Cardiac muscle injury in children and experimental animals. Reflections in ECG, especially high-resolution electrocardiography

Background and Methods: Signal-averaging ECG (SAECG), a bioelectrical processing method, is a further development of the conventional ECG. SAECG can detect voltage potentials in the microvolt range and provide a noise-reduced determination of QRS duration. Extended frequency spectra can be analysed. In adult patients after myocardial infarction it is used to predict the risk for arrhythmias and sudden cardiac death.

Results: High-frequency ECG components are not separate markers for myocardial ischaemia, but reflections of the original bioelectrical signal as demonstrated in a Langendorff model with ex vivo beating guinea-pig hearts. Increase in QT interval dispersion on conventional ECG in combination with loss of sinus rhythm were shown to be associated with sudden cardiac death in patients after Mustard or Senning operations for transposition of the great arteries. Measurements were based on manual setting of QT interval although it might be beneficial to use SAECG as a recording method.

SAECG with standard 12-lead configuration is similar in quality and quantity to conventional bipolar orthogonal setting. In newborn infants the most constant SAECG parameter is filtered QRS duration (QRSD). An upper limit of normality was determined to be 100 ms. Newborn infants with myocardial ischaemia demonstrate an increase in filtered QRSD and its variance. It was best recorded in standard 12-lead configuration and in individual leads.

Children and adolescents after cardiac transplantation showing rejection with myocytolysis in endomyocardial biopsy (EMB) specimens have an increase in filtered QRSD and its variance in 12-lead SAECG. Late potentials were found in all individual SAECG leads in patients with myocytolysis (100%), but less frequently in the vector magnitude, VM (43%). Serum levels of cardiac troponin T and creatine kinase MB as well as left ventricular performance and diastolic filling indices on echocardiogram were not conclusive in rejection diagnosis.

Conclusions: High-frequency ECG components are not pathological ischaemic markers per se. Increased QT dispersion and loss of sinus rhythm are risk factors for sudden cardiac death in patients operated upon with atrial switch techniques. Filtered QRSD and its variance are increased in newborns with myocardial ischaemia and in cardiac transplant patients with cellular rejection including myocytolysis. SAECG with 12-lead configuration may be an adjunctive method to endomyocardial biopsy in monitoring patients after cardiac transplantation.