The relationship between ventricular arrhythmias and ischemia-induced conduction delay in closed-chest animals within 24 hours of myocardial infarction

Baseline Framingham risk score does not predict future ECG-derived QRS duration over an average of 3.3 years

Background

Prolonged electrocardiogram (ECG) QRS duration has been associated with increased cardiovascular risk. It is unclear whether the main predictor of cardiovascular risk, the Framingham risk score also predicts short-term changes in ECG QRS duration. Our aim is to determine whether baseline Framingham risk score is associated with baseline or changes in QRS duration.

Methods

A retrospective cross-sectional analysis was performed using observational data obtained from two hundred two participants. Framingham risk score was calculated using an online risk calculator. QRS duration was obtained using a 10 s trace from a Welch Allyn PC-based 12-lead ECG system.

Results

Average follow-up duration was 3.3 ± 1.1 years. Mean QRS change was 1.8 ± 11.4 ms. Specifically, among two hundred two participants, there are 104 subjects with a greater QRS duration at follow-up, while 98 subjects had the same or a shorter follow-up QRS duration. Baseline Framingham risk score did not significantly predict an increase in QRSd with an odds ratio of 1.04 (P = 0.230). Regression analysis of QRS duration at baseline and Framingham risk at baseline had a weak association (R2 = 0.020; P = 0.043). The Framingham risk score at follow-up was likewise has a weak association with follow-up QRS duration (R2 = 0.045; P = 0.002).

Conclusions

Our results do not demonstrate a statistically significant association between Framingham risk parameters and future QRS duration changes over longitudinal time. QRS duration had variable changes between baseline and follow-up. This might suggest that a longer period of follow-up is required to document more stable increases in QRS duration associated with ventricular pathology. A larger population study is needed to confirm our observations.

Local conduction during acute myocardial infarction in rats: Interplay between central sympathetic activation and endothelin

We investigated the effects of autonomic dysfunction and endothelin on local conduction and arrhythmogenesis during myocardial infarction. We recorded ventricular tachyarrhythmias, monophasic action potentials, and activation sequences in wild-type and ET_B-deficient rats displaying high endothelin levels. Central sympathetic inputs were examined after clonidine administration. Clonidine mitigated early and delayed arrhythmogenesis in ET_B-deficient and wild-type rats, respectively. The right ventricular activation delay increased in clonidine-treated ET_B-deficient rats and slightly decreased in wild-type rats. The left ventricular voltage rise decreased in all groups, whereas the activation delay increased mainly in clonidine-treated ET_B-deficient rats. Central sympathetic activation and endothelin modulate ischemia-induced arrhythmogenesis. Ischemia alters excitability, whereas endothelin impairs local conduction, an action partly counterbalanced by central sympathetic activity.

Non-dipolar content of the T-wave as a measure of repolarization inhomogeneity in ST-elevation myocardial infarction

The non-dipolar content of the T-wave, i.e. the component of the signal, which cannot be explained by a dipolar model, has been suggested as a measure of the local repolarization inhomogeneity. Our purpose was to study the non-dipolar content of the T-wave during the initial course of ST-elevation myocardial infarction (STEMI), when local repolarization inhomogeneity presumably is markedly increased. Twelve-lead ECG was semicontinuously collected in 211 patients with STEMI, treated with a thrombolytic agent. The T-wave was processed by principal component analysis. The absolute and relative T-wave residues were used as measures of the non-dipolar content. The median values for each hour and for the entire monitoring time were computed. Changes in the parameters were closer studied in two windows, 0-10 respectively, 11-24 h after start of ECG-monitoring. The median of the absolute T-wave residue during the entire monitoring period was 25 000 units in the STEMI-group and 13 500 units in the comparison group. The median for hour 1 was 36 500 units and 28 800 units for hour 2. The decrease was greater in patients with >or=50% resolution of the ST-elevation at 60 min. The moment of change, identified by cumulative sum-method, showed no correlation to the time for 50% ST-resolution. We conclude, that patients with thrombolysed STEMI have an increased non-dipolar content of the T-wave. Resolution of the ST-elevation is associated with a decrease. The increased non-dipolar content reflects a property of the repolarization phase, which is related to but separated from the ST-elevation.

Time course of spontaneous ventricular arrhythmias following acute coronary occlusion in the dog

In this study, the arrhythmias occurring in dogs between 4 and 15 hr after occlusion of the left anterior descending coronary artery were continuously monitored by recording the electrocardiogram from bipolar leads. At 4.5 hr the number of dogs with less than 50% of sinus beats had increased and at 5 hr 15 min sinus beats represented on average 80% of total heart beats. In the period up to 6 hr isolated ventricular beats and ventricular salvos were seen in 95% and 63% of the dogs respectively and at 7 hr there were, on average, 50% of sinus beats and monomorphic ventricular rhythm was observed in 58% of the dogs. From 7 hr half the dogs had over 50% of ventricular ectopic beats and by 9 hr ventricular rhythm disturbances were permanently present in all the dogs. The ventricular arrhythmias reached a peak at about 11-12 hr (mean % sinus beats less than 10) when all dogs had a predominantly monomorphic (42%) and/or polymorphic (63%) ventricular heart rhythm. The characteristic time course of these cardiac disturbances suggest that it may form the basis for an experimental model that may be useful in analyzing the effects of potential antiarrhythmic drugs.

Pacing-induced angina pectoris and induction of ventricular arrhythmias in coronary artery disease

Ischemia caused by rapid pacing during electrophysiologic study could facilitate induction of ventricular arrhythmias. The results of extrastimulation were retrospectively analyzed in 32 patients with coronary artery disease (CAD) without a history of symptomatic arrhythmia. These patients were studied at cardiac catheterization for angina pectoris refractory to medical therapy. Eleven patients (group I) had typical angina during trains of rapid right ventricular pacing (repeated trains of 8 stimuli [mean cycle length (CL) 473 +/- 47 ms]) but were asymptomatic during slower trains (CL 800 +/- 100 ms). Twenty-one patients (group II) had no symptoms with either rapid (CL 448 +/- 51 ms) or slow (CL 688 +/- 105 ms) trains, despite comparable left ventricular function, CAD severity and medication. Effective refractory periods (S1S2) after rapid drive were shorter in group I than in group II patients (225 +/- 9 vs 240 +/- 14 ms, p less than 0.002), but refractory periods during slow pacing were similar (251 +/- 12 vs 253 +/- 17 ms, difference not significant). No patient in either group had sustained arrhythmia (more than 15 beats) induced by single and double ventricular extrastimuli, decrementally applied at the right ventricular apex. The number of extra beats provoked in group I when rapid trains caused angina (4.3 +/- 3.6) was similar to that induced by extra-stimulation after slower pacing without angina (4.4 +/- 3.5) and to that obtained with rapid or slow pacing in group II (3.1 +/- 3.3 and 2.8 +/- 2.2).(ABSTRACT TRUNCATED AT 250 WORDS)