Influence of acute variations in hematocrit on the QRS complex of the Frank electrocardiogram.

The influence of acute variations in hematocrit on the QRS complex of the Frank scalar electrocardiogram was studied in 31 patients with severe polycythemia secondary to cyanotic congenital heart disease and in eight patients with anemia due to thalassemia. Moderate reduction of the hematocrit in the polycythemic group resulted in a significant increase in the magnitude and a delay in both left maximal spatial voltage (LMSV) and maximal anterior force. Raising the hematocrit in the anemic group decreased the magnitude of LMSV and maximal anterior force. A change in the orientation of the spatial vector frequently accompanied induced variations in the hematocrit. Experimental and theoretical studies suggest that alterations in the hematocrit and, hence, intracardiac electrical resistivity distort the magnitude and orientation of the surface-recorded QRS voltages. It is postulated that the effect of high intracavitary blood hematocrit in polycythemia in reducing early QRS voltages is due to its influence on radial myocardial excitation propagated from endocardium to epicardium. Anemia, on the other hand, enhances the voltages due to radial spread of impulses in the myocardium, resulting in an increased magnitude of the LMSV and usually also of the maximal anterior force.