Treatment of Interventricular Conduction Delay

Understanding Interventricular Conduction Delay

Interventricular conduction delay occurs when there is abnormal electrical propagation between the ventricles, most commonly manifested as bundle branch blocks or nonspecific intraventricular conduction delay (NICD) 1
This electrical dyssynchrony can result in reduced ventricular systolic function, altered myocardial metabolism, functional mitral regurgitation, and adverse remodeling with ventricular dilatation 2
QRS prolongation occurs in approximately one-third of patients with advanced heart failure and is associated with worse outcomes 2

For patients with acute myocardial infarction and symptomatic/hemodynamically significant bradycardia due to conduction delay, temporary pacing is indicated, as recommended by the American Heart Association 3
If symptomatic or hemodynamically significant sinus bradycardia or AV block occurs at the AV nodal level, atropine administration is reasonable, according to the American College of Cardiology 4
For persistent second-degree Mobitz type II, high-grade AV block, alternating bundle-branch block, or third-degree AV block following myocardial infarction, permanent pacing is indicated after an appropriate waiting period, as suggested by the American Heart Association and the American College of Cardiology 3, 5

The American College of Cardiology recommends cardiac resynchronization therapy (CRT) for patients with left bundle branch block (LBBB), QRS duration ≥150 ms, left ventricular ejection fraction (LVEF) ≤35%, and New York Heart Association (NYHA) class II-IV symptoms despite optimal medical therapy 6, 2
CRT should be considered for patients with non-LBBB morphology, QRS duration ≥150 ms, and LVEF ≤35%, as stated by the European Society of Cardiology and the American College of Cardiology 7, 2
For NYHA class I patients with ischemic etiology, LBBB, QRS ≥150 ms, and LVEF ≤30%, CRT may be considered (Class IIb), according to the American College of Cardiology 2

The development of interventricular conduction delay following myocardial infarction reflects extensive myocardial damage rather than an isolated electrical problem, as noted by the American Heart Association and the American College of Cardiology 8, 5
Patients with anterior myocardial infarction and associated conduction impairment generally have worse prognosis than those with inferior myocardial infarction, as reported by the American Heart Association 8
For patients requiring CRT, the choice between CRT-Pacemaker and CRT-Defibrillator (CRT-D) should be based on overall risk assessment, as recommended by the American Heart Association 9

For patients with first-degree AV block or second-degree Mobitz type I AV block with unclear symptoms, ambulatory electrocardiographic monitoring is reasonable to establish correlation between symptoms and rhythm abnormalities, according to the American College of Cardiology 10

Implanting permanent pacemakers too early (<72 hours) after myocardial infarction, as conduction abnormalities may resolve with reperfusion and recovery, as cautioned by the American College of Cardiology 4
Failing to recognize that interventricular conduction delay in myocardial infarction reflects extensive myocardial damage rather than an isolated electrical problem, as emphasized by the American Heart Association 8
Overlooking the importance of QRS morphology (LBBB vs. non-LBBB) and duration (≥150 ms vs. 120-149 ms) in determining the likelihood of response to CRT, as highlighted by the American College of Cardiology 6, 2

The American College of Cardiology recommends CRT for patients with left ventricular ejection fraction (LVEF) ≤35%, sinus rhythm, left bundle branch block (LBBB) with QRS duration ≥150 ms, and NYHA class II, III, or ambulatory IV symptoms on guideline-directed medical therapy (GDMT), with approximately 30% decrease in hospitalizations and 24-36% reduction in mortality 11, 12, 13
The American College of Cardiology suggests CRT can be useful for patients with LVEF ≤35%, sinus rhythm, LBBB with QRS duration 120-149 ms, and NYHA class II, III, or ambulatory IV symptoms on GDMT 11, 14
The American College of Cardiology suggests CRT can be useful for patients with LVEF ≤35%, sinus rhythm, non-LBBB pattern with QRS duration ≥150 ms, and NYHA class III/ambulatory class IV symptoms on GDMT 11, 14
The American College of Cardiology suggests CRT can be useful in patients with atrial fibrillation and LVEF ≤35% on GDMT if the patient requires ventricular pacing or meets other CRT criteria, and AV nodal ablation or pharmacologic rate control will allow near 100% ventricular pacing 11, 14
The American College of Cardiology suggests CRT can be useful for patients on GDMT with LVEF ≤35% who are undergoing new or replacement device placement with anticipated requirement for significant (>40%) ventricular pacing 11, 14

Prolonged interventricular and intraventricular conduction causes regional mechanical delay within the left ventricle that results in reduced ventricular systolic function, altered myocardial metabolism, functional mitral regurgitation, and adverse remodeling with ventricular dilatation 12, 13
CRT improves ventricular systolic function, reduces metabolic costs, ameliorates functional mitral regurgitation, and can induce favorable remodeling with reduction of cardiac chamber dimensions 12, 13
Functional improvements include increased exercise capacity, increased 6-minute walking distance, and reduced heart failure symptoms 12, 13

QRS morphology matters: The benefit of CRT is greatest in patients with LBBB pattern compared to non-LBBB patterns 13
QRS duration is critical: Patients with QRS duration ≥150 ms show greater benefit than those with QRS duration 120-149 ms 12, 13
Response heterogeneity: Approximately two-thirds of patients randomized to CRT show clinical response compared to one-third in control groups 15
Suboptimal lead placement and areas of myocardial fibrosis may contribute to poor response to CRT in some patients 15
For patients with atrial fibrillation, AV nodal ablation may be necessary to ensure high percentage of biventricular capture 11, 14