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Background: Preexcitation syndrome is characterized by a dominant delta wave on the baseline electrocardiogram (ECG), resulting from the change in QRS initial vector by the accessory pathway (AP). This study is to explore the effect of ventricular preexcitation on the QRS initial, maximal and terminal vector in an experimental rabbit with preexcitation syndrome induced by programmed electrical stimulation., Methods: Rabbits (n = 10) were randomized for the experimental model of ventricular preexcitation. Sensing and stimulating electrode catheters were placed in the high right atrium and along epicardial surface of atrioventricular groove of the left ventricular anterior wall, respectively. Programmed premature stimulation S 2 was synchronized with P wave and utilized to stimulate the ventricle. The ECG recorded the electrical activity of the heart. As compared with the QRS complex during sinus rhythm, paced QRS was assessed regarding the initial, maximal and terminal vector. PS 2 interval and PR interval were also measured and analyzed., Results: Preexcitation was successfully simulated by ventricular pacing in the rabbits, including (1) Complete preexcitation: PS 2 interval was less than PR interval; the difference was more than or equal to 47.00 ± 7.53 ms. (2) Incomplete preexcitation: PS 2 interval was less than PR interval; the difference was less than 47.00 ± 7.53 ms. (3) Incomplete latent preexcitation: PS 2 interval was more than or equal to PR interval; the difference was less than or equal to 13.00 ± 3.50 ms. (4) Complete latent preexcitation: PS 2 interval was more than or equal to PR interval; the difference was more than 13.00 ± 3.50 ms., Conclusions: The difference in the relative conduction velocity of the atrioventricular node versus the AP pathways determines the degree of preexcitation and different manifestation on ECG. The QRS terminal vector also reflects the ventricle preexcitation, indicating a valuable sign for the diagnosis of atypical or latent preexcitation.

Objective: The P-QRS-T wave on surface electrocardiogram (ECG) reflects the changes in atrial and ventricular electrical properties. However, the atrioventricular conduction system potentials cannot be recorded to date. This study aimed to explore the possibility of micropotential of the atrioventricular conduction system recorded by surface "SAN-Atrial-AVN-His (Saah) ECG.", Methods: We randomized 100 healthy volunteers (50 females and 50 males; mean age 25.12±1.62 years) to receive "conventional 12-lead ECG" and "Saah ECG," which were recorded by the "Saah ECG" machine. We recorded and further analyzed "conventional 12-lead ECG" and "Saah ECG." According to the microwavelets before the QRS complex, the PR interval was the sum of three intervals: PAs interval (PA interval recorded on surface ECG), AHs interval (AH interval recorded on surface ECG), and HVs interval (HV interval recorded on surface ECG). The PR interval, PAs interval, AHs interval, and HVs interval were measured., Results: Not only the P-QRS-T waves but also the microwavelets before the P wave, before the QRS complex, and after the QRS complex were recorded in 100 healthy volunteers. The PAs interval, AHs interval, and HVs interval were 22-37 (31.23±2.93) ms, 60-103 (76.07±13.43) ms, and 39-55 (49.29±4.44) ms, respectively. The PAs interval, AHs interval, and HVs interval were consistent with the intracardiac measurements (PA, AH, and HV intervals) obtained in previous studies. Compared with female volunteers, male volunteers had a longer AHs interval (p<0.05)., Conclusion: Not only the P-QRS-T waves but also the microwavelets before the P wave, before the QRS complex, and after the QRS complex were recorded on surface ECG. The wavelets before the QRS complex may be related to atrioventricular nodal, His bundle (bundle branch) potentials.

In our study, not only the P-QRS-T waves but also the micro-wavelets before QRS complex (in P wave and PR segment) and after QRS complex (ST segment and upstroke of T wave) were first to be identified on surface electrocardiogram in human by the "new electrocardiogram" machine (model PHS-A10) according to conventional 12-lead electrocardiogram connection methods. By comparison to the conventional electrocardiogram in 100 cases of healthy individuals and several patients with arrhythmias, we have found that the wavelets before P wave theoretically reflected electrical activity of sinus node and the micro-wavelets before QRS complex may be related to atrioventricular conduction system (atrioventricular node, His bundle and bundle branch) potentials. Noninvasive atrioventricular node and His bundle potential tracing will contribute to differentiation of the origin of wide QRS and the location of the atrioventricular block. We also have found that the wavelets after QRS complex may be associated with phase 2 and 3 repolarization of ventricular action potential, which will further reveal ventricular repolarization changes. [ABSTRACT FROM AUTHOR]

We reported a case about the slow heart rate and regular heart rhythm that appeared after administration of digitalis, diuretics and potassium in a patient with chronic atrial fibrillation ten years. ECG characteristics demonstrated the special changes about hyperkalemia as follows: f waves disappeared; nonspecific widened QRS complex appeared; RR interval was regular; and heart rate slowed. T wave inversion reverted to be symmetrical and peaked. Laboratory investigations were noteworthy for serum potassium elevations (serum potassium was 8.50 mmol/L). In patients with chronic atrial fibrillation, digitalis administration, diuretic therapy and potassium supplementation can induce slow heart rate and regular heart rhythm. These changes may permit prompt recognition of overt digitalis toxicity-atrioventricular block. However, these have also frequently been seen in the setting of chronic renal insufficiency, resulting in hyperkalemia. The basic principles of treatment were different in these two conditions. Therefore, ECG and laboratory investigation should draw a clinician's attention. [ABSTRACT FROM AUTHOR]