QRS Alternans During Treadmill Testing in A Case of Angina

73 years male presented for treadmill stress electrocardiography. He had history suggestive of angina on effort. Resting supine heart rate was 63 beats per minute. Resting supine blood pressure was 140/80 mm Hg. Resting supine electrocardiogram (Fig.1) was within normal limits except shallow inversion of the T wave in lead aVL (marked as ) and counter clockwise rotation in horizontal plane (RS configuration with positive T wave in lead V2). Patient could exercise only for five minutes (4.1 METs) because of development of chest pain. Peak heart rate was 130 beats per minutes (88% of the age predicted maximal heart rate using the formula of 220-age). Immediate recovery electrocardiogram in supine position showed more than 2mm ST-segment depression in leads I, II, aVF, V3, V4, V5 and V6 (Fig.2 and 3, marked as ). QRS amplitude showed alternans in leads I, II, III, aVL, aVF, V3, V4, V5 and V6 (Fig.2 and 3, marked as ‘a’ and ‘b’). ST -segment was elevated in lead aVR and V1 (Fig.2 and 3, marked as ).


Introduction
Electrical alternans is an electrocardiographic finding defined as a change in the electrical activity of the heart in alternate beats in the presence of a regular rhythm [1]. All components of the P-QRS-TU complex can show alternans. QRS alternans is the commonest. It is frequently seen in the presence of sinus tachycardia and usually presents as aberrant (slow) conduction in the right bundle branch in alternate beats [2]. It does not have any clinical significance [3]. QRS alternans with sinus tachycardia, low voltage and nonspecific flattening of the T waves is a specific (but not sensitive) marker of pericardial effusion with tamponade physiology [4,5]. Paroxysmal tachycardia with narrow QRS complex and fast ventricular rate can also show QRS alternans. In such a clinical setting, QRS alternans is usually seen in atrio-ventricular reciprocating tachycardia. However, it can be seen in other narrow QRS tachyarrhythmias with fast ventricular rate. This finding does not have any independent clinical significance [6]. In the presence of acute ischemia, alternans usually affects repolarization [4] (STsegment, T wave or U wave). T wave alternans preceding diagnostic ST-segment changes has been reported during treadmill stress testing [7]. We are reporting a case of QRS alternans during treadmill stress testing. To the best of our knowledge, this finding is not reported in the literature on exercise electrocardiography [8,9,10,11,12].

Case Report
A 73 years male presented for treadmill stress electrocardiography. He had history suggestive of angina on effort. Resting supine heart rate was 63 beats per minute. Resting supine blood pressure was 140/80 mm Hg. Resting supine electrocardiogram ( Fig.1) was within normal limits except shallow inversion of the T wave in lead aVL (marked as ) and counter clockwise rotation in horizontal plane (RS configuration with positive T wave in lead V2). Patient could exercise only for five minutes (4.1 METs) because of development of chest pain. Peak heart rate was 130 beats per minutes (88% of the age predicted maximal heart rate using the formula of 220-age). Immediate recovery electrocardiogram in supine position showed more than 2mm ST-segment depression in leads I, II, aVF, V3, V4, V5 and V6 ( Fig.2 and 3, marked as ). QRS amplitude showed alternans in leads I, II, III, aVL, aVF, V3, V4, V5 and V6 ( Fig.2 and 3, marked as 'a' and 'b'). ST-segment was elevated in lead aVR and V1 ( Fig.2 and 3, marked as ).

Discussion
Significant ST-segment depression in more than six leads with elevation of the ST-segment in leads aVR and V1 at low workload and development of angina strongly suggest significant left main or multivessel disease [10,[13][14][15][16][17]. ST-segment changes appearing only during recovery have some predictive power of angiographic coronary artery disease as ST-segment changes occurring during exercise [18,19]. It is, thus, clear that our patient had significant extensive myocardial ischemia.
There is no literature on QRS alternans during treadmill stress electrocardiography. It has been suggested that this electrocardiographic finding in the presence of an underlying organic heart disease may be accompanied by pulsus alternans [2] i.e., change in the volume of arterial pulse in alternate beats. Pulsus alternans generally occurs in severe heart failure and has been attributed to cyclic changes in intracellular calcium and action potential duration [20] (Figure 4). It is possible that severe extensive ischemia during exercise resulted in exercise induced left ventricular failure and consequent QRS alternans.
Another possibility is that severe ischemia results in 'stunning' of a large part of the myocardium [21] Such myocardium could take longer period to repolarise and may be excitable only at the time of alternate QRS complex ( Figure 5). This may result in large QRS in alternate beats.

Conclusion
QRS alternans with ST-segment depression in multiple leads could be suggestive of extensive myocardial ischemia and exercise induced left ventricular dysfunction.