What does a consistent increase and decrease in QRS (electrocardiogram complex) amplitude indicate?

Consistent Increases and Decreases in QRS Amplitude on ECG

Consistent increases and decreases in QRS amplitude on ECG typically represent respiratory variation, a normal physiological finding, but can also indicate pathological conditions such as pericardial effusion, cardiac tamponade, or myocardial ischemia in certain clinical contexts. 1

Normal Physiological Variation

• In normal subjects, QRS amplitude typically increases during submaximal exercise, followed by a decrease at maximum exercise, representing normal physiological response 1
• Respiratory variation causes cyclical changes in QRS amplitude due to changes in cardiac position relative to the chest wall during breathing 1

Pathological Causes of QRS Amplitude Changes

Myocardial Ischemia

• An increase in R-wave amplitude at peak exercise (rather than the normal decrease) has been associated with myocardial ischemia, potentially correlating with left ventricular ischemic dilatation 1
• Transmural myocardial injury is associated with both QRS prolongation and enlarged R-wave amplitude in leads with ST segment elevation, distinguishing it from epicardial injury 2

Heart Failure

• QRS amplitude decreases during worsening heart failure and returns to baseline with clinical recovery 3
• A ≥16% reduction in the summed QRS amplitude of limb leads can discriminate between stable and worsening heart failure with high specificity (98%) 3
• Low QRS voltage is associated with congestive heart failure, while an increase in QRS voltage correlates with effective diuresis treatment 4

Left Ventricular Dysfunction

• Prolonged QRS duration (>0.10s) is a specific indicator of left ventricular dysfunction, with specificity increasing to 99.3% when QRS duration exceeds 0.12s 5
• Small increases in QRS duration are associated with reduced left ventricular ejection fraction, increased cardiac chamber dimensions, and risk for incident heart failure 4

Diagnostic Significance

• Exercise-induced changes in R-wave amplitude have not consistently improved diagnostic accuracy of the exercise ECG despite various lead systems and criteria being tested 1
• The QRS score (an index based on exercise-induced changes in Q, R, and S wave amplitudes) has been shown to complement ST-segment depression criteria for detecting coronary artery disease 1
• Dynamic changes in the T/QRS ratio between initial and follow-up ECGs can help distinguish disease severity and differentiate between non-ST elevation acute coronary syndrome and heart failure 6

Clinical Applications

• Monitoring QRS amplitude changes can be as useful as B-type natriuretic peptide (BNP) for tracking heart failure status, with similar area under the curve (0.78-0.84 vs. 0.88) for identifying worsening heart failure 3
• In patients with suspected pericardial effusion, a decrease in QRS amplitude across all leads may be observed, with resolution upon drainage 1
• The presence of fragmented QRS complexes (not just amplitude changes) is associated with myocardial fibrosis and increased risk of arrhythmic events 4

Pitfalls and Caveats

• QRS amplitude changes must be interpreted in clinical context, as isolated findings without other ECG or clinical abnormalities may represent normal variants 7
• Bundle branch blocks significantly alter QRS morphology and require specific criteria for interpreting amplitude changes 7
• Lead placement variations between ECG recordings can cause apparent changes in QRS amplitude that do not reflect true physiological or pathological changes 1
• Body habitus, particularly changes in body fat percentage, can affect QRS amplitude measurements, with studies showing correlation between changes in body fat percentage and QRS amplitude in limb leads 3