Letters to the Editor
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pectoris ausgelost durch vorhofstimulation, Z. Kardiol. 62:900, 1973. Costantin, L. R.: Extracardiac factors contributing to hypotension during coronary occlusion, Am. J. Cardiol. 11:205, 1963. Zelis, R., Caudill, C. C., Baggette, K., and Mason, D. T.: Reflex vasodilation induced by coronary angiography in human subjects, Circulation 63:490, 1976. Robinson, B. F., Collier, J., and Nachev, C.: Changes in peripheral venous compliance after myocardial infarction, Cardiovasc. Res. 6:67, 1972.
Spontaneous frequency
variability
in arrhythmia
To the Editor: Dr. Orr and co-workers, in their letter “Physiological sleep patterns and cardiac arrhythmias” (AM. HEART J. 97:128, January, 1979) conclude that such considerable spontaneous variability in arrhythmia frequency occurs from one monitoring period to another that the clinician must be cautious in interpreting the results of limited monitoring. We and our colleagues’ recently reported the results of extensive (three consecutive 24-hour) monitoring studies performed in 15 clinically stable patients with various cardiac disorders and frequent ventricular ectopy, and documented the extent of this variability. Using an analysis of variance we demonstrated that even in otherwise stable individual patients one may expect to see as much as 90 per cent change in mean hourly ectopic frequency from one 8-hour period to another, and more than 80 per cent change in frequency in comparing consecutive 24-hour periods. Thus, we concur in both our findings and conclusions. Eric L. Michelson, M.D. Hospital of the University of Pennsylvania Joel Morganroth, M.D. Lankenau Hospital Lancaster Ave. W. of City Line Philadelphia, Pa. 19151 REFERENCE 1.
Morganroth, Josephson, Limitations monitoring Circulation
J., Michelson, E. L., Horowitz, L. N., M. E., Pearlman, A. S., and Dunkman, W. B.: of routine long-term electrocardiographic to assess ventricular ectopic frequency, 58:408, 1978.
Carotid sinus hypersensitivity-asystole and hypotension in the same patient To the Editor: Carotid sinus hypersensitivity has been defined as cardiac asystole lasting at least three seconds, or a fall in blood pressure of 50 mm. Hg or more, in response to carotid sinus massage. Syncope may result from either mechanism, and both phenomena may be present in the same patient, although hypotension might be masked by precedent asystole. The patient described here illustrates this dual mechanism-the insertion of a cardiac demand pacemaker preventing asystole but not the hypotension induced by carotid sinus massage.
American Heart Journal
B. R. was an elderly man who fainted in an elevator, sustaining a fractured skull. Little was done diagnostically until a second episode of syncope prompted carotid sinus massage which resulted in prolonged cardiac asystole. A cardiac demand pacemaker was implanted and subsequent carotid sinus massage induced a fall in blood pressure from 170/80 mm. Hg to 80/50 mm. Hg associated with severe lightheadedness without cardiac asystole. This patient manifested both hypotension and cardiac asystole caused by carotid sinus hypersensitivity, hypotension becoming apparent only after pacemaker insertion prevented cardiac asystole. It follows that any patient with carotid sinus hypersensitivity who has a cardiac pacemaker implanted for asystole should have carotid sinus massage to ascertain blood pressure response, because subsequent syncope, lightheadedness, or weak spells may be due to hypotension rather than to pacemaker failure, thereby obviating empirical changing of the pacemaker. Herschel J. Sklaroff, M.D. Assistant Clinical Professor of Medicine Mount Sinai School of Medicine New York. N. Y. 10029
Nitroglycerin and blood oxygen curve of normal subjects
dissociation
To the Editor: Several drugs induce a shift of the oxyhemoglobin dissociation curve (ODC). The action of nitroglycerin on the ODC is controversial. Nitroglycerin (GTN) added to a solution of hemoglobin,’ administered sublingually to normal volunteers,? or added to the blood of isolated canine heart preparation& fails to change significantly the P,,. On the contrary intracoronary infusion of GTN in isolated dog heart preparations increases significantly coronary venous PO, and P,,.‘, i To our knowledge the effect of GTN on the whole ODC has never been assessed. The purpose of our work is to establish whether or not a high dosage of GTN influences the ODC of healthy normal subjects. Nitroglycerin was administered sublingually (3.0 mg.) to seven normal subjects (two females) aged from 22 to 42 years. Arterial blood was sampled for the determination of blood gases, hematocrit, hemoglobin concentration, 2,3-DPG and ODC, before and 20 and 60 minutes after intake of GTN. Blood gases were determined by a conventional analyzer (Corning 175). The levels of hemoglobin and carboxyhemoglobin were measured by the IL-CO-Oximeter 282, the hematocrit by micro-centrifugation, and the 2,3-DPG by an enzymatic method (Sigma-Kit). The oxygen affinity of the whole blood was studied at standard conditions (pH 7.4, temperature 37” C., pC0, 40 mm. Hg), with equipment constructed in this laboratory:: In each subject the blood gases were within normal limits and their mean values before and after administration of GTN are identical (Table I); no change was observed for blood gases, hematocrit, hemoglobin, mean corpuscular hemoglobin concentration, or 2,3-DPG as shown by a t test for paired data. Table I also gives the mean PO, values corresponding to various saturations: they were not influenced by GTN. Our data clearly demonstrate that high dosages of GTN
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8.
9.
10.
pectoris ausgelost durch vorhofstimulation, Z. Kardiol. 62:900, 1973. Costantin, L. R.: Extracardiac factors contributing to hypotension during coronary occlusion, Am. J. Cardiol. 11:205, 1963. Zelis, R., Caudill, C. C., Baggette, K., and Mason, D. T.: Reflex vasodilation induced by coronary angiography in human subjects, Circulation 63:490, 1976. Robinson, B. F., Collier, J., and Nachev, C.: Changes in peripheral venous compliance after myocardial infarction, Cardiovasc. Res. 6:67, 1972.
Spontaneous frequency
variability
in arrhythmia
To the Editor: Dr. Orr and co-workers, in their letter “Physiological sleep patterns and cardiac arrhythmias” (AM. HEART J. 97:128, January, 1979) conclude that such considerable spontaneous variability in arrhythmia frequency occurs from one monitoring period to another that the clinician must be cautious in interpreting the results of limited monitoring. We and our colleagues’ recently reported the results of extensive (three consecutive 24-hour) monitoring studies performed in 15 clinically stable patients with various cardiac disorders and frequent ventricular ectopy, and documented the extent of this variability. Using an analysis of variance we demonstrated that even in otherwise stable individual patients one may expect to see as much as 90 per cent change in mean hourly ectopic frequency from one 8-hour period to another, and more than 80 per cent change in frequency in comparing consecutive 24-hour periods. Thus, we concur in both our findings and conclusions. Eric L. Michelson, M.D. Hospital of the University of Pennsylvania Joel Morganroth, M.D. Lankenau Hospital Lancaster Ave. W. of City Line Philadelphia, Pa. 19151 REFERENCE 1.
Morganroth, Josephson, Limitations monitoring Circulation
J., Michelson, E. L., Horowitz, L. N., M. E., Pearlman, A. S., and Dunkman, W. B.: of routine long-term electrocardiographic to assess ventricular ectopic frequency, 58:408, 1978.
Carotid sinus hypersensitivity-asystole and hypotension in the same patient To the Editor: Carotid sinus hypersensitivity has been defined as cardiac asystole lasting at least three seconds, or a fall in blood pressure of 50 mm. Hg or more, in response to carotid sinus massage. Syncope may result from either mechanism, and both phenomena may be present in the same patient, although hypotension might be masked by precedent asystole. The patient described here illustrates this dual mechanism-the insertion of a cardiac demand pacemaker preventing asystole but not the hypotension induced by carotid sinus massage.
American Heart Journal
B. R. was an elderly man who fainted in an elevator, sustaining a fractured skull. Little was done diagnostically until a second episode of syncope prompted carotid sinus massage which resulted in prolonged cardiac asystole. A cardiac demand pacemaker was implanted and subsequent carotid sinus massage induced a fall in blood pressure from 170/80 mm. Hg to 80/50 mm. Hg associated with severe lightheadedness without cardiac asystole. This patient manifested both hypotension and cardiac asystole caused by carotid sinus hypersensitivity, hypotension becoming apparent only after pacemaker insertion prevented cardiac asystole. It follows that any patient with carotid sinus hypersensitivity who has a cardiac pacemaker implanted for asystole should have carotid sinus massage to ascertain blood pressure response, because subsequent syncope, lightheadedness, or weak spells may be due to hypotension rather than to pacemaker failure, thereby obviating empirical changing of the pacemaker. Herschel J. Sklaroff, M.D. Assistant Clinical Professor of Medicine Mount Sinai School of Medicine New York. N. Y. 10029
Nitroglycerin and blood oxygen curve of normal subjects
dissociation
To the Editor: Several drugs induce a shift of the oxyhemoglobin dissociation curve (ODC). The action of nitroglycerin on the ODC is controversial. Nitroglycerin (GTN) added to a solution of hemoglobin,’ administered sublingually to normal volunteers,? or added to the blood of isolated canine heart preparation& fails to change significantly the P,,. On the contrary intracoronary infusion of GTN in isolated dog heart preparations increases significantly coronary venous PO, and P,,.‘, i To our knowledge the effect of GTN on the whole ODC has never been assessed. The purpose of our work is to establish whether or not a high dosage of GTN influences the ODC of healthy normal subjects. Nitroglycerin was administered sublingually (3.0 mg.) to seven normal subjects (two females) aged from 22 to 42 years. Arterial blood was sampled for the determination of blood gases, hematocrit, hemoglobin concentration, 2,3-DPG and ODC, before and 20 and 60 minutes after intake of GTN. Blood gases were determined by a conventional analyzer (Corning 175). The levels of hemoglobin and carboxyhemoglobin were measured by the IL-CO-Oximeter 282, the hematocrit by micro-centrifugation, and the 2,3-DPG by an enzymatic method (Sigma-Kit). The oxygen affinity of the whole blood was studied at standard conditions (pH 7.4, temperature 37” C., pC0, 40 mm. Hg), with equipment constructed in this laboratory:: In each subject the blood gases were within normal limits and their mean values before and after administration of GTN are identical (Table I); no change was observed for blood gases, hematocrit, hemoglobin, mean corpuscular hemoglobin concentration, or 2,3-DPG as shown by a t test for paired data. Table I also gives the mean PO, values corresponding to various saturations: they were not influenced by GTN. Our data clearly demonstrate that high dosages of GTN
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