Josephson Clinical Cardiac Electrophysiology

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Chapter 5: Miscellaneous Phenomena Related to Atrioventricular Conduction ■

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385

385

385

385

385

385

385

385

I

II

III

A

A

A

A

A

A

A

A

A

HRA

A H A H V V

V

A HV AHV AHV AHV AH AHV A

H V

HBE HBE

T

A

4:3 WENCKEBACH

H

RB

LB

Recovery Time of RBB

B

QRS: RBBB

RBBB

RBBB

NORMAL

RBBB

FIGURE 5.18 “Pseudo-supernormal” conduction due to Type I (Wenckebach) second-degree block in the right bundle branch (RBB). A. Superventricular tachycardia with RBB block (RBBB) is shown at a cycle length of 385 msec. The fourth and eighth complexes (asterisks) manifest normal conduction. B. Repetitive normalization in this manner can be explained by a Wenckebach-type block in the RBBB, which is schematically presented. In A , the normal, constant H-V interval (45 msec) suggests normal conduction through the left bundle (LB) branches. Conduction through the RBB is progressively impaired because of some area of prolonged refractoriness. The first two impulses variably penetrate this area, while the third complex fails to engage the area. This effectively doubles the cycle length of the impulses that reach the critical area of delay, allowing time for recovery and subsequent normal conduction. (Reprinted from Gallagher JJ, Damato AN, Varghese PJ, et al. Alternative mechanisms of apparent supernormal atrioventricular conduction. Am J Cardiol . 1973;31:362, with permission from Elsevier.)

1 2 3 V1

A

A

A

A

A

HRA

A

V

A

A

H V

A

A H V

H

270

270

270

HBE

T

1 2 3 V1 HRA

A

A

A

A

A

A

A

V

A

A

AV’ H

H

H

HBE

295

290

255

V-V’ 455

T

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FIGURE 5.19 Facilitation of atrioventricular (A-V) modal conduction by a ventricular premature depolarization (VPD). The basic rhythm is sinus with stable 2:1 block in the A-V node. The A-H interval on conducted beats ranges from 270 to 295 msec. A ventricular extrastimulus is introduced (S), and the sinus impulse that would have expected to block in the A-V node conducts through the node with an A-H interval of 255 msec. This probably results from summation of the blocked impulse and the retrogradely concealed VPD. See text for details.