Pacing-Induced Changes in Stroke Volume in the Evaluation of Myocardial Function

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Abstract
For characterization of left ventricular function using changes in heart rate, we performed right atrial pacing in 16 patients during right and left heart catheterizations. Hemodynamic data was obtained before pacing (B), during pacing (D), and immediately after (A) the sudden interruption of pacing, for assessment of the consequences of rapid changes in stroke volume. In 10 patients with normal left ventricular function, as heart rate (HR) changed from 81 ± 4 sem (B) to 125 ± 6 (D) to 77 ± 5 beats/min (A), left ventricular end-diastolic pressure (LVEDP), from 8 ± 1 (B) to 3 ± 1 (D) to 9 ± 0.5 mm Hg (A), and stroke volume, from 74 ± 9 (B) to 46 ± 4 (D) to 77 ± 9 ml/beat (A), changed linearly. No change occurred in cardiac output (5.7 ± 0.5 liters/min) or in arterial pressure. In six patients with myocardial disease, HR changed similarly (from 86 ± 5 (B) to 126 ± 8 (D) to 90 ± 3 beats/min (A)), but LVEDP, cardiac output (CO), and stroke volume (SV) values were significantly different in comparison to the corresponding values for the subjects with normal function (LVEDP was 21 ± 3 (B), 8 ± 2 (D), and 25 ± 3 mm Hg (A), P = 0.001; CO was 4.1 ± 0.5 liters/min (B, D, and A), P = 0.01; SV was 48 ± 4 (B), 32 ± 5 (D), and 47 ± 4 ml/beat (A), P = 0.02). When pacing ventricular function curves were constructed relating left ventricular stroke work (SW) to LVEDP, normal patients exhibited a steep curve, while those with myopathies had flat responses. When the change (Δ) in SW was related to ΔLVEDP (ΔSW/ΔLVEDP), the value for normal subjects was 5.6 ± 1, and that for patients with myopathies, 0.6 ± .2 (P = 0.001). Atrial pacing may be used for characterization of left ventricular function, and permits a separation of normal and abnormal responses.