Abstract
Background: An abnormal spatial QRS-T angle (QRSTA) has a larger hazard ratio for fatal cardiac events than established cardiovascular and ECG risk factors. The spatial angle between the QRS and T axes is the angle between the directions of ventricular depolarization and repolarization. Purpose: Our hypothesis was that in the presence of an increased heart rate (HR), the QRSTA is a more sensitive marker of myocardial ischemia than ST-segment deviation during continuous monitoring in patients with left ventricular failure. Methods: Twenty-four-hour Holter studies (Mortara, Milwaukee, WI) with narrow QRS complexes (b120 milliseconds) were evaluated for HR events. An ischemic period was defined as an episode of tachycardia (≥100 beats/ min) with an accompanying HR increase of 25 beats/min or greater for more than 20 minutes. Measurements of the QRSTA were calculated from the 12-lead electrocardiogram using the QRS/Tsimple formula. The delta from pre-HR event vs HR event for both QRSTA and max ST-segment deviation (mV) was evaluated. Results: Seventy HR events were identified during 62 Holter studies. Average differences between ischemic events (n = 36, or 51%) vs nonischemic HR events (n = 34, or 49%) was 52 ± 15 vs 27 ± 7 beats/min for HR, 28° ± 25° vs 24° ± 24° for QRSTA, and 43 ± 30 vs 30 ± 26mV for ST deviation, respectively. The sensitivity and specificity for detecting ischemia by QRSTA and ST deviation based on certain cut points are illustrated in the table below. Conclusions: In patients with left ventricular, the traditional standard STsegment deviation (100 mV) is not sensitive enough to detect ischemia; an approach that uses a combination of QRSTA changes (20°) and lowthreshold ST deviation (50 mV) during tachycardia is more accurate to detect ischemia.
Published Version
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