[' ', 'Fl', 'PACING-INDUCED', 'TACHYCARDIA', 'of', 'being', 'a', 'parameter', 'measured', 'directly', 'from', 'isovolumic', 'pressure', 'and', 'dP/dt', 'without', 'extrap-', 'olation.', 'Other', 'reports', 'have', 'likewise', 'cited', 'a', 'good', 'correlation', 'between', 'these', 'two', 'indices?', '12', 'The', 'peak', 'rate', 'of', 'rise', 'of', 'left', 'ventricular', 'pressure', 'has', 'been', 'widely', 'used', 'as', 'an', 'index', 'of', 'left', 'ventricular', 'contractility.?"', 'However,', 'the', 'influence', 'of', 'preload', 'and', 'afterload', 'on', 'peak', 'dP/dt', 'limits', 'its', 'application', 'in', 'many', 'circum-', 'stances.', 'In', 'this', 'study', 'changes', 'in', 'peak', 'dP/dt', 'parallel', 'changes', 'in', 'Vinaz', 'and', 'max', 'Veg', 'in', 'some', 'instances', 'but', 'not', 'in', 'others.', 'As', 'outlined', 'in', 'table', '2,', 'following', 'the', 'onset', 'of', 'myocardial', 'ischemia', 'peak', 'left', 'ventricular', 'dP/dt', 'increased', 'in', 'six', 'of', 'eight', 'patients', 'and', 'decreased', 'in', 'only', 'two.', 'These', 'changes', 'in', 'peak', 'dP/dt', 'occurred', 'in', 'the', 'face', 'of', 'decreasing', 'ventricular', 'contractility', 'as', 'reflected', 'by', 'decreases', 'in', 'Va..', 'and', 'max', 'Ver', 'in', 'all', 'elght', 'patients.', 'This', 'apparent', 'discrepancy', 'can', 'be', 'largely', 'explained', 'by', 'changes', 'in', 'ventricular', 'loading', 'conditions', 'coincident', 'with', 'the', 'onset', 'of', 'myocardial', 'ischemia.', 'Six', 'of', 'eight', 'patients', 'had', 'increases', 'of', 'LVEDP', 'at', 'the', 'onset', 'of', 'myocardial', 'ischemia,', 'and', 'seven', 'of', 'eight', 'patients', 'developed', 'an', 'increase', 'in', 'aortic', 'diastolic', 'pressure.', 'These', 'increases', 'in', 'preload', 'and', 'afterload', 'could', 'be', 'responsible', 'for', 'an', 'increase', 'in', 'left', 'ventricular', 'peak', 'dP/dt', 'and', 'overshadow', 'o', 'concomitant', 'decrease', 'in', 'the', 'contractile', 'state', 'of', 'the', 'left', 'ventricle.', 'The', 'experimental', 'data', 'of', 'the', 'patient', 'presented', 'in', 'gure', '3', 'clearly', 'illustrates', 'these', 'points.', '-', 'Correlation', 'between', 'Vaz,', 'and', 'other', 'indices', 'of', 'ventricular', 'performance', 'has', 'been', 'reported', 'previouly2-"', 'in', 'this', 'study', 'a', 'highly', 'signifi.', 'cant', 'difference', 'was', 'noted', 'between', 'Van', 'values', 'of', 'patients', 'with', 'normal', 'ejection', 'frac-', 'tions', 'and', 'Vu.', 'values', 'of', 'patients', 'with', 'low', 'ejection', 'fractions.', 'The', 'three', 'patients', 'with', 'low', 'ejection', 'fractions', 'had', 'low', 'Va,', 'values', 'throughout', 'the', 'entire', 'range', 'of', 'heart', 'rates', 'observed.', 'Ves.', 'varied', 'only', 'slightly', 'with', 'changes', 'in', 'heart', 'rate', 'or', 'with', 'the', 'onset', 'of', 'myocardial', 'ischemia', 'in', 'these', 'patients.', 'Neither', 'Vaux', 'nor', 'ejection', 'fraction', 'can', 'be', 'regarded', 'as', 'a', 'specific', 'and', 'sensitive', 'indicator', 'nf', 'ventricular', 'contractility', 'uniter', 'all', 'candi.', 'dons,', 'This', 'may', 'explain', 'the', 'absence', 'of', 'a', 'good', 'Corcnlois.', 'Volume', 'XLVI,', 'Jaly', '1972', 'HKEO1S7109', '81', 'correlation', 'behween', 'these', 'fwo', 'parameters', 'in', 'the', 'group', '2f', '15', 'patients', 'with', 'normal', 'ejection', 'fractions.', 'Several', 'of', 'the', 'patients', 'in', 'this', 'series', 'had', 'localized', 'abnormalities', 'of', 'left', 'ventricular', 'wall', 'motion', 'which', 'may', 'have', 'influenced', 'the', 'shape', 'of', 'the', 'pressure-velocity', 'curves,', 'although', 'recent', 'evidence', 'suggests', 'that', 'Vis', 'is', 'not', 'influenced', 'by', 'such', 'kinetic', 'abnormalities.*=', '25', 'Changes', 'in', 'a', 'number', 'of', 'other', 'factors,', 'such', 'as', 'the', 'series-elastic', 'properties', 'of', 'the', 'myocar-', 'dium,', 'or', 'course', 'of', 'the', 'active', 'state,', 'could', 'theoretically', 'influence', 'pressure-velocity', '_in-', 'dices', 'independent', 'of', 'changes', 'in', 'contractility.', 'We', 'were', 'unable', 'to', 'show', 'a', 'significant', 'difference', 'between', 'mean', 'Ves,', 'valves', 'of', 'patients', 'with', 'normal', 'coronary', 'arteriograms,', 'nonischemic', 'responders', 'with', 'coronary', 'athero-', 'sclerosis,', 'and', 'ischemic', 'responders', 'with', 'coro-', 'nary', 'atherosclerosis,', 'elther', 'at', 'contro)', 'heart', 'rates', 'or', 'during', 'pacing-induced', 'tachycardia', 'prior', 'to', 'the', 'onset', 'of', 'myocardial', 'ischemia.', 'However,', 'changes', 'in', 'hemedynamic', 'parame-', 'ters', 'and', 'Vi,', 'at', 'the', 'onset', 'of', 'myocardial', 'ischemia', 'in', 'the', 'group', 'of', 'ischemic', 'responders', 'clearly', 'separated', 'these', 'patients', 'from', 'the', 'other', 'two', 'groups.', 'The', 'majority', 'of', 'patients', 'with', 'coronary', 'atherosclerosis', 'had', 'noxmal', 'ejection', 'fractions,', 'and', 'overall', 'ventriculax', 'contractility', 'in', 'these', 'patients', 'was', 'judged', 'to', 'be', 'gond', 'by', 'angiographic', 'methods.', 'It', 'is', 'therefore', 'not', 'entirely', 'surprising', 'that', 'no', 'significant', 'differ-', 'ence', 'in', 'Vas,', 'could', 'be', 'demonstrated', 'between', 'these', 'three', 'groups', 'of', 'patients', 'prior', 'to', 'the', 'onset', 'of', 'myocardial', 'ischemia.', 'A', 'number', 'of', 'assumptions', 'are', 'made', 'in', 'the', 'application', 'of', 'farce-velocity', 'principles', 'to', 'cardiac', 'muscle,', 'either', 'in', 'the', 'isolated', 'muscle', 'preparation', 'or', 'in', 'the', 'intact', 'heart.®', 'Conse-', 'quently,', 'the', 'use', 'of', 'this', 'technic', 'to', 'evaluate', 'contractility.', 'has', 'been', 'criticized,', 'and', 'the', 'specificity', 'of', 'Vas.', 'has', 'been', 'questioned.?4', '25', 'Vou', 'derived', 'from', 'pressure-velocity', 'curves', 'constructed', 'using', 'total', 'pressure,', 'as', 'in', 'this', 'study,', 'has', 'been', 'shown', 'to', 'be-', 'independent', 'of', 'preload', 'in', 'some', 'studies,', 'while', 'other', 'investi-', 'gators', 'have', 'found', 'this', 'index', 'to', 'be', 'somewhat', 'dependent', 'on', 'preload.**', 'The', 'use', 'of', 'developed', 'wantgioglar', 'groseurc,', 'rather', 'than', 'total', 'pres-', 'sure,', 'in', 'the', 'construction', 'of', 'pressure-velocity', ' ', ' ']