- Email: [email protected]
Reply: The fourth heart sound: An inadequately investigated subject
LETTERS TO THE EDITOR
17. Asokan SK, Frank MJ, Witham AC: Cardiomyopathy without cardiomegaly in alcoholics. Am Heart J 84:13-18, 1972 18. Gould L, Reddy n, Goswami K, et al: Cardiac effects of two cocktails in normal man. Chest 63:943-947, 1973 19. Turner PP, Hunter J: The atrial sound in i~chemic heart disease. Br Heart J 35: 657-662, 1973 2t. Getzee JH, Dimond EG: Saga of the fourth heart sound. Am J Cardio122:609-613, 1968 22. Shah PM! Yu PN: Gallop rhythm. Hemodynamic and clinical correlation. Am Heart J 78:823-828, 1969
REPLY: THE FOURTH H E A R T SOUND: Q U A T EL Y INVESTIGATED S U B J E C T
AN
INADE-
The $4 problem is a specific case of a more general question: unexamined acceptance of traditional wisdom. I am grateful to Abrams for the o p p o r t u n i t y to continue the dialogue on significance of fourth heart sounds. In citing our work, he has read widely b u t not always deeply. While acknowledging the validity of particular disagreements (especially some paraphrasing TaveP), I deplore the a t t e m p t to make certain points by selective citations, and by posing questions about our work t h a t we ourselves have repeatedly raised. A b r a m s ' assertion t h a t " m a n y times the so-called $4 is in reality splitting of the first heart sound" is a reasonable auscultatory generalization, b u t has he investigated t h i s - t h a t is, how m a n y times? Moreover, he ignores the reverse possibility: How many times is a so-called split $1 "in reality" an $4? How do we decide which is "in reality" which? Indeed, his reference 13 on this point does not s u p p o r t his reasoning since t h a t reference was our report, 2 which concludes t h a t "false audibility (of $4) was not related to the low-frequency component of $1 or to split $1." In fact, t h a t was so precisely among our 56 percent of subjects with false positive results. This figure is only a p p a r e n t l y a b a d result, since it is a fraction of the small total without a recordable $4. It represents only 19 of 122 patients. Curiously, Abrams omits the 25 false negative results. Yet, the false positive results weakened our auscultators' performance, possibly because of zealous belief in " S 4 " - - t h e exact counterpart of supplying nonexistent "split $1" because of zeal for the traditional belief. In this context, Abrams correctly cites "auscultator expectation." But in the absence of investigations designed to minimize biases, this factor cuts two ways. For example, "auscuttator expectation" held for many years t h a t the second heart sounds were unitary events with "A2" and "P2" on respective sides of the upper sternum. Generations of physicians and voluminous studies reported them in this way. Now we hear and report $2 as a binary event in terms of its splitting dynamics. We are listening to the same sound, but now we hear it differently. Similarly, the conventional wisdom regarding "split $1" might also provide a misleading "auscultatory expectation." To the extent t h a t our studies prove to be flawed, I will be equally guilty. Our studies have not yet provoked formal reinvestigation of $4. Although our phonocardiographic results by themselves m u s t be totally objective for the e q u i p m e n t used (that is, we recorded undeniable S4's in normal subjects and patients), the crucial question of auscultation remains. Our auscultatory study, while electronically simplistic (and currently the subject of an improved protocol), utilized the only "scoring system" possible in clinical c a r d i o l o g y ~ t h e phonocardiogram. We recognize t h a t it is impossible at present to determine exactly which vibrations are audible in a train of vibrations occurring within milliseconds of each other, such as the $4 + $1, (o-a-b-c) complex, 7 among which we usually hear only two discrete sounds. Intricate
questions of frequency-audibility thresholds, masking and reverse masking are involved. Moreover, the logarithmic response of the ear to pure audiometric tones m a y not have a direct counterpart in the vibratory complexities of actual h e a r t sounds. These formidable obstacles confront us, b u t t h e y confront our critics equally. We a t t e m p t e d to minimize t h e m by elaborate blinding p r o c e d u r e s - - a d m i t t e d l y imperfect, b u t aimed a t reducing those biases inherent in preliminary knowledge of patients' clinical d a t a and prejudices inherent in the traditional b u t unexamined concepts of $4. Abrams cites the work of Bethell and Nixon (his reference 12) to substantiate the view t h a t an audible $4 is ipso facto abnormal. Curiously, he omits the same authors' citation of work by us and others substantiating an age-related increased incidence of $4 and including their s t a t e m e n t t h a t "it m a y be a physiological event in m a n y cases" 3 (my emphasis). He further cites Fowler, Adolph and Tavel as stressing "the question of audibility versus recordability." H e does not cite the very paper by us t h a t precipitated his letter, which states: "Registration by phonocardiogram does not prove its audibility." Also not cited was our own extensive section raising caveats and questions about our own work (Abrams' reference 5), in which we declare: " T h e audibility study served to raise more questions about current concepts of $4 than it answered . . . . We believe it has not completely settled any of these issues . . . . It would be desirable to have confirmation or refutation by other controlled studies . . . . since the results of auscultation for a frequently subtle phenomenon remain highly subjective." 5 Abrams states t h a t I have " i n a d v e r t e n t l y weakened" m y position on $4 in our report of preclinical cardiac malfunction in apparently normal alcoholics. 6 He deduces that, despite poor functional indexes in the alcoholics, "normal fourth heart sounds or atrial gallops were not heard" (his emphasis). He has no evidence for this. Actually they were disregarded. I have always considered abnormal any p a l p a ble and subjectively loud $4. 2,4,5,7 In the alcoholic study any subjectively loud atrial sounds thus had to be excluded. Indeed, since our $4 studies point to the mere presence of $4 as possibly physiologic, the question could not properly arise either by auscultation or by phonocardiography. It could only have arisen if we shared the traditional view of $4. Moreover, since we cannot yet tell the pathologic from the nonpathologic, we could not consider any recorded $4. T h u s we did maintain fidelity to our $4 results, and it is Abrams who falls victim to his own view. Finally, this was a systolic interval study and here Abrams also overlooked Table I of our auscultatory study, 2 which showed a group t r e n d toward better values for systolic intervals in all those with $4 by phonocardiogram. In conclusion, let me acknowledge again t h a t our investigations have been at best imperfect and at worst invalid. B u t we tackled the $4 problem by a t t e m p t i n g to minimize subjective and objective bias. Examination of our illustrations 2,4,5 will show t h a t the phonocardiographic prevalence of $4 cannot be d e n i e d - - a t least using Maas and Weber filters (discussed elsewhereS). Our results with Hewlett-Packa r d filters do conform more closely to those of most others, s Which phonocardiographic result is "right"? Which auscult a t o r y result is "right"? This remains a problem in observer performance. In a meticulous investigation, observer performance among experienced auscultators varied astonishingly when they were "blinded" to everything else about the patient. 9 Who among t h e m was "right"? The problem m u s t be dealt with by appropriately designed studies. Evaluation of $4 is more complex t h a n the recently c o r -
October 6, 1975
The American Journal of CARDIOLOGY
Volume 36
535
LETTERS TO THE EDITOR
rected traditional concept of $2 and its components, b u t it is best to approach each question in search of T r u t h rather than to a t t e m p t to reconfirm Established Belief. (Much e a r l y phonocardiographic equipment was designed to do just that.) Goethe observed: " W h a t we know, we see," and Will Rogers provided the corollary: " I t isn't what we know t h a t causes trouble, it's what we know t h a t a i n ' t so." Addendum: Since this letter was submitted, Tavel has reported a phonocardiographic prevalence of $4 in patients over 40 identical to ours in the paper criticized by Abrams: " F o u r t h heart sounds were recorded in 71 percent (11 of 14) of normal controls" (catheterized to compare with patients with aortic stenosis, 85 percent of whom had $4) (Tavel e t a h Circulation 50: Suppl III: 247, i974). David H. Spodick, MD, FACC Department of Medicine Tufts University School of Medicine Cardiology Division Lemuel Shattuck Hospital Boston, Massachusetts
with a P - R interval of 200 msec or less, the A - H interval was normal (less than 130 msec) in 40. In their 22 cases with a P - R interval of 210 msec or greater, the A - H interval was abnormal (greater than 130 msec) in 20. Thus, the P - R interval can be used as a valid indicator of the conduction time in the A-V node, b u t is probably of little value in predicting normal or abnormal intraventricular conduction time in patients with bifascicular block. His bundle electrography is essential for this measurement. Paul R. Lightfoot, MD Department of Internal Medicine Kaiser Foundation Hospital Fontana, California Reference 1. Levites R, Haft J: Significance of first degree heart block (prolonged P-R interval) in bifascicuiar block. Am J Cardio134:259-264, 1974
PREDICTIVE VALUE OF LABORATORY TESTS
References 1. Tavel ME: The fourth heart sound. Circulation 44:1264, 1974 2. Rectra EH, Khan AN, Pigott VM, el ah Audibility of the fourth heart sound: a prospective, blind auscultatory and polygraphic investigation. JAMA 221:36-41, 1972 3. Beihell HJN, Nixon PGF: Atrial gallop in coronary heart disease without overt infarction. Br Heart J 36:682, t974 4. Swistak M, Mushlln H, Spodick DH: Comparative prevalence of the fourth heart sound in hypertensive and matched normal persons. Am J Cardio133:614-616, 1974 5. Spedick DH, Ouarry-Pigoti VM; Prevalence of the fourth heart sound by phonocardiography in the absence of cardiac disease. Am Heart J 87:11-14, 1974 6. Spodick DH, Pigolt VM, Chirife R: Preelinical cardiac malfunction in chronic alcoholism. Comparison with matched normal controls and with alcoholic cardiomyopathy. N Engt J Med 287:677-680, 1972 7. Spodick OH: The fourth heart sound. Circulation 49:1263, 1974 8. Spodiek DH: Significance of the fourth heart sound. Am Heart J 88:126, 1974 9. Caceres C, Perry L: Principles of auscultation. In, The Innocent Murmur. Boston, Little Brown, 1967, pp 21-44
AMIODARONE HYDROCHLORIDE
In answer to several inquiries concerning our article, ~ amiodarone hydrochloride was originally developed by S. A. Labaz N.V. from Brussels, Belgium. In Argentina, the drug is manufactured under the name Atlansil by Laboratorios Roemmers S.A., Buenos Aires, Argentina. Mauricio B. Rosenbaum, MD Service of Cardiology Ramos Meji'a Hospital Rivadavia 3820, P.B, A Buenos Aires, Argentina
Reference 1. Rosenbaum MB, Chiale PA, Ryba D, et ah Control of tachyarrhythmias associated with Wolff-Parkinson-White syndrome by amiodarone hydrochloride. Am J Cardiol 34:215-223, 1974
T h e precise use of terms is essential if we are to communicate effectively within and between scientific disciplines. Two of. the most commonly confused terms in medicine t o d a y are sensitivity and specificity. It is regrettable t h a t Schweitzer et a l J used these terms incorrectly. Shown is their Table I defining these terms followed by a table with the correct definitions. Sensitivity, specificity, predictive value and efficiency define the accuracy of a laboratory test. Sensitivity indicates the frequency of positive test results in patients with a particular disease, whereas specificity indicates the frequency of negative test results in patients without t h a t disease. The predictive value of a positive test result indicates the percent of patients with disease among all patients with positive test results. The predictive value of a negative test result indicates the percent of patients without disease among all patients with negative test results. T h e efficiency of a test indicates the percent of patients correctly classified (as having or not having disease) by the test (Table II). False positive results are therefore calculated as 100 percent - predictive value of the positive test. If a test has a predictive value (positive) of 90 percent, then 90 percent of the positive results are true positive results and 10 percent are false positive results. In diagnosis we are most interested in the predictive value of the positive result. These are patients who are p~esumed to have a particular disease and undergo further diTABLE I Sensitivity and Specificity of Exercise Criteria
P-R INTERVAL IN BIFASCICULAR BLOCK
Levites and Haft 1 have concluded t h a t the P - R interval is probably of some help clinically in separating normal from abnormal intraventricular conduction time in patients with right bundle branch block and left axis deviation; t h a t it is not useful as an indicator in patients with left bundle branch block or right bundle branch block with right axis deviation; and t h a t His bundle electrography is necessary in this latter group to detect H-V prolongation. However, they have failed to emphasize the most obvious conclusion in their observations of the P - R interval with bifascicular block; t h a t is, the length of the P-R interval accurately differentiates between normal and abnormal atrioventricular (A-V) nodal conduction time. In their 41 cases
536
October 6, 1975
The American Journal of CARDIOLOGY
Results of Coronary Angiography Results of Exercise Test
CAD
NCAD
Positive A B Negative C D Sensitivity of exercise criterion = A / ( A + C) expressed as percent. Specificity of exercise criterion = A / ( A + B) expressed as percent. Thus, false positive results - 100 -- specificity; false 'negative resu Its = 100 -- sensitivity. Reproduced f r o m Schweitzer et al. l CAD = coronary artery disease; NCAD = no or insignificant coronary artery disease.
Volume 36
17. Asokan SK, Frank MJ, Witham AC: Cardiomyopathy without cardiomegaly in alcoholics. Am Heart J 84:13-18, 1972 18. Gould L, Reddy n, Goswami K, et al: Cardiac effects of two cocktails in normal man. Chest 63:943-947, 1973 19. Turner PP, Hunter J: The atrial sound in i~chemic heart disease. Br Heart J 35: 657-662, 1973 2t. Getzee JH, Dimond EG: Saga of the fourth heart sound. Am J Cardio122:609-613, 1968 22. Shah PM! Yu PN: Gallop rhythm. Hemodynamic and clinical correlation. Am Heart J 78:823-828, 1969
REPLY: THE FOURTH H E A R T SOUND: Q U A T EL Y INVESTIGATED S U B J E C T
AN
INADE-
The $4 problem is a specific case of a more general question: unexamined acceptance of traditional wisdom. I am grateful to Abrams for the o p p o r t u n i t y to continue the dialogue on significance of fourth heart sounds. In citing our work, he has read widely b u t not always deeply. While acknowledging the validity of particular disagreements (especially some paraphrasing TaveP), I deplore the a t t e m p t to make certain points by selective citations, and by posing questions about our work t h a t we ourselves have repeatedly raised. A b r a m s ' assertion t h a t " m a n y times the so-called $4 is in reality splitting of the first heart sound" is a reasonable auscultatory generalization, b u t has he investigated t h i s - t h a t is, how m a n y times? Moreover, he ignores the reverse possibility: How many times is a so-called split $1 "in reality" an $4? How do we decide which is "in reality" which? Indeed, his reference 13 on this point does not s u p p o r t his reasoning since t h a t reference was our report, 2 which concludes t h a t "false audibility (of $4) was not related to the low-frequency component of $1 or to split $1." In fact, t h a t was so precisely among our 56 percent of subjects with false positive results. This figure is only a p p a r e n t l y a b a d result, since it is a fraction of the small total without a recordable $4. It represents only 19 of 122 patients. Curiously, Abrams omits the 25 false negative results. Yet, the false positive results weakened our auscultators' performance, possibly because of zealous belief in " S 4 " - - t h e exact counterpart of supplying nonexistent "split $1" because of zeal for the traditional belief. In this context, Abrams correctly cites "auscultator expectation." But in the absence of investigations designed to minimize biases, this factor cuts two ways. For example, "auscuttator expectation" held for many years t h a t the second heart sounds were unitary events with "A2" and "P2" on respective sides of the upper sternum. Generations of physicians and voluminous studies reported them in this way. Now we hear and report $2 as a binary event in terms of its splitting dynamics. We are listening to the same sound, but now we hear it differently. Similarly, the conventional wisdom regarding "split $1" might also provide a misleading "auscultatory expectation." To the extent t h a t our studies prove to be flawed, I will be equally guilty. Our studies have not yet provoked formal reinvestigation of $4. Although our phonocardiographic results by themselves m u s t be totally objective for the e q u i p m e n t used (that is, we recorded undeniable S4's in normal subjects and patients), the crucial question of auscultation remains. Our auscultatory study, while electronically simplistic (and currently the subject of an improved protocol), utilized the only "scoring system" possible in clinical c a r d i o l o g y ~ t h e phonocardiogram. We recognize t h a t it is impossible at present to determine exactly which vibrations are audible in a train of vibrations occurring within milliseconds of each other, such as the $4 + $1, (o-a-b-c) complex, 7 among which we usually hear only two discrete sounds. Intricate
questions of frequency-audibility thresholds, masking and reverse masking are involved. Moreover, the logarithmic response of the ear to pure audiometric tones m a y not have a direct counterpart in the vibratory complexities of actual h e a r t sounds. These formidable obstacles confront us, b u t t h e y confront our critics equally. We a t t e m p t e d to minimize t h e m by elaborate blinding p r o c e d u r e s - - a d m i t t e d l y imperfect, b u t aimed a t reducing those biases inherent in preliminary knowledge of patients' clinical d a t a and prejudices inherent in the traditional b u t unexamined concepts of $4. Abrams cites the work of Bethell and Nixon (his reference 12) to substantiate the view t h a t an audible $4 is ipso facto abnormal. Curiously, he omits the same authors' citation of work by us and others substantiating an age-related increased incidence of $4 and including their s t a t e m e n t t h a t "it m a y be a physiological event in m a n y cases" 3 (my emphasis). He further cites Fowler, Adolph and Tavel as stressing "the question of audibility versus recordability." H e does not cite the very paper by us t h a t precipitated his letter, which states: "Registration by phonocardiogram does not prove its audibility." Also not cited was our own extensive section raising caveats and questions about our own work (Abrams' reference 5), in which we declare: " T h e audibility study served to raise more questions about current concepts of $4 than it answered . . . . We believe it has not completely settled any of these issues . . . . It would be desirable to have confirmation or refutation by other controlled studies . . . . since the results of auscultation for a frequently subtle phenomenon remain highly subjective." 5 Abrams states t h a t I have " i n a d v e r t e n t l y weakened" m y position on $4 in our report of preclinical cardiac malfunction in apparently normal alcoholics. 6 He deduces that, despite poor functional indexes in the alcoholics, "normal fourth heart sounds or atrial gallops were not heard" (his emphasis). He has no evidence for this. Actually they were disregarded. I have always considered abnormal any p a l p a ble and subjectively loud $4. 2,4,5,7 In the alcoholic study any subjectively loud atrial sounds thus had to be excluded. Indeed, since our $4 studies point to the mere presence of $4 as possibly physiologic, the question could not properly arise either by auscultation or by phonocardiography. It could only have arisen if we shared the traditional view of $4. Moreover, since we cannot yet tell the pathologic from the nonpathologic, we could not consider any recorded $4. T h u s we did maintain fidelity to our $4 results, and it is Abrams who falls victim to his own view. Finally, this was a systolic interval study and here Abrams also overlooked Table I of our auscultatory study, 2 which showed a group t r e n d toward better values for systolic intervals in all those with $4 by phonocardiogram. In conclusion, let me acknowledge again t h a t our investigations have been at best imperfect and at worst invalid. B u t we tackled the $4 problem by a t t e m p t i n g to minimize subjective and objective bias. Examination of our illustrations 2,4,5 will show t h a t the phonocardiographic prevalence of $4 cannot be d e n i e d - - a t least using Maas and Weber filters (discussed elsewhereS). Our results with Hewlett-Packa r d filters do conform more closely to those of most others, s Which phonocardiographic result is "right"? Which auscult a t o r y result is "right"? This remains a problem in observer performance. In a meticulous investigation, observer performance among experienced auscultators varied astonishingly when they were "blinded" to everything else about the patient. 9 Who among t h e m was "right"? The problem m u s t be dealt with by appropriately designed studies. Evaluation of $4 is more complex t h a n the recently c o r -
October 6, 1975
The American Journal of CARDIOLOGY
Volume 36
535
LETTERS TO THE EDITOR
rected traditional concept of $2 and its components, b u t it is best to approach each question in search of T r u t h rather than to a t t e m p t to reconfirm Established Belief. (Much e a r l y phonocardiographic equipment was designed to do just that.) Goethe observed: " W h a t we know, we see," and Will Rogers provided the corollary: " I t isn't what we know t h a t causes trouble, it's what we know t h a t a i n ' t so." Addendum: Since this letter was submitted, Tavel has reported a phonocardiographic prevalence of $4 in patients over 40 identical to ours in the paper criticized by Abrams: " F o u r t h heart sounds were recorded in 71 percent (11 of 14) of normal controls" (catheterized to compare with patients with aortic stenosis, 85 percent of whom had $4) (Tavel e t a h Circulation 50: Suppl III: 247, i974). David H. Spodick, MD, FACC Department of Medicine Tufts University School of Medicine Cardiology Division Lemuel Shattuck Hospital Boston, Massachusetts
with a P - R interval of 200 msec or less, the A - H interval was normal (less than 130 msec) in 40. In their 22 cases with a P - R interval of 210 msec or greater, the A - H interval was abnormal (greater than 130 msec) in 20. Thus, the P - R interval can be used as a valid indicator of the conduction time in the A-V node, b u t is probably of little value in predicting normal or abnormal intraventricular conduction time in patients with bifascicular block. His bundle electrography is essential for this measurement. Paul R. Lightfoot, MD Department of Internal Medicine Kaiser Foundation Hospital Fontana, California Reference 1. Levites R, Haft J: Significance of first degree heart block (prolonged P-R interval) in bifascicuiar block. Am J Cardio134:259-264, 1974
PREDICTIVE VALUE OF LABORATORY TESTS
References 1. Tavel ME: The fourth heart sound. Circulation 44:1264, 1974 2. Rectra EH, Khan AN, Pigott VM, el ah Audibility of the fourth heart sound: a prospective, blind auscultatory and polygraphic investigation. JAMA 221:36-41, 1972 3. Beihell HJN, Nixon PGF: Atrial gallop in coronary heart disease without overt infarction. Br Heart J 36:682, t974 4. Swistak M, Mushlln H, Spodick DH: Comparative prevalence of the fourth heart sound in hypertensive and matched normal persons. Am J Cardio133:614-616, 1974 5. Spedick DH, Ouarry-Pigoti VM; Prevalence of the fourth heart sound by phonocardiography in the absence of cardiac disease. Am Heart J 87:11-14, 1974 6. Spodick DH, Pigolt VM, Chirife R: Preelinical cardiac malfunction in chronic alcoholism. Comparison with matched normal controls and with alcoholic cardiomyopathy. N Engt J Med 287:677-680, 1972 7. Spodick OH: The fourth heart sound. Circulation 49:1263, 1974 8. Spodiek DH: Significance of the fourth heart sound. Am Heart J 88:126, 1974 9. Caceres C, Perry L: Principles of auscultation. In, The Innocent Murmur. Boston, Little Brown, 1967, pp 21-44
AMIODARONE HYDROCHLORIDE
In answer to several inquiries concerning our article, ~ amiodarone hydrochloride was originally developed by S. A. Labaz N.V. from Brussels, Belgium. In Argentina, the drug is manufactured under the name Atlansil by Laboratorios Roemmers S.A., Buenos Aires, Argentina. Mauricio B. Rosenbaum, MD Service of Cardiology Ramos Meji'a Hospital Rivadavia 3820, P.B, A Buenos Aires, Argentina
Reference 1. Rosenbaum MB, Chiale PA, Ryba D, et ah Control of tachyarrhythmias associated with Wolff-Parkinson-White syndrome by amiodarone hydrochloride. Am J Cardiol 34:215-223, 1974
T h e precise use of terms is essential if we are to communicate effectively within and between scientific disciplines. Two of. the most commonly confused terms in medicine t o d a y are sensitivity and specificity. It is regrettable t h a t Schweitzer et a l J used these terms incorrectly. Shown is their Table I defining these terms followed by a table with the correct definitions. Sensitivity, specificity, predictive value and efficiency define the accuracy of a laboratory test. Sensitivity indicates the frequency of positive test results in patients with a particular disease, whereas specificity indicates the frequency of negative test results in patients without t h a t disease. The predictive value of a positive test result indicates the percent of patients with disease among all patients with positive test results. The predictive value of a negative test result indicates the percent of patients without disease among all patients with negative test results. T h e efficiency of a test indicates the percent of patients correctly classified (as having or not having disease) by the test (Table II). False positive results are therefore calculated as 100 percent - predictive value of the positive test. If a test has a predictive value (positive) of 90 percent, then 90 percent of the positive results are true positive results and 10 percent are false positive results. In diagnosis we are most interested in the predictive value of the positive result. These are patients who are p~esumed to have a particular disease and undergo further diTABLE I Sensitivity and Specificity of Exercise Criteria
P-R INTERVAL IN BIFASCICULAR BLOCK
Levites and Haft 1 have concluded t h a t the P - R interval is probably of some help clinically in separating normal from abnormal intraventricular conduction time in patients with right bundle branch block and left axis deviation; t h a t it is not useful as an indicator in patients with left bundle branch block or right bundle branch block with right axis deviation; and t h a t His bundle electrography is necessary in this latter group to detect H-V prolongation. However, they have failed to emphasize the most obvious conclusion in their observations of the P - R interval with bifascicular block; t h a t is, the length of the P-R interval accurately differentiates between normal and abnormal atrioventricular (A-V) nodal conduction time. In their 41 cases
536
October 6, 1975
The American Journal of CARDIOLOGY
Results of Coronary Angiography Results of Exercise Test
CAD
NCAD
Positive A B Negative C D Sensitivity of exercise criterion = A / ( A + C) expressed as percent. Specificity of exercise criterion = A / ( A + B) expressed as percent. Thus, false positive results - 100 -- specificity; false 'negative resu Its = 100 -- sensitivity. Reproduced f r o m Schweitzer et al. l CAD = coronary artery disease; NCAD = no or insignificant coronary artery disease.
Volume 36