Normal ECG still doesn't rule out PE

ECGs from a prospective study of patients in the ED with suspected pulmonary embolism were studied to identify the relative frequency of ECG features of pulmonary hypertension. For a patient to be eligible for enrollment, a physician was required to have sufficient suspicion for pulmonary embolism to order objective diagnostic testing in the ED. Such testing included D-dimer measurement, computed tomography pulmonary angiography, ventilation/perfusion scanning, or venous ultrasonography.
ECGs were done in 6049 patients, 354 (5.9%) of whom were diagnosed with pulmonary embolism. The frequency, positive likelihood ratio (LR+) and 95% confidence interval (CI) of each predictor were as follows:

  • S1Q3T3 8.5% with pulmonary embolism versus 3.3% without pulmonary embolism (LR+ 3.7; 95% CI 2.5 to 5.4)
  • nonsinus rhythm, 23.5% versus 16.6% (LR+ 1.4; 95% CI 1.2 to 1.7)
  • inverted T waves in V1 to V2, 14.4% versus 8.1% (LR+ 1.8; 95% CI 1.3 to 2.3)
  • inversion in V1 to V3, 10.5% versus 4.0% (LR+ 2.6; 95% CI 1.9 to 3.6)
  • inversion in V1 to V4, 7.3% versus 2.0% (LR+ 3.7; 95% CI 2.4 to 5.5)
  • incomplete right bundle branch block, 4.8% versus 2.8% (LR+ 1.7; 95% CI 1.0 to 2.7)
  • tachycardia (pulse rate>100 beats/min), 28.8% versus 15.7% (LR+ 1.8; 95% CI 1.5 to 2.2).

The authors point out that the study may be subject to reporting bias or incorporation bias because those patients with ECG abnormalities may have then been more likely to undergo further evaluation for PE.
Overall, they summarise that the main findings were that the S1Q3T3 pattern and precordial T-wave inversions had the highest LR(+) values with lower-limit 95% CIs above unity, whether or not the patient had preexisting cardiopulmonary disease, but emphasise that the sensitivities of each of these findings were low, and clinicians should not decrease their suspicion for pulmonary embolism according to their absence.
Likelihood ratios and specificities were similar when patients with previous cardiopulmonary disease were excluded from analysis.
12-Lead ECG Findings of Pulmonary Hypertension Occur More Frequently in Emergency Department Patients With Pulmonary Embolism Than in Patients Without Pulmonary Embolism
Ann Emerg Med. 2010 Apr;55(4):331-5