ABSTRACT
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.
Subject(s)
Humans , Male , Female , Middle Aged , Heart Block/physiopathology , Atrioventricular Node/physiopathology , Purkinje Fibers , Electrocardiography , Heart Block/therapy , Cardiac Pacing, Artificial , Bundle of His/physiopathologyABSTRACT
Avaliar a funçäo do nó A-V (NAV) pela determinaçäo do período de Wenckebach (PW) e pela resposta à atropina nos casos de intervalo PR normal, no limite máximo normal e prolongado, todos com WRS estreito. Cento e vinte e nove pacientes, 79 homens, idades de 59 ñ 20 anos, assintomáticos ou com queixas de palpitaçöes, tonturas, pré-síncope e síncope, com ECG de taquicardia supraventricular, bloqueio A-V de 1§ grau (BAV 1§), de 2§ grau tipo Mobitz I intermitente e doença de nó nsinusal. Excluídos síndrome de pré-excitaçäo e dissociaçäo longitudinal do nó A-V. Cardioestimulaçäo atrial transesofágica realizou-se em todos os casos para avaliaçäo de atropina. Segundo o PW obtido, os pacientes foram divididos em 3 grupos: I, PW >= 125 ppm (N = 88); II, PW entre 125 e 110 ppm (N = 16) e III, PW <= 110 ppm (N = 25). Houve correlaçäo linear decrescente entre o PR e PW somente no grupo II (5 = 0,76 e p < 0,01). Houve incidência significativamente maior de PR > 240 ms no grupo III em relaçäo aos outros grupos e a resposta à atropina foi melhor nos casos de PR <= 240 ms, onde houve maior número de normalizaçäo do PW. Há correlaçäo linear decrescente entre o PR do ECG e o PW para indivíduos com PW <= 110 ppm: PR maior de 240 ms correspondeu melhor a PW abaixo de 110 ppm (em torno de 90 ppm), a maioria näo se normalizou com a atropina, considerando-se adequada a denominaçäo para estes casos de "bloqueio" A-V de 1§ grau. Para os BAV 1§ com PR menores de 240 ms, que se normalizaram com a atropina ...