Paradigm Shifts in Cardiac Pacing: Where Have We Been and What Lies Ahead?

Figures

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  Figure 2. Results of Landmark Trials of Cardiac Resynchronization Therapy. ICM = ischemic cardiomyopathy; NICM = non-ischemic cardiomyopathy; QRSd = QRS duration; LVEDD = left ventricular end diastolic volume; 6MWD = 6-min walk distance; OMT = optimal medical therapy; CRT-D = cardiac resynchronization with defibrillation capabilities; CRT-P = cardiac resynchronization with pacing therapy only; NYHA = New York Heart Association; QOL = quality of life; HR = hazard ratio; HF = heart failure; HFH = heart failure hospitalization; CV = cardiovascular; MIRACLE [41]: CRT-P resulted in significant improvement in LVEF (p < 0.001); fewer HFH in CRT-P group (15 vs. 8%, p < 0.05); all patients in sinus rhythm; LBBB in almost 70% of patients; COMPANION [42]: CRT-P and -D both reduced the risk of the primary outcome by approximately 20%; no significant difference in mortality with CRT-P; addition of defibrillator significantly reduced risk of all-cause mortality by 36%; all patients in sinus rhythm; LBBB in almost 70% of patients; CARE-HF [43]: Patients with QRSd 120–149 must have 2 out of 3 for inclusion: 1. aortic pre-ejection delay >140 ms; 2. Interventricular mechanical delay >40 ms; 3. Delayed…

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  Figure 1. Various Methods of Cardiac Pacing. RV = right ventricle; HB = His bundle; LBBA = left bundle branch area; AV = atrioventricular.

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  Figure 3. Schematic Demonstrating the Concept of Longitudinal Fascicular Dissociation. Histological studies have demonstrated that the His-Purkinje (HP) system is composed of multiple fibers with few transverse connections between fibers due to insulating collagen that runs along the longitudinal axis. A significant proportion of “infra-Hisian” block is in fact “intra-Hisian”. This explains how patients with conduction system disease (bundle branch block) can experience normalization of conduction when pacing at a more distal location within the HP system. HB = His bundle; RB = right bundle; LAF = left anterior fascicle; LPF = left posterior fascicle.

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  Figure 4. ECG results after conduction system pacing. (A) Left bundle branch pacing (bipolar); (B) left bundle branch pacing (unipolar).

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  Figure 5. Chest X-Ray After Implantation of a Leadless Pacemaker. (A) PA projection; (B) lateral projection.