Correlation between R wave amplitude and exercise ischemic electrocardiographic indices

The ECG exercise test (ET) is still widely used for diagnosis of coronary artery disease (CAD) and new ECG indices are introduced or old indices reevaluated. In this study we investigated the relation between R wave amplitude (RWA) and ST depression magnitude as well as other approved ischemic ECG indices during ET in patients (pts) with coronary artery disease (CAD). We also examined the potential relation between ECG indices and the presence and extent of reversible ischemia in thallium-201 scanning.MethodsWe studied 49 pts, mean age 60 ± 10, with angiographically documented CAD, including significant left anterior descending (LAD) disease and an ECG positive ET. All pts underwent a treadmill ET on the Bruce protocol as well as a Tl-201 SPECT scan. RWA was measured in all leads both at rest and during ET. ECG indices measured and/or calculated on exercise were: ST depression in all leads, ΔST/ΔHR in V5 and Athens QRS score. A total Tl-201 ischemic reversibility score was derived as the sum of segmental score over 3 segments (scale 0-3, where 0=scar, 1=ischemia and scar, 2=reversible ischemia, 3=normal).ResultsMean % maximal achieved heart rate was 86 ± 13% and mean maximal ST depression was 2.5 ± 0.9 mm. Twenty two (45%) pts reported angina during ET. The most significant correlation between RWA at rest and ST depression at peak exercise was shown in leads III (r = 0.70, p < 0.01), aVF (r = 0.71, p < 0.01) and V4 (r = 0.52, p < 0.01). There was a significant correlation between RWA at rest and RWA during ET (r = 0.89, p < 0.01 for lead V5 and r = 0.88, p < 0.01 for lead aVF). RWA at rest correlated with ΔST/ΔHR (V5) (r = 0.48, p < 0.01).No correlation was shown between ΔST/ΔHR and Tl-201 total score. A statistically significant correlation was shown between the segmental Tl-201 score in the lateral wall and both ST depression magnitude at peak exercise in lead V4 (r = − 0.43, p < 0.01), as well as the number of diseased vessels (r = − 0.32, p < 0.05).An RWA ≥ 10 mm in lead II at rest can predict a ≥ 1 mm ST depression in this lead with a 90% sensitivity and 100% specificity, while RWA ≥ 10mm in lead V4 at peak exercise can predict a ≥ 2 mm ST depression in the same lead with an 80% sensitivity and 67% specificity. ST depression is unusual (3 - 6%) in leads with a low RWA (≤ 5 mm) despite a reversible Tl-201 defect. Findings were similar concerning a subgroup of 18 pts with single LAD disease.ConclusionRWA both at rest and during ET correlates with the magnitude of ST depression changes in the same leads. Greater ST changes appear on leads with highest RWA. Thus lead selection strongly influences interpretation of ECG ischemic changes during ET in pts with CAD. An electrocardiographic result negative for ischemia, as assessed by ST-segment depression, could be explained in patients manifesting leads with low R wave voltage. In these patients, echocardiographic and scintigraphic methods of recording ischemia should be sought. This finding may also have practical significance in selecting leads for Holter monitoring of ischemia