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Definition of ventricular tachycardia
LEllERS” DEFINITION
OF VENTRICULAR
TACHYCARDIA
The careful and meticulously analyzed study by Bigger et al.,l while undoubtedly of value in further characterization of postinfarction ventricular tachycardia (VT), starts with an unfortunate choice of definitions and channels its discussion to the hardly novel “clinical implication” that “VT may be the harbinger of subsequent arrhythmic death.” To define VT as the authors did-as 3 consecutive complexes of ventricular origin regardless of their rate-would include ventricular escape rhythms, including those produced by electrical pacemakers. The authors’ definition is at variance with the standard electrocardiographic nomenclature over the past several decades.2-4 The only “justification” for this appears to be a similar mortality observed for rates above and below 100 beata/min. This may be spurious, since there is no way of knowing how the patients actually died with respect to the authors’ subdivision. The implication about subsequent arrhythmic death is similarly unwarranted, given that the observed 1,370 episodes of VT behaved rather innocuously at the time of the recording. Their predictive value is further weakened by the reported lack of quantitative relation between the frequency of VT and subsequent death in individual patients Furthermore, the rarity of the R-on-T phenomenon in this series and its frequency in the cases of sudden death observed outside hospital58 tend to imply different arrhythmic mechanisms at the time of actual sudden death. The strong predictive indexes of sudden death, namely the left ventricular contraction abnormalities and the anatomy of the coronary artery disease,7*8 are substituted by the somewhat imprecise category of clinical left ventricular failure, presumably present in 29% of the authors’ patients, for comparison with the predictive value of VT. The case for the indenendent nredictive value of VT in this setting has yet to be made. _ _ George Nlkollc, MB, BB, FRACP, Woden, Australia 1. Slggor JT. Wefd FM, Rolnltzky LM. F’revalence. characteristics and significance of ventricular tachycardta (three or mwe wmplaxas) detected with ambulatory electrc+ caidiographk recwdlng in the late hospital phase of acute myocardlal infarction. Am J Cardfol 1961;46:615-823. 2. Critwta Committee of tha New York Heart Assoclatkn. Nomenclature and Criteria for Diagnosis of Diseases of the Heari and Great Vessels. Sostc+x Little, &own 1873: 34. 3. Tenth Setbesda Conference on Optimal ElectrocwdiDgraphy of ttze American College of Cardfokgy. Task Fwce I: Standardization of Terminology and Interpretation. Am J cardfol 1976;41:130-145. 4. wH0llS.C Task Force: Definition of Terms Related to Cardiac Rhythm. Am Heart J 1978:95:796-606. 5. Nffwfk 0, Sbhop RL, Stngb JS. Sudden death recorded during Ho&r monitoring. Circulation 1962;6&21&225. 6. Ad~oy AA, Gwffn JE, W&b SW, Yufhofland HC. lnltiation of ventricular fibrlltatlon out&de hospital in patients with acute ischaemic heart disease. Sr Heart J 1982:47: 55-61. 7. fMtman EM, Ebsanl AA, Camptmfl MK, Scltecblman K, Roberts R, Sobel SE. The influence of locatIon and extent of myocardlal infarction on long-term ventricular dysrhythmla and mortality. Circulation 1979;60:805-814. 8. Callff RM. Swks JM. Sobar VS. MaradlrJR. Waafw GS. Relationshks among venklcufar~ias,&~tiely di~&~iogaphicandelect;ocardiograFhic indicators of myocardlal fibrosis. Circulation 1978;57:725-730.
REPLY: We appreciate Dr. Nikolic’s interest in ventricular arrhythmias occurring in the late hospital phase of acute myocardial infarction. His comment8 indicate dissatisfaction with our current knowledge in this area and a desire to have answers to many unresolved questions. We share his interest in these matters. Dr. Nikolic posed questions about 3 issues raised in our report on ventricular tachycardia (VT): (1) our definition of VT, (2) the hypothesis that the presence of VT in a predischarge Holter recording may indicate future ar&ythmic death, and (3) the relation between VT and other
Letters (from the United States) concerning a particular article in the &urn& must be received within 2 months of the article’s publication, and limited (with rare exceptions) to 2 double-space~Itypewritten pages. Two copies must be submitted. l
functional risk predictors, especially left ventricular dysfunction. All of these are controversial and worthy of discussion. Definition of VT: VT has been variously defined in terms of the number of consecutive ventricular premature depolarizations and the rate. Although the modal electrocardiographic definition for VT is three or more consecutive ventricular premature depolarizations, definitions requiring 4 or 5 consecutive ventricular complexes are still used by some workers. Clinical electrophysiologista often use 5 or 10 consecutive ventricular premature depolarizations in response to progammed ventricular stimulation as a definition of nonsustained VT. Also, the rate requirement in the definition of VT varies; the 3 most common in order of frequency of use are 100 beats/min, 120 beatslmin, and any rate. lp2Our decision a priori to include all spontaneous episodes of 3 or more consecutive ventricular premature depolarizations in our study was made because of the total ignorance about the prevalence, characteristics, and significance of VT in the late hospital phase of myocardial infarction when we began our study. We anticipated that we might find some justification for a rate component in the definition of VT by examining the relation between the average VT rate and subsequent clinical events (see Figure 1B in our report). In this analysis, 2 interesting facts emerged. First, the interectopic interval in an episode of VT often is extremely variable. Second, there is not yet any hint of a relation between the rate of an episode of consecutive ventricular premature depolarizations and mortality. A study by Kleiger et aI took an approach similar to ours. To avoid the semantic problem of using the term tachycardia for episodes with rates less than 100 beats/min, they chose the term ventricular runs. This addresses the issue in an intelligent way, permitting continuing studies of ventricular arrhythmias without aggravating traditional definitions. Very large studies will be needed to resolve the questions about the significance of various characteristics of ventricular runs. We would encourage investigators to keep data on a full range of rates to enhance our knowledge in an area where there is a great void. Implications about mechanisms of death: This is another difficult and controversial topic. Epidemiologist8 are frustrated in their attempts to classify deaths in a functional, that is, mechanistic sense. At present, the fact that death has occurred, the time between symptoms and death, and the cardiac or noncardiac nature of death are the mainstays of classification. Attempts to attribute death to ischemia, left ventricular power failure, or arrhythmias are fraught with difficulty because of data available at the time of death and because of complex interrelations among these functional entities. In our section on clinical implications, we discussed the hypothesis that VT may predict arrhythmic death but emphasized that the complex interactions among functional risk factors make alternative hypotheses tenable. Also, we discussed how to gather information about the interactions and how to use it in managing patients at present. We also are frustrated by the limitations in classifying postinfarction deaths and encourage efforts to advance the state of the art.4*5 Relation between VT and other risk factors: This is one of the most difficult issues raised by Dr. Nikolic since the studies to date, including our own, are so small. Dissection of the relations among VT, ischemia, left ventricular dysfunction, and death requires a large effort and has not yet been achieved. ls6-8First, a study with a large number of patients with VT and a large number of deaths is needed; about 100 of each would be desirable. The sample should be unbiased, that is, representative. Second, acceptable measures for ischemia, left ventricular dysfunction, and VT are needed. Finally, an accurate assessment of death in functional terms is needed. Our current hypothesis about what might be found in such a study is that VT would be significantly and importantly related to left ventricular dysfunction and significantly less so to ischemia. In addition, adjusting for these interactions, VT would have a significant and important association with cardiac death in the year after myocardial infarction. We are not at all certain that VT would be more strongly associated with “arrhythmic death’ than other modes of death, if, indeed, the functional mode of death can be identified with sufficient precision.
November 1982
J. Thomas Bigger, Jr., MD, Francis M. Weld, MD, and Linda M. Rolnltzky, MS, New York, New York
The Amerkan Journal of CARDIOLOGY Volume 50
1197
OF VENTRICULAR
TACHYCARDIA
The careful and meticulously analyzed study by Bigger et al.,l while undoubtedly of value in further characterization of postinfarction ventricular tachycardia (VT), starts with an unfortunate choice of definitions and channels its discussion to the hardly novel “clinical implication” that “VT may be the harbinger of subsequent arrhythmic death.” To define VT as the authors did-as 3 consecutive complexes of ventricular origin regardless of their rate-would include ventricular escape rhythms, including those produced by electrical pacemakers. The authors’ definition is at variance with the standard electrocardiographic nomenclature over the past several decades.2-4 The only “justification” for this appears to be a similar mortality observed for rates above and below 100 beata/min. This may be spurious, since there is no way of knowing how the patients actually died with respect to the authors’ subdivision. The implication about subsequent arrhythmic death is similarly unwarranted, given that the observed 1,370 episodes of VT behaved rather innocuously at the time of the recording. Their predictive value is further weakened by the reported lack of quantitative relation between the frequency of VT and subsequent death in individual patients Furthermore, the rarity of the R-on-T phenomenon in this series and its frequency in the cases of sudden death observed outside hospital58 tend to imply different arrhythmic mechanisms at the time of actual sudden death. The strong predictive indexes of sudden death, namely the left ventricular contraction abnormalities and the anatomy of the coronary artery disease,7*8 are substituted by the somewhat imprecise category of clinical left ventricular failure, presumably present in 29% of the authors’ patients, for comparison with the predictive value of VT. The case for the indenendent nredictive value of VT in this setting has yet to be made. _ _ George Nlkollc, MB, BB, FRACP, Woden, Australia 1. Slggor JT. Wefd FM, Rolnltzky LM. F’revalence. characteristics and significance of ventricular tachycardta (three or mwe wmplaxas) detected with ambulatory electrc+ caidiographk recwdlng in the late hospital phase of acute myocardlal infarction. Am J Cardfol 1961;46:615-823. 2. Critwta Committee of tha New York Heart Assoclatkn. Nomenclature and Criteria for Diagnosis of Diseases of the Heari and Great Vessels. Sostc+x Little, &own 1873: 34. 3. Tenth Setbesda Conference on Optimal ElectrocwdiDgraphy of ttze American College of Cardfokgy. Task Fwce I: Standardization of Terminology and Interpretation. Am J cardfol 1976;41:130-145. 4. wH0llS.C Task Force: Definition of Terms Related to Cardiac Rhythm. Am Heart J 1978:95:796-606. 5. Nffwfk 0, Sbhop RL, Stngb JS. Sudden death recorded during Ho&r monitoring. Circulation 1962;6&21&225. 6. Ad~oy AA, Gwffn JE, W&b SW, Yufhofland HC. lnltiation of ventricular fibrlltatlon out&de hospital in patients with acute ischaemic heart disease. Sr Heart J 1982:47: 55-61. 7. fMtman EM, Ebsanl AA, Camptmfl MK, Scltecblman K, Roberts R, Sobel SE. The influence of locatIon and extent of myocardlal infarction on long-term ventricular dysrhythmla and mortality. Circulation 1979;60:805-814. 8. Callff RM. Swks JM. Sobar VS. MaradlrJR. Waafw GS. Relationshks among venklcufar~ias,&~tiely di~&~iogaphicandelect;ocardiograFhic indicators of myocardlal fibrosis. Circulation 1978;57:725-730.
REPLY: We appreciate Dr. Nikolic’s interest in ventricular arrhythmias occurring in the late hospital phase of acute myocardial infarction. His comment8 indicate dissatisfaction with our current knowledge in this area and a desire to have answers to many unresolved questions. We share his interest in these matters. Dr. Nikolic posed questions about 3 issues raised in our report on ventricular tachycardia (VT): (1) our definition of VT, (2) the hypothesis that the presence of VT in a predischarge Holter recording may indicate future ar&ythmic death, and (3) the relation between VT and other
Letters (from the United States) concerning a particular article in the &urn& must be received within 2 months of the article’s publication, and limited (with rare exceptions) to 2 double-space~Itypewritten pages. Two copies must be submitted. l
functional risk predictors, especially left ventricular dysfunction. All of these are controversial and worthy of discussion. Definition of VT: VT has been variously defined in terms of the number of consecutive ventricular premature depolarizations and the rate. Although the modal electrocardiographic definition for VT is three or more consecutive ventricular premature depolarizations, definitions requiring 4 or 5 consecutive ventricular complexes are still used by some workers. Clinical electrophysiologista often use 5 or 10 consecutive ventricular premature depolarizations in response to progammed ventricular stimulation as a definition of nonsustained VT. Also, the rate requirement in the definition of VT varies; the 3 most common in order of frequency of use are 100 beats/min, 120 beatslmin, and any rate. lp2Our decision a priori to include all spontaneous episodes of 3 or more consecutive ventricular premature depolarizations in our study was made because of the total ignorance about the prevalence, characteristics, and significance of VT in the late hospital phase of myocardial infarction when we began our study. We anticipated that we might find some justification for a rate component in the definition of VT by examining the relation between the average VT rate and subsequent clinical events (see Figure 1B in our report). In this analysis, 2 interesting facts emerged. First, the interectopic interval in an episode of VT often is extremely variable. Second, there is not yet any hint of a relation between the rate of an episode of consecutive ventricular premature depolarizations and mortality. A study by Kleiger et aI took an approach similar to ours. To avoid the semantic problem of using the term tachycardia for episodes with rates less than 100 beats/min, they chose the term ventricular runs. This addresses the issue in an intelligent way, permitting continuing studies of ventricular arrhythmias without aggravating traditional definitions. Very large studies will be needed to resolve the questions about the significance of various characteristics of ventricular runs. We would encourage investigators to keep data on a full range of rates to enhance our knowledge in an area where there is a great void. Implications about mechanisms of death: This is another difficult and controversial topic. Epidemiologist8 are frustrated in their attempts to classify deaths in a functional, that is, mechanistic sense. At present, the fact that death has occurred, the time between symptoms and death, and the cardiac or noncardiac nature of death are the mainstays of classification. Attempts to attribute death to ischemia, left ventricular power failure, or arrhythmias are fraught with difficulty because of data available at the time of death and because of complex interrelations among these functional entities. In our section on clinical implications, we discussed the hypothesis that VT may predict arrhythmic death but emphasized that the complex interactions among functional risk factors make alternative hypotheses tenable. Also, we discussed how to gather information about the interactions and how to use it in managing patients at present. We also are frustrated by the limitations in classifying postinfarction deaths and encourage efforts to advance the state of the art.4*5 Relation between VT and other risk factors: This is one of the most difficult issues raised by Dr. Nikolic since the studies to date, including our own, are so small. Dissection of the relations among VT, ischemia, left ventricular dysfunction, and death requires a large effort and has not yet been achieved. ls6-8First, a study with a large number of patients with VT and a large number of deaths is needed; about 100 of each would be desirable. The sample should be unbiased, that is, representative. Second, acceptable measures for ischemia, left ventricular dysfunction, and VT are needed. Finally, an accurate assessment of death in functional terms is needed. Our current hypothesis about what might be found in such a study is that VT would be significantly and importantly related to left ventricular dysfunction and significantly less so to ischemia. In addition, adjusting for these interactions, VT would have a significant and important association with cardiac death in the year after myocardial infarction. We are not at all certain that VT would be more strongly associated with “arrhythmic death’ than other modes of death, if, indeed, the functional mode of death can be identified with sufficient precision.
November 1982
J. Thomas Bigger, Jr., MD, Francis M. Weld, MD, and Linda M. Rolnltzky, MS, New York, New York
The Amerkan Journal of CARDIOLOGY Volume 50
1197