Sudden Cardiac Death (SCD) is the largest cause of natural deaths in the USA, accounting for over 300,000 deaths annually. The major reason for SCD is Ventricular Arrhythmia (VA). Therefore, there is need for exploration of approaches to predict increased risk for VA. Alternans of the T wave in the ECG (TWA) is widely investigated as a potential predictor of VA, however, clinical trials show that TWA has high negative predictive value but poor positive predictive value. A possible reason that TWA has a large number of false positives is that a pattern of alternans known as concordant alternans, may not be as arrhythmogenic as another pattern which is discordant alternans. Currently, it is not possible to discern the pattern of alternans using clinical ECGs. Prior studies from our group have showed that alternans of the maximum rate of depolarization of an action potential also can occur when Action Potential Duration (APD) alternans occurs and the relationship between these two has the potential to create spatial discord. These results suggest that exploration of the co-occurrence of depolarization and repolarization alternans has the potential to stratify the outcome of TWA tests. In order to investigate the link between depolarization alternans and changes in ECGs, we used a mathematical model created previously in our research group which simulated ECGs from the cellular level changes observed in our experimental studies. These results suggest that the changes in ECGs should appear as alternating pattern of the amplitude of the R wave. Because there are a variety of factors which may also cause the R wave amplitude to change, we used signal analysis and statistical modeling to determine the link between the observed changes in R wave amplitude and depolarization alternans. Results from ECGs recorded from patients show that amplitude of the R wave can change as predicted by our experimental results and mathematical model. Using TWA as the marker of repolarization alternans and R Wave Amplitude Alternans (RWAA) as the marker of depolarization alternans, we investigated the phase relation between depolarization and repolarization alternans in clinical grade ECG and observed that this relationship does change spontaneously, consistent with our prior results from animal studies. Results of the present study support further investigation of the use of RWAA as a complementary method to TWA to improve its positive predictive value.

Elektrokardiografi är en vanligt förekommande undersökning inom hälso- och sjukvården då undersökningen är icke-invasiv och ger en bra överblick över hjärtats elektrofysiologiska status. Ett vanligt fel vid EKG är elektrodplacering i andra respektive tredje intercostala utrymmet istället för i fjärde intercostala utrymmet (IC4), vilket bland annat kan medföra reducering av R-vågs amplituden samt påverka datortolkningen. Syftet med arbetet var att se om avvikande EKG-kurvor uppstår vid omplacering av elektroderna V1 och V2 i andra och tredje intercostala utrymmet vid jämförelse med fjärde intercostala utrymmet på friska vuxna. I studien ingår 50 deltagare i åldern 18-48. Den statistiska analysen utfördes med hjälp av parvis T-test samt Fisher exact test. Jämförelsen mellan de olika placeringarna resulterade i en signifikant minskning av R-vågsamplituden (p <0,001) för samtliga kombinationer. En signifikant minskning visades i R-vågsduration i jämförelsen Intercostalrum 2 (IC2) versus (vs) IC4 i V2. För ST-sträckan visade båda avledningarna för jämförelsen IC2 vs IC4 en signifikant skillnad (p<0,001). Datortolkningen visade en signifikant skillnad för IC2 vs IC4 (p0,006) samt IC3 vs IC4 (p<0,001).  Omplacering av elektroder medför förändrad datortolkning när det vid en standardplacering visar ett normalt EKG, vilket kan ge en inverkan på patientens fortsatta handläggning och eventuella diagnos. / Electrocardiography is commonly used in healthcare as the examination is non-invasive and provides a good overview of the heart's electrophysiological status. A common error in ECG positioning is placement in the second or third intercostal space, which among other things can lead to a reduction in R wave amplitude and affect the computer interpretation. The aim of the study is to see if deviant ECG curves occur when repositioning the electrodes V1 and V2 in the second and third intercostal space when compared to the fourth intercostal space. The study includes 50 healthy adults aged 18-48. The statistical analysis was performed using paired t tests and Fisher exact test. The comparison resulted in a significant reduction in R wave amplitude (p <0.001) for all combinations. A significant decrease was shown in R wave duration in the comparison of IC2 vs IC4 in V2. For the ST segment, both leads for the comparison IC4 vs IC2 a significant difference was presented (p <0.001). For the computer interpretation, a significant difference was shown for IC2 vs IC4 (p0.006) and IC3 vs IC4 (p<0.001). Repositioning of electrodes leads to a different computer interpretation when in standard positioning shows a normal ECG, which may lead to misdiagnosis.