Monophasic action potential oftheright atrium inparoxysmal atrial flutter andfibrillation

In7patients with paroxysmal atrialflutter, themonophasic action potential oftheright atrium was recorded, using a suction electrode catheter technique. Inall, 34arrhythmic episodes wererecorded andanalysed; each episode ofarrhythmia being initiated byapremature beat. Itwaspossible torecord only one or twoflutter wavesfollowing anatrial premature beat. Thewidevariation ofthevulnerable period andcritical modifications oftherefractoriness oftheatrial myocardium may explain theonsetandthecessation ofparoxysmal dysrhythmic episodes. Experimental studies (Hoffman etal., I959) have shownthatmonophasic action potentials recorded witha suction electrode fromisolated perfused rabbit hearts havethesameshape andduration as transmembrane action potentials obtained with intracellular microelectrodes. Itwasalsosuggested thatthestudy ofthemonophasic action potential fromintact humanheart mayprovide additional information abouttheelectrophysiological events during sinusrhythmandvarious arrhythmias (Olsson, I971,1972). Inaformer study (Gavrilescu andCotoi, 1972) it wasfound that monophasic action potential recordings during thetransition fromatrial flutter tosinus rhythm, whichfollowed DC shock, showed aprogressive prolongation oftheduration offlutter complexes. Whenacritical duration wasreached sinus rhythm occurred spontaneously. Thesedatawere interpreted astheexpression oftheprolongation of therefractory period oftheatrial muscle whichmay interrupt there-entry mechanism. Thepresent paper describes thedataobserved in 7patients withparoxysmal atrial flutter andfibrillation where 34episodes ofarrhythmia wererecorded, whereitwaspossible tostudy theonsetaswell as thespontaneous cessation of thearrhythmic episodes. Technique andsubjects