Extraction of buried P waves from printed electrocardiograms

BACKGROUND

Morphologic identification of ectopic P-waves from surface ECGs can be challenging, particularly when the P-wave is buried in the QRST wave complex. Because ECGs are often available on paper and not digitally, we developed a method of subtracting the T-wave from the buried P-wave complex on paper ECGs.

METHODS

To validate our system, an atrial extrastimulus was introduced during and following the T-wave. The ECGs were scanned and then transformed from an image format to a digital format. A computer algorithm digitally subtracted a QRST with no buried P-wave from one with a buried P-wave, thus resulting in an extracted P-wave. The extracted P-waves were compared to the nonburied P-wave by determining correlation coefficients and by visual grading by two independent reviewers.

RESULTS

Visual grading comparing the buried P-wave with the exposed paced P-wave was 94%. The median correlation coefficient was 85%.

CONCLUSIONS

An ectopic atrial P-wave obscured by a coincident QRST wave complex can be accurately derived from printed ECG using this PC-based system. Addition of this technique to the existing methods may aid in the localization and ablation of ectopic atrial foci.

Does dual chamber or atrial pacing prevent atrial fibrillation? The need for a randomized controlled trial

Partially due to recent reports that cardiac antiarrhythmic therapy may have adverse effects on patient survival, clinicians have become more interested in the nonpharmacological prevention of atrial fibrillation. There is a large body of literature that suggests that the rate of development of atrial fibrillation in paced sick sinus syndrome patients is much lower in those patients who have received an atrial-based system, rather than a VVI system. However, all the published studies to date are retrospective, and fraught with potential bias favoring the AAI or DDD group. The authors strongly believe that the only way to determine if these suggestive but uncertain retrospective analyses are correct is to apply the same scientific rigor to this problem as has been applied to many other problems in cardiovascular medicine and perform a prospective randomized trial. A proposed trial design is discussed.

Reversible acute pulmonary edema due to uncontrolled hyperglycemia in diabetic individuals with renal failure

On eight separate occasions, four functionally anephric diabetic patients (on maintenance hemodialysis) experienced episodes of severe hyperglycemia with acute interstitial and alveolar pulmonary edema demonstrated clinically and by chest x-ray without electrocardiographic or enzymatic evidence of an acute myocardial lesion. Three patients had normal stress 201T1 scanning. The fourth patient, who experienced three such episodes, had normal coronary angiograms and only a mild elevation of the left-ventricular end-diastolic pressure. Clinical and chest x-ray improvement were immediate following insulin therapy and control of hyperglycemia, without phlebotomy or dialysis. Since these episodes were observed during a 1-yr period, this syndrome may be more common than suspected. It is concluded that in functionally anephric diabetic individuals: (1) pulmonary edema can be precipitated by uncontrolled diabetes; (2) endogenous fluid shifts may contribute to the cause of acute pulmonary edema; (3) clinical and radiologic improvement can be achieved with adequate insulin therapy; and (4) blood glucose levels should be monitored and controlled in diabetic patients with renal failure.