T wave alternans detection during exercise stress test and during dobutamine stress. A comparative study in patients with a recent myocardial infarction.
BACKGROUND
Beat to beat electrical alternans of the T wave (TWA) on the electrocardiogram is a risk marker for the occurrence of life-threatening ventricular tachyarrhythmias. Atrial pacing or exercise are commonly used to increase heart rate to the critical level for TWA detection. However, atrial pacing requires invasive procedures while exercise may cause significant noise on the electrocardiographic recording or may be not performed by a number of patients with cardiac diseases. Dobutamine stress testing is routinely used in post-myocardial infarction patients and may represent an alternative means to detect TWA. However, the comparability of data obtained with exercise and dobutamine needs to be proven.


METHODS
We measured TWA during exercise and/or dobutamine stress in 42 patients with a recent myocardial infarction. TWA was detected using a commercially available software while the heart rate was increased to the target range of 105-130 b/min. Each patient performed the two tests in random order with an adequate recovery time in between.


RESULTS
The mean level of noise during data acquisition for TWA detection was significantly lower during the dobutamine test than during exercise (1.003 +/- 0.67 vs 1.46 +/- 1.20 microV, p < 0.01). With exercise, 32 (78%) patients had a determinable TWA. Of these, 9 (27%) were TWA positive and 23 TWA negative. In the other patients noise (n = 8) or exercise-induced arrhythmias (n = 1) prevented an appropriate TWA determination. One patient could not exercise. With dobutamine stress, 38 (87%) of the 42 patients studied had a determinable TWA. Arrhythmias prevented TWA determination in the remaining 4 patients. Dobutamine and exercise testing provided comparable proportions of TWA determinability. However, by combining exercise and dobutamine testing, a greater (p = 0.0071) proportion of the patients (41/42, 98% vs 32/42, 76%) had a determinable TWA when compared with exercise alone. A comparative TWA study could be performed in 29 patients who completed both the dobutamine and the exercise stress tests. All 22 patients TWA negative at exercise were so at dobutamine testing also. On the other hand, 5 of the 7 patients TWA positive at exercise were so at dobutamine testing also. Overall, 27 (93%) of the 29 patients in whom internal comparison could be performed showed a concordant result.


CONCLUSIONS
Dobutamine testing allows TWA detection with results comparable to those obtained at exercise testing. Combining exercise and dobutamine stress allows TWA determination in most of post-myocardial infarction patients. The present study provides the evidence for a safe and effective TWA determination for risk stratification after myocardial infarction.
Caffarone
A
A
Department of Cardiology, IRCCS Policlinico S. Matteo, University, of Pavia, Italy.
Martinelli
A
A
Valentini
P
P
Vanoli
E
E
D000328:Adult; D000368:Aged; D002316:Cardiotonic Agents; D004280:Dobutamine; D004562:Electrocardiography; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000503:physiopathology*; D013997:Time Factors
D002316:Cardiotonic Agents; D004280:Dobutamine