P wave area for quantitative electrocardiographic assessment of left atrial remodeling

Abstract

Background: Left atrial (LA) dilation provides a substrate for mitral regurgitation (MR) and atrial arrhythmias. ECG can screen for LA dilation but standard approaches do not assess LA geometry as a continuum, as does non-invasive imaging. This study tested ECG-quantified P wave area as an index of LA geometry.

Methods and results: 342 patients with CAD underwent ECG and CMR within 7 (0.1±1.4) days. LA area on CMR correlated best with P wave area in ECG lead V1 (r = 0.42, p<0.001), with lesser correlations for P wave amplitude and duration. P wave area increased stepwise in relation to CMR-evidenced MR severity (p<0.001), with similar results for MR on echocardiography (performed in 86% of patients). Pulmonary arterial (PA) pressure on echo was increased by 50% among patients in the highest (45±14 mmHg) vs. the lowest (31±9 mmHg) P wave area quartile of the population. In multivariate regression, CMR and echo-specific models demonstrated P wave area to be independently associated with LA size after controlling for MR, as well as echo-evidenced PA pressure. Clinical follow-up (mean 2.4±1.9 years) demonstrated ECG and CMR to yield similar results for stratification of arrhythmic risk, with a 2.6-fold increase in risk for atrial fibrillation/flutter among patients in the top P wave area quartile of the population (CI 1.1-5.9, p = 0.02), and a 3.2-fold increase among patients in the top LA area quartile (CI 1.4-7.0, p = 0.005).

Conclusions: ECG-quantified P wave area provides an index of LA remodeling that parallels CMR-evidenced LA chamber geometry, and provides similar predictive value for stratification of atrial arrhythmic risk.

Figure 1. P wave and Left Atrial Area Quantification.

Representative examples of LA quantification methods: For ECG (top), total P wave area was quantified based on geometric area (green shading) between the electrical waveform and the isoelectric line. Corresponding indices of amplitude (red line) and duration (blue line) were measured within the total P wave complex, as well as its positive and negative components. For CMR (bottom), LA area was measured by planimetry of chamber borders (green line) at ventricular end-systole. Note heterogeneity in P wave morphology among patients with LA enlargement: Whereas both patient examples demonstrate LA dilation by CMR, a bimodal P wave with large negative terminal component is present in 1A, whereas a bifid but upright P wave is present in 1B.

Figure 2. Left Atrial Size.

Scatter plots relating CMR-quantified LA size to P wave morphology as measured in ECG lead V1. Data presented for total P wave area (1A), negative terminal area (1B), duration (1C), and maximum amplitude (1D). Patient data stratified based on normal (grey) and dilated (black) left atrial size on cine-CMR using an established diagnostic cutoff (>15 cm²/m²) .

Figure 3. Mitral Regurgitation Severity.

P wave area in lead V1 (mean ± standard deviation) in relation to MR severity on cine-CMR (3A) and echo (3B). Note that P wave area increased stepwise in relation to MR severity as measured by both modalities, with greatest magnitude of increase at a threshold of moderate-severe MR (black bars).

Figure 4. Pulmonary Arterial Pressure.

Pulmonary arterial systolic pressure (mean ± standard deviation) among population subgroups stratified based on lead V1 P wave area quartiles (≤1.92 | 1.93–2.70 | 2.71–3.65 | >3.65 mV·msec). Black bar = top P wave area quartile.

Figure 5. Atrial Fibrillation/Flutter Risk as Stratified by LA Remodeling Indices.

Kaplan-Meier plots relating baseline P wave area (5A) and body surface area indexed LA area (5B) to follow-up risk for AF/AFl. Note that both ECG and CMR indices demonstrated increased risk for AF/AFl among patients in the highest quartile of LA remodeling.