QRS amplitudes, QTc intervals and ECG abnormalities in pheochromocytoma patients before, during and after treatment.

QRS amplitudes (S1 + R5), Minnesota Code ECG abnormalities and QTc intervals were analyzed in ECGs from 31 pheochromocytoma patients on admission to hospital, after 17 +/- 7.2 (SD) days of preoperative phenoxybenzamine therapy in a dosage of 148 +/- 45.0 (SD) mg/day and after a mean postoperative follow-up of 6 years. QRS voltage decreased significantly from 3.37 +/- 1.48 on admission, to 2.26 +/- 0.69 mV at postoperative follow-up (p less than 0.001). The prevalence of total Minnesota Code changes increased or was unchanged on the different occasions. Severe to moderate changes, however, became less prevalent, while mild changes increased. The QTc interval was 0.44 +/- 0.04 s on admission and 0.41 +/- 0.02 s at follow-up (p less than 0.01). No significant differences were observed during treatment with phenoxybenzamine. Pathological ECGs are common findings in patients with pheochromocytoma and significant improvements occur after surgery. Significant effects of phenoxybenzamine therapy were only found in patients with sustained hypertension.