What Is Biventricular Pacing (BiVent) and How It Works

Bivent is shorthand for two distinct medical technologies depending on the setting. In cardiology, it refers to biventricular pacing, also called cardiac resynchronization therapy (CRT), a treatment for heart failure that uses a specialized pacemaker to coordinate the pumping of both sides of the heart. In the intensive care unit, BIVENT refers to a ventilation mode (biphasic positive airway pressure) that lets critically ill patients breathe spontaneously while still receiving mechanical support. The cardiac meaning is far more common in everyday medical conversations, and it is where the bulk of the clinical evidence sits.

What Biventricular Pacing Actually Does

In a healthy heart, electrical signals travel through the conduction system in a coordinated wave, causing the left and right ventricles to squeeze almost simultaneously. In many people with heart failure, that coordination breaks down. The electrical signal reaches one side of the heart much later than the other, so the walls contract out of sync. This is called dyssynchrony, and it makes an already weak heart pump even less efficiently.

A biventricular pacemaker addresses this by placing pacing leads on both ventricles. A conventional pacemaker typically has one lead in the right ventricle. A CRT device adds a second lead, threaded through the coronary sinus (a vein on the surface of the heart) to reach the left ventricle. When both leads fire in a timed sequence, the two ventricles contract together again. Research has confirmed that this restores both the timing between the left and right ventricles (interventricular synchrony) and the coordination within the left ventricle’s own walls (intraventricular synchrony), and that the degree of improvement correlates with how delayed the left ventricular electrical activation was before pacing.¹

Who Is a Candidate

Biventricular pacing is not for everyone with heart failure. Guidelines generally recommend it for people who have a reduced pumping fraction (typically 35% or below), a wide QRS complex on their ECG (120 milliseconds or more, with the strongest evidence at 150 ms and above), and persistent symptoms despite medication. The electrical pattern on the ECG matters as well. Patients with a left bundle branch block pattern get the most benefit, because their dyssynchrony tends to be the most pronounced.² People with a right bundle branch block pattern show a weaker hemodynamic response to CRT.³ That doesn’t mean CRT is never tried in those patients, but expectations are more tempered.

Survival and Hospitalization Benefits

The evidence backing biventricular pacing is strong. Five landmark randomized trials enrolling over 6,500 patients collectively showed a roughly 29% reduction in the risk of death over two years (an average hazard ratio of 0.71).⁴ That same analysis noted that the survival benefit grows nonlinearly over time, meaning real-world gains over many years are likely larger than what the original trial follow-up periods captured. The benefit also tends to be greatest in lower-risk patients, which makes intuitive sense: people who are less sick at the start have more years of life to gain.

Beyond survival, CRT reduces heart-failure hospitalizations, a major quality-of-life and cost driver. Meta-analyses of randomized trials confirm reductions in both mortality and hospital admissions for patients with moderate-to-severe symptoms.⁵

Reverse Remodeling and Mitral Regurgitation

One of the more striking effects of biventricular pacing is something called reverse remodeling. A failing heart gradually enlarges and changes shape, becoming rounder and less efficient. CRT can partially reverse this, causing the heart to shrink back toward a more normal size. Part of this relates to mitral regurgitation, the backward leakage of blood through the valve between the left atrium and left ventricle. CRT tends to immediately and sustainably reduce that leakage. In patients with severe regurgitation before device implant, the heart’s shrinkage over the following months was even more pronounced.⁶

Why Some Patients Do Not Respond

Despite its track record, roughly a third of patients implanted with a CRT device do not improve meaningfully. Understanding why is one of the biggest open questions in the field. One important predictor is scar tissue. In patients with ischemic heart disease (heart failure caused by prior heart attacks), the amount of scarring in the heart muscle strongly predicts whether CRT will work. Patients who responded to CRT had significantly fewer scarred segments than those who did not. When the pacing lead happened to sit on top of scar tissue rather than healthy muscle, outcomes were worse.⁷ Having three or more scarred segments identified non-responders with reasonable accuracy.

Other factors play a role too. A narrow QRS (especially below 130 ms), right bundle branch block morphology, and the absence of mechanical dyssynchrony on imaging all reduce the odds of a good response. Some non-response simply comes down to lead placement: if the coronary sinus anatomy forces the lead into a suboptimal vein, the electrical correction may not reach the latest-activating part of the ventricle.

CRT-P Versus CRT-D

Biventricular devices come in two flavors. A CRT-P is a pacemaker only: it resynchronizes the heart but does nothing if a dangerous arrhythmia occurs. A CRT-D combines the pacing function with a built-in defibrillator, which can deliver a shock to terminate life-threatening rhythms. Choosing between them involves a judgment about how high the patient’s risk of sudden cardiac death is relative to their other health burdens.

In older patients, this choice gets nuanced. A real-world study of octogenarians found that three-year mortality was essentially the same whether patients received CRT-D or CRT-P (about 37–39%), though CRT-D recipients had fewer hospitalizations.⁸ Findings like these underscore that a defibrillator is not always the better option, especially in patients whose competing health issues make sudden arrhythmic death a smaller fraction of their overall risk.

Lead Placement and Complications

Getting the left ventricular lead into the right spot is the trickiest part of a CRT implant. The lead must be threaded through the coronary sinus and into a tributary vein that overlies the lateral or posterolateral wall of the left ventricle. The anatomy of these veins varies enormously from person to person. In one surgical series, about a third of coronary sinus lead attempts encountered a significant complication, including failed placement, lead dislodgement, unacceptably high pacing thresholds, diaphragm stimulation from the nearby phrenic nerve, and occasional coronary sinus dissection.⁹

Early in the technology’s history, lead dislodgement rates were especially high, around 30% in the late 1990s, dropping to about 11% after 1999 as tools and techniques improved.¹⁰ When coronary sinus placement fails entirely, a surgeon can place the lead directly on the outside of the heart (an epicardial approach), which requires a small surgical incision but tends to have fewer lead-specific complications afterward.¹¹ In rare cases where the usual approach is impossible, such as a patient with a mechanical valve blocking access to the right heart, creative routing through the coronary sinus has been reported successfully.¹²

Quadripolar Leads and Device Optimization

One engineering advance that has improved outcomes is the quadripolar lead, which has four electrodes instead of one or two. This gives the clinician multiple pacing configurations to choose from after the lead is in place. If one electrode sits over scar or triggers phrenic nerve stimulation, the device can be reprogrammed to pace from a different electrode along the same lead, avoiding a second procedure. Electrodes can be positioned at the site of the latest mechanical or electrical activation and away from trouble spots.¹³

Separately, clinicians can fine-tune the timing delays in the device: specifically the interval between the atrial signal and ventricular pacing, and the interval between the right and left ventricular pacing pulses. Optimization has been attempted using echocardiography, intracardiac electrograms, and automated algorithms built into the device. The reality, though, is that routine optimization in unselected patients has not shown a clear benefit over standard empiric settings. Automated methods have been disappointing so far.¹⁴ Optimization may still help individual patients who are not responding as expected, but as a blanket strategy it has not moved the needle.

Upgrading From a Standard Pacemaker

A meaningful number of CRT candidates are people who already have a conventional right-ventricular pacemaker and have developed heart failure partly because of chronic right-ventricular-only pacing, which can itself cause dyssynchrony over time. Upgrading these patients to biventricular pacing is well supported by evidence. A systematic review of randomized trials found that upgrading improved the heart’s pumping fraction by about 8 percentage points and led to meaningful gains in exercise capacity and symptom scores.¹⁵

In young patients, the results can be dramatic. A small series of young people who developed dilated cardiomyopathy from chronic right-ventricular pacing saw their pumping fractions improve from about 34% to 60% after upgrading to biventricular pacing, and all were weaned off heart-failure medications and removed from transplant waiting lists.¹⁶ The upgrade also benefits patients with atrial fibrillation, a common companion to heart failure. In a trial sub-analysis of patients who had atrial fibrillation at the time of enrollment, upgrading from a standard defibrillator to CRT-D cut the combined risk of heart-failure hospitalization or death by roughly two-thirds compared with staying on the original device.¹⁷

Left Bundle Branch Area Pacing as a Challenger

The biggest evolution in the CRT field right now is left bundle branch area pacing (LBBAP), a technique that achieves resynchronization by pacing the heart’s own conduction system rather than bypassing it with a coronary sinus lead. A thin screw-in lead is advanced through the right side of the septum until it captures the left bundle branch fibers directly. Because the electrical signal then spreads through the native pathways, the resulting QRS is narrower and more physiologic than what a traditional biventricular setup produces.

Head-to-head evidence is accumulating fast. A randomized trial found that LBBAP-CRT produced a significantly greater improvement in pumping fraction at six months compared to standard biventricular pacing, with a mean difference of about 5.6 percentage points.¹⁸ A larger multicenter comparison found that LBBAP narrowed the QRS more than biventricular pacing, improved ejection fraction more (a gain of about 13 versus 10 percentage points), and reduced the combined risk of heart-failure hospitalization or death.¹⁹

A systematic review and meta-analysis confirmed the pattern across pooled data: LBBAP was associated with better pump function, greater QRS narrowing, fewer heart-failure hospitalizations, and improved survival compared to biventricular pacing. It also required less radiation exposure during implant and had lower pacing thresholds, meaning less battery drain.²⁰ Whether LBBAP will eventually replace traditional biventricular pacing is an open question, but the early evidence is hard to ignore. One cost-utility analysis found LBBAP saved an average of roughly €2,400 per patient while providing a small quality-of-life gain, making it the economically dominant strategy.²¹

Biventricular Pacing in Children

Children are not simply small adults, and that applies to CRT as well. In kids undergoing surgery for congenital heart disease, biventricular pacing can improve cardiac output and restore synchrony when dyssynchrony is present at baseline. One study found that temporary biventricular pacing after surgery shortened the QRS, improved the cardiac index, and restored the coordinated contraction pattern between the right and left ventricles compared to conventional right-ventricular-only pacing.²²

However, children who already have normal conduction and synchrony after their surgery do not benefit. A separate study found that biventricular pacing offered no improvement in cardiac output over intrinsic rhythm or right-ventricular pacing in children who had undergone routine biventricular congenital heart surgery and did not have pre-existing dyssynchrony.²³ The lesson is the same as in adults: CRT fixes a specific problem (dyssynchrony), and if that problem is not there, the technology has nothing to fix.

Cost-Effectiveness

CRT devices are expensive, typically costing tens of thousands of dollars more than a conventional pacemaker or defibrillator. Whether that extra cost is justified has been studied repeatedly. A cost-effectiveness analysis of the BLOCK-HF trial found that biventricular pacing yielded about 0.41 additional quality-adjusted life years compared with right-ventricular pacing, at an added cost of about $12,500. The resulting cost per quality-adjusted year was around $31,000, comfortably below the commonly used U.S. threshold of $50,000 per quality-adjusted year.²⁴ Longer-term modeling has consistently shown CRT to be economically attractive.²⁵

BIVENT as a Ventilation Mode in the ICU

Outside cardiology, you may hear “bivent” in an intensive care unit, where it refers to a ventilator mode formally called biphasic positive airway pressure. BIVENT alternates between two pressure levels on a timed cycle, and the key feature is that patients can breathe spontaneously on top of either pressure level at any point in the cycle. This makes it a partial-support mode rather than a fully controlled one, and it sits somewhere between conventional pressure-controlled ventilation and airway pressure release ventilation.²⁶

The theoretical advantage is that letting patients breathe on their own improves gas exchange and blood flow while also helping recruit collapsed lung regions, especially near the diaphragm. Animal research has shown that BIVENT has a lower biological impact on lung tissue than fully controlled pressure ventilation in mild acute lung injury, though the benefit varied depending on how much spontaneous breathing the patient was actually doing and what caused the lung injury in the first place.²⁷ In clinical practice, BIVENT is often used as a step in weaning patients off mechanical ventilation, allowing their respiratory muscles to participate while still guaranteeing a baseline level of support.

Thirty Years and Counting

The first permanent biventricular pacing system was implanted over 30 years ago, and the technology has gone through several generations since then.²⁸ What began as an experimental concept for the sickest heart-failure patients has expanded to include people with milder symptoms and even some who need a pacemaker for other reasons but are at risk of developing pacing-induced dyssynchrony. Meanwhile, conduction-system pacing techniques like LBBAP are pushing the field toward a future where biventricular pacing via the coronary sinus may no longer be the default approach. For now, though, traditional biventricular pacing remains the most widely implanted and best-validated form of CRT worldwide, with decades of trial data and clinical experience behind it.