Abstract 14010: ST Segment Shortening Without QT Interval Shortening is a Unique and Novel Marker of Asymmetric Cardiac Sympathetic Activation
Introduction: Sympathetic nerve stimulation results in intra-myocardial norepinephrine release with subsequent myocyte action potential duration (APD) shortening. Heterogeneity in this response (as seen in conditions causing myocardial scarring) increases arrhythmogenicity of the ventricular myocardium. A surface electrocardiographic (ECG) marker of heterogeneity in functional response to sympathetic stimulation is lacking. The purpose of this study was to identify novel surface ECG markers of asymmetric cardiac sympathetic stimulation.
Methods: Yorkshire pigs (n= 8) underwent thoracotomy to expose the heart, left and right stellate ganglia (LSG and RSG respectively). ECG leads were placed on the posterior thorax to mirror typical anterior positions, and recorded continuously. Intra-myocardial norepinephrine (NE) was sampled by microdialysis, and a multipolar electrode catheter was placed on the anterior epicardial surface to measure activation recovery intervals (ARIs), a measure of APD. LSG or RSG stimulation was performed at 10V, using repeated square wave pulses (5ms) delivered at 5 Hz. ECG parameters of myocardial repolarization were measured in the standard fashion, along with myocardial NE levels and ARIs before and during LSG or RSG stimulation.
Results: LSG or RSG stimulation resulted in significant ST-segment shortening (308±10ms to 121±18ms, p<0.0001 and 286±23ms to 109±6ms p=0.0001, respectively) without significant shortening of the corrected QT interval (QTc) (564±16 to 584±16 p=NS and 534±19ms to 489±21 p=NS, respectively). An increase in the T-wave duration was observed with LSG and RSG stimulation (109±15ms to 321±30ms p<0.0001 and 120±9ms to 160±15ms p=0.019, respectively). LSG stimulation resulted in a 4.2-fold increase in myocardial NE levels (p=0.03), while RSG stimulation resulted in a 50% increase (p=NS). ARI was shortened by 18.4±5% (p=0.028) during LSG stimulation and by 39.7±8.6% (p=0.026) for RSG.
Conclusion: To our knowledge, this is the first description of ST segment shortening without concomitant QTc interval shortening. This finding may be a unique marker of asymmetric cardiac sympathetic activation, and is likely due to increased myocardial NE release, and subsequent myocyte APD shortening.
- © 2011 by American Heart Association, Inc.