High-resolution and signal-averaged electrocardiography to separate post-myocardial infarction patients with and without ventricular tachycardia.

High-resolution and signal-averaged ECG, 24 h Holter recording and ejection fraction were used to separate post-myocardial infarction patients with and without ventricular tachycardia (VT) among 150 individuals: 26 patients with an old myocardial infarction and documented sustained VT, 104 patients with an acute myocardial infarction without sustained VT, who were followed-up for 2 years, and 20 healthy volunteers. Bipolar orthogonal XYZ leads were recorded, high-pass filtered at cut-off frequencies of 25, 40, 60, 80 and 100 Hz, and combined to vector magnitude square root of X2 + Y2 + Z2. The filtered QRS duration, the root-mean-square voltages of different time intervals and the durations of low amplitude signals under different thresholds, both from the initial and terminal QRS, were calculated. The sensitivity and specificity of each parameter alone and in every combination of two, three and four parameters (17 million different combinations) were computed both from non-averaged and averaged data. The best separation was achieved by 12 combinations all including four signal-averaged ECG parameters, with a sensitivity of 81% and a specificity of 79%. The parameters represented most were: filtered QRS duration at 25 Hz, RMS voltage of the last 50 ms at 25 Hz, terminal LAS duration at 80 Hz, and RMS voltage of the last 20 ms at 80 Hz. Parameters of the initial QRS complex did not improve either the sensitivity or the specificity of the method. In logistic regression analysis, the best combinations of four signal-averaged ECG parameters separated VT patients better (P < 0.001) than non-sustained ventricular tachycardia at Holter (P = 0.001); left ventricular ejection fraction (P = 0.01); or age (P = 0.006). Parameters calculated from averaged data gave better results than parameters calculated from non-averaged data.

Magnetocardiography: supraventricular arrhythmias and preexcitation syndromes.

Magnetocardiography is an elegant non-invasive method with which to study the electrical activity of the heart. The localization of cardiac electric sources, such as arrhythmia foci, would, in particular, be an interesting clinical application. In addition the detection of different abnormalities that could lead to cardiac depolarization and repolarization gives insight into how cardiac arrhythmias and arrhythmia mechanisms are generated. We have studied patients with supraventricular arrhythmias, especially those suffering from the Wolff-Parkinson-White (WPW) syndrome. Magnetocardiographic localization of the preexcitation site was performed in 26 WPW patients, with an average accuracy of 2 +/- 1 cm in comparison to the results obtained by invasive catheter mapping. By inspection of spatial isofield maps during atrial depolarization, the risk of atrial fibrillation was classified correctly in 11/20 (55%) patients with documented atrial fibrillation, and in 4/6 (67%) patients without atrial fibrillation. In a case of focal atrial tachycardia, magnetocardiographic localization of the origin of the arrhythmia was performed during tachycardia. In addition, the level of conduction block was successfully determined in six patients with third-degree congenital atrioventricular block.

Identification of patients with ventricular tachycardia after myocardial infarction by high-resolution magnetocardiography and electrocardiography.

The value of time domain analysis of late fields in the high-resolution magnetocardiogram in the identification of myocardial infarction patients with ventricular tachycardia was investigated in 30 subjects: 10 patients with documented sustained ventricular tachycardia and old myocardial infarction, 10 patients with old myocardial infarction without complex ventricular arrhythmias, and 10 normal volunteers. The duration of the QRS complex in the magnetocardiogram was significantly longer in ventricular tachycardia patients compared to myocardial infarction patients (144 (SD, 33) vs 109 (SD, 8) ms; p = 0.004). The root-mean-square field of the last 60 ms of the QRS complex was smaller in ventricular tachycardia patients than in myocardial infarction patients (830 (SD, 650) vs 1,480 (SD, 730) fT, respectively; p = 0.047). Also, the duration of the low-amplitude signal less than 700 fT was longer in ventricular tachycardia patients than in myocardial infarction patients (47 (SD, 28) vs 28 (SD, 8) ms, respectively; p = 0.048). The sensitivity and specificity in identifying ventricular tachycardia patients were both 80%, and the positive and negative predictive values were 78% and 86%, respectively. High-resolution electrocardiography recorded during the same session performed slightly better: sensitivity 90%, specificity 90%, and positive and negative predictive values 90%. The signal-to-noise ratio of electrocardiogram was higher (approximately 2 x) than that of magnetocardiogram. It is concluded that the new magnetocardiographic technique seems helpful in screening patients at risk of ventricular arrhythmias after myocardial infarction. The results encourage further refinement of the technique and application in prospective studies.

The effects of thrombolytic therapy on the high-resolution electrocardiogram after myocardial infarction.

The effects of thrombolytic treatment was studied in 109 consecutive patients 9-11 days after their first acute myocardial infarction by high-resolution electrocardiography (ECG), 24 h Holter monitoring, exercise test and radionuclide ventriculography. Thirty-seven patients were treated with intravenous thrombolytic agents. Thrombolytic treatment was assessed by clinical criteria to be successful in 22 patients and probably successful in 12 patients. Thrombolysis failed in three patients and 72 patients did not receive thrombolytic treatment (control group). Measurements made on the high-resolution and filtered (60 Hz high-pass) vectormagnitude complex included the total duration, the duration of the potential less than 40 microV, the root mean square (RMS) voltage in 10 ms intervals over the first 50 ms and RMS voltage of the last 40, 50 and 60 ms. The filtered QRS duration was significantly shorter in reperfused patients compared with the control group (83 +/- 10 vs 89 +/- 12 ms; P = 0.017). In inferior infarcts (n = 57) the filtered QRS duration was 83 +/- 11 ms in reperfused and 89 +/- 10 ms in non-reperfused patients (P = 0.044), but in anterior infarcts (n = 52) there was no difference. The RMS voltage of the initial 50 ms of the QRS was higher in the reperfused than in non-reperfused anteroseptal infarcts (38 +/- 14 v 23 +/- 10 microV; P = 0.022). Patients successfully treated with thrombolytic agents within the first 2 h had higher RMS voltage of the terminal 40 ms of the QRS than patients treated within 2-4 h (38 +/- 17 vs 27 +/- 17 microV; P = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of accessory pathways in Wolff-Parkinson-White syndrome by high-resolution magnetocardiographic mapping.

Fifteen patients with Wolff-Parkinson-White syndrome were studied with standard 12-lead electrocardiogram, invasive electrophysiologic study, and high-resolution magnetocardiographic (MCG) mapping. In addition, intraoperative epicardial mapping was performed in seven surgically treated patients. The MCG characteristics of ventricular preexcitation for different locations of the atrioventricular accessory pathways were described in terms of morphology and field patterns. Three mathematical source models in semi-infinite conducting space were used for localization computations: the current dipole model, the truncated current multipole model and the magnetic dipole model. Finally, the localization results of MCG and invasive mappings and electrocardiograms were compared. The mean three-dimensional distance between the localization results obtained from MCG maps and electrophysiologic study was 3.9 cm for the magnetic dipole model, 4.8 cm for the truncated current multipole model, and 7.3 cm for the current dipole model. The corresponding distances in the seven intraoperatively mapped cases were 2.3 cm for the magnetic dipole model, 5.2 cm for the truncated current multipole model, and 6.3 cm for the current dipole model. In conclusion, noninvasive MCG mapping may significantly contribute to the invasive catheter mapping for optimal preoperative localization of preexcitation site and atrioventricular accessory pathways in Wolff-Parkinson-White syndrome.

Magnetocardiographic functional localization using current multipole models.

High-resolution magnetocardiographic mapping was applied to localize the ventricular preexcitation site in ten patients suffering form Wolff-Parkinson-White syndrome. Three different source models were tested, consisting of the dipole and quadrupole moments in a general multipole expansion. Noninvasive localizations were performed by computations based on measured magnetic maps without a priori assumptions of the source location and without imposing any constraints. In all cases, the computed results were compared with invasive localization results obtained by catheter mapping technique. Preoperative catheterization localizes the atrial end of the accessory pathway, while our method localizes the ventricular preexcitation site. Of the models used, the average three-dimensional difference between the invasive localization results and the HR-MCG results was smallest 2.9 cm for the source model consisting of the magnetic dipole. The preexcitation site was very deep in all cases. The current dipole alone was inaccurate in estimating the source depth, but inclusion of the quadrupole moments improved the results. Two of the patients underwent surgery to interrupt the accessory pathway, which provided further validation for the noninvasive localizations.

Late cardiac effects of mediastinal radiotherapy in patients with Hodgkin's disease.

Twenty-eight patients younger than age 40 years, treated for Hodgkin's disease with mediastinal irradiation, were examined no less than 5 years after the irradiation in order to evaluate the frequency of cardiac abnormalities. Twelve patients (43%) had had some pericardial event after radiation: a diagnosed pericarditis, remarkably increased heart volume, or a conspicuous change of cardiac silhouette, suggesting pericardial fluid. On evaluation, 50% of the patients complained of symptoms, and 13 patients had to stop the exercise test on a low level because of chest pain, dyspnea, or general fatigue. In 13 patients some of the following abnormalities in the electrocardiogram (ECG) was found: right bundle branch block (four), first-degree atrioventricular block (four), abnormal P terminal force (five), or a low voltage (two). In ten patients (38%) an increase of the pericardial fluid was seen in the echocardiogram, and in nine patients the right ventricle wall thickness had increased. In two patients a severe coronary artery disease was found. One died suddenly after an acute myocardial infarction (AMI), and the other had a large anterior AMI. Two patients with chronic pericardial fluid underwent partial pericardectomy. Two cases of mild pulmonary valve stenosis, one pulmonary subvalvular stenosis and two aortic valve deformities were discovered. Eight patients went through cardiac catheterization, and in all but one case the pressures were slightly elevated suggesting diminished diastolic compliance. In summary, 19 of 28 patients had some abnormal cardiac findings, but only three of them were serious ones.

The mortality and case fatality rates in acute myocardial infarction in Finland. The results of Helsinki Coronary Register during 1970-1977.

In 1970 the Helsinki Coronary Register gathered data on 1191 AMI cases and 470 deaths from AMI of Helsinki residents under 65 years of age. Since then the mortality (deaths within the first 28 days per 1000 habitants of Helsinki) from AMI declined by 1.8% a year during the period 1970-1977, and there were no statistically significant differences in trends between women and men, or between different age groups (P greater than 0.10). The case fatality rate varied from 39% in 1970 to 35% in 1977, and the statistical analysis could not reveal any significant permanent decreasing trend in any age or sex group. These results, together with our previously reported AMI incidence trends, show that at least in 1970-1977 the declining trend in mortality from AMI was due to an equal fall in the incidence of AMI. Therefore there is reason to think that the effect is due to the prevention of AMI, rather than to more effective acute care.

On the accuracy of source localisation in cardiac measurements.

This paper describes a localisation study of the sources of bioelectrical activity in the human heart. In particular, the atrial activation (P wave) and the activation of an extra pre-excitation area in the WPW syndrome are investigated. Different models based on the current multipole expansion are used to calculate the inverse solution. A comparison between calculated results, invasive electrophysiological studies and known physiological data is performed. The best results were obtained by the current multipole model with dipole and quadrupole terms. Non-invasive localisation of cardiac electric sources can be useful in studies of arrhythmia patients in the future.

Stress, coronary disease, and coronary death.

Evidence of a positive association between cardiovascular illness and psychological stress presented in the literature is generally not totally convincing, which in part is due to methodological problems in defining and measuring psychophysiological and psychosocial variables. However, both reports in the literature and the clinical experience of most physicians present numerous examples of sudden, unexpected cardiac death, in which the event in all probability has been either induced or hastened by stressful life experiences. This applies to fatal and non fatal cardiac attacks, since both are often preceded by emotional stress. There is pathoanatomical evidence of specific myocardial damage induced by catecholamine release during stressful emotions. Histochemical studies have revealed copious amounts of noradrenaline stored in myocardium especially in patients with ischaemic heart disease. Epidemiological surveys on the relationships between life-stress and coronary mortality and morbidity have demonstrated certain positive associations in many cross-sectional studies as well as in certain prospective studies. Most positive evidence has been accumulated from studies on the influence of loneliness on cardiovascular morbidity and mortality. Animal experiments have demonstrated repeatedly that psychological stress evoked by aversive sensoric stimuli or unsuccessful social striving induce cardiovascular pathology including myocardial damage, hypertension, vascular changes and increased risk of sudden cardiac death.

Usefulness of QTc interval on the discharge electrocardiogram for predicting survival after acute myocardial infarction.

The corrected QT (QTc) interval was measured on the discharge electrocardiogram of 457 consecutive patients who had survived the first 28 days after a first acute myocardial infarction (AMI). The patients were followed for 4 years. The QTc interval was not related to long-term survival after the acute phase of AMI. Sixteen percent of the patients had a QTc interval above the normal upper limit of 440 ms. Of them, 71% survived 4 years and 77% with a shorter QTc interval survived (p = 0.31). When mortality per 100 patient-years was calculated for different QTc intervals, with 10 ms accuracy, no consistent relation between the 2 variables was seen. Results that indicate a strong relation between QTc-interval prolongation and sudden death after AMI should be reevaluated. The QTc interval is not a useful prognostic tool after AMI.

The declining trend in the incidence of acute myocardial infarction in Finland. The results of Helsinki Coronary Register during 1970-1977.

The results from Helsinki Coronary Register during the period 1970-1977 show that the incidence of acute myocardial infarction (AMI) among people under 65 years of age reached its peak in 1972 and declined annually by 2.8% from 1972 to 1977. The trend was clearest in patients under 50 years, but statistical analysis showed that no 5-year age group, either in women or men, differed statistically significantly from the general declining trend.