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Sudden death and arterial embolism are unpredictable hazards of quinidine therapy for atrial fibrillation that act as deterrents to its most effective use. In this paper an attempt is made to determine the incidence of these accidents as reported in the literature. The mechanism of sudden death is also examined. The difficulty of determining the role of quinidine in producing these accidents in seriously ill patients is clarified.

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tances in potassium iodate and iodine pentafluoride are assumed to be even approximately correct then it would seem evident that two cases must be distinguished. If a vacant orbital exists in the coordination polyhedron, the unshared pair may occupy that orbital and its effect on the iodine radius will be small and may be correlated with the formal charge on the central atom. If no such vacant orbital exists, then the extra electrons become an "inert pair'' having no steric effect, but causing a relatively large increase in the iodine radius.The Structure.-The coordination of oxygen and fluorine atoms about potassium is irregular but it is probable that the packing of the IO2F2groups is the determining factor in the structure.The K-0 and K-F contacts are: O1 -K = 2.75, 2.76A.; 011-K = 2.63, 3.03 A.; FI-K = 2.64, 3.06 A. ; F I I -K = 2.74, 3.04 A.The interatomic distances which are less than 3.50 A. between oxygen and fluorine atoms of different anion groups are: F I -F I I = 2.77, 3.23 A.;There are, in addition, two distances between iodine atoms and oxygen atoms in different I02F2groups that are shorter than three Angstroms : 1-01 = 2.82 A.; 1-011 = 2.88 A.The similarity between this structure and that reported for potassium iodate may be seen if one considers an altered KI02F2 in which the 1-0 contacts just mentioned are made real bonds so that each oxygen atom is shared between two iodine atoms. If, then, the iodine atoms and bonds to oxygen atoms are placed in the x-z plane, then FI -011 = 3.40 A. ; F I I -0 1 = 3.24 A. this plane will be identical with a plane z = 0 for the potassium iodate structure. In this altered structure the I-F bonds will be in a vertical position along the lines x = z = 0, etc. If now one atom of oxygen is substituted for two atoms of fluorine and this atom shared between two iodine atoms the structure would become the cubic structure attributed to potassium iodate. It is suggested that the similarity, although not very great, is sufficient to cause the orientation effects observed on photographs of KI02F2 in which some of the salt had hydrolyzed. The powder lines had quite definite maxima a t positions corresponding to the equator and layer lines for potassium iodate oriented with the cube edges parallel to the orthorhombic axes of KI02F2. SummaryFrom a determination of the crystal structure of KI02F2 it has been found that the I02F2group is composed of an iodine atom forming bonds a t approximately 100' with two oxygen atoms, and perpendicular to the plane of these three atoms, two opposed bonds at 180' to fluorine. The configuration may perhaps best be thought of as that of a trigonal bipyramid in which one of the three equivalent orbitals is occupied by an unshared electron pair. The interatomic distances in the ion were found to be: I -0 = 1.93 * 0.05 A.; I -F = 2.00 A. * 0.05 h. The 0-1-0 bond angle = 100 * 10'. The influence of the unshared pair on the bond distance is discussed.Previous of this series have described the redistribution reaction for the interchange of alkyl rad...