誘発された左室流出路圧較差に対しIa群抗不整脈薬が効果を示した閉塞性肥大型心筋症の2例

Attenuation of Provoked Left Ventricular Pressure Gradient by Class Ia Antiarrhythmic Drugs in Two Patients with Hypertrophic Obstructive Cardiomyopathy

　症例は43歳と36歳の男性．主訴は労作時の失神およびめまい．心臓超音波検査などで閉塞性肥大型心筋症（HOCM）を疑い，心臓カテーテル検査を施行．左室流出路圧較差は安静時に両者とも30mmHg以下であったが，前者でisoproterenol点滴静注，後者では心房ペーシングによる心拍数の上昇に加え心室性期外収縮後の圧較差の観察を行ったところ，それぞれ最高132mmHg，155mmHgの圧較差を生じた．前者でdisopyramide，後者でcibenzolineを静注し，圧較差の消失をみた．以後，経口で前者はdisopyramideとpropranolol，後者はcibenzolineを投与し，それぞれ17ヵ月，7ヵ月の経過中失神の再発はなく症状は軽減している．HOCMで労作時に失神などの重篤な症状を認める場合，安静時圧較差が軽度であっても負荷による圧較差の増大の有無を確認する必要がある．その誘発された圧較差に対しては従来より用いられているIa群抗不整脈薬のdisopyramideと同様，cibenzolineも有効と考えられた．

　Two male patients, aged 43 and 36 respectively had suffered from syncope and dizziness on exertion. Under the diagnosis of hypertrophic obstructive cardiomyopathy (HOCM) by echocardiogram, a study of cardiac catheterization was made. Left ventricular pressure gradients at the base line state were less than 30 mmHg in both cases. After provocation with isoproterenol infusion, atrial pacing or post ventricular extrasystolic potentiation increased the maximum pressure gradient by more than 130 mmHg. The intravenous administration of disopyramide and cibenzoline in each patient respectively during catheterization abolished the provoked pressure gradient. Therefore, oral disopyramide combined with propranolol was given to the first patient and oral cibenzoline was given to the second patient. These treatments were effective and resulted in the improvement of clinical symptoms.

　In HOCM, some patients despite showing a mild pressure gradient at the baseline state show severe symptoms like syncope particularly on exertion. For such patients a provocative test to induce a ventricular pressure gradient across the outflow tract seems to be useful. Class Ia antiarrhythmic drugs including cibenzoline were effective in preventing syncope by the attenuation of the provoked outflow tract pressure gradient.