doi: 10.1161/01.CIR.0000160856.09169.80
(Circulation. 2005;111:e180-e181.)
© 2005 American Heart Association, Inc.
Correspondence |
Letter Regarding Article by Wichterle et al, "Prevalent Low-Frequency Oscillation of Heart Rate: Novel Predictor of Mortality After Myocardial Infarction"
St. Louis University School of Medicine, St. Louis, Mo, watanabe{at}slu.edu
Poznan University of Medical Sciences, Poznan, Poland
Wichterle et al recently presented in this journal a novel parameter of heart rate variability called prevalent low-frequency oscillation of heart rate (PLF).1 Using 2 groups of postinfarction patients derived from the EMIAT (European Myocardial Infarction Amiodarone Trial) and ATRAMI (Autonomic Tone and Reflexes After Myocardial Infarction) studies, they specifically compared and showed a predictive value for PLF that was stronger than that for heart rate turbulence (HRT) parameters using univariate analysis. They further showed that with Cox’s multivariate regression model, the relative risk for PLF remained high (4.6 and 3.6 in EMIAT and ATRAMI, respectively), whereas HRT parameters turbulence slope and turbulence onset lost their independence. Their study is noteworthy because in previous comparisons of measures of HRT and heart rate variability in large studies, HRT has consistently outperformed heart rate variability.2–4
We would like to point out that the prognostic ability of risk factors is changing significantly with declining mortality from acute ischemic events as a result of improved treatment protocols, and that the superiority of PLF may not hold true in a contemporary population. For example, we found that late potentials lost their predictive ability entirely in a modern population of patients, 90% of whom received percutaneous coronary intervention and 84% received statins.5 In contrast, the hazard ratio of HRT in multivariate analysis improved from 3.2 in the EMIAT placebo arm population, in whom only 60% of the patients had received thrombolysis,2 to 5.9 in the modern population.4
There were also some methodological differences in the analysis of HRT between the PLF article and previous HRT publications. For example, combining turbulence slope and turbulence onset usually provides the best predictive ability.2,3 Wichterle et al did not show how the combined HRT parameters performed against PLF. The end point for the ATRAMI population was cardiac mortality or resuscitated cardiac arrest, in contrast to all-cause mortality, which is commonly used in HRT studies. Finally, it is unclear why Wichterle et al used different criteria for admissible Holter recordings for their 2 patient populations based on the number of ventricular premature complexes—a minimum of 1 in the ATRAMI versus 5 for the EMIAT. It is generally accepted that a larger number of ventricular premature complexes for HRT calculation produces more stable values.
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 Top References References |
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1. Wichterle D, Simek J, La Rovere MT, Schwartz PJ, Camm AJ, Malik M. Prevalent low-frequency oscillation of heart rate: novel predictor of mortality after myocardial infarction. Circulation. 2004; 110: 1183–1190.
2. Schmidt G, Malik M, Barthel P, Schneider R, Ulm K, Rolnitzky L, Camm JA, Bigger JT Jr, Schömig A. Heart-rate turbulence after ventricular premature beats as a predictor of mortality after acute myocardial infarction. Lancet. 1999; 353: 1390–1396.[CrossRef][Medline] [Order article via Infotrieve]
3. Ghuran A, Reid F, La Rovere MT, Schmidt G, Bigger JT Jr, Camm AJ, Schwartz PJ, Malik M; ATRAMI Investigators. Heart rate turbulence-based predictors of fatal and nonfatal cardiac arrest (The Autonomic Tone and Reflexes After Myocardial Infarction substudy). Am J Cardiol. 2002; 89: 184–190.[CrossRef][Medline] [Order article via Infotrieve]
4. Barthel P, Schneider R, Bauer A, Ulm K, Schmitt C, Schömig A, Schmidt G. Risk stratification after acute myocardial infarction by heart rate turbulence. Circulation. 2003; 108: 1221–1226.
5. Bauer A, Guzik P, Barthel P, Schneider R, Ulm K, Watanabe MA, Schmidt G. Reduced prognostic power of ventricular late potentials in post-infarction patients of the reperfusion era. Eur Heart J. Published online January 26, 2005. DOI: 10.1093/eurheartj/ehi101. Available at: http://eurheartj.oupjournals.org/cgi/content/abstract/ehi101. Accessed March 14, 2005.
Response
Department of Cardiological Sciences, St. George’s Hospital Medical School, London, UK
General University Hospital, Prague, Czech Republic
Division of Cardiology, Fondazione "S. Maugeri" IRCCS, Montescano, Italy
Department of Cardiology, Policlinico S. Matteo IRCCS, Pavia, Italy
Watanabe and Guzik are naturally right that postinfarction risk stratification aims at a moving target. A sufficient follow-up period, which is needed for meaningful risk studies, makes each investigation immediately outdated because advances in acute and follow-up treatment continue in the meantime. This problem is widely known and recognized. Among others, this problem contributes to the understanding that accurate risk assessment models need to be multifactorial, combining different predictors. We were therefore glad that our study1 was able to add another independent marker to the mosaic of existing risk factors. As shown,1 the proposed index of prevalent low frequency heart rate oscillation (PLF) is different from established facets of heart rate variability analysis.
Finding the predictive value of PLF to be stronger than that of heart rate turbulence (HRT) does not imply that HRT should be abandoned. Because in 2 independent populations the predictive value of PLF performed strongly, it reflects true physiological mechanisms that are worth investigating further. We have no reason to claim and/or interest in claiming that PLF will always be the strongest predictor. Databases will surely appear without PLF performing this strongly. We are not concerned about this being the case. HRT indexes also appear useless in some postinfarction databases,2 but this does not decrease their established value. Watanabe and Guzik also are right that HRT suffers from a lack of standards. With moderate success, we attempted to improve its performance in our study.
It may be tempting to believe that a particular risk factor is the absolute and solitary answer to all risk stratification. This is counterproductive and leads to unfounded speculations, distorted assertions, or both. For instance, the argument that the predictive power of HRT improves with modern treatment is clearly stretched far. The seminal publication on HRT3 found the same multivariate risk in MPIP (Multicentre Post-Infarction Program) and EMIAT (European Myocardial Infarction Amiodarone Trial) that differed in the proportion of thrombolyzed patients very considerably (0% versus 60%). Likewise, it is not true that our ATRAMI (Autonomic Tone and Reflexes After Myocardial Infarction) outcome variable was different from previous investigations; the same outcome (cardiac mortality+resuscitated cardiac arrest) was prospectively defined in the original study and subsequently used consistently, including that in the HRT substudy.4
Although we can understand the enthusiasm of Watanabe and Guzik for HRT, they will surely agree that different risk factors have no conflict of interest. Our goal is in improving the risk assessment, not in shielding one risk factor. None of the known risk predictors, including HRT and PLF, is or can ever be the omnipotent outcome determinant.
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TopReferencesReferences |
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1. Wichterle D, Simek J, La Rovere MT, Schwartz PJ, Camm AJ, Malik M. Prevalent low-frequency oscillation of heart rate: novel predictor of mortality after myocardial infarction. Circulation. 2004; 110: 1183–1190.
2. Malik M, Hnatkova K, Batchvarov VN. Post infarction risk stratification using the 3-D angle between QRS complex and T-wave vectors. J Electrocardiol. 2004; 37 (suppl): 201–208.[Medline] [Order article via Infotrieve]
3. Schmidt G, Malik M, Barthel P, Schneider R, Ulm K, Rolnitzky L, Camm AJ, Bigger JT Jr, Schömig A. Heart-rate turbulence after ventricular premature beats as a predictor of mortality after acute myocardial infarction. Lancet. 1999; 353: 1390–1396.[CrossRef][Medline] [Order article via Infotrieve]
4. Ghuran A, Reid F, La Rovere MT, Schmidt G, Bigger JT Jr, Camm AJ, Schwartz PJ, Malik M; ATRAMI Investigators. Heart rate turbulence-based predictors of fatal and nonfatal cardiac arrest (The Autonomic Tone and Reflexes After Myocardial Infarction substudy). Am J Cardiol. 2002; 89: 184–190.[CrossRef][Medline] [Order article via Infotrieve]
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