Prognostic value of heart rate variability after acute myocardial infarction in the era of immediate reperfusion

IntroductionThe incidence and significance of impaired heart rate variability (HRV) after acute myocardial infarction (AMI) have not yet been evaluated in cohorts of patients in whom early reperfusion was systematically attempted. Therefore, HRV was evaluated in 412 unselected patients with AMI (311 men, mean age: 60±12 years, anterior AMI in 172 patients) treated with direct coronary angioplasty (PTCA) within 12 hours of symptom onset (mean 3.5±2.0 h). Standard deviation of normal RR intervals (SDNN), square root of the mean of the sum of the squares of differences between adjacent RR intervals (RMSSD) and left ventricular ejection fraction (LVEF, mean: 55±15%) were measured 11±9 days after AMI before discharge. Angiotensin-converting enzyme (ACE) inhibitors and beta-blockers were prescribed at discharge in 81.1% and 70.1% of patients, respectively.ResultsMean SDNN was 94±30 ms (range 14–155). SDNN was <50 ms in 7% of patients. Mean RMSSD was 34±32 ms (range 2–234). RMSSD was <15 ms in 21% of patients. Low SDNN (<50 ms) was unrelated to gender, age, infarct location or extension of CHD but was related to low LVEF (p<0.001, logistic regression analysis). During mean follow-up of 4.3±3 years, there were 31 deaths; 24 were cardiac. SDNN was higher in long-term survivors (102±39 ms) as compared to nonsurvivors (81±33 ms, p=0.02) but RMSSD was unrelated to the long-term vital status. Four-year survival of patients with a SDNN <50 ms vs >50 ms was 80% vs 92%, respectively (p<0.001, Kaplan Meier analysis). Low SDNN (odds ratio OR=2.0, p<0.05) but not RMSSD was an independent denominator for long-term mortality as were low LVEF (OR=1.0 decrease in LVEF, p<0.01, proportional hazards model) and age (OR=1.1, p<0.001). Only 3/31 fatalities and 1/24 cardiac deaths were predicted by a SDNN <50 ms and only 5/31 fatalities by a RMSSD <15 ms.ConclusionThe incidence of severely depressed HRV in patients after AMI is low (<10%) in the era of early reperfusion of the infarct vessel using direct PTCA. Mortality in patients with a very low HRV when assessed by SDNN is substantial but the positive predictive value of this parameter is low.ZusammenfassungEinleitungDie Inzidenz und Bedeutung der verminderten Herzfrequenzvariabilität (HRV) nach akutem Myokardinfarkt (AMI) ist bei Patienten, die eine frühe Reperfusion erhielten, bisher nicht systematisch untersucht. Deshalb wurde bei 412 unselektierten Patienten mit AMI eine HRV-Bestimmung (311 Männer, mittleres Alter 60±12 Jahre, Vorderwandinfarkt bei 172 Patienten) durchgeführt. Diese Patienten erhielten eine direkte PTCA innerhalb von 12 Stunden nach Symptombeginn. Die Standardabweichung der RR-Intervalle (SDNN), die Quadratwurzel des Mittelwertes der quadrierten Differenzen der RR-Intervalle (RMSSD) und die linksventrikuläre Ejektionsfraktion (LVEF, im Mittel: 55±15%) wurden 11±9 Tage nach AMI gemessen. ACE-Hemmer und Betablocker wurden in 81.1% bzw. 70.1% der Fälle verordnet.ErgebnisseDer mittlere SDNN-Wert betrug 94±30 ms (14–155). Bei 7% der Patienten war die SDNN <50 ms. Die mittlere RMSSD lag bei 34±32 ms (2–234). Bei 21% der Patienten konnte eine RMSSD <15 ms festgestellt werden. Niedrige SDNN (<50 ms) zeigte keinen signifikanten Zusammenhang zu Geschlecht, Alter, Infarktlokalisation oder Ausmaß der koronaren Herzerkrankung. Bei Patienten mit niedriger SDNN und reduzierter LVEF konnte eine hohe Signifikanz (p<0.001) festgestellt werden. Während der Nachbeobachtung von 4.3±3 Jahren gab es 31 Todesfälle: 24 davon kardial. SDNN war höher in Langzeit-Überlebenden (102±39 ms) als im Vergleich zu Nicht-Überlebenden (81±33 ms, p=0.02). RMSSD zeigte keinen signifikanten Zusammenhang mit Langzeit- Parametern. Die 4-Jahre-Überlebensrate betrug bei Patienten mit SDNN <50 ms 80%, im Vergleich zu SDNN >50 ms 92% (p<0.001, Kaplan-Meier-Analyse). Niedrige SDNN (odds ratio OR=2.0, p<0.05), reduzierte LVEF (OR=1.0, p<0.01) und Alter (OR=1.1, p<0.001) waren Prädiktoren der Langzeit-Mortalität, aber nicht RMSSD. Nur 3 von 31 Todesfällen und 1 von 24 kardialen Todesfällen konnten durch eine SDNN <50 ms sowie 5 von 31 Todesfällen durch eine RMSSD <15 ms vorhergesagt warden.ZusammenfassungDie Inzidenz der deutlich reduzierten HRV bei Patienten nach AMI in der Ära der frühen Reperfusion des Infarktgefässes durch direkte PTCA ist niedrig (<10%). Die Mortalität bei Patienten mit einer sehr niedrigen HRV, beurteilt durch SDNN, ist beachtlich, aber der positive prädiktive Wert dieses Parameters ist gering.

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