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Purpose: To evaluate the mechanisms and dynamics of episodes of progression to high degree (HD) atrioventricular (AV) block (B) analyzed during incremental atrial pacing (St), in patients with previous 2:1 His-Purkinje (HP) AVB., Methods: Data from 4 patients were analyzed. All of them with history of syncope and ECG exhibiting 2:1 AVB with wide QRS pattern. The AVB was in the HP system (HPS) in all. Every patient was submitted to electrophysiologic study with incremental atrial pacing, by which the conduction sequences and the AV conduction ratios (AVR) were analyzed. The basal (B) cycle length (CL) was defined as the shortest interval between two conducted beats (spontaneous or pacing-induced). The incremental atrial stimulation was performed beginning with CL 10 msec shorter than BCL until reaching 250 msec., Results: Nineteen episodes of progression to HD-AVB were seen. A) With StCL between 31 and 26% of BCL, AVR were 3:1, 4:1 and 5:1, with only one blocking zone (BZ) in the HPS; B) with StCL between 24 and 22% of BCL, AVR were 5:1, 7:2, 9:2e11:3. In this situation a 2nd BZ ensues-on proximal, site of a decremental conduction, situated in the AV node (AVN) or in the HPS, and the other (distal level) always in HPS; C) with StCL between 24 and 16% of BCL, AVR were 5:1, 6:1, 10:2, 11:2 and 12:3. Here, these AVR were explained by postulating 3 BZ where 2 were in AVN and 1 in HPS, or inversely with 1 in AVN and 2 in HPS. The decremental conduction occurred in 1 or 2 out 3 BZ and an integral conduction (like 2:1 or 3:1) in the others., Conclusion: The BCL is the determinant of the AVR observed. As the StCL is shortened (< 26% BCL) a 2nd or 3rd BZ in the AVN or in the HPS ensues. These observations suggest that the mechanisms and dynamics of progression to HD-AVB apply only during incremental atrial pacing and there is a clear difference with what has been observed with the progression occurring exclusively at AV node.

Purpose: To study the autonomic behavior of the escape rhythm in congenital complete heart block (CCHB), using heart rate variability (HRV)., Methods: A group of 10 asymptomatic patients with CCHB and narrow QRS was studied, 7 females; mean age = 14 +/- 9 years. The following time domain indexes were analyzed from a 24 hour Holter monitoring. The mean of all RR intervals (NN); the standard deviation of the mean (CLV5); the mean of all standard deviations (SDNN); the percent of successive differences longer than 50 ms (pNN50); the shortest cycle (CC) and the longest cycle (CL). The results were compared with a control group, using the Wilcox test for statistical analysis., Results: The results were: NN = 1016 +/- 276 ms in CHB and 725 +/- 121 ms in control (p < 0.01); CLV5 = 184 +/- 97 ms in CHB and 125 +/- 38 ms in control (p = NS); SDNN = 102 +/- 32 ms in CHB and 88 +/- 29 ms in control (p = NS); rMSSD = 113 +/- 69 ms in CHB and 78 +/- 28 ms in control (p = NS); pNN50 = 43 +/- 26% in CHB and 33 +/- 12% in control (p = NS); CC = 582 +/- 129 ms in CHB and 333 +/- 49 ms in control (p = 0.05)., Conclusion: No statistical difference was noted by comparing HRV indexes in CHB with control subjects, showing that the autonomic behavior of the escape rhythm in CCHB is similar to the sinus node in asymptomatic patients. The differences in NN, CC and CL are probably related to intrinsic properties of each command.

In a prospective study 51 consecutive patients who survived the acute phase of inferior wall myocardial infarction underwent coronary arteriography. Eleven patients developed some degree of atrioventricular (AV) block in the acute phase of infarction that disappeared within a few days and was considered by electrocardiographic analysis to be located in the AV node. Patients with AV block during acute myocardial infarction had a significantly higher prevalence of left anterior descending coronary artery obstruction (91 versus 55%, p less than 0.05) than did patients without AV block and the obstruction preceded the exit of the first septal perforator branch in 73% of cases with heart block and in 30% of cases without block (p less than 0.01). The sensitivity, specificity and predictive values were 31, 95 and 91%, respectively, for the existence of left anterior descending coronary artery obstruction when AV block occurred during acute inferior myocardial infarction, and 40, 90 and 73%, respectively, for the occurrence of the coronary artery obstruction before the exit of the first septal perforator branch. Patients with inferior myocardial infarction and left anterior descending coronary artery obstruction have a sixfold greater chance of developing heart block in the acute phase of infarction than do patients with inferior infarction without such obstruction (p less than 0.05). These findings also support the observations that the proximal AV conduction system usually has a dual arterial blood supply from both the right and left anterior descending coronary arteries, and may explain the transient behavior of heart block and lack of necrosis of the AV node seen in these patients.