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Treadmill stress test is commonly used for the evaluation of patients with cardiovascular diseases. Electrocardiographic changes during treadmill stress test are important. We observed three instances of two T waves following one QRS complex. We could not find any similar observation in literature.
A 30-year-old male presented with atypical chest pain. During treadmill stress test, supine electrocardiogram (ECG) was within normal limits except that there were two T waves (marked T1 and T2) following the first QRS complex in all leads [Figure 1]a.
The pause between QRS of the first and second beats was longer than that of the R-R interval of other beats [Figure 1]a. The patient could exercise for 9:19 min (10.2 METs). The peak heart rate was 182/min. The peak blood pressure was 160/90 mmHg.
He had no symptoms and no electrocardiographic signs of myocardial ischemia during the exercise and up to 8 min of recovery. We could not explain the genesis of two T waves following the first QRS.
A 56-year-old male presented with complaint of effort breathlessness. During treadmill stress test, he could exercise for 7 min (9.6 METs). The peak heart rate was 198/min, and the peak blood pressure was 190/100 mmHg. During the 1st min of recovery, we observed that alternating QRS complexes were followed by two T waves [Figure 2]a – T1, T2]. The pause between beats showing two T waves was 1.5 times the interval between beats showing one T wave [Figure 2]a.
There was no electrocardiographic evidence of inducible myocardial ischemia during the exercise and up to 8 min of recovery. Once again, we could not understand the cause of two T waves in alternating beats.
Treadmill stress test was performed on a 64-year-old male for the complaint of effort breathlessness. He could exercise for 6 min (7.1 METs). The peak heart rate was 153/min, and the peak blood pressure was 170/90 mmHg. During the 6th min of recovery, he had mild ST-segment depression in leads V2 and V3. Once again, there were two T waves [Figure 3]a, T1 and T2] after the third QRS with a longer pause between the 3rd and 4th QRS [Figure 3]a. However, this time, we observed that the first T wave (T1) suddenly terminated without taking full course [marked arrow in [Figure 3]a and was followed by the second complete T wave [T2 in [Figure 3]a.
All the tests were performed on the same machine.
Sudden termination of the first T wave in case number 3 gave us a clue that there could be some transient fault with the printer. We took out another copy of the electrocardiographic prints of all the cases from the same machine. This time, the ECGs were absolutely normal. There was no second T wave [Figure 1]b, [Figure 2]b, and [Figure 3]b. This confirmed our finding that in the first instance, the printer stopped transiently producing the abnormal finding. We placed the lead II of abnormal ECG and normal ECG of the same stage and time below the other [Figure 1]c, [Figure 2]c, and [Figure 3]c. It became clear that the apparent two T waves were because of transient stopping of the printer at a point marked with a broken vertical dotted line.
In the first case, the recorder stopped printing little after the end of the T wave of the first beat marked with a broken vertical line (T1). It did not record the ensuing T-P interval, next P wave, P-R interval, next QRS, and ST-segment (almost 0.6 s of electrical activity) [Figure 1]c. It then restarted and recorded the T wave of the hidden QRS (T2). Recording of extra T wave resulted in prolongation of the R-R interval between the 1st and 2nd QRS. In the second case, the printer stopped after alternate T wave for a period of 0.4 s. In the third case, the printer stopped even before the completion of the first T wave (T1) of the third beat and did not record the ensuing T-P interval, Pwave, P-R interval, and QRS (0.52 s of electrical activity). It restarted just before the T wave (T2) of the hidden QRS.
Recognition of such error in the working of printer is important. If this possibility is not kept in mind, second T wave may be wrongly interpreted as transient abnormal U wave. In our cases, there are several points against the possibility of a U wave. First, the configuration of second wave (T2) exactly resembled the first T wave in all leads. Second, the R-R interval having second T wave (T2) was prolonged. Third, there was no U wave in other beats. We could not find any similar reference in literature.
Transient error in the movement of printer of treadmill stress test system can produce transient abnormalities in the ECG. This possibility should be kept in mind if one finds a transient unexplained abnormality in the ECG. Taking another print of the same time of stress test and careful analysis of ECG help in preventing a wrong diagnosis.

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I found two hundred and sixty "i"s in the provided passage.
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