Electrocardiographic Q-Wave "Remodeling" in Reperfused STEMI: Validation Study With CMR

Authors, Journal, Affiliations, Type, DOI

• Authors: Anca Florian, Massimo Slavich, Pier Giorgio Masci, Stefan Janssens, Jan Bogaert
• Journal: JACC: Cardiovascular Imaging, Vol. 5, No. 10, October 2012, pp. 1003–13
• Affiliations: Department of Radiology, UZ Leuven, Belgium; Cardiac MRI and Cardiovascular Medicine, Fondazione CNR "G. Monasterio," Pisa, Italy; Department of Cardiovascular Diseases, UZ Leuven, Belgium
• Type: Original prospective cohort study (retrospective identification from a double-blind RCT)
• DOI: https://doi.org/10.1016/j.jcmg.2012.02.018

Overview

This 5-year prospective validation study (n=46, Leuven) followed patients after a first successfully reperfused STEMI treated with primary PCI, performing serial ECG and LGE-CMR at 4 time points (1 week, 4 months, 1 year, 5 years). ECG-based Q-wave detection using ESC/ACCF/AHA/WHF consensus criteria was found to be unreliable and progressively worsens after reperfusion — 23% of patients had non-diagnostic ECGs within 1 week of infarction, nearly doubling to 44% by 5 years. Q-wave presence is primarily driven by infarct size (not transmurality), with a relative infarct size cutoff of 6.2% at 1 year predicting Q-wave presence with 89% sensitivity and 74% specificity (AUC 0.85). LGE-CMR confirms persistent irreversible scar in ECG-normalized patients, establishing that Q-wave regression represents pseudo-normalization, not true healing.

Keywords

Cardiac magnetic resonance, electrocardiography, myocardial infarction

Key Takeaways

Study Design and Population

• 46 patients with first reperfused STEMI (primary PCI within 12 h); 50% anterior (LAD), 50% nonanterior (RCA/CX); mean age 54±9 years; 89% male
• Serial ECG and CMR at day 4 (CMR) and day 7 (ECG) baseline, then 4 months, 1 year, and 5 years
• CMR on 1.5T (Philips); LGE-CMR used as reference standard for infarct presence, location, size, and transmurality; T2-weighted imaging for area at risk (AAR)
• ESC/ACCF/AHA/WHF criteria used for Q-wave assessment (pathological Q wave: ≥0.02 s in V2-V3; ≥0.03 s and 0.1 mV deep in I, aVL, V4-6, II, III, aVF); blinded analysis by 2 cardiologists

Electrocardiographic Q-Wave Expression at Baseline

• At 1 week post-STEMI, 36 of 46 patients (78%) had a diagnostic ECG; 23% were non-diagnostic despite confirmed LGE-CMR infarction
• Non-diagnostic ECGs associated with significantly smaller infarct size (8.6±7.0 g vs 22.5±15.9 g; p<0.0001), smaller AAR, smaller LV volumes and mass
• All anterior MIs (n=17) were correctly localized by ECG; in 7 of 19 nonanterior Q-wave infarcts, the location or extent was misjudged
• None of the baseline non-diagnostic patients developed Q waves at any follow-up time point

Q-Wave Remodeling Over 5 Years

• At 4-month/1-year follow-up, 10 patients (21%) developed non-diagnostic ECGs (3 anterior, 7 nonanterior); ECG remained non-diagnostic at 5-year follow-up
• All new non-diagnostic ECGs emerged within the first year; no new conversions between 1 and 5 years
• The frequency of non-diagnostic ECGs rose from 23% at baseline to 44% at 5 years
• Infarct size significantly decreased (20±12 g → 12±9 g → 10±8 g → 9±7 g; p<0.001 for trend); anterior infarcts remained larger than nonanterior at all time points
• The number of Q waves did not change significantly over time; a moderate correlation between relative infarct size and Q-wave count emerged for anterior infarcts at long-term follow-up (r≈0.56–0.58, p<0.01) — absent in the acute phase

Infarct Size as the Determinant of Q-Wave Presence

• Infarct size, not transmurality, is the primary ECG determinant — consistent with prior CMR literature
• ROC analysis: relative infarct size predicted diagnostic ECG with AUC 0.76 at baseline, increasing to AUC 0.84 at 5 years
• A relative infarct size of 6.2% of LV mass at 1 year was the optimal cutoff: sensitivity 89%, specificity 74%, AUC 0.85 (95% CI 0.75–0.96)
• This 6.2% cutoff is substantially lower than the 17% cutoff reported by Kaandorp et al. (pre-reperfusion era, larger infarcts) — the threshold is era- and treatment-dependent

LGE-CMR vs ECG: Pseudo-Normalization

• LGE-CMR at 5 years confirmed persistent scar in all patients including those with non-diagnostic ECGs — Q-wave regression is pseudo-normalization, not true healing
• Infarct transmurality maintained at 5 years in 14/15 anterior and 12/17 nonanterior transmural MIs
• ECG correctly locates anterior MI but frequently fails for nonanterior territories; lateral infarcts often electrically silent (multiple prior studies cited: Rovai, Cino)
• ECG-derived infarct size estimates correlate only modestly with LGE-CMR, especially for lateral infarcts

Clinical Significance of Electrically Silent Infarcts

• Electrically silent MIs (no Q waves but confirmed LGE scar) have prognosis equivalent to overt Q-wave MIs (referenced from Barbier 2006, Krittayaphong 2009, Kwong 2008)
• Non-diagnostic ECGs are clinically silent but represent true irreversible myocardial damage
• LGE-CMR is the recommended technique to detect myocardial damage in patients with suspected previous MI and non-diagnostic ECG

Limitations of the Document

• Small sample size (n=46) — most important limitation; underpowered for subgroup analyses
• Population retrospectively identified from a bone marrow stem cell transfer RCT (Janssens 2006, Lancet 367:113–21); may not represent all STEMI patients
• Patients with ECG confounders (LBBB, LVH, paced rhythm) excluded — reduces applicability to a large clinical subgroup
• Only ESC/ACCF/AHA/WHF criteria used; pre-PCI ECG not analyzed; no inferences about post-PCI ST-segment shifts and their effect on subsequent Q-wave expression
• Qualitative rather than scoring system approach (Sylvester score excluded as less accurate in reperfusion era)
• Single centre, 1.5T CMR; study population included patients from a controlled trial rather than consecutive STEMI cohort

Key Concepts Mentioned

• concepts/Q-Wave-Remodeling — central subject; pseudo-normalization; size vs transmurality determinism; 6.2% cutoff
• concepts/Late-Gadolinium-Enhancement — reference standard for MI detection; persistent scar despite ECG normalization
• concepts/ST-T-Changes — Q-wave criteria used (ESC/ACCF/AHA/WHF consensus)
• concepts/Myocardial-Viability — transmural LGE extent and scar persistence

Key Entities Mentioned

• entities/Acute-Coronary-Syndrome — STEMI patient population; reperfusion with primary PCI context

Wiki Pages Updated

• Created: wiki/sources/qwave-mri-jacc-imaging-2012.md
• Created: wiki/concepts/Q-Wave-Remodeling.md
• Updated: wiki/concepts/Late-Gadolinium-Enhancement.md (added Post-MI Scar Detection subsection; source_count 4→5)
• Updated: wiki/concepts/ST-T-Changes.md (added Q-Wave Formation and Regression subsection; source_count 1→2)
• Updated: wiki/wikiindex.md
• Updated: wiki/sourceindex.md