviation but also heart rate related events. The very similar signature of ST modifications in ischemia and heart rate related events have driven us to look for other ECG indexes allowing to discriminate between them. Heart rate-based indexes, correlation between the absolute ST segment deviation and heart rate series, the interval between T apex and T end and changes in the upward/downward slopes of the QRS complex have been shown as significant discriminant parameters, getting a sensitivity for the ischemic events SE = 82.2%, specificity SP = 88.4%, positive predictivity value + PV = 87.6% and negative predictivity value - PV = 83.2% in ST events of the Long Term ST database.